CHAPTER 24 Male Reproductive SystemSTUDENT LEARNING OBJECTIVES

CHAPTER 24 Male Reproductive System
STUDENT LEARNING OBJECTIVES
At the completion of this chapter, you should be able to do the
following:
1.Explain how sexual reproduction and asexual reproduction
differ.
2.Briefly outline the male reproductive organs.
3.Discuss the structure and function of the testes.
4.Describe how testosterone works in the male body.
5.Outline the roles of FSH and LH in the male reproductive
system.
6.Discuss the functions of the various reproductive ducts
(epididymis, vas deferens, ejaculatory duct, and urethra)
7.Outline the role of the accessory reproductive glands.
8.List some factors that affect male fertility.
LANGUAGE OF SCIENCE AND MEDICINE
Before reading the chapter, say each of these terms out loud.
This will help you avoid stumbling over them as you read.
accessory organ (ak-SES-oh-ree OR-gan)
[access- extra, -ory relating to, organ instrument]
acrosome (AK-roh-sohm)
[acro- top or tip, -some body]
anal triangle (AY-nal)
[an- ring (anus), -al relating to]
androgen (AN-droh-jen)
[andro- male, -gen produce]
androgen-binding protein (ABP) (AN-droh-jen-BYND-ing PRO-
teen)
[andro- male, -gen produce, prote- first rank, -in substance]
asexual reproduction (ay-SEK-shoo-al re-proh-DUK-shun)
[a- without, sexu- sex, -al relating to, re- again, -produc- bring
forth, -tion process]

benign prostatic hypertrophy (BPH) (be-NYNE proh-STAT-ik
hye-PER-troh-fee)
[benign kind, pro- before, -stat- set or place, -ic relating to,
hyper- excessive or above, -troph- nourishment, -y state]
bulbourethral gland (BUL-boh-yoo-REE-thral)
[bulb- swollen root, -ure- urine, -thr- agent or channel (urethra),
-al relating to]
capacitation (kah-pass-ih-TAY-shun)
clone (klohn)
[clon a plant cutting]
corpus cavernosum (KOHR-pus kav-er-NO-sum)
[corpus body, cavern- large hollow, -os- relating to, -um thing]
pl., corpora cavernosa (KOHR-poh-rah kav-er-NO-sah)
corpus spongiosum (KOHR-pus spun-jee-OH-sum)
[corpus body, spong- sponge, -os- relating to, -um thing] pl.,
corpora spongiosa (KOHR-poh-rah spun-jee-OH-sah)
cremaster muscle (kreh-MASS-ter MUSS-el)
[cremastos- hanging, mus- mouse, -cle little]
ejaculation (ee-jak-yoo-LAY-shun)
[e- out or away, -jacula- throw, -ation process]
ejaculatory duct (ee-JAK-yoo-lah-toh-ree)
[e- out or away, -jacula throw, -ory relating to, ducere- lead]
emission (ee-MISH-un)
[e- out or away, -mis- send, -sion process]
epididymis (ep-ih-DID-ih-mis)
[epi- upon, -didymis pair] pl., epididymides (ep-ih-DID-ih-mih-
deez)
erection (ee-REK-shun)
essential organ (OR-gan)
[organ instrument]
external genitalia (eks-TER-nal jen-ih-TAIL-yah)
[extern- outside, -al relating to, gen- produce, -al relating to]
gamete (GAM-eet)
[gamete marriage partner]
glans penis (glans PEE-nis)

[glans acorn, penis male sex organ] pl., glandes penes (GLAN-
deez PEE-neez)
gonad (GO-nad)
[gon- offspring, -ad relating to]
head
hyaluronidase (hye-al-yoo-RAHN-id-ayz)
[hyal- glass, -uron- urine, -id- relating to, -ase enzyme)
inhibin (in-HIB-in)
[inhib- inhibit, -in substance]
interstitial cell (in-ter-STISH-al sell)
[inter- between, -stit- stand, -al relating to, cell storeroom]
midpiece (MID-pees)
[mid- middle, -piece portion]
orgasm (OR-gaz-um)
[orgasm excitement]
penis (PEE-nis)
[penis male sex organ] pl., penes or penises (PEE-neez, PEE-
nis-ez)
perineum (pair-ih-NEE-um)
[peri- around, -ine- excrete, -um thing] pl., perinea (pair-ih-
NEE-ah)
prepuce (PREE-pus)
[pre- before, -puc- penis]
prostate (PROSS-tayt)
[pro- before, -stat- set or place]
scrotum (SKROH-tum)
[scrotum bag] pl., scrota or scrotums (SKROH-tah, SKROH-
tumz)
semen (SEE-men)
[semen seed]
seminal vesicle (SEM-ih-nal VES-ih-kul)
[semen- seed, -al relating to, vesic- blister, -cle little]
sexual reproduction (SEK-shoo-al re-proh-DUKshun)
[sexu- sex, -al relating to, re- again, -produce bring forth, -tion
process]

spermatic cord (sper-MAT-ik kord)
[sperma- seed, -ic relating to]
spermatogenesis (sper-mah-toh-JEN-eh-sis)
[sperma- seed, -gen- produce, -esis process]
spermatozoon (sper-mah-tah-ZOH-on)
[sperma- seed, -zoon animal] pl., spermatozoa (sper-mah-tah-
ZOH-ah)
sustentacular cell (sus-ten-TAK-yoo-lar sell)
[sustent- support, -acular relating to, cell storeroom]
testis (TES-tis)
[testis witness (male gonad)] pl., testes (TES-teez)
testosterone (tes-TOS-teh-rohn)
[test- witness (testis), -stero- solid or steroid derivative, -one
chemical]
tunica albuginea (TOO-nih-kah al-byoo-JIN-ee-ah)
[tunica tunic or coat, albuginea white] pl., tunicae albuginea
(TOO-nih-kee al-byoo-JIN-ee-ah)
urethra (yoo-REE-thrah)
[ure- urine, -thr- agent or channel]
urogenital triangle (yoor-oh-GEN-ih-tal)
[uro- urine, -gen- produce, -al relating to]
vas deferens (vas DEF-er-enz)
[vas duct or vessel, deferens carrying away] pl., vasa deferentia
(VAS-ah def-er-EN-shee-ah)
vasectomy (vah-SEK-toh-mee)
[vas- duct or vessel (vas deferens), -ec- out, -tom- cut, -y
action]
CARLOS and his wife had been trying for years to have a baby
with no success. Carlos had always assumed they just had bad
timing. But recently they had started tracking Maria's cycle and
found everything seemed to be on schedule. Finally, at Maria's
request, they made an appointment with an infertility specialist.
Carlos was expecting them to order expensive tests. But after
the introductions, one of the first things the doctor asked about
was what kind of underwear and pants Carlos typically wore.
“What business is that of yours?” Carlos thought. Then the

specialist added, “…because that may affect the average
temperature of the testes.”
It may seem odd to you, but Carlos wearing tight underwear and
tight pants may really affect Maria's chance of getting pregnant.
You may already know something about testes and temperature,
but in this chapter you'll get “the rest of the story.”
Remember Carlos and Maria from the Introductory Story? See if
you can answer the following questions about Carlos' fertility
now that you have read this chapter.
1.Sperm production occurs optimally at what temperature?
a.3° C above body temperature
b.At body temperature
c.3° C below body temperature
d.Optimal temperature changes with the seasons
Next, Carlos was asked to provide a sperm sample. “We're
going to analyze the sperm count and morphology,” said the
doctor.
2.What number should Carlos' sperm count be above for that
factor to be ruled out as a cause of the couple's infertility?
a.250 million/ml
b.25 million/ml
c.2500/ml
d.250/ml
3.Which is the correct pathway the sperm would take during
ejaculation?
a.Seminiferous tubules, rete testis, efferent ductules,
epididymis, vas deferens, ejaculatory duct, urethra
b.Rete testis, seminiferous tubules, efferent ductules,
epididymis, vas deferens, urethra, ejaculatory duct
c.Epididymis, vas deferens, seminiferous tubules, rete testis,
ejaculatory duct, urethra
d.Seminiferous tubules, rete testis, epididymis, vas deferens,
efferent ductules, urethra, ejaculatory duct
4.What hormone directly stimulates sperm production?
a.Estrogen
b.Progesterone

c.LH
d.Testosterone
To solve these questions, you may have to refer to the glossary
or index, other chapters in this textbook, A&P Connect,
Mechanisms of Disease, and other resources.
The importance of reproductive system function is notably
different from that of any other organ system of the body.
Ordinarily, body systems function to maintain the relative
stability and survival of the individual organism. The
reproductive system, on the other hand, ensures survival not of
the individual but of the genes that characterize the human
species. In both sexes, organs of the reproductive system are
adapted for the specific sequence of functions that are
concerned primarily with transferring genes to a new generation
of offspring. A male reproductive system in one parent and a
female reproductive system in another parent are needed to
reproduce.
This chapter begins with a brief description of the male
reproductive system. Chapter 26 then follows with the story of
the female reproductive system.
SEXUAL REPRODUCTION
During sexual reproduction, a male and female each contribute
half the number of chromosomes required to create the next
generation of children. (Asexual reproduction requires just one
parent who produces an offspring identical to it—a clone.) One
advantage of sexual reproduction is that the process allows for
the exchange and mixing of genes as sex cells are made and
then recombined. Mixing the genetic deck of cards, so to speak,
allows us tremendous, almost infinite variability in our
children. This is vitally important to the survival and success of
our species. Why is this important? Because such natural
variation makes it more likely that at least some individuals will
be able to survive new and evolving pathogens or other life-
threatening changes that may occur over time in our internal or
external environments.
Our reproductive systems also produce hormones that regulate

the development of secondary sex characteristics that promote
successful reproduction. For example, a variety of hormones
creates structural and behavioral differences in the sexes. These
differences permit adults to form sexual attractions with the
opposite sex. In fact, reproductive hormones and other
regulatory mechanisms provide us with the urge to have sex.
Our sex drives are thus essential to successful reproduction.
FIGURE 24-1 Male reproductive organs. Sagittal section of
inferior abdominopelvic cavity showing placement of male
reproductive organs.
MALE REPRODUCTIVE ORGANS
The male reproductive system consists of organs whose
functions are to produce, transfer, and introduce mature sperm
into the female reproductive tract. Here, the genes from each
parent join to form a new individual.
Organs of the male reproductive system (Figure 24-1) are
classified as (1) essential organs (primary organs) for the
production of gametes (sex cells or sperm) and (2) accessory
organs (secondary organs) that support gamete formation and
viability.
The essential organs or gonads of a male are the testes. The
accessory organs of male reproduction include the genital ducts,
glands, and other supportive structures. Reproductive ducts
(genital ducts) together are responsible for delivering sperm
outside the body. The ducts include a pair of epididymides
(singular, epididymis), the paired vasa deferentia (singular, vas
deferens), a pair of ejaculatory ducts, and the urethra.
Accessory glands in the reproductive system produce secretions
that serve to nourish, transport, and mature sperm. The glands
include a pair of seminal vesicles, a prostate, and a pair of
bulbourethral glands. Supporting structures include the scrotum,
the penis, and a pair of spermatic cords. You may be familiar
with a number of these structures, at least in name, but we will
go over each in some detail.
Perineum

The perineum in the male is an area between the thighs, shaped
roughly like a diamond (Figure 24-2). It extends from the pubic
symphysis anteriorly to the coccyx posteriorly. Its most lateral
boundary on either side is the
FIGURE 24-2 Male perineum. Sketch showing outline of the
urogenital triangle (red) and anal triangle (blue).
ischial tuberosity (see Chapter 9, page 168). A line drawn
between the two ischial tuberosities divides the perineal area
into a larger urogenital triangle and a smaller anal triangle. The
urogenital triangle contains the external genitals (penis and
scrotum), and the anal triangle surrounds the anus.
1. What is the most significant difference between the
reproductive system and other systems of your body?
2. Identify the essential and accessory organs of the male
reproductive system.
3. Describe the perineum and its triangles.
TESTES
Structure and Location
The testes (singular, testis) are small, egg-shaped glands. They
are about 4 to 5 cm in length and weigh 10 to 15 grams each. In
a normal male, both testes are enclosed in a supporting sac, the
scrotum. Both testes are suspended in the scrotum by
attachments to the scrotal wall and by the spermatic cords
(Figure 24-3). In addition to the vas deferens, note that the
nerves, blood vessels, and lymphatics to the testis pass and are
contained within the spermatic cord.
FIGURE 24-3 Tubules of the testis and epididymis. Illustration
showing epididymis lifted free of testis. The ducts and tubules
are exaggerated in size.
FIGURE 24-4 Testis. Low-power view showing several
seminiferous tubules surrounded by septa containing interstitial
(Leydig) cells.

A dense, white, fibrous capsule called the tunica albuginea
encases each testis and then enters each gland. It sends dividing
walls called septa that extend into the interior of the testis,
dividing the gland into 200 or more cone-shaped lobules. Each
lobule contains scattered interstitial cells and one to three tiny,
coiled seminiferous tubules. Unraveled, each of these minute
tubules would stretch more than 75 cm (2 feet) in length! The
tubules from each lobule come together to form a network
called the rete testis. Sperm ducts called efferent ductules drain
the rete testis. The tubes then pass through the tunica albuginea
to enter the head of the epididymis.
Microscopic Anatomy of the Testis
Figure 24-4 shows a low-power view of testicular tissue. Note
that a number of seminiferous tubules have been cut. This
reveals numerous interstitial cells (Leydig cells) in the
surrounding connective septa. Maturing sperm appear as dense
nuclei; their flagella or “tails” project into the lumen of the
tubule. The wall of each seminiferous tubule may contain five
or more layers of these cells.
At puberty, when sexual maturity begins, sperm-forming cells in
different stages of development appear. At this time, the
hormone-producing interstitial cells become much more
prominent in the surrounding septa.
The sustentacular cells (Sertoli or nurse cells) are long,
irregular cells. They provide mechanical support and protection
for the developing sperm attached to their surface. Sustentacular
cells also secrete the hormone inhibin, which inhibits follicle-
stimulating hormone (FSH) production in the anterior pituitary
(see Chapter 15, p. 333). A drop in FSH lowers the rate of
sperm production. This starts a negative feedback mechanism in
which the supportive sustentacular cells can slow down sperm
production, if conditions require.
At sexual maturity, sustentacular cells begin to secrete
androgen-binding protein (ABP). This protein adheres to the
steroid hormone testosterone, making it more water soluble. The
testosterone-ABP complex increases the testosterone

concentration within the seminiferous tubules. This is important
because high concentrations of testosterone are required for
normal germ cell maturation. Thus sustentacular cells play an
important role in spermatogenesis (the process of sperm
formation, discussed later).
Sustentacular cells extend from the basement membrane all the
way to the surface facing the lumen of the seminiferous tubules
(Figure 24-5). Tight junctions (see Chapter 3, p. 56)
FIGURE 24-5 Seminiferous tubule. Wedge from a cross section
of the tubule, showing spermatogenesis and the relationship of
the developing spermatozoa (sperm cells) to the sustentacular
(Sertoli) cells. Mitotic cell division was explained in Chapter 5.
Meiotic cell division, which reduces the number of
chromosomes by half, will be explained further in Chapter 26.
exist between the sustentacular cells. These junctions divide the
wall of the tubule into two compartments. The compartment
near the basement membrane houses sperm-producing cells
called spermatogonia. The compartment near the surface facing
the lumen houses meiotically active cells.
Function of Testes and Testosterone
The testes perform two primary functions: spermatogenesis and
secretion of hormones.
Spermatogenesis is the production of spermatozoa (sperm)—the
male reproductive cell. The sperm are produced in the
seminiferous tubules. The cross section of a seminiferous tubule
in Figure 24-5 shows two cell divisions that result in a
reduction of chromosomes from 46 in a normal body cell to 23
in a normal sperm. You'll find a complete discussion of this
special type of division—called meiosis—in Chapter 26.
As you probably know, testosterone is the major androgen
(masculinizing hormone) of males. This steroid hormone is
produced by interstitial cells. Actually, testosterone has a
number of important functions. First, it promotes “maleness.”
By this we mean the development and maintenance of male
secondary sexual characteristics and accessory organs such as

the prostate and seminal vesicles. Testosterone also develops
and maintains adult male sexual behavior.
Testosterone also helps regulate metabolism. In fact, it
stimulates protein anabolism (see Chapter 2, page 26), which in
turn promotes growth of skeletal muscle. This, of course, is
responsible for greater male muscular development and
strength. Unfortunately, various synthetic versions of
testosterone are sometimes used by athletes in ill-advised
attempts to enhance muscular strength.
Testosterone also stimulates bone growth and promotes closure
of the epiphyses in long bones (see Chapter 8, p. 144). Early
sexual maturation leads to early epiphyseal closure. The
opposite is also true: Late sexual maturation delays epiphyseal
closure. As a result, tallness tends to be enhanced by late
epiphyseal closure.
Testosterone also affects fluid and electrolyte bal ance. It has a
mild stimulating effect on kidney tubule reabsorption of sodium
and water, and promotes kidney tubule excretion of potassium.
Hormonal Control of Reproduction
The anterior pituitary gland controls the testes by means of its
gonadotropin-releasing hormone (GnRH). As we've seen in
Chapter 15 (p. 341), there are two major hormones involved,
specifically follicle-stimulating hormone (FSH) and luteinizing
hormone (LH). FSH stimulates the seminiferous tubules to
produce sperm more rapidly. In the male, LH stimulates
interstitial cells to increase their secretions of testosterone.
Note the negative feedback mechanism in Figure 24-6. If the
blood concentration level of testosterone reaches a high level, it
will inhibit secretion of GnRH from the hypothalamus. As a
FIGURE 24-6 Negative feedback loop controlling testosterone
secretion. Diagram shows the negative feedback mechanism that
controls anterior pituitary gland secretion of LH and interstitial
cell secretion of testosterone. A similar negative feedback loop
exists between inhibin-secreting sustentacular cells in the testis
and FSH-secreting cells in the anterior pituitary gland.

result, the anterior pituitary secretion of LH will decrease and
testosterone levels will return to the normal set point value.
Increasing blood levels of inhibin, produced by the
sustentacular cells, will selectively decrease FSH secretion by
the anterior pituitary and decrease the rate of sperm production.
However, if sperm counts decrease below the normal set point,
inhibin secretion will decrease, FSH secretion will increase, and
sperm numbers will increase back to normal levels.
The negative feedback loops regulating testosterone secretion
involve the hypothalamus (GnRH), the anterior pituitary gland
(FSH and LH), and the hormone-producing cells of the testes
(testosterone and inhibin).
Small but measurable amounts of estrogen are present in healthy
adult males. In fact, much of the estrogen, a steroid hormone
derived from testosterone, is made in the interstitial cells .
However, estrogen in males is also made in the liver and other
tissues. Possible roles for estrogen in men include (1) regulation
of spermatogenesis, (2) feedback inhibition of FSH and LH, and
(3) promotion of normal male sexual behavior. We are sure to
learn much more about the role of estrogen in males. Recent
research suggests that, in addition to gonadotrophins and
testosterone, estrogens are likely playing a relevant role in
spermatogenesis and human male gamete maturation. Take a
moment to review the male reproductive hormones and their
actions listed for you in Table 24-1.
TABLE 24-1 Male Reproductive Hormones
HORMONE
SOURCE
TARGET
ACTION
Dehydroepiandrosterone (DHEA)
Adrenal gland, testis, other tissues
Converted to other hormones
Eventually converted to estrogens, testosterone, or both
Estrogen
Testis (interstitial cells), liver, other tissues

Testis (spermatogenic tissue), other tissues
Role of estrogen in men is still uncertain; may play role in
spermatogenesis, inhibition of gonadotropins, male sexual
behavior and partner preference
Follicle-stimulating hormone (FSH)
Anterior pituitary (gonadotroph cells)
Testis (spermatogenic tissue)
Gonadotropin; promotes development of testes and stimulates
spermatogenesis
Gonadotropin-releasing hormone (CnRH)
Hypothalamus (neuroendocrine cells)
Stimulates production and release of gonadotropins (FSH and
LH) from anterior pituitary
Inhibin
Testis (interstitial cells)
Inhibits FSH production in the anterior pituitary
Luteinizing hormone (LH)
Conadotropin; stimulates production of testosterone by
interstitial cells of testis
Testosterone
Spermatogenic cells, skeletal muscle, bone, other tissues
Stimulates spermatogenesis, stimulates development of primary
and secondary sexual characteristics, promotes growth of
muscle and bone (anabolic effect)
Structure of Spermatozoa
The long, “tailed” spermatozoa you see in the seminiferous
tubules of Figure 24-7, A, may appear fully formed. However,
they undergo further maturation as they pass through the genital
ducts before ejaculation. Even then the process is not complete.
After ejaculation, sperm must undergo a process called
capacitation, which takes place in the vagina. Only after this

process is complete is a sperm cell capable of fertizing an
ovum.
You can see the basic features of a normal spermatozoon in
Figure 24-7, B and C. Each is composed of a head, middle
piece, and lashlike “tail.” The head is a compact package of 23
chromosomes. The head has no organelles and virtually no
cytoplasm.
An acrosome containing hydrolytic enzymes forms the cap over
the head of the sperm. These hydrolytic enzymes first break
down the cervical mucus, allowing sperm to pass into the uterus
and uterine tubes.
The cylindrical midpiece of the sperm consists of a helix-like
arrangement of mitochondria joined end-to-end. The “tail” is
actually a flagellum capable of propelling a sperm cell great
distances.
A&P CONNECT
Many physicians encourage male patients to perform regular
selfexamination of their testes, especially if they are at a high
risk for a getting a disorder. Check out Male Genital Self-
Examination online at A&P Connect.
4. Describe the basic features of the testis.
5. List the two primary functions of the testes. What are the
different cell types involved in these activities?
6. List several important functions of testosterone outside those
of reproduction.
7. Identify the structural components of a mature sperm.
FIGURE 24-7 Development and structure of sperm. A,
Spermatid cells in a seminiferous tubule. B, Mature sperm. C,
Enlarged view of head and midpiece. D, Micrograph of sperm.
Note glowing nuclear material in sperm heads caused by uptake
with a fluorescent dye.
FIGURE 24-8 The male reproductive system. A, Illustration

shows the testes, epididymis, vas (ductus) deferens, and glands
of the male reproductive system in an isolation/dissection
format. B, Cross section of the shaft of the penis. Note the
urethra within the substance of the corpus spongiosum.
REPRODUCTIVE DUCTS
Epididymis
Each epididymis is a single, tightly coiled tube enclosed in a
fibrous casing. Although its diameter is just barely visible with
the naked eye, the tube measures 6 meters (20 feet) when
uncoiled! It lies along the top of and behind the testis (see
Figure 24-3). Shaped roughly like a comma, the epididymis is
divided into several sections. The head is connected to the testis
by the efferent ductules from the testis. A central body
separates the head from the tail—a tapered portion that is
continuous with the vas deferens.
Sperm must pass through the epididymis from the testis to the
vas deferens. Each epididymis stores sperm, nourishing them
with nutrients, from 1 to 3 weeks. The epididymal secretions
also eventually become a small portion of the seminal fluid
(semen) that is ejaculated during intercourse. After about 3
weeks, any unused sperm break down and are reabsorbed by the
body.
Vas Deferens
The vas deferens (plural, vasa deferentia) is also a tube but,
unlike the epididymis, it has a thick, muscular wall (see Figure
24-3). It can be felt (palpated) in the scrotal sac as a smooth,
movable cord.
The vas deferens has a layered, muscular wall. Contractions of
the muscles in the wall of the vasa deferentia help propel sperm
through the duct system. The vas deferens from each testis
ascends from the scrotum and passes through the inguinal canal
as part of the spermatic cord. This cord, enclosed by fibrous
connective tissue, contains muscle, blood vessels, nerves, and
lymphatics, as we've seen (see Figure 24-3). The vas deferens
continues into the abdominal cavity, where it extends over the
top and down the posterior surface of the bladder. Here an

enlarged and winding portion called the ampulla joins the duct
from the seminal vesicle to form the ejaculatory duct (Figures
24-1 and 24-8, A).
Functionally, the vas deferens connects the epididymis with the
ejaculatory duct. Sperm may remain in the vas deferens for
varying periods of time, depending on the degree of sexual
activity and the frequency of ejaculations. Storage time may
exceed 1 month with no loss of fertility. A vasectomy (severing
or clamping off of the vas deferens) makes a man sterile
because it effectively stops the flow of sperm to the urethra.
Ejaculatory Duct and Urethra
The two ejaculatory ducts are short tubes about 1 cm long that
pass through the prostate gland and terminate in the urethra. As
you can see in Figure 24-8, these ducts are formed by the union
of the vas deferens with the ducts from the seminal vesicle.
The male urethra serves a double function in males. It transfers
both urine from the bladder and semen with sperm from the
reproductive ducts.
ACCESSORY REPRODUCTIVE GLANDS
Seminal Vesicles
The seminal vesicles are highly convoluted pouches nearly 15
cm in length when extended. They lie along the lower part of
the posterior surface of the bladder, directly in front of the
rectum (see Figures 24-1 and 24-8, A). The secretory epithelium
of the seminal vesicles is highly branched and convoluted.
The seminal vesicles secrete an alkaline, viscous, creamy-
yellow liquid that makes up about 60% of the semen volume.
The alkalinity helps neutralize the acid pH environmen t of the
terminal male urethra and of the vagina. Fructose in the semen
serves as an energy source for sperm motility after ejaculation.
Other important components include prostaglandins.
Prostate Gland
The prostate lies just below the bladder and is shaped roughly
like a doughnut. The fact that the urethra passes through the
small hole in the center of the prostate is clinically important.
This is because many older men suffer from a noncancerous

enlargement of this gland known as benign prostatic
hypertrophy (BPH). As the prostate enlarges, it squeezes the
urethra, frequently closing it so completely that urination
becomes nearly impossible. Urinary retention results, which can
be uncomfortable and even painful. Surgical removal of all or
part of the prostate is required if other less invasive methods
fail.
The prostate secretes a watery, milky-looking, and slightly
acidic fluid that constitutes about 30% of the seminal fluid
volume. Citrate in the prostatic fluid provides additional
nutrients for sperm. Other constituents include enzymes such as
hyaluronidase and prostate-specific antigen (PSA). The
functions of these components are discussed later in this
chapter. Box 24-1 discusses different methods for prostate
cancer screening. Overall, prostatic fluid with its many
components plays an important role in sperm activation,
viability, and motility.
BOX 24-1 Diagnostic Study
Prostate Cancer Screening
Many of the 32,000 men who die each year from prostate
cancer—the most common nonskin type of cancer in American
men—could be saved if the cancer were detected early enough
for effective treatment. Several screening tests are available for
the detection of prostate cancer once it develops. Cancerous
growths in the gland can often be palpated through the wall of
the rectum (see figure).
Sometimes, rectal examinations are performed in conjunction
with a screening test called the PSA test. This test is a type of
blood analysis that screens for prostate-specific antigen (PSA),
a substance sometimes found to be elevated in the blood of men
with prostate cancer. Unfortunately, PSA levels may not be
elevated with prostate cancer and may be high in some men
without prostate cancer. Thus the PSA test is most useful when
used with other screening methods.
A nuclear medicine bone scan is often used either to exclude
metastatic spread of prostate cancer or to locate areas of the

body where secondary prostate cancer tumors have already
developed.
Palpation of the prostate gland. A physician inserts a lubricated,
gloved finger through the anus to feel the prostate through the
thin anterior wall of the rectum.
Bulbourethral Glands
The two bulbourethral glands (Cowper's glands) resemble peas
in size and shape. You can see the location of these compound
glands in Figure 24-8, A. A duct approximately 2.5 cm (1 inch)
long connects each gland with the penile portion of the urethra.
Like the seminal vesicles, the bulbourethral glands secrete an
alkaline fluid. This fluid is important for counteracting the acid
environment of the male urethra and the female vagina. Mucus
produced in these glands serves to lubricate the urethra and
helps protect sperm from damage due to friction during
ejaculation.
A&P CONNECT
Infections of the reproductive tract, often acquired through
sexual contact with infected individuals, can progress into
conditions that may cause sterility—or even death. These
sexually transmitted diseases (STDs) are discussed in Sexually
Transmitted Diseases online at A&P Connect.
8. List, in order, the reproductive ducts that sperm must pass
through from their formation to ejaculation.
9. Describe the problems associated with the relationship of the
prostate gland and the urethra.
10. Briefly compare the pH and composition of the secretions
produced by the accessory reproductive glands.
SUPPORTING STRUCTURES
Scrotum
The scrotum is a skin-covered pouch suspended from the
perineal region. Internally, it is divided into two sacs by a
septum. Each sac contains a testis, epididymis, and lower part

of a spermatic cord. Just below the skin lie the dartos fascia and
dartos muscles. Contraction of the dartos muscle wrinkles the
scrotal skin and can elevate or move the testes slightly.
However, it is the cremaster muscles that are primarily
responsible for testicular movement within the scrotal pouch.
These two bands of skeletal muscle extend through the inguinal
canal on either side as part of the spermatic cord (see Figure 24 -
8, A), and then attach to the posterior aspect of the testes. When
contracted these “suspender” muscles, which arise from the
internal oblique muscles of the lower abdominal wall, can
dramatically elevate the testes during sexual arousal, exposure
to cold, or threat of injury.
The temperature required for optimal sperm formation is about
3° C below normal body temperature. This is the “functional”
reason that justifies placement of the testes outside the body
cavity (where they are constantly exposed to potential
environmental shock and traumatic injury). In a warm
environment, the scrotum becomes elongated and its skin
appears loose. This permits the testes to descend in the sac
away from the body, thereby keeping them cool. However, in
the cold, the scrotum elevates and becomes heavily wrinkled.
Contraction of the cremaster muscles effectively pulls the testes
upward toward the body wall, keeping them warmer. Both
actions help maintain the temperature of the testes at a more
constant level. Of course, factors other than temperature,
including blood flow dynamics and even sexual selection, are
also cited as reasons for the scrotal placement of the testes.
Penis and Spermatic Cords
The penis (see Figure 24-8) is composed of three cylindrical
masses of erectile tissues. These cavernous tissues are enclosed
in a separate fibrous covering and held together by a covering
of skin. The two larger and uppermost of these cylinders are the
corpora cavernosa. The smaller, lower cylinder, which contains
the urethra, is called the corpus spongiosum (see Figure 24-8,
B). The distal part of the corpus spongiosum overlaps the
terminal end of the two corpora cavernosa. Here it forms a

slightly bulging structure, the glans penis. A loose-fitting,
retractable prepuce (foreskin) encloses most of the glans penis
but leaves the urethral opening unobstructed for urination.
The penis contains the urethra—the terminal duct for both
urinary and reproductive tracts. During sexual arousal, the
erectile tissue of the penis fills with blood. This causes the
organ to become rigid and enlarged in both diameter and length.
The end result is called an erection, which allows the penis to
penetrate the vagina during intercourse. The scrotum and penis
together constitute the external genitalia of males.
The spermatic cords are cylindrical casings of white, fibrous
tissue located in the inguinal canals between the scrotum and
the abdominal cavity. They enclose the vasa deferentia, blood
vessels, lymphatics, and nerves (see Figure 24-8, A).
COMPOSITION OF SEMINAL FLUID
Let's summarize the components of the semen (seminal fluid)
we discussed earlier:
1.The testes and epididymis secretions comprise less than 5% of
the seminal fluid volume.
2.Seminal vesicles secrete approximately 60% of the seminal
fluid volume.
3.The prostate gland secretes about 30% of the seminal fluid
volume.
4.The bulbourethral glands secrete less than 5% of the seminal
fluid volume.
The seminal fluid serves to lubricate, protect, provide
nourishment, and aid in the process of maturing sperm for
ejaculation and survival. Note that sperm originate in the testes
(glands located outside the body), travel inside the abdominal
cavity, and then are expelled outside. In Box 24-2, we outline
the basic neural controls of the male sexual response.
BOX 24-2 FYI
Neural Control of the Male Sexual Response
Recall that all body functions but one have for their ulti mate
goal survival of the individual. Only the function of
reproduction serves a different, longer range, and (in nature's

scheme) more important purpose—survival of the human
species.
Male functions in reproduction consist of the production of
male sex cells (spermatogenesis) and introduction of these cells
into the female body (coitus or sexual intercourse). For coitus
to take place, erection of the penis must first occur, and for
sperm to enter the female body, both the sex cells and
secretions from the accessory glands must be introduced into
the urethra (emission) and semen must be ejaculated from the
penis.
Erection is a parasympathetic reflex initiated mainly by certain
tactile, visual, and mental stimuli. It consists of dilation of the
arteries and arterioles of the penis, which in turn floods and
distends spaces in its erectile tissue and compresses its veins.
Therefore, more blood enters the penis through the dilated
arteries than leaves it through the constricted veins. As a result,
the penis becomes larger and rigid: erection occurs.
Emission is the reflex movement of sex cells, or spermatozoa,
and secretions from the genital ducts and accessory glands into
the prostatic urethra. Once emission has occurred, ejaculation
will follow.
Ejaculation of semen is also a reflex response. It is the usual
outcome of the same stimuli that initiate erection. Ejaculation
and various other responses—notably accelerated heart rate,
increased blood pressure, hyperventilation, dilated skin blood
vessels, and intense sexual excitement—characterize the male
orgasm, or sexual climax.
MALE FERTILITY
Male fertility depends on many factors, but primarily on the
number of sperm ejaculated as well as their size, shape, and
motility (activity). In fact, fertile sperm typically have a
uniform size and shape and are highly motile. Although it takes
just one sperm (and only one sperm) to fertilize an egg, it
appears now that millions of sperm must be ejaculated for this
to occur. According to one recent estimate, when the sperm
count falls below about 25 million/ml of semen, functional

sterility can result.
One hypothesis that may explain why so many sperm must be
ejaculated is that enough sperm must be present to secrete
sufficient hyaluronidase and other hydrolytic enzymes. These
enzymes liquefy the intercellular substance between the cells
that encase each ovum. Without this, a single sperm cannot
penetrate the layer and thus cannot fertilize the egg. Apparently
it takes a large number of sperm to ensure fertilization. In
effect, fertilization is a community effort!
If an ovum (egg) is present in the female reproductive tract
when semen is introduced, then the release of additional
capacitation enzymes from the multitude of sperm come into
play. This mass release of hydrolytic enzymes is vital to
fertilization because it allows the first sperm contacting the
plasma membrane of the egg to actually enter the egg. Once the
plasma membrane of the egg is penetrated, a series of events
take place that eventually culminates in fertilization.
Infertility can also be caused by the production of antibodies
some men make against their own sperm. This is called immune
infertility and is caused by an antigenantibody reaction.
Figure 24-9 shows that, as average plasma testosterone levels
increase during puberty, sperm production begins.
FIGURE 24-9 Testosterone levels and sperm production. Plasma
testosterone levels (red line) rise during fetal development,
when testosterone stimulates early development of male sexual
organs. Testosterone rises again briefly around the time of
birth, which facilitates descent of the testes into the scrotum.
Then at puberty, testosterone rises enough to support sperm
production (blue line) and later tapers off in advanced old age.
Testosterone levels—and thus sperm production—reach a peak
in early adulthood and remain high into old age. In advanced
old age, testosterone production tapers off, causing a drop in
sperm count and fertility.
11. What are the structures that compose the external genitals of

the male?
12. Name the three cylindrical masses of erectile tissue in the
penis.
13. What is the function of the dartos muscle? The cremaster
muscle? How do their actions potentially influence fertility?
14. What factors may influence male fertility?
Cycle of LIFE
Our reproductive systems are unlike other systems in our bodies
with regard to normal changes that occur throughout our life
spans. All other systems perform their functions from the time
they develop in utero until advanced old age. However, both
male and female reproductive systems are “delayed” in that they
cannot function until puberty.
Initial development of the male reproductive organs begins
before birth. At about the seventh week of embryonic
development, genes in the Y chromosome trigger the production
of enough testosterone to stimulate the development of male
reproductive organs from the undifferentiated reproductive
tissues. Without the early secretion of testosterone, the organs
would instead develop into their female counterparts.
Several months before birth, the immature testes descend from
behind the parietal peritoneum and down into the scrotum
(Figure 24-10). At this point, each testis is guided in its descent
by the threadlike, fibrous gubernaculum. It is not uncommon for
the testes to be late in their descent. And sometimes, they fail to
descend until several weeks after birth. There is a spurt of
testosterone levels around the time of birth—this stimulates the
descent of the testes.
The testes and other reproductive organs remain in an immature
state until puberty, when high levels of reproductive hormones
stimulate the final stages of their development. From puberty
until advanced old age, the male reproductive system continues
to operate successfully. In fact, men can sire children until the
time of death!
MECHANISMS OF DISEASE
Disorders of the male reproductive system include a variety of

conditions that cause infertility and even sterility. In addition,
there are occasional disorders resulting from reproductive tract
infections that cause decreased sperm production. Older males
may suffer from benign prostatic hypertrophy, an enlargement
of the prostate, and many older males exhibit various stages of
prostate cancers. Beyond these conditions and diseases are
disorders of the penis and scrotum, including erectile
dysfunction, hydrocele, and hernias.
Find out more about these diseases and disorders of the male
reproductive system online at Mechanisms of Disease: Male
Reproductive System.
FIGURE 24-10 Descent of the testes. Prior to birth, the testes
move from their location near the kidneys and through the
inguinal canal to the scrotum.
The BIG Picture
Reproduction of genes by individual humans provides the
potential contribution of genes to the gene pool of the next
generation of humans—truly a “big picture!” In males, the
reproductive and urinary tracts converge terminally so that
sometimes they are referred to as the genitourinary tract (or
urogenital tract). This “sharing” also means functional sharing
as well. For example, the urethra conducts urine during
micturition but conducts semen during ejaculation. Nervous
regulation of the muscles controlling the bladder, urethra, and
ejaculatory duct prevents the flow of urine from the bladder and
backflow of semen into the bladder during sexual activity.
As we've seen, both the primary and secondary sexual functions
in males depend on complex interrelationships involving
nervous, endocrine, muscular, urinary, and circulatory system
structures. Even the skin can be perceived as a sexual organ—it
receives many of the stimuli needed to produce the sexual
response.
CHAPTER SUMMARY
To download an MP3 version of the chapter summary for use
with your iPod or other portable media player, access the Audio

Chapter Summaries online at http://evolve.elsevier.co m.
Scan this summary after reading the chapter to help you
reinforce the key concepts. Later, use the summary as a quick
review before your class or before a test.
SEXUAL REPRODUCTION
A. The reproductive system is an important part of our
individual homeostasis
1. Vital part of our continuing survival and evolution as humans
2. Organs of the reproductive system are adapted to transferring
genes from parents to their offspring
3. Reproductive systems produce hormones that regulate the
development of secondary sex characteristics that promote
successful reproduction
B. Sexual reproduction—male and female each contribute half
the number of chromosomes required to create the next
generation of children
1. Advantage of sexual reproduction is that the process allows
for the exchange and mixing of genes as sex cells are made and
then recombined
MALE REPRODUCTIVE ORGANS
A. Functions are to produce, transfer, and introduce mature
sperm into the female reproductive tract (Figure 24-1)
1. Classified as essential organs (primary organs) and accessory
organs (secondary organs)
a. Essential organs or gonads of a male are the testes
b. Accessory organs of male reproduction include the genital
ducts, glands, and other supportive structures
B. Perineum—in males, it is an area between the thighs, shaped
roughly like a diamond; extends from the pubic symphysis
anteriorly to the coccyx posteriorly (Figure 24-2)
1. Urogenital triangle—contains the external genitals (penis and
scrotum)
2. Anal triangle—surrounds the anus
TESTES
A. Structure and location
1. Small, egg-shaped glands enclosed in a supporting sac called

the scrotum
2. Suspended in the scrotum by attachments to the scrotal wall
and by the spermatic cords (Figure 24-3)
3. Dense, white, fibrous capsule called the tunica albuginea
encases each testis and then enters each gland
4. Seminiferous tubules in testis open into a plexus called the
rete testis, which is drained by a series of efferent ductules that
emerge from the top of the organ and enter the head of
epididymis
B. Microscopic anatomy of the testis
1. Interstitial (Leydig) cells—hormone-producing cells between
the seminiferous tubules
2. Sustentacular cells (Sertoli or nurse cells)—provide
mechanical support and protection for the developing sperm
attached to their surface
a. Secrete inhibin—inhibits follicle-stimulating hormone (FSH)
production in the anterior pituitary
b. Produce androgen-binding protein that adheres to the steroid
hormone testosterone; makes it more water soluble
c. Sustentacular cells play an important role in spermatogenesis
d. Tight junctions exist between sustentacular cells to divide the
wall of the tubule into two compartments
C. Functions of testis and testosterone (Figure 24-5)
1. Spermatogenesis
a. Production of spermatozoa (sperm)
b. Involves meiosis—a special type of cell division that halves
the number of chromosomes (see Chapter 26)
2. Secretion of hormones by interstitial cells
a. Testosterone—major androgen (masculinizing hormone)
b. Functions of testosterone include: develops and maintains
male secondary sexual characteristics and accessory organs;
develops and maintains adult male sexual behavior; stimulates
protein anabolism; affects fluid and electrolyte balance
D. Hormonal control of reproduction
1. Anterior pituitary gland controls the testes by means of its
gonadotropin-releasing hormone (GnRH)

2. Two major hormones
a. Follicle-stimulating hormone (FSH)—stimulates the
seminiferous tubules to produce sperm more rapidly
b. Luteinizing hormone (LH)—stimulates interstitial cells to
increase their secretions of testosterone
E. Structure of spermatozoa (Figure 24-7)
1. Consists of a head (covered by acrosome), neck, midpiece,
and tail (Figure 24-7, B and C)
REPRODUCTIVE DUCTS
A. Epididymis—single, tightly coiled tube enclosed in a fibrous
casing
1. Lies along the top of and behind the testis (Figure 24-3)
2. Anatomical divisions include head, central body, and tail
3. Each epididymis stores sperm, nourishing them with nutrients
from 1 to 3 weeks
4. Epididymal secretions also eventually become a small portion
of the seminal fluid (semen)
B. Vas deferens—tube but, unlike the epididymis, it has a thick,
muscular wall
1. Contractions of the muscles in the wall of the vasa deferentia
help propel sperm through the duct system
2. Functionally, the vas deferens connects the epididymis with
the ejaculatory duct
C. Ejaculatory duct and urethra
1. Formed by the union of the vas deferens with the ducts from
the seminal vesicle (Figure 24-8)
2. Urethra serves a double function in males; transfers both
urine from the bladder and semen with sperm from the
reproductive ducts
ACCESSORY REPRODUCTIVE GLANDS
A. Seminal vesicles
1. Convoluted pouches nearly 15 cm in length when extended
2. Lie along the lower part of the posterior surface of the
bladder, directly in front of the rectum (Figures 24-1 and 24-8)
3. Secrete an alkaline, viscous, creamy-yellow liquid that makes
up about 60% of the semen volume

B. Prostate gland
1. Lies just below the bladder; shaped roughly like a doughnut
2. Secretes a watery, milky-looking, and slightly acidic fluid
that constitutes about 30% of the seminal fluid volume
C. Bulbourethral glands (Cowper's glands) (Figure 24-8)
1. Resemble peas in size and shape
2. A duct approximately 2.5 cm (1 inch) long connects each
gland with the penile portion of the urethra
3. Secrete an alkaline fluid; important for counteracting the acid
environment of the male urethra and the female vagina
SUPPORTING STRUCTURES
A. Scrotum
1. Skin-covered pouch suspended from the perineal region
(Figure 24-8)
2. Divided internally into two sacs by a septum
3. Each sac contains a testis, epididymis, and lower part of a
spermatic cord
4. Dartos wrinkles the scrotal skin and cremaster muscles
elevate the scrotal pouch
B. Penis and spermatic cords
1. Penis is composed of three cylindrical masses of erectile
tissues (Figure 24-8)
2. Functions—contains the urethra, the terminal duct for both
urinary and reproductive tracts; during sexual arousal, penis
becomes erect, serving as a penetrating copulatory organ during
sexual intercourse
3. Spermatic cords—cylindrical casings of white, fibrous tissue
located in the inguinal canals between the scrotum and the
abdominal cavity
a. Enclose the vasa deferentia, blood vessels, lymphatics, and
nerves (Figure 24-8)
COMPOSITION OF SEMINAL FLUID
A. Seminal fluid serves to lubricate, protect, provide
nourishment, and aid in the process of maturing sperm for
ejaculation and survival
MALE FERTILITY

A. Depends on many factors, but primarily on the number of
sperm ejaculated, size, shape, and motility
B. Functional sterility—when the sperm count falls below about
25 million/ml of semen
C. Sufficient numbers of sperm must be present to secrete
enough hyaluronidase (enzymes that liquefy the substance that
encases an ovum) so that one sperm can penetrate the ovum
D. Infertility can also be caused by the production of antibodies
some men make against their own sperm—immune infertility
E. Male fertility begins at puberty and extends into old age
(Figure 24-9)
REVIEW QUESTIONS
Write out the answers to these questions after reading the
chapter and reviewing the Chapter Summary. If you simply
think through the answer without writing it down, you won't
retain much of your new learning.
1.Name the accessory glands of the male reproductive system.
2.List the genital ducts in the male.
3.List the supporting structures of the male reproductive
system.
4.What is the tunica albuginea? How does it aid in dividing the
testis into lobules?
5.What are the two primary functions of the testes?
6.What are the general functions of testosterone?
7.Discuss the structure of a mature spermatozoon.
8.What is meant by the term capacitation?
9.List the three functions of the epididymis.
10.List the anatomical divisions of the epididymis.
11.Discuss the formation of the ejaculatory ducts.
12.Discuss the type of secretion typical of the prostate gland
and seminal vesicles.
13.What and where are the bulbourethral glands?
14.Describe the structure, location, and function or functions of
the scrotum.
15.Name the three cylindrical masses of erectile, or cavernous,
tissue in the penis.

16.What and where is the glans penis? The prepuce, or foreskin?
17.What is the spermatic cord? From what does it extend, and
what does it contain?
CRITICAL THINKING QUESTIONS
After finishing the Review Questions, write out the answers to
these items to help you apply your new knowledge. Go back to
sections of the chapter that relate to items that you find
difficult.
1.How does the function of reproduction differ from all other
body functions?
2.Can you identify the functions of the male reproductive
system?
3.What is the relationship between the rete testis, seminiferous
tubules, and efferent ductules?
4.How is the prostate gland related to the urethra? What
problems can result from this relationship?
5.Can you list the structures in the reproductive system that
contribute to the formation of seminal fluid?
6.Trace the course of seminal fluid from its formation to
ejaculation.
7.What is the chemical in seminal fluid that is important to
fertility? What is its function?
8.How is the structure of the spermatozoon related to its
function?
CHAPTER 25 Female Reproductive System
STUDENT LEARNING OBJECTIVES
At the completion of this chapter, you should be able to do the
following:
1.Briefly describe the functions of the female reproductive
system.
2.Differentiate between essential organs and accessory organs
of the female reproductive system.
3.Describe the structure of the ovaries and list their functions.
4.Make an outline of oogenesis, listing the major structures
involved.

5.Discuss the layers comprising the walls of the uterus, and the
functions of these layers.
6.Describe the basic functions of the following: uterus, uterine
tubes, vagina.
7.Outline the major components of the external genitalia and
describe their basic functions.
8.Outline in general the recurring cycles of the female
reproductive system.
9.Discuss the roles of hormones in the recurring cycles of
female reproduction.
10.Identify the factors that affect female fertility.
11.Describe the structures involved in breast milk production
and identify the hormones that affect its production.
LANGUAGE OF SCIENCE AND MEDICINE
Before reading the chapter, say each of these terms out loud.
This will help you avoid stumbling over them as you read.
accessory organ (ak-SES-oh-ree OR-gan)
[access- extra, -ory relating to, organ instrument]
alveolus (al-VEE-oh-lus)
[alve- hollow, -olus little] pl., alveoli (al-VEE-oh-lye)
ampulla (am-PUL-ah)
[ampu- flask, -ulla little] pl., ampullae (am-PUL-ee)
anal triangle (AY-nal)
[an- ring (anus), -al relating to]
anterior fornix (an-TEER-ee-or FOR-niks)
[ante- front, -er- more, -or quality, fornix arch] pl., fornices
(FOR-nih-seez)
areola (ah-REE-oh-lah)
[are- area or space, -ola little] pl., areolae, areoles, or areolas
(ah-REE-oh-lee, ah-REE-ohlz, ah-REE-oh-lahz)
body [of the uterus]
(BOD-ee)
cervix (SER-viks)
[cervix neck] pl., cervices or cervixes (SER-veh-seez, SER-
viks-ehz)

clitoris
(KLIT-oh-ris) pl., clitorides (klit-OH-rih-deez)
corpus albicans (KOHR-pus AL-bih-kanz)
[corpus body, albicans whitening] pl., corpora albicantia
(KOHR-pohr-ah al-bih-KAN-shee-ah)
corpus luteum (KOHR-pus LOO-tee-um)
[corpus body, lute- yellow, -um thing] pl., corpora lutea
(KOHR-pohr-ah LOO-tee-ah)
cortex (KOHR-teks)
[cortex bark] pl., cortices (KOR-tih-sees)
ectopic pregnancy (ek-TOP-ik)
[ec- out of, -top- place, -ic relating to]
endometrium (en-doh-MEE-tree-um)
[endo- within, -metr- womb, -um thing] pl., endometria (en-doh-
MEE-tree-ah)
episiotomy (eh-piz-ee-OT-oh-mee)
[episi- vulva, -tom- cut, -y action]
essential organ (OR-gan)
[organ instrument]
estrogen (ES-troh-jen)
[estr- frenzy, -gen produce]
fimbria (FIM-bree-ah)
[fimbria fringe] pl., fimbriae (FIM-bree-ee)
follicle-stimulating hormone (FSH) (FOL-ih-kul-STIM-yoo-lay-
ting HOR-mohn)
[foll- bag, -icle little, hormon- excite]
follicular phase (foh-LIK-yoo-lar fayz)
[foll- bag, -icul- little, -ar relating to]
fornix (FOR-niks)
[fornix arch] pl., fornices (FOR-nih-seez)
fundus (FUN-duss)
[fundus bottom] pl., fundi (FUN-dye)
glans clitoris (glans KLIT-oh-ris)
[glans acorn]
granulosa cell (gran-yoo-LOH-sah sell)
[gran- grain, -ul- little, -osa relating to, cell storeroom]

greater vestibular gland (ves-TIB-yoo-lar)
[vestibul- entrance hall, -ar relating to, gland acorn]
hymen (HYE-men)
[hymen Greek god of marriage]
imperforate hymen (im-PER-fah-rayt HYE-men)
[im- not, -perfor- pierce, -ate state, hymen Greek god of
marriage]
infertility (in-fer-TIL-ih-tee)
[in- not, -fertil- fruitful, -ity state]
infundibulum (in-fun-DIB-yoo-lum)
[infundibulum funnel]
isthmus (iSS-muss)
[ithmus narrow connection or passage]
labia majora (LAY-bee-ah mah-JOH-rah)
[labia lips, majora large] sing., labium majus (LAY-bee-um
MAY-jus)
labia minora (LAY-bee-ah mih-NO-rah)
[labia lips, minora small] sing., labium minor (LAY-bee-um
MYE-nor)
labor
(LAY-bor)
lactation (lak-TAY-shun)
[lact- milk, -ation process]
lactiferous duct (lak-TIF-er-us)
[lact- milk, -fer- bear or carry, -ous relating to, duct lead]
luteal phase (LOO-tee-al fayz)
[lute- yellow, -al relating to]
luteinization (loo-tee-in-ih-ZAY-shun)
[lute- yellow, -ization process]
luteinizing hormone (LH) (loo-tee-in-EYE-zing HOR-mohn)
[lute- yellow, -izing process, hormon- excite]
mammary gland (MAM-er-ee)
[mamma- breast, -ry relating to, gland acorn]
mature follicle
medulla (meh-DUL-ah)

[medulla middle] pl., medullae or medullas (meh-DUL-ee, meh-
DUL-ahz)
menarche (meh-NAR-kee)
[men- month, -arche beginning]
menopause (MEN-oh-pawz)
[men- month, -paus- cease]
menses (MEN-seez)
[menses months] sing., mensis (MEN-sis)
menstrual period (MEN-stroo-al)
[mens- month, -al relating to]
menstruation (men-stroo-AY-shun)
[mens- month, -ation process]
mons pubis (monz PYOO-bis)
[mons mountain, pubis groin] pl., montes pubis (MON-teez
PYOO-bis)
myometrium (my-oh-MEE-tree-um)
[myo- muscle, -metr- womb, -um thing]
nipple (NIP-el)
[nip- beak, -le small]
oogonium (oh-oh-GO-nee-um)
[oo- egg, -gon- offspring, -um thing] pl., oogonia (oh-oh-GO-
nee-ah)
oral contraceptive (OR-al kon-tra-SEP-tiv)
[contra- against, -cept- take or receive (conception), -ive agent]
ovarian follicle (oh-VAIR-ee-an FOL-ih-kul)
[ov- egg, -arian relating to, foll- bag, -icle little]
ovarian medulla (oh-VAIR-ee-an meh-DUL-ah)
[ov- egg, -arian relating to, medulla middle] pl., medullae or
medullas (meh-DUL-ee, meh-DUL-ahz)
ovary (OH-var-ee)
[ov- egg, -ar- relating to, -y location of process]
ovulation (ov-yoo-LAY-shun)
[ov- egg, -ation process]
ovum (OH-vum)
[ovum egg] pl., ova (OH-vah)
perimetrium (pair-ih-MEE-tree-um)

[peri- around, -metr- womb, -um thing]
perineal body (pair-ih-NEE-al BOD-ee)
[peri- around, -ine- excrete (perineum), -al relating to]
perineum (pair-ih-NEE-um)
[peri- around, -ine- excrete, -um thing] pl., perinea (pair-ih-
NEE-ah)
peritonitis (pair-ih-toh-NYE-tis)
[peri- around, -ton- stretch (peritoneum), -itis inflammation]
placenta (plah-SEN-tah)
[placenta flat cake] pl., placentae or placentas (plah-SEN-tee,
plah-SEN-tahz)
posterior fornix (pohs-teer-ee-or FOR-niks)
[poster- behind, -or quality, fornix arch]
prepuce (PREE-pus)
[pre- before, -puc- penis]
primary follicle (PRY-mair-ee FOL-ih-kul)
[prim- first, -ary state, folli- bag, -cle small]
progesterone (pro-JES-ter-ohn)
[pro- provide for, -gester- bearing (pregnancy), -stero- solid or
steroid derivative, -one chemical]
proliferative phase (PROH-lif-er-eh-tiv fayz)
[proli- offspring, -fer- bear or carry, -at- process, -ive relating
to]
retroflexion (ret-roh-FLEK-shen)
[retro- backward, -flex- bend, -ion process]
salpingitis (sal-pin-JYE-tis)
[salping- tube, -itis inflammation]
secretory phase (SEEK-reh-toh-ree fayz)
[secret- separate, -ory relating to]
urogenital triangle (yoor-oh-GEN-ih-tal)
[uro- urine, -gen- produce, -al relating to]
uterus (YOO-ter-us)
[uterus womb]
vagina (vah-JYE-nah)
[vagina sheath]
vaginal orifice (VAH-jih-nal OR-ih-fis)

[vagina- sheath, -al relating to, ori- mouth, -fice- something
made]
vulva (VUL-vah)
[vulva wrapper]
CARLOS and his wife had been trying for years to have a baby
with no success. After a visit to an infertility specialist, they
found that Carlos had a low sperm count. Before suggesting a
solution, the physicians will also check Maria's reproductive
system to confirm that there is an open pathway for the egg.
Finding no blockage in Maria's reproductive tract, the
physicians recommended an intrauterine insemination (IUI). To
increase the chances of a sperm encountering an egg, a
medication called Clomid (clomiphene) was prescribed for
Maria. Clomid works as an ovulatory stimulant and acts as an
antiestrogen agent, causing the body to perceive low estrogen
levels. It is given on about days 5 to 10 of the menstrual cycle.
As you read the rest of this chapter, keep Carlos and Maria in
mind, and see if you can answer questions about their situation
at the end of the chapter.
Now that you have read this chapter, see if you can answer
these questions about Carlos and Maria from the Introductory
Story of this chapter and Chapter 24.
1. What effect will Clomid have on FSH production?
a. Increase FSH production
b. Decrease FSH production
c. No change in FSH production
d. Slight decrease in FSH production followed by a sharp
increase
2. After ovulation, the follicular cells first transform into what?
a. Corpus lucidum
b. Corpus luteum
c. Corpus rubrum
d. Corpus albicans
3. Where in the female reproductive tract should the sperm and
the oocyte meet (hopefully completing the process of
fertilization)?

a. In the cervix
b. In the uterus
c. In the uterine tubes
d. In the ovaries
To solve these questions, you may have to refer to the glossary
or index, other chapters in this textbook, A&P Connect,
Mechanisms of Disease, and other resources.
OVERVIEW OF THE FEMALE REPRODUCTIVE SYSTEM
Function of the Female Reproductive System
The female reproductive system produces gametes called ova
(eggs). The haploid nucleus of the egg must combine with the
haploid nucleus of the sperm if successful fertilization is to
occur. The process and function of sex cell formation
emphasizes the similarity between the male and female
reproductive systems. However, this is where the similarity
ends. Unlike the male system, the female reproductive system
also provides protection and nutrition to the developing
offspring for up to several years after conception, as we shall
see.
Structural Plan of the Female Reproductive System
A number of organs make up the female reproductive system,
making it somewhat complex. For this reason, we need to look
first at the structural plan of the system as a whole (Figure 25-
1). As we stated in the previous chapter, reproductive organs
can be classified as essential organs or accessory organs,
depending on how directly they are involved in producing
offspring. The gonads of women are the paired ovaries (the
essential organs), which produce the ova. The accessory organs
of reproduction in women consist of the following structures:
▪A series of ducts or modified duct structures that includes the
uterine tubes, uterus, and vagina
▪The vulva, or external reproductive organs
▪Additional glands, including the mammary glands (highly
modified sebaceous glands), which secrete milk for the
nourishment of newborn children

FIGURE 25-1 Female reproductive organs. Diagram (sagittal
section) of pelvis showing location of female reproductive
organs.
You can see most of the essential and accessory organs of the
female reproductive system in Figures 25-1, 25-2, and 25-3.
Refer to these figures often as you read through the following
pages.
FIGURE 25-2 Female perineum. Sketch showing outline of the
urogenital triangle (red) and anal triangle (blue).
Perineum
The female perineum is a muscular region within a diamond-
shaped area between the thighs and the vaginal orifice and the
anus (see Figure 25-2). It extends from the pubic symphysis
anteriorly to the coccyx posteriorly. Its lateral boundary on
either side is the ischial tuberosity. A line drawn between the
ischial tuberosities divides the area into two triangles. The
larger urogenital triangle contains the external genitals (labia,
vaginal orifice, clitoris) and urinary opening; the smaller anal
triangle surrounds the anus.
The perineum has great clinical importance because it may be
torn during childbirth. Such tears are often deep, have irregular
edges, and may extend all the way through the perineum,
through the muscular perineal body, and even through the anal
sphincter. Such damage may result in seepage from the rectum
until the laceration is repaired. To avoid these possibilities in a
woman prone to such injuries, a surgical incision known as an
episiotomy may be made in the perineum, particularly at the
birth of a first baby. In current medical practice, episiotomy
procedures are decreasing in frequency and are no longer
performed on a routine basis preceding vaginal delivery of a
baby.
1. What are the essential organs of the female reproductive
system?
2. List the major accessory organs of the female reproductive

system.
3. What is the purpose of an episiotomy?
FIGURE 25-3 Internal female reproductive organs. Posterior
view. Diagram shows left side of uterus and upper portion of
the vagina and the left uterine tube and ovary in a frontal
section. The broad ligament has been removed from the
posterior surface of the uterus and adjacent structures.
OVARIES
Location of the Ovaries
The ovaries are homologous (share the same embryonic origin)
to the testes of the male. They are nodular oval glands with a
puckered, uneven surface. After puberty, they resemble large
almonds in size and shape. One ovary lies on each side of the
uterus, below and behind the uterine tubes.
Each ovary weighs about 3 grams and is attached to the
posterior surface of the broad ligament by the mesovarian
ligament (mesovarium). This structure carries blood vessels,
nerves, and lymphatics. The ovarian ligament anchors the ovary
to the uterus. The distal portion of the uterine tube has fimbriae
that form a cup of fingerlike extensions around the ovary. Note,
however, that most of the fimbriae do not actually attach to it
(see Figure 25-3). Only one of these, the ovarian fimbria,
actually attaches directly with the ovary. Unfortunately, this
configuration makes it possible for a pregnancy to begin in the
pelvic cavity instead of in the uterus, as is normal. Development
of the fetus in a location other than the uterus is referred to as
an ectopic pregnancy (from the Greek ektopos, “displaced”).
Structure and Function of the Ovaries
The ovary, like many organs in the body, consists of two major
layers of tissue: an outer cortex and an inner medulla. Covering
the outer cortex is a layer of flattened epithelial cells called the
germinal epithelium. Deep to the surface layer of germinal
epithelium is a tough layer of connective tissue called the tunica
albuginea. This tough layer covers the ovarian cortex. Hundreds
of thousands of microscopic ovarian follicles are embedded in

the connective tissue matrix of the cortex. Each follicle contains
an immature female sex cell, or oocyte, as well as its
surrounding cells. After puberty, the oocytes and the specialized
cells that surround them are present in varying stages of
development. The ovarian medulla contains supportive
connective tissue cells, blood vessels, nerves, and lymphatics.
Overview of Oogenesis
Now look at Figure 25-4 for a moment and follow the
development of a female sex cell from its origin through its
release (ovulation).
Throughout the process of ovarian development the oocyte
grows in size. So, too, does the number of cell layers
surrounding it. Initially, there is a single layer of flat epithelial
cells that originate from the surface epithelium covering
FIGURE 25-4 Stages of ovarian follicle development. Artist's
rendition shows the successive stages of ovarian follicle and
oocyte development. Begin with the first stage (primary
follicle) and follow clockwise to the final stage (degenerating
corpus luteum). Note that all the stages shown occur over time
to a single follicle. The presence of all these stages at a single
point in time is an artificial arrangement for learning purposes
only.
the ovary. These epithelial cells then change from flat to
cuboidal to produce a layer of stratified cuboidal epithelial cells
called granulosa cells. The multiple layers of granulosa cells
completely surrounds the primary follicle. As maturation
proceeds, the number of granulosa cell layers increases. These
cells then begin secreting increasing amounts of an estrogen-
rich fluid that pools around the oocyte in an enlarging space
called an antrum. The primary follicle matures into a secondary
follicle and, eventually, a mature or Graafian follicle. The
release of an ovum from the mature follicle at the end of
oogenesis is called ovulation. Granulosa cells also secrete the
zona pellucida, a clear gel-like shell that surrounds the oocyte.
When ovulation occurs, blood from the modified granulosa cell

layer fills the antrum. A small quantity of blood may also enter
the peritoneal cavity and irritate its pain-sensitive surface. This
causes the transient lower abdominal pain many women
experience at the time of ovulation. Proliferating granulosa cells
soon replace the blood filling the antrum, forming a yellow
body called the corpus luteum. In turn, the corpus luteum
secretes the hormones progesterone, inhibin, relaxin, and
limited amounts of estrogen. Progesterone and inhibin suppress
follicle-stimulating hormone (FSH) secretion. They also prevent
the continued development of new follicles during the
functional life of the corpus luteum. The small amounts of
relaxin secreted by the corpus luteum each month help “quiet”
or “calm” uterine contractions. This action improves the
chances for successful implantation if fertilization should occur.
If pregnancy does occur, larger amounts of these hormones
continue to be produced by the placenta, as we shall see.
In addition to oogenesis, the ovaries are also endocrine organs,
secreting the female sex hormones. Estrogens (chiefly estradiol
and estrone) and progesterone are secreted by cells of ovarian
tissues. These hormones help regulate reproductive function in
the female—making the ovaries even more essential to female
reproductive function.
We will have a more thorough discussion of oogenesis and
fertilization in Chapter 26. Further discussion of hormonal
regulation of reproductive functions, as well as associated
changes within the ovaries, appears later in this chapter.
4. Briefly describe the location and shape of the ovaries.
5. What is the function of the ovarian follicles?
6. List the major functions of the ovaries.
UTERUS
Location and Support of the Uterus
The uterus is located in the pelvic cavity between the urinary
bladder in front and the rectum behind. However, age,
pregnancy, and distention of related pelvic viscera such as the
bladder may alter the position of the uterus.

Between birth and puberty, the uterus descends gradually from
the lower abdomen into the true pelvis. (Recall from Chapter 9
that the true pelvis is the “lesser pelvis” located below the
pelvic rim. It houses the urinary and reproductive organs.) At
menopause, the uterus decreases in size and assumes a position
deep in the pelvis.
Normally the uterus lies over the superior surface of the
bladder, pointing forward and slightly upward (see Figure 25-
1). The cervix is the lower, narrow part of the uterus: It points
downward and backward, joining the vagina at nearly a right
angle. Two vault-like recesses, the anterior fornix and posterior
fornix, are created where the cervix protrudes into the lumen of
the vagina. These corner spaces may help increase the
probability of fertilization by pooling seminal fluid for a brief
period following intercourse. This in turn helps increase the
number of sperm that enter the uterus, and ultimately, the
uterine tubes where fertilization occurs.
Several ligaments hold the uterus in place but allow its body
considerable movement. In addition, fibers from several
muscles that form the pelvic floor converge to form a node
called the perineal body (see Figure 25-2). This structure also
serves an important role in support of the uterus.
Eight uterine ligaments (three pairs, two single ones) hold the
uterus in its normal position by anchoring it in the pelvic
cavity. These ligaments include the broad (paired), uter osacral
(paired), posterior (single), anterior (single), and round (paired)
ligaments. Six of these so-called ligaments are actually
extensions of the parietal peritoneum running in different
directions. However, the round ligaments are fibromuscular
cords. You can see most of these structures in Figures 25-1 and
25-3.
The uterus may lie in any one of several abnormal positions,
largely because the ligaments hold it so loosely. A common
abnormal position is retroflexion, in which the entire organ is
tilted backward. Retroflexion may allow the uterus to prolapse,
or descend, into the vaginal canal, which can cause chronic

discomfort and pain.
Shape and Structure of the Uterus
In a woman who has never been pregnant, the uterus is pear
shaped and measures approximately 7 cm (3 inches) in length, 5
cm (2 inches) in width at its widest part, and 3 cm (1 inch) in
thickness. Note in Figure 25-3 that the uterus has two main
parts: a wide, upper portion (the body), and a lower, narrow
“neck” (the cervix). The body of the uterus rounds into a
bulging prominence, the fundus. The dome-shaped fundus is
superior to the points of entry of the uterine tubes on both sides.
Three layers comprise the walls of the uterus: (1) the inner
endometrium, (2) a middle myometrium, and (3) an outer
incomplete layer of parietal peritoneum.
Endometrium
A ciliated mucous membrane called the endometrium lines the
uterus. During menstruation and after delivery of a baby, the
outer layers of the endometrium slough off. The endometrium
varies in thickness from 0.5 mm just after the menstrual flow to
about 5 mm near the end of the endometrial cycle.
The endometrium has a rich supply of blood capillaries. It also
has numerous exocrine uterine glands that secrete mucus and
other substances onto the endometrial surface. The mucous
glands in the lining of the cervix produce mucus that changes in
consistency during the female reproductive cycle. Most of the
time, cervical mucus acts as a barrier to sperm. Around the time
of ovulation, however, cervical mucus becomes more slippery
and actually facilitates the movement of sperm through the
cervix and into the body of the uterus.
Myometrium
The myometrium is the thick, middle layer of the uterine wall.
It consists of three layers of smooth muscle fibers. These
muscle fibers extend in all directions: longitudinally,
transversely, and obliquely—and thus give the uterus great
strength. The bundles of smooth muscle fibers are interlaced
with elastic and connective tissue components. The result is a
blending into the endometrial lining with no sharp boundary

between the two layers. The myometrium is thickest in the
fundus and thinnest in the cervix—a good example of the
principle of structural adaptation to function. The fundus must
contract more forcibly than the lower part of the uterine wall to
expel the fetus; the cervix must stretch or dilate to
accommodate the fetus.
Perimetrium
The outermost serous layer of the uterus (the visceral peritoneal
covering), is called the perimetrium. This layer does not
completely cover the surface of the uterus. It is absent over the
entire cervix and the lower one-fourth of the anterior surface of
the uterine body. Look carefully at Figure 25-1 and note that the
parietal peritoneum of the anterior pelvic wall folds back on
itself and becomes the visceral peritoneum covering the top of
the bladder. It then turns upward to cover the upper three
fourths of the anterior surface of the uterine body and continues
up over the fundus and down the posterior surface of the uterus
to the top of the cervix where it is then reflected back to cover
the rectum. The perimetrium, although continuous with the
peritoneal lining, is incomplete in that it does not cover the
entire surface of the uterus. The fact that the entire uterus is not
covered with peritoneum may seem silly to point out, but it has
clinical significance. It makes it possible to perform operations
on this organ without the same risk of infection that occurs in
procedures that cut through the peritoneum.
Function of the Uterus
The uterus has many functions important to successful
reproduction. It serves as part of the female reproductive tract,
permitting sperm from the male to ascend toward the uterine
tubes. If fusion of gametes (fertilization, or conception) occurs,
the developing offspring implants in the endometrial lining of
the uterus and continues its development during the term of
pregnancy (gestation). The tiny endometrial glands produce
nutrient secretions—sometimes called “uterine milk”—to
sustain the developing offspring until a placenta can be
produced. The placenta is a unique organ that permits the

exchange of materials between the offspring's blood and the
maternal blood. A rich network of endometrial capillaries
promotes efficiency of this exchange function. Regular
contractions of the myometrium, or labor, are inhibited during
gestation but become rhythmic and intense as the time of
delivery approaches.
If conception or the successful implantation of the embryo fails,
then the outer layers of the endometrium are shed during
menstruation. Menstruation is a regular event of the female
reproductive cycle. It permits the endometrium to renew itself
in anticipation of conception and implantation during the next
cycle. The myometrial contractions seem to aid menstruation by
promoting the complete sloughing of the outer endometrial
layers (the “period”). Fatigue of the myometrial muscle tissues
may contribute to the abdominal cramping sometimes associated
with menstruation.
UTERINE TUBES
Position and Structure of the Uterine Tubes
The uterine tubes are also sometimes called fallopian tubes, or
oviducts. They are about 10 cm (4 inches) long and are attached
to the uterus at its upper outer angles (see Figures 25-1 and 25-
3). You can see that the uterine tubes lie in the upper free
margin of the broad ligaments. From here they extend upward
and outward toward the sides of the pelvis before curving
downward and backward toward the uterus.
The same three layers (mucous, smooth muscle, and serous) of
the uterus also comprise the uterine tubes. In fact, the mucosal
lining of the tubes is continuous with the peritoneum lining the
pelvic cavity. This has great clinical significance because the
tubal mucosa is also continuous with that of the uterus and
vagina. As a result, the continuous reproductive lining can
become infected by gonococci or other organisms introduced
into the vagina. Inflammation of the tubes (salpingitis) may
readily spread to become inflammation of the peritoneum
(peritonitis)—a very serious condition. Inflammation of the
uterine tubes may also lead to scarring and partial or complete

closure of the lumen. This can happen even if the original
infection is cured with antibiotics. (Note: In the male, there is
no such direct route by which microorganisms can reach the
peritoneum from the exterior.)
Divisions and Tissues of the Uterine Tubes
Each uterine tube consists of three divisions (see Figure 25-3):
(1) a connecting part called the isthmus; (2) a dilated portion
called the ampulla; and (3) a funnel-shaped end called the
infundibulum. The infundibulum lies just above and extends
laterally over the ovary. It opens directly into the peritoneal
cavity, dividing into fringelike projections called fimbriae.
BOX 25-1 FYI
Tubal Ligation
Tubal ligation literally means “tying a tube.” For this reason,
this surgical procedure is often referred to as “having one's
tubes tied.” Tubal ligation involves tying a piece of suture
material around each uterine tube in two places, then cutting
each tube between these two points (see figure). Because sperm
and eggs are thus blocked from meeting, fertilization and
subsequent pregnancy are prevented. Tubal ligation is also
called surgical sterilization and is comparable to vasectomy in
the male.
Tubal ligation.
Function of the Uterine Tubes
The uterine tubes are really extensions of the uterus that
communicate loosely with the ovaries. This arrangement allows
an ovum released from the surface of the ovary to be collected
by the fimbriae. From here the ovum is swept along the uterine
tube by ciliary action toward the body of the uterus.
However, the uterine tubes serve as more than mere transport
channels. The uterine tube is also the site of fertilization. Sperm
and ova most often meet, and fertilization occurs, in the
ampulla of the uterine tube. A relatively small number of the
sperm deposited in the vagina during sexual intercourse move
up the uterine tube, where they meet the ovum being swept

down toward them. Here is where fertilization usually takes
place. Totally blocking the openings into either the distal
(abdominal) or proximal (uterine) ends of both uterine tubes,
for any reason, results in sterility (Box 25-1).
7. Describe the three principal layers of the uterine wall.
8. Describe the anatomical position of the uterus. How is it hel d
in place?
9. List the major functions of the uterus.
10. What are the functions of the uterine (fallopian) tubes?
VAGINA
Structure of the Vagina
The vagina is a collapsible tube about 8 cm (3 inches) long,
situated between the rectum, and the urethra, and the bladder. It
is capable of enormous distention during delivery of a baby. It
is composed mainly of smooth muscle and is lined with mucous
membrane arranged in rugged folds called rugae. The vaginal
mucosa contains numerous tiny exocrine mucous glands that
secrete lubricating fluid during the female sexual response.
Note that the anterior wall of the vagina is shorter than the
posterior wall because of the way the cervix protrudes into the
uppermost portion of the tube (see Figure 25-1). In some
cases—especially in young girls—a fold of mucous membrane,
the hymen, forms a border around the external opening of the
vagina, partially closing the orifice. Occasionally, this structure
completely covers the vaginal outlet, a condition referred to as
imperforate hymen. Perforation must be performed at puberty
before the menstrual flow can escape.
Function of the Vagina
The vagina has several important functions. During sexual
intercourse, the lining of the vagina lubricates and stimulates
the glans penis, which in turn triggers the ejaculation of semen.
Thus the vagina also serves as a receptacle for semen, which
often pools in the anterior or posterior fornix of the vagina.
Here the semen meets the cervix of the uterus. Sperm within the
semen may move further into the female reproductive tract by

“climbing” along fibrous strands of mucus in the cervical canal.
The vagina also serves as the lower portion of the birth canal.
At the time of delivery, the baby is pushed from the body of the
uterus, through the cervical canal, and finally through the
vagina and out of the mother's body. The placenta, or
“afterbirth,” is also expelled through the vagina.
Another important function of the vagina is transport of blood
and tissue shed from the lining of the uterus during
menstruation.
VULVA
Structure of the Vulva
Figure 25-5 shows you the structures that, together, constitute
the female external genitalia. Collectively, these structures are
called the vulva. We've summarized the various components and
their functions for you in the following paragraphs.
The mons pubis is a skin-covered pad of fat over the pubic
symphysis. Coarse pubic hairs appear on this structure at
puberty and persist throughout life.
The labia majora (Latin, “large lips”) are covered with
pigmented skin and hair on the outer surface and are smooth
FIGURE 25-5 Vulva (pudendum). Sketch showing major
features of the external female genitals (genitalia).
and free from hair on the inner surface. Each labium majus is
composed mainly of fat and connective tissue with numerous
sweat and sebaceous glands on the inner surface. Together the
labia majora are homologous to the scrotum in the male.
The labia minora (Latin, “small lips”) are located medially to
the labia majora. Each labium minus is covered with hairless
skin.
The clitoris is composed of erectile tissue. A small portion of it
is visible just behind the junction of the labia minora. Most of
the erectile tissue lies buried beneath the skin of the vulva. The
structure of this organ is homologous to the penile structure of
the male. Like the erectile tissue of the male, the clitoris
becomes engorged with blood during the sexual response.

The glans clitoris is the only visible part of the erectile
structures of the clitoris. It is equivalent to the glans penis in
the male. The glans clitoris is covered with highly sensitive
skin that, during sexual stimulation, produces most of the
female sexual response.
A clitoral foreskin or prepuce forms a hood over the superior
surface of the glans clitoris.
The external urinary meatus (urethral orifice) is the small
opening of the urethra, situated between the clitoris and the
vaginal orifice. The vaginal orifice has a much larger opening
than the urinary meatus. It is located posterior to the meatus.
The greater vestibular glands are two bean-shaped glands, one
on each side of the vaginal orifice. Each gland opens by means
of a single, long duct into the space between the hymen and the
labium minus. These glands, which are also called Bartholin
glands, are of clinical importance because they can be infected
(bartholinitis or Bartholin abscess), particularly by gonococci.
They are homologous to the bulbourethral glands in the male.
Function of the Vulva
The various components of the external genitals of the female
operate alone or separately to accomplish several functions
important to successful reproduction. For example, the
protective features of the mons pubis and labia help prevent
injury to the delicate tissues of the clitoris and vestibule. The
clitoris becomes erect during sexual stimulation. Like the male
glans, it possesses a large number of sensory receptors that feed
information back to the sexual response areas of the brain.
A&P CONNECT
There are many sexually transmitted diseases (STDs) that can
affect the female reproductive tract. Review examples of
important STDs in Sexually Transmitted Diseases online at
A&P Connect.
11. List several functions of the vagina.
12. What is another name for the external genitals of the

female?
13. List the basic features and functions of the external female
genitalia.
14. How are the clitoris of the female and the glans penis of the
male similar in structure and function? Can you explain this?
FEMALE REPRODUCTIVE CYCLES
Recurring Cycles
Many changes recur periodically in the female during the years
between the onset of the menses (menarche) and their cessation
(menopause). Most obvious, of course, is menstruation—the
outward sign of changes in the endometrium. Most women also
note periodic changes in their breasts. But these are only two of
many changes that occur over and over again at fairly uniform
intervals during the approximately three decades of female
reproductive maturity.
We will first look at the major cyclical changes, and then
discuss the mechanisms that produce them.
Ovarian Cycle
Before a female child is born, precursor cells in her ovarian
tissue, called oogonia, begin a type of cell division called
meiosis, which reduces the number of chromosomes in the
daughter cells by half (review Chapter 5, p. 87). By the time the
child is born, her ovaries contain about 250,000 primary
follicles, each containing an oocyte that has temporarily
suspended the meiotic process before it is complete.
Once each month, on about the first day of menstruation, the
oocytes within several primary follicles resume meiosis. At the
same time, the follicular cells surrounding them increase in
number and start to secrete estrogens (and tiny amounts of
progesterone). Usually, only one of these developing follicles
matures and migrates to the surface of the ovary. Just before
ovulation, the meiosis within the oocyte of the mature follicle
stops again. It is this cell (which has not quite completed
meiosis) that is expelled from the ruptured wall of the mature
follicle during ovulation. Meiosis is completed only when, and
if, the head of a sperm cell is later drawn into the ovum during

the process of fertilization.
When does ovulation occur? This is a question of great practical
importance and one that in the past was given many answers.
Today it is known that ovulation usually occurs 14 days before
the next menstrual period begins. (Only in a 28-day menstrual
cycle is this also 14 days after the beginning of the preceding
menstrual cycle, as explained later in this chapter.)
Immediately after ovulation, cells of the ruptured follicle
enlarge. Because of the appearance of lipid-like substances in
them, they are transformed into a golden-colored body, the
corpus luteum. The corpus luteum grows for 7 or 8 days. During
this time, it secretes progesterone in increasing amounts. Then,
provided fertilization of the ovum has not taken place, the size
of the corpus luteum and the amount of its secretions gradually
diminish. In time, the last components of each nonfunctional
corpus luteum are reduced to a white scar called the corpus
albicans, which moves into the central portion of the ovary and
eventually disappears (see Figure 25-4).
Endometrial (Menstrual) Cycle
During menstruation, parts of the compact and spongy layers of
the endometrium slough off. The bleeding that ensues produces
a dark menstrual discharge that generally does not clot.
Between 30 and 100 ml of blood is expelled, with a majority
lost during the first 3 days of the menses. As with the length of
the menstrual cycle, considerable variation is normal. After
menstruation, the cells of these layers proliferate (increase in
size and number), causing the endometrium to reach a thickness
of 2 or 3 mm by the time of ovulation. During this period,
endometrial glands and arterioles grow longer and more coiled.
These two factors contribute to the thickening of the
endometrium.
After ovulation, the endometrium grows still thicker, reaching a
maximum of about 4 to 6 mm. Most of this increase, however, is
probably caused by swelling produced by fluid retention rather
than by further proliferation of endometrial cells. The
increasingly coiled endometrial glands start to secrete their

nutrient fluid during the time between ovulation and the next
menses. Then, the day before menstruation starts again, a drop
in progesterone causes muscle in the walls of the tightly coiled
arterioles to constrict, producing endometrial ischemia. This
leads to death of the tissue, sloughing, and once again,
menstrual bleeding.
The menstrual cycle is customarily divided into phases, named
for major events occurring in each: menses, postmenstrual
phase, ovulation, and premenstrual phase.
1. The menses, or menstrual period, occur on days 1 to 5 of a
new cycle. There is some individual variation, however.
2. The postmenstrual phase occurs between the end of the
menses and ovulation. It is also called the preovulatory phase as
well as the proliferative phase. In a 28-day cycle, it usually
includes cycle days 6 to 13 or 14. However, the length of this
phase varies more than the others. It lasts longer in long cycles
and ends sooner in short cycles. This phase is also called the
follicular phase, because of the high blood estrogen level
resulting from secretion by the developing follicle. Increases in
estrogen levels cause predictable changes in the appearance,
amount, and consistency of cervical mucus. Collectively, these
changes can be used as a fertility sign to predict ovulation (Box
25-2).
3. Ovulation is the rupture of the mature follicle with expulsion
of its ovum into the pelvic cavity (Figure 25-6). It occurs most
often on cycle day 14 in a 28-day cycle. However, ovulation can
occur on different days in cycles of different length, depending
on the length of the preovulatory phase. For example, in a 32-
day cycle the preovulatory phase probably lasts until cycle day
18. Ovulation would then occur on cycle day 19 instead of 14.
Because the majority of women show some month-to-month
variation in the length of their cycles, the day of ovulation in a
current or future cycle cannot be predicted with accuracy based
on the length of previous cycles (see again Box 25-2). However,
there is typically a decrease in basal body temperature just
before ovulation and a rise in temperature at the time of

ovulation. This constitutes yet another “fertility sign” (see
Figure 25-9).
BOX 25-2FYI
Fertility Signs Used in Predicting the Time of Ovulation
Many rhythmic and recurring events that a woman may
recognize on almost a monthly schedule during her reproductive
years are called “fertility signs.” These “signs” represent the
body changes required to permit successful reproduction. They
include cyclical changes in (1) the ovaries, (2) the amount and
consistency of the cervical mucus produced during each cycle,
(3) the myometrium, (4) the vagina, (5) gonadotropin secretion,
(6) body temperature, and (7) mood or “emotional tone.”
Accurately predicting the time of ovulation in any given
menstrual cycle by recognizing one or more of these recurring
fertility signs would obviously be of help in either avoiding or
achieving conception. However, knowing the length of a
previous cycle or even a series of cycles cannot ensure with any
degree of accuracy the time of appearance of other fertility
signs in a current cycle. Nor can it predict how many days the
preovulatory phase will last in the next or some future cycle.
Unfortunately, this means that prior cycle length is not an
accurate fertility sign. This fact accounts for most of the
unreliability of the calendar rhythm method of fertility
planning. Other more sophisticated natural family planning
(NFP) methods are available that are not based on a knowledge
of previous cycle lengths to predict the day of ovulation.
Instead, such natural methods base their judgments about
fertility at any point in a woman's cycle on other changes. For
example, women hopeful of becoming pregnant can predict their
general state of receptiveness through the measurement of basal
body temperature—body temperature taken after awakening at
the same time each day. They can also monitor the cyclical
changes in the amount and consistency of cervical mucus during
their cycle. Changes in basal body temperature and the amount
and consistency of cervical mucus occur in response to changes
in circulating hormones that control ovulation. Typically, use of

NFP for 1 year to avoid pregnancy will result in approximately
25 of every 100 women becoming pregnant.
The time of ovulation also can be approximated by over-the-
counter urine tests that detect the high levels of luteinizing
hormone (LH) associated with ovulation (“LH surge”).
4.The premenstrual phase occurs between ovulation and the
onset of the menses. This phase is also called the luteal phase or
secretory phase, because the corpus luteum secretes
progesterone only during this time. The length of the
premenstrual phase is fairly constant, lasting usually
FIGURE 25-6Ovulation. The rupture of a mature follicle on the
surface of an ovary results in the release of an ovum into the
pelvic cavity. This process of ovulation often occurs on day 14
in a 28-day menstrual cycle, but its exact timing depends on the
length of the postmenstrual (preovulatory) phase. Notice in this
photograph that the ovum released during ovulation is
surrounded by a mass of cells.
14 days—or cycle days 15 to 28 in a 28-day cycle. Differences
in length of the total menstrual cycle therefore exist mainly
because of differences in duration of the postmenstrual rather
than of the premenstrual phase.
Gonadotropic Cycle
As we saw in Chapter 15, the anterior pituitary gland secretes
two hormones called gonadotropins that influence female
reproductive cycles. Their names are follicle-stimulating
hormone (FSH) and luteinizing hormone (LH). The amount of
each gonadotropin secreted varies with a rhythmic regularity
that can be related, as we shall see, to the rhythmic ovarian and
uterine changes just described.
15. Define menarche and menopause.
16. What is the function of the corpus luteum?
17. What is the difference between the proliferative phase and
the luteal or secretory phase?
18. Briefly describe the four phases of the menstrual cycle.

Control of Female Reproductive Cycles
Hormones play a major role in producing the cyclical changes
characteristic of women during their reproductive years. The
following paragraphs provide a brief description of the
mechanisms that produce cyclical changes in the ovaries and
uterus and in the amounts of gonadotropins secreted.
Control of Cyclical Changes in the Ovaries
Cyclical changes in the ovaries result from cyclical changes in
the amounts of gonadotropins secreted by the anterior pituitary
gland. An increasing FSH blood level has two effects: (1) it
stimulates one or more primary follicles and their oocytes to
start growing, and (2) it stimulates the follicular cells to secrete
estrogens. (Developing follicles also secrete very small amounts
of progesterone.)
Because of the influence of FSH on follicle secretion, the level
of estrogens in blood increases gradually for a few days during
the postmenstrual phase. Then suddenly, on about the twelfth
cycle day, it leaps upward to a maximum peak. Scarcely 12
hours after this “estrogen surge,” an “LH surge” occurs and
presumably triggers ovulation a day or two later. This hormone
surge is the basis of the over-the-counter “ovulation test” (see
Box 25-2).
The control of cyclical ovarian changes by the gonadotropins
FSH and LH is summarized for you in Figure 25-7. Refer to this
diagram as you read the following description of cyclical
changes in the ovary.
1. Completion of growth of the follicle and oocyte maturation
with increasing secretion of estrogens before ovulation. LH and
FSH act as synergists to produce these effects.
2. Rupturing of the mature follicle with expulsion of its ovum
(ovulation). Because of this function, LH is sometimes also
called “the ovulating hormone.”
3. Formation of a yellowish body, the corpus luteum, in the
ruptured follicle (process called luteinization). The name
luteinizing hormone refers, obviously, to this LH function—a
function to which, experiments have shown, FSH also

contributes.
The corpus luteum functions as a temporary endocrine gland. It
secretes only during the luteal (postovulatory, or premenstrual)
phase of the menstrual cycle. It secretes progesterone and
estrogen. The blood level of progesterone rises rapidly after the
“LH surge” described earlier. It remains at a high level for
about a week, and then decreases to a very low level
approximately 3 days before menstruation begins again. This
low blood level of progesterone persists during both the
menstrual and the postmenstrual phases. What are its sources?
Not the corpus luteum, which secretes only during the luteal
phase, but the developing follicles and the adrenal cortex.
Blood's estrogen content increases during the luteal phase but to
a lower level than develops before ovulation.
If pregnancy does not occur, lack of sufficient LH and FSH
causes the corpus luteum to regress in about 14 days. The
corpus luteum is then replaced by the corpus albicans. To make
sure you've understood this process, review again Figure 25-4,
which shows the cyclical changes in the ovarian follicles.
Control of Cyclical Changes in the Uterus
Changing blood concentrations of estrogens and progesterone
also bring about cyclical changes in the uterus. As blood
estrogens increase during the postmens trual phase of the
menstrual cycle, they produce the following changes in the
uterus:
▪Thickening of the endometrium
▪Growth of glands and spiral arteries within the endometrium
▪Increase in the water content of the endometrium
▪Increase of myometrial contractions
Increasing blood progesterone concentration during the
premenstrual phase of the menstrual cycle produces changes in
the uterus due to the actions of progesterones. These changes
are favorable for pregnancy—specifically the following:
▪Preparation of the endometrium for the implantation of a
fertilized ovum
▪Increase in the water content of the endometrium

CHAPTER 24 Male Reproductive SystemSTUDENT LEARNING OBJECTIVES

CHAPTER 24 Male Reproductive SystemSTUDENT LEARNING OBJECTIVES

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CHAPTER 24 Male Reproductive SystemSTUDENT LEARNING OBJECTIVES