Chapter 28

Copyright © John Wiley & Sons, Inc. All rights reserved.
Chapter 28
The Reproductive Systems

 Sexual Reproduction is the process in which organisms
produce offspring by means of uniting gametes (sperm
and egg)
o Male reproductive organs secrete androgen hormones,
produce gametes (sperm), and facilitate fertilization
o Female reproductive organs secrete female hormones,
produce gametes (ova), facilitate fertilization and
sustain growth of the embryo and fetus
Reproduction Overview

 Urology is the medical specialty that treats disorders and
diseases of the male reproductive system
 Gynecology is the medical specialty that treats disorders
and diseases of the female reproductive system
o Obstetrics focuses on the care of women during
pregnancy
Reproduction Overview

 The genitals are all the structures of reproduction
o The gonads (the testes in males and ovaries in females)
are the site for gamete production and hormone
secretion
o Various ducts store and transport gametes
o Accessory sex glands produce secretions to protect and
support the gametes
o Supporting structures deliver and/or assist in joining
gametes (penis in male, vagina and uterus in female)
Male ReproductiveAnatomy

 The male gonads are the testes (singular: testis)
o The ducts of the male reproductive system are the:
 vas deferens (ductus deferens)
 ejaculatory ducts
 urethra
o Male reproductive
glands are the:
 seminal vesicles (2)
 Prostate (1)
 bulbourethral glands (2)

 The scrotum is a supporting structure for the testes
o It consists of a sac of loose skin and superficial fascia
that hangs from the root of the penis
o The location and contraction
of muscle fibers (dartos and
cremaster muscles) regulates
the testicular temp to that
required for sperm production
(2-3o
below the core temp)

 The spermatic cord is a supportive structure that
ascends “out of” the scrotum, and consists of:
o The vas deferens
o The testicular artery (of course this
is going into the scrotum)
o Veins and lymphatics that
drain the testes and carry
testosterone to the body
o Autonomic nerves

 The spermatic cord and ilioinguinal nerve pass through
the inguinal canal, a passageway in the aponeuroses of
the abdominal muscles (transversus abdominus, internal
oblique, and external
oblique muscles)
o In women, the round
ligament of the uterus and
the ilioinguinal nerve pass
through a very small
inguinal canal

 The tunica albuginea (collagen) forms septa that divide
each testis into compartments
called lobules
o Each lobule contains 1-3
seminiferous tubules
where sperm are
produced

 Prenatal secretion of testosterone assists testicular
descent and development of male external genital
 Secretion of testosterone at puberty leads to
development of male secondary sexual characteristics
 stimulation of anabolism (musculoskeletal and
protein growth)
 hair growth patterns
 lowering of the voice
 development of libido (sexual drive)
Male Reproductive Physiology

 Spermatozoa are produced in the seminiferous tubules
by sperm stem cells called spermatogonia
 At the beginning of puberty, the
anterior pituitary increases secretion
of the gonadotrophs LH and FSH
o Follicle-stimulating hormone
(FSH) stimulates Sertoli cells
and increases the rate of
spermatogenesis
Spermatogenesis

 LH stimulates Leydig cells, which are located between
seminiferous tubules, to secrete the hormone
testosterone (synthesized from cholesterol)
 Once the degree of spermatogenesis (sperm formation)
required for male reproductive functions
has been achieved,
Sertoli cells release
inhibin, a hormone
that inhibits FSH
Spermatogenesis

Spermatogenesis

 Each day about 300 million sperm complete the process
of spermatogenesis. A sperm contains several structures
that are highly adapted for reaching and penetrating a
secondary oocyte
o The major parts of a sperm are the head and the tail
 the nucleus contains 23 highly condensed
chromosomes (half the normal number)
 covering the anterior two-thirds of the nucleus is
the acrosome
Spermatozoa

 The acrosome is a cap-like vesicle filled with enzymes
(hyaluronidase and proteases)
that help a sperm to penetrate
a secondary oocyte to bring about
fertilization
 The middle piece contains many
mitochondria which provide
the energy (ATP) for locomotion
Spermatozoa

 Before ejaculation, sperm travel via the following route:
o Seminiferous tubules
o Rete testis (network)
o Efferent ducts
o Ductus epididymis
o Vas (ductus)
deferens…
Spermatozoa

 Sperm travelogue continued:
o Vas (ductus) deferens …
o Ejaculatory duct (within
the prostate gland)
o Urethra, which has 3
portions to it:
prostatic
membranous
penile
Spermatozoa

 The accessory glands contribute greatly to the
constituents of the ejaculate
o Seminal vesicles secrete a viscous, alkaline fluid
(mainly during ejaculation) which makes up 60% of
the total volume. It contains fructose (for energy),
prostaglandins (to stimulate smooth muscle
contractions), and clotting proteins (fibrinogen)
 the alkalinity neutralizes the acidity of the male
urethra and the female reproductive tract
Accessory Glands

 The prostate is a chestnut-sized, donut-shaped gland
that secretes about 25% of ejaculate volume. Prostatic
fluid is a milky, slightly acidic solution containing citric
acid (for energy), acid phosphatase, and proteolytic
enzymes (PSA and hyaluronidase)
 The bulbourethral (Cowper’s) gland is a pea-sized gland
inferior to the prostate. It secretes a protective alkaline
mucus that decreases sperm damage in the urethra
Accessory Glands

Accessory Glands

 Semen is a mixture of sperm and seminal fluid, a liquid
that consists of the secretions of the seminiferous
tubules, seminal vesicles, prostate, and bulbourethral
glands
o The volume of semen in a typical ejaculation is 2.5–5
milliliters (mL), with 50–150 million sperm per mL
 when the number falls below 20 million/mL, the
male is likely to be infertile
Semen

 The penis contains the urethra and is a passageway for
the ejaculation of semen and the excretion of urine
o It is cylindrical in shape and consists
of a body, glans penis, and a root
 The body of the penis is composed
of three cylindrical masses of
tissue, each surrounded by
fibrous tissue called the
tunica albuginea
The Penis

 The two dorsolateral masses are the corpora cavernosa
penis, and the smaller midventral mass is the corpus
spongiosum penis (contains
the spongy urethra and
keeps it open during
Ejaculation)
The Penis

 Upon sexual stimulation (visual, tactile, auditory,
olfactory, or imagined), sacral parasympathetic fibers
initiate and maintain an erection
o Under the influence of nitric oxide released from
parasympathetic neurons (“neurogenic NO”), arteries
that supply the penis dilate and blood enters penile
sinuses in the erectile tissue; NO also causes the
smooth muscle within the erectile tissue to relax,
resulting in widening of the blood sinuses
The Male Sexual Response

 After an erection, sympathetic stimulation is necessary
for the rest of the sexual response, including ejaculation
o The smooth muscle sphincter at the base of the urinary
bladder must close, followed by semen being propelled
into the penile portion of the urethra (emission)
o Powerful peristaltic contractions culminate in the
release of semen from
the urethra to
the exterior
The Male Sexual Response

 The organs of the female reproductive system include
the ovaries (female gonads);
the uterine tubes
(fallopian tubes); the
uterus; the vagina;
and the external
organs (collectively
called the vulva,
or pudendum)
Female ReproductiveAnatomy

 The histology of the ovaries reveals the following parts:
o The germinal epithelium covers the surface of the
ovary, but does not give rise to ova – those cells arise
from the yolk sac and migrate to the ovaries
o The ovarian cortex contains the ovarian follicles
o The ovarian medulla
contains blood vessels,
lymphatic vessels
and nerves

 The primary role of the ovaries are to produce mature
2o
oocytes (female gametes) and release one (ovulation)
during each monthly ovarian cycle
o another important
function of the ovaries
are to secrete the female
hormones estrogen,
progesterone, inhibin,
and relaxin

 After receiving the 2o
oocyte at the infundibulum the
uterine tubes provide a site for fertilization, and then
transport for
the ovum if
fertilization occurs
o The uterine
tubes also have
an ampulla and
an isthmus

 The main anchors for the ovaries are the suspensory
ligaments of the ovary (for pelvic wall attachment), and
the ovarian
ligament
(provides an
attachment to
the side wall of
the uterus)

 The broad ligament is a
major support for the
uterus (provides side-to
-side and rotation
support)
oOther supportive
ligaments of the uterus
are depicted in these
graphics

 The uterus is a pear shaped organ situated between the
urinary bladder and the rectum
o It serves as part of the pathway for sperm deposited
in the vagina to reach the uterine tubes
o It is also the site of implantation of a fertilized ovum,
development of the fetus during pregnancy, and
labor
o During reproductive cycles when implantation does
not occur, the uterus is the source of menstrual flow

 Anatomical subdivisions of the uterus include:
o A dome-shaped superior portion called the fundus
o A central portion called the body, that tapers to a
narrow isthmus
o the inferior-most
cervix opens into
the vagina through
the cervical
canal

 The interior of the body of the uterus is called the
uterine cavity
 The cervical canal
has an internal os
and an external os
that opens into
the uterine
cavity and the
vagina, respectively

 The vagina is a fibromuscular canal lined with mucous
membrane that extends from the exterior of the body to
the uterine cervix. It is composed of both longitudinal
and circular muscle, and has 3 basic functions:
o Serve as a passageway
for menstrual flow
o Receive sperm
o Form the lower
birth canal

 The vulva (female external genitalia) refers to the:
o Mons pubis (created by adipose tissue)
o Erectile tissue of the clitoris
o Labia majora (outer limits of
vulva) and labia minora
(covers the vestibule)
o Vestibule, the
area between the
labia minora
o Vaginal orifice
(opening)

 Anterior to the vaginal orifice and posterior to the
clitoris is the opening of the external urethral orifice
o Mucus-secreting paraurethral glands flank the orifice
(homologous to the prostate gland in males)
 On either side of the vaginal orifice itself are the greater
vestibular (Bartholin’s) glands which open by ducts into
a groove between the hymen and labia minora. They
produce a small quantity of lubricating mucous during
sexual arousal

 The perineum denotes the diamond-shaped area medial
to the thighs and buttocks of females (and males) – the
entire undersurface of the pelvis
o It contains the external
genitalia and
anus

 The breasts (mammary glands) are modified sudoriferous
glands that produce milk: Each contains 15–20 lobes
divided into lobules
o Each lobule is
composed of milk-
secreting glands called
alveoli. The nipple has a
pigmented area (areola)
and openings for the
lactiferous ducts

 During reproductive years, nonpregnant females
normally exhibit cyclical changes in the ovaries and
uterus
o Each cycle takes about a month and involves both
oogenesis (ovarian cycle) and preparation of the uterus
to receive a fertilized ovum with hormones secreted by
the hypothalamus, anterior pituitary, and ovaries
controling the main events
Female Reproductive Physiology

 The hormones secreted in the brain constitute the part
of the cycle called the hypothalamic/pituitary cycle.
Those hormones are GnRH, FSH, and LH
oThe reproductive organs in the female pelvis respond
to the brain hormones by cycling at two “lower” levels
 the ovarian cycle occurs in the ovaries where 1o
, 2o
and 3o
follicles are formed
 the uterine cycle refers to the monthly cycling of
the endometrium when a woman is not pregnant
The Female Reproductive Cycle

 The formation of gametes in the ovaries is termed
oogenesis. In contrast to spermatogenesis, which begins
in males at puberty, oogenesis is more complex and
begins in females before they are even born
o During early fetal development, primordial germ cells
migrate from the yolk sac to the ovaries where they
differentiate into oogonia
 Oogonia are diploid (2n) stem cells that divide
mitotically to produce millions of germ cells
The Ovarian Cycle

 Even before birth, most oogonia degenerate, though a
few develop into larger cells called 1o
oocytes that enter
prophase of meiosis I (during fetal development) but do
not complete it until a fortunate few are called upon to
do so during the reproductive years
o During the interim (an arrested
stage of development), each 1o
oocyte is surrounded by follicular
cells in a primordial follicle
The Ovarian Cycle

 At puberty, under the influence of LH and FSH (the brain
gonadotropins), several primordial follicles will be
stimulated each month, although only one will typically
reach the maturity needed for ovulation
o Maturing oocytes within maturing follicles undergo a
series of developmental stages which ultimately brings
one 2o
oocyte within a 3o
follicle to the point of
ovulation
 the ovulated 2o
oocyte will have completed meiosis I,
and so have the haploid number of chromosomes (1n)
The Ovarian Cycle

 As the 1o
oocyte is prepared for ovulation, and receives
the signal to complete meiosis I, two haploid (1n) cells of
unequal size are produced – each with 23 chromosomes
o The smaller cell is called the first
polar body (essentially a packet
of discarded nuclear material)
The Ovarian Cycle
The ovarian cortex with many
follicles in different stages of
development.
o The larger 2o
oocyte inherits
most of the
cytoplasm

 Be aware that the events depicted in these graphics
depict two separate, yet interrelated events: Oocyte
maturation vs. follicle maturation
o The follicle
has important
functions beyond
hosting an
oocyte!
The Ovarian Cycle

The Ovarian Cycle

High levels of
estrogens from
almost mature
follicle stimulate
release of more
GnRH and LH
Hypothalamus
Anterior pituitary
Ovary
Corpus hemorrhagicum
(ruptured follicle)
Almost mature
(graafian) follicle
LH
GnRH
1 High levels of
estrogens from
almost mature
follicle stimulate
release of more
GnRH and LH
Hypothalamus
Anterior pituitary
GnRH promotes
release of FSH
and more LH
Ovary
(ruptured follicle)
Almost mature
(graafian) follicle
LH
GnRH
1
2
High levels of
estrogens from
almost mature
follicle stimulate
release of more
GnRH and LH
LH surge
brings about
ovulation
Ovulated
secondary
oocyte
Hypothalamus
Anterior pituitary
GnRH promotes
release of FSH
and more LH
Ovary
(ruptured follicle)
Almost mature
(graafian) follicle
LH
GnRH
1
2
3
Ovulation

 At ovulation the 3o
follicle (mature Graafian follicle)
ruptures to expel the 2o
oocyte into the pelvic cavity,
normally to be swept into the uterine tube - if not
fertilized, it degenerates
o if sperm are
present and
one penetrates
the 2o
oocyte,
meiosis II resumes
The Ovarian Cycle

 The events of
oogenesis described
thus far are depicted
in this graphic
o The 2o
oocyte is
the cell that most
people call
“the egg”
The Ovarian Cycle

 In the ovary, the mature Graafian follicle has become a
corpus luteum, a temporary structure essential for
establishing and maintaining pregnancy in females
o It secretes estrogens and progesterone, which are
responsible for the thickening of the endometrium and
its development and maintenance, respectively
o After approx. 14 days, if the 2o
oocyte is not fertilized,
the corpus luteum stops secreting progesterone and
degenerates into a corpus albicans (just a mass of
fibrous scar tissue)
The Ovarian Cycle

 Without estrogen, and then with abrupt progesterone
withdrawal, the uterine lining cannot be maintained and
it sloughs (menses) – more on the uterine cycle shortly
 If, on the other hand, pregnancy occurs, the corpus
luteum is “rescued” from degeneration by an LH-like
hormone called human chorionic gonadotrophin (hCG –
produced by the developing embryo). With hCG support,
the corpus luteum goes on to produce hormones well into
the 1st trimester until the placenta can take over
The Ovarian Cycle

 The window of opportunity for fertilization to happen
is approximately 2 days before ovulation to 1 day after
ovulation (the sperm can survive 48-72 hrs. in the
uterine tube)
 At the moment of conception, the successful sperm
penetrates the plasma membrane of the 2o
oocyte and
the nuclear material of the two cells unite to
reconstitute the normal number of chromosomes (2n)
o The new diploid cell is called a zygote
The Ovarian Cycle

 The events of
oogenesis and
follicular
development
are summarized
here
The Ovarian Cycle

 Estrogen, progesterone, relaxin, and
inhibin are all secreted by ovaries
(and the placenta during pregnancy)
o Estrogen is responsible for the
presence of secondary sex characteristics
(adipose tissue in the breasts, mons pubis, abdomen,
and hips, voice pitch, and broad pelvis)
 It also lowers blood cholesterol and assists with
fluid and electrolyte balance and protein anabolism
Ovarian Hormones

 Progesterone is the principal hormone responsible for
maturation of the uterine endometrium, as well as an
important player in stimulating breast development
o It inhibits GnRH and LH through a negative feedback
loop
Ovarian Hormones

 Relaxin is released by the corpus luteum; it relaxes the
myometrium and the pubic
symphysis at the
end of pregnancy
 Inhibin is released by
granulosa cells, and then in
large amount by the corpus
luteum; it inhibits FSH
and LH
Ovarian Hormones

 In many ways the uterine or menstrual cycle closely
parallels the events happening in the ovaries
o Under the influence of the ovarian hormones, the
uterine lining undergoes cyclic events (4 phases)
every 28 days (on average)
 Menses marks the beginning of the cycle
 This is followed at day 5 by the pre-ovulatory phase
 Ovulation occurs on about day 14, after which the
post-ovulatory phase begins
The Uterine Cycle

The Uterine Cycle

 Menses manifests as a degeneration of the endometrium
when levels of progesterone become insufficient
o Prostaglandin released by the “unsupported”
endometrium causes constriction of supply arteries
causing a reduction in blood flow: Bloody endometrial
tissue eventually sloughs, and is passed out through
the two uterine os and into the vagina
 Menstruation lasts 1–7 days with 50–150 ml of
fluids and cells lost
The Uterine Cycle

 Under the influence of estrogens released from the new
developing follicles the pre-ovulatory (proliferative
phase) begins, and the uterine epithelium is restored
 The post-ovulatory (secretory phase) begins around the
time of ovulation. Endometrial glands increase the
secretion of mucous-rich glycogen and the
endometrium reaches maximum thickness and maturity
under the influence of estrogens and progesterone
The Uterine Cycle

 Equivalent  structures
during fetal development
 testes ≈ ovaries
 sperm ≈ ovum (2o
oocyte)
 scrotum ≈ labia majora
 spongy urethra and penile
skin ≈ labia minora
 glans penis ≈ clitoris
 prostate gland ≈
paraurethral glands
 bulbourethral glands ≈
vestibular glands
Homologous Structures

 As in the male, the initiation of the sexual response
results in stimulation of sacral parasympathetic fibers
and nitric oxide dilation of the erectile tissues – in this
case, of the clitoris
o Orgasm occurs at the peak of the plateau phase of the
sexual response. Sexual climax culminates in a
sympathetic discharge, accompanied by quick cycles of
muscle contraction in the lower pelvic muscles and an
intense feeling of euphoria
The Female Sexual Response

 The period after orgasm is known as the refractory
period. During this time, release of the neurohormones
oxytocin and prolactin produce a feeling of relaxation
o Release of these hormones (and others, like
vasopressin) also serves as a reward mechanism that
regulates pair-bonding and sexual imprinting
between the partners
The Female Sexual Response

 Benign prostatic hypertrophy is an enlargement of the
prostate gland in the absence of cancer. It is a very
common affliction as men age, resulting in obstruction of
urine flow and inability to completely empty the bladder
 Impotence is the inability to maintain erection long
enough for sexual intercourse
 Primary infertility describes couples who have never
been able to become pregnant after at least 1 year of
unprotected sex
Disruptions of Homeostasis

 Menstrual Abnormalities
o Amenorrhea is the absence of menstruation
o Dysmenorrhea describes unusual menstrual discomfort
(usually indicates an excess of prostaglandin secretion)
o Disfunctional uterine bleeding (DUB) is abnormal
uterine bleeding in the absence of organic disease
(usually an estrogen/progesterone imbalance)
o PMS (premenstrual syndrome) indicates a mild distress
near end of postovulatory (luteal) phase
Disruptions of Homeostasis

Chapter 28

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