Reprodactive Physiology

1. CHAPTER 9
Reproductive physiology
1

2. Introduction
• Reproductive system:
does not contribute to homeostasis and is not essential for
survival of an individual
Significance
Procreation: serves primarily the purpose of perpetuating
the species
For recreational and relational purposes
2

3. Sex determination and differentiation
• Somatic(body) cells contain 46 chromosomes (the diploid
number) or 23 pairs of homologous chromosomes
• Gametes – germ cells or sex cells
- functional reproductive cells (ova or spermatozoa)
- a haploid cells (contain only one member of each
homologous pair)
- sperm + egg (fertilization)  zygote (diploid cell)
Sex determination
• 23 pairs of chromosomes 22 pairs=autosomal
chromosomes
1 pair =sex chromosomes
3

4. • The sex of an individual is determined by the combination of
sex chromosomes
– Genetic males  XY sex chromosomes
– Genetic females XX sex chromosomes
• Fertilization  genetic sex
– If X-bearing sperm + X-bearing ovum = genetic female
– If Y-bearing sperm + X-bearing ovum = genetic male
• Genetic sex (depends on the combination of sex chromosomes
at the time of conception) determines gonadal sex (i.e.,
whether testes or ovaries develop)
4

5. The Male and Female Reproductive Physiology
• The two most basic components of the reproductive system are
the gonads and the reproductive tract.
• The gonads (testes and ovaries) perform dual function
Producing gametes (gametogenesis) - spermatozoa
(sperm) in the male & ova (eggs) in the female
Secreting sex hormones - testosterone in males and
estrogen and progesterone in females
• The reproductive tract is involved in several aspects of
gametes(egg and sperm) development, transport and, in
women, allows fertilization, implantation, and gestation
6

6. The Male Reproductive System
• The male reproductive system includes:
 the two testes (singular: testis)
 the system of ducts that store and transport sperm to
the exterior
the glands that empty into these ducts
 the penis
• The duct system, glands, and penis constitute the male
accessory reproductive organs.
• Function:
1. Production of sperm (spermatogenesis)
2. Delivery of sperm to the female
7

7. 8

8. • The rete testis is continuous with small ducts, the efferent
ductules, that lead the sperm out of the testis into the head of
the epididymis on the superior pole of the testis.
• Once in the epididymis, the sperm pass from the head, to the
body, to the tail of the epididymis and then to the vas (ductus)
deferens.
• Viable sperm can be stored in the tail of the epididymis and the
vas deferens for several months
• Seminiferous tubules/lobules → Tubuli recti → Rete testis →
Ductuli efferentes→ Epididymis →Vas deferens → Ejaculatory
duct→ Urethra
10

9. 11

10. 12

11. Spermatogenesis
• The process of continuous germ cell differentiation to produce
spermatozoa
• Occurs in the seminiferous tubules as the result of stimulation
by anterior pituitary gonadotropic hormones
• Begins at an average age of 13 years
• Spermatogenesis involves the processes of mitosis and meiosis.
• During formation of the embryo, the primordial germ cells
migrate into the testes and become immature germ cells called
spermatogonia
13

12. • Three phases of spermatogenesis are:
1. Proliferation of spermatogonia by mitosis
2. Generation of genetic diversity by meiosis
3. Maturation of sperm
14

13. Spermatogonium (at puberty)
Mitosis (in the outermost layer)
spermatogonium A + spermatogonium B
Final mitotic division
primary spermatocyte
Meiosis I
secondary spermatocyte
Meiosis II
spermatids
spermiogenesis
spermatozoa(in lumen)
• The process of spermatogenesis takes about 72 days
15

14. 16

15. 17

16. 18

17. Anatomy of a spermatozoon
• Spermatozoon has 3 parts
1. Head
• Contains:
– Nucleus - the house of genetic information (DNA)
– Acrosome (the tip of the nucleus ) - contains several
enzymes that play an important role in the process of
fertilization (for penetration the ovum)
2. Midpiece:
– Rich in mitochondria - provide the energy for movement
3. Tail
– Provides a swimming action
19

18. 20
Parts of spermatozoon

19. Hormonal Factors That Stimulate
Spermatogenesis
• Testosterone, secreted by the Leydig cells located in the
interstitium of the testis
essential for both mitosis and meiosis of the germ cells
• LH, secreted by the anterior pituitary gland, stimulates the
Leydig cells to secrete testosterone.
• FSH, also secreted by the anterior pituitary gland, stimulates
the sertoli cells
without this stimulation, the conversion of the spermatids to
sperm (the process of spermiogenesis) will not occur
needed for spermatid remodeling
21

20. • Estrogens, formed from testosterone by the sertoli cells when
they are stimulated by FSH, are probably also essential for
spermiogenesis
• Growth hormone
• ↑ Leydig cells response to LH
22

21. Maturation of Sperm in the Epididymis
• Sperm removed from the seminiferous tubules and from the
early portions of the epididymis are nonmotile, and they cannot
fertilize an ovum
• However, after the sperm have been in the epididymis for some
18 to 24 hours, they develop the capability of motility, even
though several inhibitory proteins in the epididymal fluid still
prevent final motility until after ejaculation.
• Sperm’s capacity to fertilize is enhanced even further by
exposure to secretions of the female reproductive tract
• Enhancement of sperm’s capacity in the male and female
reproductive tracts is known as capacitation
23

22. Storage of Sperm
• The two testes of the human adult form up to 120 million
sperm each day.
• A small quantity of these can be stored in the epididymis, but
most are stored in the vas deferens.
• They can remain stored, maintaining their fertility, for at least
a month.
• The sertoli cells and the epithelium of the epididymis secrete a
special nutrient fluids (simple sugars), to nourish sperm, that
is ejaculated along with the sperm
24

23. Physiology of the Mature Sperm
• The normal motile, fertile sperm are capable of flagellated
movement through the fluid medium at velocities of 1 to 4
mm/min.
• The activity of sperm is greatly enhanced in a neutral and
slightly alkaline medium but it is greatly depressed in a
mildly acidic medium.
• A strong acidic medium can cause rapid death of sperm.
• The activity of sperm increases markedly with increasing
temperature, but so does the rate of metabolism, causing the
life of the sperm to be considerably shortened
25

24. Effect of Sperm Count on Fertility
• The usual quantity of semen ejaculated during each coitus
averages about 3.5 milliliters, and in each milliliter of semen
is an average of about 120 million sperm
• When the number of sperm in each milliliter falls below about
20 million, the person is likely to be infertile
26

25. Effect of Sperm Morphology and Motility on Fertility
• Sometimes as many as one half the sperm are found to be
abnormal physically, having two heads, abnormally shaped
heads, or abnormal tails, at other times they are either entirely
nonmotile or relatively nonmotile.
• Whenever the majority of the sperm are morphologically
abnormal or are nonmotile, the person is likely to be infertile

26. Sertoli Cells
• Sertoli cells are the true epithelial cells of the seminiferous
epithelium and extend from the basal lamina to the lumen
Functions of the sertoli cells
1. Provide Sertoli cell barrier to chemicals in the plasma
2. Nourish developing sperm
3. Secrete luminal fluid, including androgen-binding protein
- to maintain a very high level of testosterone
4. Respond to stimulation by testosterone and FSH to secrete
paracrine agents that stimulate sperm proliferation and
differentiation
5. Secrete the protein hormone inhibin, which inhibits FSH
secretion from the pituitary
28

27. 6. Secrete paracrine agents that influence the function of Leydig
cells
7. Phagocytize defective sperm
8. Secrete, during embryonic life, Müllerian inhibiting substance
(MIS), which causes the primordial female duct system to
regress
29

28. Leydig cells
• Leydig cells are steroidogenic stromal cells (produce
testosterone )
• Are almost nonexistent in the testes during childhood when the
testes secrete almost no testosterone, but they are numerous in
the newborn male infant for the first few months of life and in
the adult male any time after puberty
• Stimulated by LH from the anterior pituitary gland
30

29. Testosterone and Other Male
Sex Hormones
• The testes secrete several male sex hormones, which are
collectively called androgens
- Testosterone
- Dihydrotestosterone
- Androstenedione
• Testosterone is so much more abundant than the others
31

30. Effects of Testosterone in the Male
1. Required for initiation and maintenance of spermatogenesis
(acts via Sertoli cells)
2. Decreases GnRH secretion via an action on the hypothalamus
3. Inhibits LH secretion via a direct action on the anterior
pituitary
4. Induces differentiation of male accessory reproductive organs
and maintains their function
5. Induces male secondary sex characteristics; opposes action of
estrogen on breast growth
32

31. 33

32. 6. Stimulates protein anabolism, bone growth, and cessation of
bone growth
7. Required for sex drive and may enhance aggressive behavior
8. Stimulates erythropoietin secretion by the kidneys
9. Cause descent of the testes into the scrotum during the last 2
to 3 months of gestation
Cryptorchidism
• Failure of a testis to descend from the abdomen into the
scrotum at or near the time of birth of a fetus
10. Testosterone increases muscle development
34

33. 11. Causes growth of hair
 over the pubis
 upward along the linea alba of the abdomen sometimes to
the umbilicus and above, on the face, usually on the chest,
and less often on other regions of the body, such as the
back.
12. Testosterone decreases the growth of hair on the top of the
head
35

34. Functions of The Male Accessory Sex Glands
Function of the Seminal Vesicles
1. Supply fructose, which serves as the primary energy source
for ejaculated sperm
2. Secrete prostaglandins, which stimulate contractions of the
smooth muscle in both the male and female reproductive
tracts, thereby helping to transport sperm from their storage
site in the male to the site of fertilization in the female oviduct
3. Provide about 60% of the semen volume, which helps wash
the sperm into the urethra and also dilutes the thick mass of
sperm, enabling them to become mobile
4. Secrete fibrinogen, a precursor of fibrin, which forms the
meshwork of a clot
36

35. Function of the Prostate Gland
1. Secretes an alkaline fluid that neutralizes the acidic vaginal
secretions
2. Provides clotting enzymes
-helping keep the ejaculated sperm in the female
reproductive tract during withdrawal of the penis
3. Releases prostate specific antigen(PSA)
- a fibrin-degrading enzyme, thus releasing mobile sperm
within the female tract
During sexual arousal, the bulbourethral glands secrete a
mucus-like substance that provides lubrication for sexual
intercourse.
37

36. Semen
• Semen, which is ejaculated during the male sexual act, is
composed of the fluid and sperm from the vas deferens (about
10 %of the total), fluid from the seminal vesicles (almost
60%), fluid from the prostate gland (about 30%), and small
amounts from the mucous glands, especially the bulbourethral
glands.
• Is a mixture of accessory sex gland secretions, sperm, and
mucus
• The average pH of the combined semen is about 7.5
38

37. Male Sexual Act
• The most important source of sensory nerve signals for initiating the
male sexual act is the glans penis.
Stages of the Male Sexual Act
 Penile erection and lubrication
- Hardening of the normally flaccid penis to permit its entry into
the vagina
- Accomplished by engorgement of the penis erectile tissue
with blood as a result of marked parasympathetically induced
vasodilation of the penile arterioles and mechanical compression of
the veins
- Parasympathetic impulses promote secretion of lubricating
mucus from the bulbourethral glands and the urethral glands
39

38.  Ejaculation
- forceful expulsion of semen into the urethra and out of the penis
1. Emission phase:
- Emptying of sperm and accessory sex gland secretions (semen)
into the urethra
- Accomplished by sympathetically induced contraction of the
smooth muscle in the walls of the ducts and accessory sex glands
2. Expulsion phase:
- Forceful expulsion of semen from the penis
- Due to motor-neuron-induced contraction of the skeletal muscles
at the base of the penis
40

39. • The entire period of emission and expulsion is called the male
orgasm.
 At its termination, the male sexual excitement disappears
almost entirely within 1 to 2 minutes and erection ceases, a
process called resolution
41

40. The Female Reproductive System
• The female reproductive system is composed of the gonads,
called ovaries, and the female reproductive tract(oviducts,
uterus, cervix, vagina) and external genitalia
• Function:
1. Production of ova (oogenesis)
2. Reception of sperm
3. Transport of the sperm and ovum to a common site for
union ( =fertilization, or conception)
4. Maintenance of the developing fetus
5. Giving birth to the baby (=parturition)
6. Nourishing the infant after birth by milk production
(=lactation)
42

41. 43

42. 44

43. The Ovary
• Location:- within a fold of peritoneum called the broad
ligament, usually close to the lateral wall of the pelvic cavity.
• Consists of an outer cortex and an inner medulla, without a
sharp demarcation
• The medulla contains nerves and blood vessels.
• The cortex of the ovary is composed of a densely cellular
stroma. Within this stroma reside the ovarian follicles which
contain a primary oocyte surrounded by follicle cells.
• There are no ducts emerging from the ovary to convey its
gametes to the reproductive tract
45

44. 46

45. Ovarian Functions
1. Oogenesis, the production of gametes during the fetal period
2. Maturation of the oocyte
3. Expulsion of the mature oocyte (ovulation)
4. Secretion of the female steroidal sex hormones, (estrogen
and progesterone), as well as the peptide hormone inhibin
47

46. Oogenesis
• The process through which the mature female gamete is
formed
• At birth, the ovaries contain an estimated total of two to
four million eggs, and no new ones appear after birth.
• Only a few, perhaps 400, will be ovulated during a
woman’s life time. All the others degenerate at some point
in their development
• During early in utero development, the primitive germ
cells, or oogonia (singular, oogonium), a term analogous
to spermatogonia in the male, undergo numerous mitotic
divisions
48

47. • Around the 7th month after conception, the fetal oogonia cease
dividing, & from this point on no new germ cells are generated
• Still in the fetus, all the oogonia develop into primary oocytes
(analogous to primary spermatocytes), which then begin a
first meiotic division by replicating their DNA. They do not,
however, complete the division in the fetus.
• Accordingly, all the eggs present at birth are primary oocytes
containing 46 chromosomes, each with two sister chromatids.
The cells are said to be in a state of meiotic arrest.
49

48. • This state continues until puberty and the onset of renewed
activity in the ovaries.
• The first meiotic division will be completed during puberty
• This first meiotic division is analogous to the division of the
primary spermatocyte, and each daughter cell receives 23
chromosomes, each with two chromatids
• In the first meiotic division, however, one of the two daughter
cells, the secondary oocyte, retains virtually all the cytoplasm.
• The other, termed the first polar body, is very small and
nonfunctional.
• Thus, the primary oocyte, which is already as large as the egg
will be, passes on to the secondary oocyte half of its
chromosomes but almost all of its nutrient-rich cytoplasm.
50

49. • The second meiotic division occurs in a fallopian tube after
ovulation, but only if the secondary oocyte is fertilized—that
is, penetrated by a sperm.
• As a result of this second meiotic division, the daughter cells
each receive 23 chromosomes, each with a single chromatid.
• The net result of oogenesis is that each primary oocyte can
produce only one ovum. In contrast, each primary
spermatocyte produces four viable spermatozoa.
51

50. 52

51. 53

52. Follicular development(Folliculogenesis)
• is the process by which follicles develop & mature
• Throughout their life in the ovaries, the eggs exist in
structures known as follicles.
• Follicles begin as primordial follicles, which consist of one
primary oocyte surrounded by a single layer of cells called
granulosa cells.
• Further development from the primordial follicle stage is
characterized by an increase in the size of the oocyte, a
proliferation of the granulosa cells into multiple layers, and
the separation of the oocyte from the inner granulosa cells by
a thick layer of material, the zona pellucida
54

53. • The granulosa cells secrete estrogen, small amounts of
progesterone just before ovulation, and the peptide hormone
inhibin.
• As the follicle grows by mitosis of granulosa cells, connective
tissue cells surrounding the granulosa cells differentiate and
form layers known as the theca, which play an important role
in estrogen secretion by the granulosa cells
• The newly acquired theca cells are analogous to testicular
Leydig cells in that they reside outside the epithelial "nurse"
cells, express the LH receptor, and produce androgens. the
major product of theca cells is androstenedione, as opposed
to testosterone
55

54. • Shortly after this, the primary oocyte reaches full size (115 m
in diameter), and a fluid-filled space, the antrum, begins to
form in the midst of the granulosa cells as a result of fluid
they secrete.
• Only one of the larger antral follicles, the dominant follicle,
continues to develop, and the other follicles (in both ovaries)
that had begun to enlarge undergo a degenerative process
called atresia (an example of programmed cell death, or
apoptosis).
• The eggs in the degenerating follicles also die.
56

55. • As the dominant follicle enlarges, mainly as a result of its
expanding antrum (increase in fluid), the granulosa cell layers
surrounding the egg form a mound that projects into the
antrum and is termed the cumulus oophorous(corona
radiata)
• As the time of ovulation approaches, the egg (a primary
oocyte) emerges from meiotic arrest and completes its first
meiotic division to become a secondary oocyte
• The cumulus separates from the follicle wall so that it and the
oocyte float free in the antral fluid.
57

56. • The mature follicle (also termed a graafian follicle) becomes so
large (diameter about 1.5 cm) that it balloons out on the surface of
the ovary.
• Ovulation occurs when the thin walls of the follicle and ovary at
the site where they are joined rupture because of enzymatic
digestion.
• The secondary oocyte, surrounded by its tightly adhering zona
pellucida and granulosa cells, as well as the cumulus, is carried out
of the ovary and onto the ovarian surface by the antral fluid.
• All this happens on approximately day 14 of the menstrual cycle.
58

57. • After the mature follicle discharges its antral fluid and egg, it
collapses around the antrum and undergoes a rapid
transformation. The granulosa cells enlarge greatly, and the
entire glandlike structure formed is known as the corpus
luteum, which secretes estrogen, progesterone, and inhibin.
59

58. 60

59. 61

60. 62

61. Sites of Synthesis of Ovarian Hormones
• Estrogen is synthesized and released into the blood during the
follicular phase mainly by the granulosa cells. After ovulation,
estrogen is synthesized and released by the corpus luteum.
• Progesterone, the other major ovarian steroid hormone, is
synthesized and released in very small amounts by the
granulosa and theca cells just before ovulation, but its major
source is the corpus luteum.
• Inhibin, a peptide hormone, is secreted by both the granulosa
cells and the corpus luteum.
63

62. Control of Ovarian Function
• The major factors controlling ovarian function are analogous
to the controls described for testicular function.
• They constitute a hormonal system made up of GnRH, the
anterior pituitary gonadotropins FSH and LH, and gonadal sex
hormones—estrogen and progesterone.
64

63. Menstrual Cycle
• Menstruation : periodic shedding of the stratum functionale
of the endometrium, which becomes thickened prior to
menstruation under the stimulation of ovarian steroid hormones
• The duration of the cycle averages 28 days
• A woman’s first menstruation, termed menarche, occurs around
age 12 years
65

64. • There are two significant results of the female sexual cycle.
• First, only a single ovum is normally released from the ovaries
each month, so that normally only a single fetus will begin to
grow at a time.
• Second, the uterine endometrium is prepared in advance for
implantation of the fertilized ovum at the required time of the
month.
66

65. Phases of the Menstrual Cycle
Cyclic Changes in the Ovaries
• Because it is a cycle, there is no beginning or end and the
changes are generally gradual. However, it is convenient to call
the first day of menstruation “day 1” of the cycle .
• It is also convenient to divide the cycle into phases based on
changes that occur in the ovary and in the endometrium.
• The ovaries are in the follicular phase from the first day of
menstruation until the day of ovulation.
• After ovulation, the ovaries are in the luteal phase until the
first day of menstruation
67

66. Follicular Phase
• During the follicular phase of the ovaries, which lasts from
day 1 to about day 13 of the cycle (this duration is highly
variable), some of the primary follicles grow, develop
vesicles, and become secondary follicles.
• Toward the end of the follicular phase, one follicle in one
ovary reaches maturity and becomes a graafian follicle.
• As follicles grow, the granulosa cells secrete an increasing
amount of estradiol (the principal estrogen), which reaches
its highest concentration in the blood two days before
ovulation at about day 12 of the cycle.

67. • The growth of the follicles and the secretion of estradiol are
stimulated by, and dependent upon, FSH secreted from the
anterior pituitary.
• FSH and estradiol also stimulate the production of LH
receptors in the graafian follicle. This prepares the graafian
follicle for the next major event in the cycle
• The LH surge begins about 24 hours before ovulation and
reaches its peak about 16 hours before ovulation.
• The surge in LH secretion causes the wall of the graafian
follicle to rupture at about day 14 and causes ovulation
69

68. Luteal Phase
• After ovulation, the empty follicle is stimulated by LH to
become a new structure—the corpus luteum
• The corpus luteum secretes both estradiol and progesterone.
• Progesterone rises rapidly to a peak level during the luteal
phase, approximately one week after ovulation
• The high levels of progesterone combined with estradiol
during the luteal phase exert an inhibitory, or negative
feedback, effect on FSH and LH secretion
70

69. • There is also evidence that the corpus luteum produces inhibin
during the luteal phase, which may help to suppress FSH
secretion or action.
• Estrogen and progesterone levels fall during the late luteal
phase (starting about day 22) because the corpus luteum
regresses and stops functioning.
• With the declining function of the corpus luteum, estrogen and
progesterone fall to very low levels by day 28 of the cycle.
• The withdrawal of ovarian steroids causes menstruation and
permits a new cycle of follicle development to progress.
71

70. Cyclic Changes in the Endometrium
• Three phases can be identified on the basis of changes in the
endometrium:
(1) The proliferative phase
(2) The secretory phase
(3) The menstrual phase
Proliferative(estrogen) phase
• Occurs while the ovary is in its follicular phase.
• The increasing amounts of estradiol secreted by the developing
follicles stimulate growth (proliferation) of the stratum
functionale of the endometrium.
• Coiled blood vessels called spiral arteries develop in the
endometrium during this phase.
72

71. Secretory (progestational) phase
• Occurs when the ovary is in its luteal phase.
• In this phase, increased progesterone secretion by the corpus
luteum stimulates the development of uterine glands.
• As a result of the combined actions of estradiol and
progesterone, the endometrium becomes thick, vascular,
and “spongy” in appearance, and the uterine glands become
engorged with glycogen during the phase following ovulation.
• The endometrium is therefore well prepared to accept and
nourish an embryo if fertilization occur.
73

72. Menstrual phase
• Characterized by discharge of blood and endometrial debris
from the vagina
• Occurs as a result of the fall in ovarian hormone secretion
during the late luteal phase.
• Necrosis (cellular death) and sloughing of the stratum
functionale of the endometrium may be produced by
constriction of the spiral arteries.
74

73. Some Effects of Female Sex Steroids
Estrogen
1. Stimulates growth of ovary and follicles (local effects)
2. Stimulates growth of smooth muscle and proliferation of
epithelial linings of reproductive tract.
3. Stimulates external genitalia growth, particularly during
puberty
4. Stimulates breast growth, particularly ducts and fat deposition
during puberty
5. Stimulates female body configuration development during
puberty: narrow shoulders, broad hips, female fat distribution
(deposition on hips and breasts)
75

74. 6. Stimulates bone growth and ultimate cessation of bone growth
(closure of epiphyseal plates)
7. Has feedback effects on hypothalamus and anterior pituitary
8. Stimulates prolactin secretion but inhibits prolactin’s milk-
inducing action on the breasts
9. Protects against atherosclerosis by effects on plasma
cholesterol, blood vessels, and blood clotting
76

75. Progesterone
1. Converts the estrogen-primed endometrium to an actively
secreting tissue suitable for implantation of an embryo
2. Induces thick, sticky cervical mucus
3. Decreases contractions of fallopian tubes and myometrium
4. Decreases proliferation of vaginal epithelial cells
5. Stimulates breast growth, particularly glandular tissue
6. Inhibits milk-inducing effects of prolactin
7. Has negative feedback effects on FSH and LH secretion
during luteal phase
8. Increases body temperature (at the time of ovulation)
77

76. Fertilization
• The union of the two germ cells, the ovum and the sperm
• Restores chromosome number to 46 and initiating the
development of a new individual
• Occurs in the ampulla
• Thus, both the ovum and the sperm must be transported from
their gonadal site of production to the ampulla.
Ovum Transport to The Oviduct
• The ovum is released into the peritoneal cavity at ovulation
• It picked up by fimbria of the oviduct
• Within the oviduct, the ovum is rapidly propelled by peristaltic
contractions and ciliary action to the ampulla
78

77. Sperm Transport to The Oviduct
• Under estrogen dominance (around the time of ovulation),
cervical mucus becomes thin and watery enough to permit
sperm to penetrate
• Muscular contractions of the vagina, cervix, and uterus; ciliary
movement; peristaltic activity; and fluid flow in the oviducts
assist transport
79

78. Process of fertilization
1. The fertilizing sperm penetrates the corona radiata via
membrane-bound enzymes in the plasma membrane of its
head and binds to ZP3 receptors on the zona pellucida.
2. Binding of sperm to these receptors triggers the acrosome
reaction, in which hydrolytic enzymes in the acrosome are
released onto the zona pellucida
3. The acrosomal enzymes digest the zona pellucida, creating a
pathway to the plasma membrane of the ovum. When the
sperm reaches the ovum, the plasma membranes of the two
cells fuse.
4. The sperm nucleus enters the ovum cytoplasm
80

79. 5. The sperm stimulates release of enzymes stored in cortical
granules in the ovum, which in turn, inactivates ZP3 receptors
& harden the zona pellucida leading to the block to polyspermy.
Note : 1. Ovum survives about 24 hrs
- Fertilization must therefore occur within 24 hours after
ovulation
2. Sperm typically survive about 48 hours but can survive up
to 5 days in the female reproductive tract
- so sperm deposited from 5 days before ovulation to 24hrs
after ovulation may be able to fertilize the released ovum
81

80. 82

81. Early stages of development from fertilization to implantation
• The fertilized ovum progressively divides and differentiates
into a blastocyst as it moves from the site of fertilization in the
upper oviduct to the site of implantation in the uterus
• Zygote  blastomeres (24-36 hrs)  morula (96 hrs)
enters the uterine cavity (at around 4 days)  blastocyst (at 6
days)  implants into the uterine wall (at day 7)
• Implantation: the burrowing of a blastocyst into the
endometrial lining
• Trophoblast :
– the thin outermost layer of the blastocyst
– accomplishes implantation, after which it develops into the
fetal portion of the placenta.
83

82. 84

83. Placenta
• Specialized organ of exchange between the maternal and
fetal blood
• Derived from both trophoblastic and decidual tissue
• It is composed of tissues of two organisms: the
embryo/fetus and the mother.
85

84. Formation of the Placenta
• Trophoblast cells  syncytiotrophoblasts (form blood–filled
cavities=Lacunae) & cytotrophoplasts (chorion)
• Blood filled cavities invaded by extensions of cytotrophoplast
(=chorionic villi)
• Chorionic villi extensively branched to produce the chorionic
frondosum
• The maternal tissue in contact with the chorion frondosum is
called decidus basalis
Chorion frondosum + decidus basalis= placenta
• Umblical cord - a lifeline b/n the fetus &placenta
- 2 arteries + one vein
86

85. 87

86. 88

87. 89
Maintenance of pregnancy
FUNCTION :

88. Placental Hormones and Their Function
• Human Chorionic Gonadotropin (hCG):
– Maintains the corpus luteum of pregnancy (prevent luteolysis)
– Stimulates secretion of testosterone by the developing testes in
XY embryos
• Estrogen:
– Stimulates growth of the myometrium, increasing uterine
strength for parturition
– Helps prepare the mammary glands for lactation
• Progesterone:
– Suppresses uterine contractions to provide a quiet
environment for the fetus
– Promotes formation of a cervical mucus plug to prevent
uterine contamination
– Helps prepare the mammary glands for lactation
90

89. • Human Chorionic Somatomammotropin:
– Reduces maternal use of glucose and promotes the
breakdown of stored fat (similar to growth hormone) so
that greater quantities of glucose and free fatty acids may
be shunted to the fetus
– Helps prepare the mammary glands for lactation (similar to
prolactin)
• Relaxin:
– Softens the cervix in preparation for cervical dilation at
parturition
– Loosens the CT between the pelvic bones in preparation for
parturition
91

90. • Placental PTHrp (parathyroid hormone related peptide):
– Increases maternal plasma Ca2+level for use in calcifying
fetal bones
– If necessary, promotes localized dissolution of maternal
bones, mobilizing their Ca2+stores for use by the
developing fetus
92

91. The Physiology of Parturition
Def.  delivery of the baby.
• Duration of gestation/pregnancy:
- In human : 38 wks from conception (40 wks from
the end of the last menstrual period)
93

92. Mechanisms: not known completely
Mechanical factors
a. Distension of the uterus.
• Fetal age size (critical conceptus size) → distension (↑ the
stretching of the smooth muscle, inherent rhythmicity) → ↑
contractility
b. Uterine contractions (Braxton-Hicks contractions +ve
feedback)
↑ Distension + effect of hormones
↓
Uterine contractions
↓
The increased pressure of the baby’s head against the cervix with
each contractions excites the fundus or body of utreus to contract
↓
94

93. Dilation of cervix & distension of vagina
↓
Stimuli from the cervix + vagina
↓
↑ Secretion of oxytocin
↓
↑ Uterine contraction until they are strong enough to expel
the baby
95

94. Neuroendocrine factors
a. Progesterone withdrawal
• ↓Toward the end of gestation period →↓No of
myometrial progesterone receptors.
• Antagonistic effect of progesterone to oxytocin + Pgs:↓
• ↓ Progesterone →↑ gap junctions between uterine cells
→ synchronizing uterine contractility
96

95. b. Estrogen
• ↑ E (in amount) →↑ prostaglandin synthase activity in
the tissues of the uterus + fetal membrane →↑ myometrial
contractions.
• ↑E →↑ myometrial + endometrial oxytocin receptors
• ↑E →↑oxytocin production & secretion by the
neurohypophysis
c. Oxytocin
• ↑ Uterine contractions (secretion due to distension + E )
• ↑ Oxytocin →↑PgFα → stimulate uterine smooth muscle
contraction → expulsion of the fetus.
• Regulation of the expulsion phase of labour +
contraction of uterus to reduce blood loss following
delivery.
97

96. d. Relaxin
• Relaxes the pubic ligaments + relaxes the lower part of
the uterus.
• Soften cervix → so eases the passage of the offspring
at birth.
• ↑ Sensitivity of the uterus to oxytocin.
e. Prostaglandins
• ↑ E →↑Pg synthesis →↑ Intracellular Ca2+ in the
myometrium →uterine contractions
• Paracrine
• Act synergistically with oxytocin (cervical ripening,
softening, dilatation, contractions).
98

97. Mechanics of Labor
a. Uterine contractions begins at the fundus + spread downward
over the body of the uterus.
b. Intensity of contraction is stronger at the fundus than in the
lower segment of the uterus (each uterine contraction tends to
force the baby downward toward the cervix).
c. Frequency of contractions: onset: once in every 30min
later: once in 1 to 3 min.
• Intermittent contraction will not stop the blood flow thru the
placenta and the fetus will not die.
99

98. d. Labor pain
Early: compression of the blood vessels to the uterus →
hypoxia of the uterine muscle (hypogastric nerves)
2nd stage: cervical, perineal stretching, and stretching or
tearing of structures in the vaginal canal (somatic nerves)
e. The pain from the uterus and birth canal elicits a neurogenic
reflex from the spinal cord to initiate intense contractions of
the abdominal muscles.
100

99. f. Stages
1st stage: the period of progressive cervical dilatation, lasting
till the opening is as large as the head of the fetus (8-24hrs
or less).
2nd stage: the time interval from the full dilatation of the
cervix till delivery is effected (hrs to minutes).
3rd stage: the time taken for separation and delivery of the
placenta (10-45min)
Duration of each stage tends to be longer in a primipara than
in a multipara.
101

100. 102
The interactions of fetal and maternal factors regulate parturition or the onset of birth

101. The Mammary Glands and Lactation
• Mammary glands: replaces the nourishing function of the
placenta after birth.
• Lactation → (the secretion of milk) occurs at the final
phase of the reproductive process.
• Mammogenesis :the differentiation and growth of the
mammary glands
• Neonate: Witch’s milk (in response to↓ placental steroids)
• Puberty: ↑ estrogen → duct growth
↑ progestrone→ lobuloalveolar growth
Permissive role : GH+cortisol+PRL+thyrosine +
Insulin.
Pregnancy: milk secretion doesn’t occur (Inhibition of
placental E + P
Following delivery placental E+P ↓→ lactation begins
103

102. 104

103. Lactation
a. Milk synthesis: initiated during the last part of pregnancy
(PRL)
b. Lactogenesis: synthesis of milk by alveolar cells & its
secretion into alveolar initiated by the loss of placental steroids
after birth.
c. Galactopoiesis: maintenance of established lactation,
controlled by PRL (suckling ↑PRL)
d. Milk ejection: passage of milk from alveolar lumen to the
duct system and its collection in the ampulla and larger ducts
and its delivery to the infant.
• Controlled by oxytocin.
105

104. Milk Ejection Reflex
Nipples (Mechanoreceptors → suckling)
↓
Somatic touch pathways (Multisynaptic pathway)
↓
Hypothalamic nuclei (SON, PVN)
↓
Oxytocin neurons release oxytocin
↓
Suckling of mammary gland
↓
Induces contraction of myoepithelial cells that surround alveoli
and ducts
(↑ IC Ca2+)
↓
Contraction of myoepithelial cells mobilizes milk from the
alveoli and duct system to the nipple
↓
Producing the sensation of ‘Milk -let down’ in the mother.
106

105. Milk Secretion Reflex
Suckling of nipples (mechanoreceptors)
↓
Somatic touch pathways (Multisynaptic pathway)
↓
Hypothalamic nuclei
↓
Inhibition of PIH secretion
↓
Secretion of PRL from the anterior pituitary
↓
Stimulation of milk secretion by the mammary glands
107

106. Components of milk
Protein: casein, α-lactalbumin, β-lactoglobulin
CHO: lactose, fat, minerals (Ca, Mg, P, Fe)
Electrolytes: Cl-, K+, Na+
Vitamins
Immunoglobulins: IgAs, macrophages, lymphocytes
(provide passive immunity to the infant by acting on the
GI tract)
108

107. Lactation and Menstrual Cycle
• Mothers who do not nurse → menses (6 wks after
delivery)
• Regular nursing→ amenorrhoeic (25-30 wks)
• 50% of the cycles in the first 6 months → anovulatory
Lactation as a Contraceptive
a. Suckling →↑ PRL secretion → inhibits GnRH/LHRH
secretion
b. Inhibits the action of GnRH on gonadotropes
c. Anatgonizes the action of gns in the ovaries.
109

108. Fertility Control: Contraception
Types:
2. Temporary methods
• Rhythm methods: abstinence during the fertile period.
• Calendar method
• Temperature method
• Cervical mucus/Ovulation method
110

109. 111

110. b. Withdrawal method /Coitus interruptus/ Onanism
c. Barrier methods: Blocking sperm entry into the cervix
i. Mechanical (diaphragms, condoms, rings)
Mech: Prevention of sperm ascension thru the cervical
mucus
ii. Chemicals: spermicides
d. IUCD/ Intrauterine contraceptive device
i. Induces a sterile inflammatory process → Prevent blastocyst
implantation.
ii. ↑ Pgs + immunoglobulins
iii. Produce asynchronous development of the endometrium.
112

111. e. Hormonal
• Combination: E-P, 21d, 7d, Phasic E-P, P-only
• ↑ E2, ↑ P → ↓ Gns (↓LH, ↓FSH) → inhibition of follicular
maturation →inhibit the LH surge → NO Ovulation
i. Progestational component:
• Suppresses LH secretion by a -ve feedback effect on H-P
axis.
• Produces a decidualized endometrium which is not
receptive to implantation.
• Produces thick cervical mucus
• Alter tubal motility
113

112. ii. Estrogen component
• Enhances the -ve feedback of the progestin
• Supresses FSH secretion
• Stabilizes the endometrium to prevent irregular bleeding
Overall effects:
a. Transport of gametes in fallopian tubes
b. Hospitality of uterine environment
c. Penetrability of cervical mucus to spermatozoon
d. pH of the vaginal mucosa
114

113. II. Postcoital contraceptives /the morning-after pill
• Interference with implantation & delay or interruption of
ovulation
III. Subdermal progestin/norplant, 5years
• Inhibition of ovulation
• Thickening of cervical mucus → Preventing sperm
penetration)
IV. Depo-medroxy progestrone acetate 150mg, im, once/3months
• Prevention of the LH surge + ovulation)
2. Permanent/sterilizations
a. Tubal Ligations (F)
b. Bilateral Vasectomy (M)
115

114. Menopause
Def. time at which the final menstrual bleeding occurs.
• A state that occurs in all women as they age.
• A period of female climacteric during which reproductive
cyclicity gradually disappears.
Features:
a. Loss of follicular development
b. ↓ [ Estradiol] → ↑ gonadotropins (↑ FSH, ↑LH)
c. Cessation of menstruation
• No association with the age of menarche, parity, age at the
time of the first pregnancy, race, body size, socioeconomic
factors.
116