2. Sexual Differentiation
• Early embryonic gonads can become testes or
ovaries
– Y chromosome induces formation of testes
• Testosterone (T) from testes induces formation of male
sex organs
• In absence of T, female sex organs develop
20-4
3. Sexual Reproduction
• Gametes (sperm or
eggs) are formed in
gonads by meiosis
– Each has haploid
number of
chromosomes (23)
– Fusion of sperm &
egg during fertilization
results in diploid
zygote with 43
chromosomes
Fig 20.1
20-5
4. Hypothalamus & Pituitary
• Hypothalamus controls
release of LH & FSH from
anterior pituitary (Ant Pit) with
GnRH
• LH & FSH stimulate
production of sperm & eggs, & Fig 20.9
gonadal sex steroids; &
maintain size of gonads
• Sex steroids provide negative
feedback on hypothalamus &
Ant Pit
• Gonads also secrete hormone
inhibin which negatively feeds
back on FSH secretion
20-19
6. Male Reproductive System
• Testes contain
seminiferous tubules
(STs) where
spermatogenesis
occurs; & interstitial
tissue housing
T-secreting Leydig
cells
• Sertoli cells of STs
contain receptors for
FSH
– FSH stimulates
spermatogenesis
• Leydig cells contain
LH receptors
– LH stimulates
secretion of T
Fig 20.12
20-26
7. Control of LH & FSH Secretion
• Is by negative
feedback
– T inhibits LH & GnRH
secretion but not
FSH
– Inhibin from Sertolis
provides negative
feedback on FSH
Fig 20.13
20-27
8. Spermatogenesis
• Germ cells that
migrate from yolk sac
during development
become
spermatogonia (stem
cells)
– Spermatogonia
replicate selves
throughout life by
mitosis
– Give rise to haploid
sperm by meiosis
Fig 20.16
20-31
9. Spermatozoa
• Have oval-shaped head that contains DNA & the
acrosome (a cap of digestive enzymes)
• Have a midpiece & flagellar tail
– Tail will become motile in epididymus
Fig 20.19
20-36
11. Female Reproductive System
• Ovaries contain large
number of follicles
that produce female
gametes (eggs or
ova) in ovarian cycle
• Extensions of
fallopian tubes called
fimbriae partially
cover each ovary
– The cilia of its lining
draw in ovulated eggs Fig 20.24
20-47
12. Female Reproductive System continued
• Uterus has 3 layers:
• Perimetrium is outer
layer of connective
tissue
• Myometrium is middle
layer of smooth
muscle
• Endometrium is
hormonally-
responsive inner
epithelial layer that is
shed during
menstruation Fig 20.24
• Between uterus &
vagina is cervix
20-48
13. Ovarian Cycle
• 1o oocytes are contained in 1o follicles
– Consisting of oocyte + follicle cells
• In response to FSH some follicles enter ovarian cycle & grow,
producing layers of granulosa cells
• Some 1o follicles continue, developing vesicles & becoming 2o
follicles
Fig 20.29
20-51
14. Ovarian Cycle continued
• One follicle continues growth
– Vesicles fuse, forming fluid-filled cavity called an antrum
• Is now called a Graafian follicle
Fig 20.29
20-52
15. Ovarian Cycle continued
• As Graafian follicle
develops, 1o oocyte
completes meiosis I
• This is an assymetric
division because 1
daughter cell (the 2o
oocyte) gets all cytoplasm
– Other daughter becomes a Fig 20.31
small polar body which will
degenerate
– 2o oocyte arrests at
metaphase II
• Only fertilized eggs
complete meiosis II
20-53
16. Ovarian Cycle continued
• 2o oocyte is part of graafian follicle
• Granulosa cells form layer around outside of follicle
• Oocyte sits on mound in this layer called cumulus oophorus
• 2o oocyte is enclosed by ring of granulosa cells called corona
radiata
• Between oocyte & radiata is gelatinous layer called zona
pellucida
– Which forms barrier to sperm penetration
20-54
17. Ovulation
• By 10-14 days after
menstruation
begins, only 1
follicle survives
– Others become
atretic follicles
(degenerate)
• Surviving graafian
follicle forms bulge
on surface of ovary
– Secretes increasing
levels of E
Fig 20.29
20-55
19. Ovulation continued
• If fertilized, egg
completes meiosis
II with formation of Fig 20.31
another polar body
• Egg degenerates
in 2 days if not
fertilized
20-57
20. Ovulation
• LH causes empty
follicle to become
corpus luteum (CL)
– Which secretes
progesterone (P) &
estrogen
– If no fertilization,
becomes corpus
albicans (non-
functional remnant)
Fig 20.32
20-58
22. Menstrual Cycle
• Is ≈ month-long cycle of ovarian activity seen in higher
primates
• Characterized by shedding of endometrial lining &
bleeding (menstruation)
– & sexual receptivity throughout cycle
• Other animals have estrous cycles in which there is no
shedding of endometrium & receptivity is limited
– In estrous animals that bleed (dogs & cats), it is due to high
estrogen (E) that accompanies receptive period
20-60
23. Menstrual Cycle continued
• In humans is ≈28 days
• Day 1 is taken to be first day of menstruation
• Days 1 thru ovulation constitute the follicular
phase
• Time from ovulation to menstruation is luteal
phase
• Endometrial changes are called: menstrual,
proliferative, & secretory phases
20-61
24. Follicular Phase
• Lasts from day 1 to
about 13
• Is dominated by
growth & death of a
cohort of 1o follicles
into 2o follicles
– With 1 survivor
becoming a graafian
follicle
• Which will undergo
ovulation
– As follicles grow,
secrete larger
amounts of E
• Reaching peak about
day 12 Fig 20.33
20-62
25. Follicular Phase continued
• Follicular growth & E
secretion are dependent
on FSH from Ant Pit
– FSH & E induce formation
of FSH receptors in
granulosa cells
• Causing follicles to
become increasingly
sensitive to same level of
FSH
• At same time, FSH & E
recruit LH receptors in
graafian follicle
Fig 20.33
20-63
26. Follicular Phase continued
• Rapidly rising E
secretion causes:
– Hypothalamus to increase
pulses of GnRH
– & Ant Pit sensitivity to
GnRH to increase,
resulting in greater LH
secretion
• A positive feedback
between E & Ant Pit
secretion develops
– Resulting in LH surge that
peaks 16 hrs before
ovulation
• & causes ovulation
Fig 20.33
20-64
27. Luteal Phase
• After ovulation,
LH causes
empty follicle to
become the
corpus luteum
(CL) which
secretes E & P
Fig 20.34
20-65
28. Luteal Phase continued
• P levels rise & peak about a week after ovulation
• Development of new follicles & another ovulation are inhibited
by:
– High P & E exert strong negative feedback on LH & FSH
– Inhibin from CL further suppresses FSH
Fig 20.34
20-66
29. Luteal Phase continued
• With no fertilization, CL regresses
– Consequently E & P levels decline
• Causing menstruation & allowing new cycle of follicle development
Fig 20.34
20-67
30. Cyclic Changes in the Endometrium
• Are driven by cyclic changes in E & P levels
• Proliferative phase occurs during follicular phase; E levels
increase
– E stimulates growth of endometrial lining
• Spiral arteries develop
– E causes cervical mucus to become thin & watery to allow sperm
penetration
Fig 20.34
20-68
31. Cyclic Changes in the Endometrium continued
• Secretory phase occurs during luteal phase; endometrium
becomes ready for implantation
– P stimulates development of uterine glands
– P & E cause endometrium to become thick, vascular, & spongy
– P causes cervical mucus to thicken & become sticky
Fig 20.34
20-69
32. Cyclic Changes in the Endometrium continued
• Menstrual phase results from drop in P & E following CL
degeneration
– Low P causes constriction of spiral arteries
– Blood flow stops, causing necrosis & sloughing of endometrium
Fig 20.34
20-70
