R3 30 Nov., 2005

v .... Male sex hormones (concluded)

vFemale reproductive structures

vComparative development of male and female reproductive systems

Effects of testosterone . . .
iv) . . . throughout adulthood

v maintains changes induced at puberty

v stimulates spermatogenesis:

v diffuses from interstitial cells into central compartment of seminiferous tubules

v there, it stimulates Sertoli cells, which in turn stimulate division and differentiation of sperm cells

v regulates its own secretion by negative feedback involving the gonadotropins . . .

b) Gonadotropins (“directed at gonads”): LH, FSH

- both Gns are secreted by anterior pituitary
- both are named for their functions in female

LH (luteinizing hormone) in male - stimulates interstitial cells of testes to produce testosterone

Note: HCG from placenta @ LH in structure
- HCG stimulates testes of early male fetus to secrete the testosterone needed for proper male development

FSH (follicle-stimulating hormone) in male -
stimulates spermatogenesis by activating receptors on Sertoli cells, which then influence developing sperm

c) Regulatory hormones from brain & testes regulate androgen & Gn secretion

GnRH (gonadotropin-releasing hormone -- see diagram):
- is secreted in hypothalamus, and travels to ant. pituitary via portal vessels in pituitary stalk (remember?); there, GnRH ® secretion of FSH and LH (by same cells)

Inhibin released by active Sertoli cells inhibits FSH secretion
(prevents FSH from driving spermatogenesis too hard)

To prevent [testosterone] from rising too high, testosterone regulates its own secretion by
2 negative feedback actions:

1. it inhibits LH (also FSH) secretion by pituitary cells
2. it inhibits GnRH release in hypothalamus

These hormonal interactions ® fairly steady secretion of testosterone in adulthood, after earlier fluctuations (see diagram)

FEMALE REPRODUCTIVE SYSTEM

Beyond roles of producing and uniting gametes, it:

1. produces a monthly sexual cycle designed to

- release a single egg and
- supply optimal nutrition for fertilized ovum

2. sustains the fetus through pregnancy
3. delivers and nourishes the infant

Female reproductive STRUCTURES

Ovaries (2) = female gonads, ~ 4 x 2 x 1 cm in size
- source of female gametes (oöcytes) & most sex steroids

Oviducts (2) (= Fallopian tubes, uterine tubes)
- 1 connected to top of uterus on each side, with its other end opening into abdominal cavity near ovary
- passage for egg & sperm transport, & site of fertilization

Oviduct walls contain:
a) smooth muscle to propel egg toward uterus;
b) cilia (inner lining) “ “ “
c) secretory cells (inner lining) to nourish egg or zygote
Fimbriae (ciliated smooth m. fingers at far end) pull egg in

Tuboligation (cutting and tying oviducts) sterilizes female without altering sexual cycle
[Û vasectomy in male]

Uterus = womb: site of fetal development
- ~ 6.5 cm long and 3 cm across in non-pregnant state
- gives off 2 oviducts at top end
- opens into vagina through cervix at bottom end

- its thick wall has 3 layers:
- outer perimetrium (connective tissue)
- middle myometrium (visceral smooth muscle)
- inner endometrium (nutritive glands)

Vagina - 7.5-10 cm long passage from cervix to exterior
(to drain menstrual discharge, receive penis & sperm during coitus, and act as birth canal)

- its thin wall (easily stretched) also has 3 tissue layers: connective t., smooth m., & inner mucosal epithelium

External genitalia (= vulva), including
- labia majora (larger, hairy outer lips)
- labia minora (smaller hairless inner lips), enclosing the

- vestibule, into which open the
- vagina near the back
- urethra near the front, and the
- 4 vestibular glands (2 greater behind vagina, 2 lesser in front of it)

- clitoris, erectile, sensitive structure with shaft & glans like male penis but much smaller, in front of vestibule

Erectile vestibular bulbs extend below surface from clitoris around both sides of vestibule (hence around vagina)

Comparative development of f and m structures

f and m genital structures are identical for first 7-8 weeks of fetal development, and then diverge to yield homologous sets of f and m organs (i.e., from same embryonic origins):

f structure Ü Early structure Þ m structure

glans of clitoris Ü genital tubercle Þ glans of penis

labia minora Ü urethral folds Þ shaft of penis

labia majora Ü genital swellings Þ scrotum

ovary Ü primordial gonad Þ testis

vestibular bulbs Ü Þ corpus spongiosum
vestibular glands Ü Þ prostate, bulbourethral glands
bulbospongiosus muscle Ü Þ bulbospongiosus muscle

But several tract organs don’t have homologues in the other sex:

female Ü Early structure Þ male
oviducts & uterus Ü Müllerian ducts Þ degeneration
degeneration Ü Wolffian ducts Þ epididymides, vasa deferentia, seminal vesicles

All early fetuses, f & m, have both Müllerian & Wolffian ducts.

What controls which system develops and which degenerates?

- the presence or absence of 2 signals from male fetus’s testes . . .

Two signals from male fetus’s testes:

1. Wolffian ducts develop in male because testes secrete testosterone, which stimulates Wolffian duct development

v they degenerate in female because testosterone is absent

2. Müllerian ducts are driven to degenerate in male by MIH (Müllerian-inhibiting hormone), also from fetal testes

v they develop in female because MIH is absent

i.e., the female duct development pattern is the “default” option, followed if both testosterone and MIH are absent
- if both are present (from testes), male pattern is followed