Physiology of Reproduction - Chapter 20
3-hormone Control of Gonads
Hypothalamus  GnRH into hypophysial portal vein  Anterior Pituitary FSH, LH in plasma gonads 
gametogenesis and secrete sex hormones  sex hormones in plasma  reproductive tract responds. Abbreviations:
Gn = gonadotropin, GnRH = gonadotropin releasing hormone.
Onset of Puberty
Secretion of FSH and LH is elevated at birth and stays high for the first 6 months of postnatal life; this declines to
almost nothing until puberty.
Puberty begins with a release of LH (pulsatile).
Due to declining sensitivity of the hypothalamus to negative feedback effects of gonadal hormones
This results in increases in testosterone or estradiol-17β secretion.
These hormones produce secondary sex characteristics.
Secondary Sex Characteristics
In girls: growth spurt, breast development, menarche (first menstrual flow)
In boys: later growth spurt; body, muscle, penis, and testis growth
In both sexes: body hair is stimulated by androgens from adrenal gland at puberty
Age of the onset of puberty
Depends on activity levels and amount of body fat
Leptin secreted by adipose cells is required for the onset of puberty.
Exercise may inhibit GnRH secretion.
More active, slimmer girls begin puberty later.
Melatonin from the pineal gland may play a role, but this is not proven in humans.
Role of Sertoli Cells
Sertoli cells
nourish sperms
secrete MIS in fetus for inhibition of Mullerian duct system = female reproductive system
secrete Inhibin protein hormone to inhibit FSH secretion by anterior pituitary
serve as Sertoli barrier = Testes-Blood Barrier to chemicals in plasma
phagocytosis on defective sperms.
Spermatogenesis
Androgonial Cells   androgonial cells by mitosis; 2n  2n
Androgonial cell  Primary Spermatocyte (bigger in size); 2n
Primary Spermatocyte  Secondary Spermatocyte (Meisosis-1); 2n  n
Secondary Spermatocytespermatid (Meiosis-2); n  n
Spermiogenesis: Spermatids  sperms
Erectile Dysfunction
Erection requires dilation of arteries and constriction of veins in penis. Erectile dysfunction is failure to achieve or
maintain erection
Autonomic neurons secrete Nitric Oxide, the gaseous neurotransmitter. It causes dilation of arteries and results in a
rigid penis. Nitric Oxide activates guanylyl cyclase and converts GTP --> cGMP, a 2nd messenger that after several
steps causes the relaxation of smooth muscles in arteries. The cycle ends by the breaking of c GMP by enzyme PDE5
(PhosphoDiestraseType5).
PDE5 (PhosphoDiestrase type 5) inhibitors – Orally active Drugs, like Viagra or Cialis or Levitra, block the action of
enzyme responsible for breaking c GMP. It allows higher levels of c GMP and normal erection. However, these drugs
cannot be taken by people with hypertension or weak heart; if taken the consequences can be serious including
death.
Oogenesis
Is formation of eggs from follicles in ovaries.
Oogonia    oogonia by mitosis; 2n  2n
Oogonia  primary oocyte by mitosis/differentiation; 2n  2n
Primary oocyte  meiotic arrest till puberty
Primary oocyte  secondary oocyte + 1st polar body; 2n  n; completed in ovary just before ovulation
Only on entry of sperm into it, Secondary oocyte  Ovum + 2nd polar body, n  n, in fallopian tube , completed just
after fertilization
Ovarian follicles
Primordial follicles (in fetus) – primary oocyte covered by single layer of granulosa cells  Primary follicles (at the
time of birth to puberty) – primary oocyte enlarges and gets surrounded by thick material zona pellucida 
Secondary follicles (very small # continue to develop during childhood) develop several layers of grannulosa cells
that secrete estrogen, and get surrounded by connective tissue cells – Theca  Early Mature follicles – granulosa
cells secrete a fluid to form a cavity Antrum, surrounded by granulose cells  Mature follicle = Graafian follicle gets
huge and can be seen at the surface of ovary and has antrum surrounding the primary oocyte from all sides except
one = cumulus oophorus, follicle is ready to ovulate.
Ovarian or menstrual cycle
Ovarian Cycle: usually has 28 days but can vary a lot in some women. It has 2 phases Follicular and Luteal separated
by ovulation – usually between 10th - 14th day. At the beginning of follicular phase several (10-25) follicle start
developing. Around 7th day one follicle becomes dominant others degenerate; the process is called Atresia, an
example of programmed death = Apoptosis. Dominant follicle matures in 2nd week. Ovulation occurs. Secondary
oocyte is released. Empty follicle regresses around antrum but under the influence of LH its granulosa cells enlarge
in size and follicle develop into endocrine gland – Corpus Luteum. It secretes estrogen, progesterone and inhibin. If
no pregnancy takes place, corpus luteum degenerates from 25 – 28 day and sets on menstruation.
Regulation of Hormones
Hypothalamus  GnRH  Anterior Pituitary  LH  Theca Cells  androgens
Hypothalamus  GnRH  Anterior Pituitary FSH  Granulosa cells  androgens to estrogen, secrete inhibin and
influence oocytes
Menopause
1. Characterized by cessation of ovarian activity and menses
2. Due to changes in the ovaries, not to decreases in FSH and LH
3. FSH and LH levels are actually elevated due to lack of negative feedback.
4. Usually occurs after age 50
Breast Feeding and Immunity
1. IgG antibodies are passed from mother to child in utero.
2. IgA antibodies are passed to the child in breast milk.
3. These provide passive immunity for the first several months of life until the baby can
antibodies.
4. Also promotes development of the baby’s own active immunity.
Natural contraception
1. Breast-feeding inhibits GnRH which inhibits gonadotropins and ovulation
2. It is most effective in women with limited calorie intake who nurse at regular intervals.
develop its own