Reproduction – The Male
- 80% of testis mass is the seminiferous tubules. Combined length of tubes is 250 meters.
Features of spermatogenesis
- Spermatogonia are attached to the basement membrane. These cells undergo mitotic
division. Adjacent Sertoli cells create blood-testis barrier via tight junctions.
- Spermatogonia possess 2N (are diploid) number of chromosomes.
- Speratocytes – cells in the process of becoming sperm
- Require temperatures lower than 34 degrees
Features of spermiogenesis
- Cell acquires a vesicle of enzymes called the acrosome. The nucleus must condense. The
cytoplasm is greatly reduced. Cells acquires a flagellum. Mitochondria accumulates in
- Fluid is added by the seminal vesicles, prostate gland and Cowper’s gland.
Factors which affect spermatogenesis
- requires temperatures lower than 34 degrees. High levels of testosterone required. FSH is
required for the initial waves of spermatogenesis and when is must be re-initiated. Sertoli
cells have FSH receptors, binding initiates the production and secretion of androgen
binding protein which functions to maintain high local concentrations of testosterone.
- Entire process takes about 64 days
- sperm reside in the epididymis for 2 weeks. Testosterone required. While testicular sperm
used glucose as an energy substrate and for conversion to a.a’s and lipids, capacity to do
this is lost in the epididymis. Surface charge also becomes more negative.
- StAR (rate-limiting protein),
moves cholesterol into
- P450scc (sidechain cleavage)
turns cholesterol into
- 17-B-hydroxy steroid
- cholesterol is the principle precursor for all steroid hormones. Although most is carried in
from blood, can also be made from acetate. Androgens can be converted to estrogens by a
process called aromatization.
- A steroid is terpenoid lipi with a four fused rings in a 6-6-6-5 fashion
- LH stimulation by testosterone increases cAMP and results in increased side chain
cleavage of cholesterol in mitochondria.
- Androgens: (1) Non-reproductive tissues, muscle anabolism, bone proliferation of
chondrocytes, skin sebaceous glands becomes active.
(2) Secondary Sex Characteristics: body hair distribution, chest and shoulder growth, larynx,
behaviour, general body growth spurt in conjunction with GH (3) Required for differentiation of epididymis, vas deferens, prostate/seminal vesicles,
penis/scrotum and required for maintenance of epididymis and function of the seminal
vesicles and prostate. (4) Required for spermatogenesis
- 75% of testosterone is bound to sex hormone binding globulin and 20% to albumin. The
unbound form is biologically active
- Testosterone is first reduced to dihydrotestosterone by 5a-reductase. Can also be
aromatized (occurs in the CNS and adipose tissues). Androgen receptor (AR) is a ligand
gated transcription factor. Affect Liver is primary organ involved in biologic inactivation
(gets conjugated) and rendered more soluble.
- Mechanism of action of GnRH is calcium influx, calmodulin binding and activation of PI
- Relevance to pulsatile secretion of GnRH is because constant exposure would decrease
LH secretion and pubertal and seasonal changes that need increase in LH are often
reflected in increases in GnRH frequency rather than amplitude.
- mitotic processes being during fetal life. Oogonia formation stops at 7 months and begin
meiotic divisions but become arrested in the prophase of the first meiotic division.
- Being with 6x10-6 germ cells in utero, by puberty only 200,000-400,00 follicles will
being active reproductive life.
- During each cycle, 20-50 primary oocytes will begin to mature but only one will become
the dominant follicle (usually the one with the most FSH receptors).
- When exposed to a preovulatory surge of LH, the dominant follicle will resume meiosis
and extrude the first polar body. Thus, only one will form a secondary oocyte.
- The second meiotic division is completed and second polar body excruded prior to the
pronuclei of the mother and father joining.
Features of steroidogenesis in the ovary
- theca interna cells, when stimulated by LH form androgen for aromatization
- the primary site of aromatization of testosterone to estrogen is in the granulose cell of the
collicle. This is stimulated by FSH.
- Transported from granulose cells to theca cells by low-density lipoproteins
o Both are cAMP mediated mechanisms.
o Eventually the cells make up the corpus luteum
Release, Transportation, Mechanism of Action and Inactivation
- once made it readily diffuses out. In serum, estradiol binds to steroid hormone binding
globulin and albumin. The progesterones are bound primarily to albumin and cortisol
- Liver also excretes, but progesterone is not conjugated, the catabolic products are
- early development of primordial follicles is hormone independent.
Zona pellucida – seceted by granulose cells, is a glycoprotein material.
- theca cell layer is vascularized (unlike granulose cells).
- Pre-antral follicle begins showing LH and FSH receptors in layers. - Antral follicle, granulose cells secrete follicular fluid into the antrum
- Production of estradiol and progesterone increases toward the end of the follicular phase,
this elecits a pre-ovulatory surge of LH. This causes the resumption of meiosis (first polar
body). Also changes the granulose cells, from the LH receptors they required in the
process of follicular maturation, the LH will now stimulate the granulose cells to make
- The ovulatory surge of LH is the signal that causes rupture of the follicle.
Ovulation – rising estrogen levels act on the endometrium and stimulate LH (progesterone can
block this), LH blocks oocyte maturation inhibitor (OMI) which causes the follicle to complete
the first meiotic division. Under LH, the now empty follicle develops into a corpus luteum,
- Collapsed follicle now forms into a corpus luteum. The granulose cells of the corpus
luteum primarily make progesterone. Occurs for about 1 week, then signal occurs for
luteolysis and it forms the corpus albicans.
Menopause – follicles become less responsive to LH and FSH and thus begin to secrete less
estrogen. FSH and LH levels keep rising.
- Non sexual tissues: stimulates bone growth and ultimate cessation of bone growth,
protects against osteoporosis, protects against atherosclerosis, antagonizes the effects of
PTH, promotes blood clottinh
- Secondary Sex Characteristics: stimulates female body development, narrow shoulder,
broad hips, female body fat distribution. Stimulates breast development, stimulates
female body hair pattern.
- Secondary Sex Organs: stimulates growth of external genitalia, increase contractions and
ciliary activity of fallopian tubes, stimulates proliferation of epithelial linings of
reproductive tract, increases layer of vaginal epithelium, prepares uterine endometrium
for progesterone’s actions by inducing progesterone receptor synthesis.
- Non-sexual characteristics: increases body temp
- Secondary Sex characteristics: promotes mammary alveolar development
- Reproductive Tract tissues: decreases contractions of fallopian tubes, converts
endometrium into glandular structure ready for embryo implantation
Pregnancy and Parturition
Fimbrium ampulla isthmus uterus
- Window of opportunity: ovum viable for 12 hours, sperm viable for 48 hours.
- Vaginal sperm 250,000, uterine sperm 100,000, ampullary sperm 50.
- Blastocyte implants on day 7
- Sperm may reach egg within 15 minutes
Capacitation – metabolic rate of sperm increases, changes in protein components of the sperm