Male Reproductive Physiology

Topics: Sertoli cell, Testicle, Spermatogenesis Pages: 17 (3510 words) Published: April 17, 2011

- 2 compartments: interstitial tissue containing the Leydig cells that synthesize and secrete testosterone and the seminiferous tubules that produce spermatozoa and contain Sertoli cells

Leydig cells and testosterone synthesis
- Leydig cells mainly produce testosterone
- T is a prohormone for synthesis of estradiol (vs. aromatase) and DHT (via. 5-alpha-reductase) - many effects of T are mediated via estradiol (esp in bone and brain) or DHT (secondary sexual characteristics o DHT is converted locally, so will not see high systemic levels ▪ has a higher affinity for androgen receptor, much more potent o T ( estradiol important for neg. feedback (esp at hypothalamus) and epiphyseal closure - LH from ant.pituitary acts at Leydig cells to stimulate synthesis and secretion of T (which will just diffuse out since it is steroid hormone)

Seminiferous Tubules and Spermatogenesis
- seminiferous tubules make up bulk of testicular volume - spermatozoa are synthesized within the seminefous epithelium, and pass thru a series of ducts into the epididymis - the seminiferous tubules have Sertoli cells

- spermatogenesis under FSH control

Regulation of Testicular Function
Role of GnRH
- GnRH released in pulses, to drive pulsatile gonadotropin release from ant. pituitary - Leydig cells respond to this pulsatile release by releasing pulses of testosterone Negative Feedback Regulation

- secretions from testes feedback on the hypothalamus and the anterior pituitary to inhibit the release of LH - the Sertoli cells also produce inhibin which will have a negative feedback on FSH - castrated animals have high levels of FSH and LH

o replacing T in these animals brings LH back to normal levels, but not FSH o this is because FSH inhibition also requires inhibin

Function of Sertoli Cells
- Junctional contacts between Sertoli cells form the structural basis of the blood-testis barrier - allows for fluid composition inside the seminiferous tubule and rete testes to be different from that of testicular blood and lymph - the barrier excludes small molecules from entering the STs where developing sperm are located to protect them from potential mutagenic agents - Sertoli cells also play an important role in formation and maturation of spermatozoa - Sertoli cells contain abundant amounts of androgen receptors and FSH receptors (indicates need both hormones for spermatogenesis) - T is converted to the more potent DHT within the Sertoli cells - Sertoli cells also produce androgen binding proteins (ABPs) thereby maintaining high concentrations of tubular androgens - androgen is required to maintain spermatogenesis, but induction requires FSH - Sertoli cell function under FSH and T influence:

o secretion of nutrients required for spermatogenesis
o formation of the blood-testis barrier
o secretion of a watery fluid for transport of spermatozoa through the semineferous tubule and into the epididymis o synthesis and secretion of inhibin

Effects of Androgens
Descent of Testes
- the testes are in the upper lumbar region, but will eventually descend thru abdominal cavity and over the pelvic brim to arrive in scrotum - testis is firmly attached to then posterior abdominal wall by fibrous remains of mesonephric tissues, and behind by a fibrous structure, the gubernaculums - under the influence of T, the gubernalcumlum shortens, pulling the testis into the scrotum - the location of the testes is important for spermatogenesis by providing more optimal temperature for sperm production o location outside of body wall

o countercurrent exchange between cooler Pampiniform plexus and warm arterial blood - Failure of testes descending = cryptorchidism
o men will be infertile if not corrected before puberty
o T production is...
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