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Unformatted text preview: Lecture 34 Male Reproduction Functions of the testes- Produce androgens- Produce sperm- Two functions are segregated anatomically into two compartments- Seminiferous tubules produce sperm- Interstitial compartment produces androgens Testes- Primordial germ cells migrate to gonadal ridge as in the ovary- Identification of gonad as testes ( distinct from ovary ) occurs between 6-7 weeks gestation o Very early on there is identification - Testicular development is complete by 12 weeks and descent into scrotum occurs slowly and is usually complete between 7 th and 9 th month of pregnancy o First near the kidneys migrate downward Testes: Endocrine function- Leydig Cells o Leydig cells are found in the intersitial stromal compartment of the testes o Scattered between the seminiferous tubules o Primary site of testosterone (T) production o Account for 95% of testosterone in circulation- Role of LH in testosterone biosynthesis o LH is secreted from the pituitary in response to GnRH o Secreted in pulses approximately every 90 minutes o Binds to LH receptors on Leydig cells to stimulate testosterone production o hCG acts identically to LH to stimulate testosterone production- feedback negative loop o LH and testosterone o FSH and inhibin/activin FSH stimulate the tubules (testicles) Inhibin (peptide) primary negative feedback for the FSH - Testosterone biosynthesis o Circulating LDL provides source for cholesterol precursor **cholesterol lead to androgen synthesis o LH stimulates T production from Leydig cells o Circulates bound to specific carrier protein; sex hormone binding globulin (SHBG) o Only 1-2% of circulating T is free and bioactive 30% bound to SHBG 68% bound to albumin o T decreases SHBG production from the liver o Estrogens increase SHBG production from liver Makes sense because estrogen would decrease T (via the SHBG)- Testosterone: Circadian Rhythm o Maximal secretion occurs between 2-4 a.m. o Lowest levels between 4-6 p.m. o Circadian excursions decrease with age- Estrogens in Men o Both estrone and estradiol circulate in men o Only 10-30% of circulating estrogens are produced in the testes o Majority results from aromatization of androgens to estrogens in peripheral tissue o Aromatase is found in fat, muscle and liver- Biologic action of androgens o Masculinization o Body growth and muscular development (anabolic) o Facilitation of libido and sexual potency o Production of assertive and aggressive behavior Testes: Exocrine function- Semiiferous tubules (makes up the major of the testes) o 70-80% of testes is composed of seminiferous tubul o Tightly coiled tubules up to 70 cm (27 inches) in length o Both ends empty into rete testes which empties into epididymis o Tubules lined with sertoli cells and spermatocytes...
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This note was uploaded on 09/14/2011 for the course PHARM ERM taught by Professor Staff during the Spring '11 term at UCSD.
- Spring '11