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Lecture 34 - Male Reproduction System

Lecture 34 - Male Reproduction System - Lecture 34 Male...

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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 The sertoli cells
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