Male Reproductive Physiology Lecture Notes PDF

Lecture 8: Physiology - Male Reproductive Physiology Physiology of testes: consist of seminiferous tubules lined by Sertoli cells w/ interstitial Leydig cells b/w the tubules which produce testosterone; maintained at 2° C below body temp for spermatogenesis Sertoli cells: surround & nourish develop...

Lecture 8: Physiology - Male Reproductive Physiology Physiology of testes: consist of seminiferous tubules lined by Sertoli cells w/ interstitial Leydig cells b/w the tubules which produce testosterone; maintained at 2° C below body temp for spermatogenesis Sertoli cells: surround & nourish developing sperm, secrete growth factors that regulate development of spermatozoa; connected by tight junctions to form blood-testis barrier; secrete fluid & androgen binding protein (ABP); require testosterone & FSH to initiate & maintain spermatogenesis Leydig cells: synthesize & secrete testosterone (T) under the stimulation of luteinizing hormone (LH) Endocrine role: mainly production of T, ~7 mg/day in young adult male, mostly bound to albumin & sex hormone binding globulin (SHGB) in circulation Dihydrotestosterone (DHT): the more potent form of testosterone; created through the action of 5-alpha reductase (found in skin, prostate, & other genital tissues) ​ Aromatase: converts T to 17-beta estradiol (E2); found in brain, adipose tissue, & breast Testosterone biosynthesis: conversion of cholesterol to pregnenolone via side chain cleavage enzyme → cleavage of C-17 side chain → conversion to dehydroepiandrosterone (DHEA) → becomes T Androgens actions: T & DHT bind intracellular androgen receptor (DHT has more affinity) → alter transcription → stimulate growth/function of accessory reproductive organs, development of male secondary sex characteristics, & spermatogenesis Testosterone: needed for maturation of Wolffian duct structures, formation of male internal genitalia, spermatogenesis, and increased muscle mass & libido DHT: needed for development of the male external genitalia, enlargement of prostate (& probably penis) during puberty, facial hair, increased acne, & recession of the hairline at the temples Hypothalamic-pituitary-gonadal axis: gonadotropin releasing hormone released in pulsatile fashion (~every 3 hr) by hypothalamus → stimulates release of FSH & LH → LH acts on Leydig cells to stimulate T release → T acts w/ FSH to stimulate Sertoli cells to support spermatogenesis Feedback loop: T inhibits GnRH & LH secretion by decreasing pulse frequency, FSH causes Sertoli cells to produce inhibin (feedback directly inhibits FSH secretion by pituitary) Ducts & accessory glands: main function is sperm transport & creation of semen Semen contribution: seminal vesicles secrete about ½ volume, prostate secretes ~20% of total volume Semen components: sperm (gamete from seminiferous tubules), mucus (lubricant from bulbourethral glands), water (liquid medium from all accessory glands), buffers (for vagina, from prostate & bulbo- urethral glands), nutrients (fructose, citric acid, vitamin C, carnitine), enzymes (clot semen in vagina, then liquify), zinc (unknown function/origin), prostaglandins (for smooth muscle contraction, may aid sperm transfort, from seminal vesicles) Sperm concentration: avg 100 million/mL semen, low fertility = 20-50 mil/mL, infertility =