Male Reproduction Felix E. Grissom, Ph.D. 2219 Numa P.G. Adams Howard University Tel. 202 806-4512

Male Reproductive Anatomy and Physiology Testis Epididymis Vas deferens Seminal vesicle Prostate Bulbourethral Ejaculatory duct Urethra Penis

Major Testicular Steroids () = Relative activity where T activity=100 Androgens are C19 steroids Majority of 5 a-DHT is formed in peripheral tissues

Male Sex Steroid Synthesis Cholesterol may be from plasma or de novo synthesis T may be converted in peripheral tissues to estradiol & androstenedione Androstenedione is the major source of estradiol in men Delta-5 pathway is the major route in men

Transport of Sex Steroids in Males Major Sex Steroid Binding Proteins Testosterone-Estrogen Binding Protein One high affinity binding site (T1/2=22 seconds) Binding affinity order for sex steroids = DHT (100) >T (33) >E (25) Albumin One low affinity binding site (T 1/2-=1 second) Cortisol Binding Globulin No binding to DHT, T or E2. Binds Progesterone Normal Distribution in Blood TEBG (30%), Albumin (68%), Free (2%) Active fraction includes free + albumin-bound fraction

Androgen Activity Increased Spermatogenesis Increased Bone Growth Increased bone matrix, calcium deposition and promotes epiphyseal closure Increased Nitrogen Balance Increased muscle mass, larynx size Increased atheletic performance Increased basal metabolic rate, red blood cell density oxygen utilization Altered Skin Function Increased thickness, melanin deposition sebaceous gland secretion

Androgen Activity Androgen-Receptor Interactions Both testosterone (T) and dihydrotestosterone (DHT) interact with same androgen receptor DHT has a higher affinity for the androgen receptor than T T-Androgen Receptor Interaction Feedback regulation of gonadotropin secretion Differentiation of Wolffian duct in utero DHT-Androgen Receptor Interaction External genitalia differentiation in utero Virilization during puberty

Male Reproductive Anatomy and Physiology Figure 26-9a: ANATOMY SUMMARY: Male Reproduction

Spermatogenesis: Sperm Production in the Testis Seminiferous tubules Spermatids Spermatocytes Spermatozoa Sertoli cells Interstitial tissue Leydig cells Capillaries

Testicular Compartmentalization

Sertoli Cell Function Sertoli Cells Nourish healthy cells & phagocytize damaged germ cells Synthesize luminal proteins Maintain tubular fluid Convert androgens to estrogens Are site for hormonal modulation of tubular function

Spermatogenesis: Sperm Production in the Testis Figure 26-9b-e: ANATOMY SUMMARY: Male Reproduction

Spermatozoa Structure and Functions in Review Head Acrosome: Nucleus: Midpiece Centrioles: Mitochondria: Tail: flagellum Microtubules: Figure 26-10: Sperm structure

Regulation of Spermatogenesis GnRH  LH  Leydig cells  testosterone  20 sex charact. GnRH  FSH  Sertoli cells  spermatoctye maturation Inhibin feedback – FSH, testosterone – short & long loops

Regulation of Spermatogenesis Figure 26-11: Hormonal control of spermatogenesis

Testicular Cell Interactions Sertoli cell products estradiol, inhibin, activin and other proteins modulate leydig cell activity Sertoli cell products modulate germ cell function Leydig cell testosterone modulate peritubular & Sertoli cell function Peritubular cell products influence Sertoli cell activity

Hypothalamic-Pituitary regulation of Testicular Function