Male Reproductive and Hormonal Functions PDF

Male Hormonal System  Functional Anatomy of Testis Testis is the primary sex organ in males. Consists of 200 – 300 lobules. Each lobule contains coiled tubules known as the seminiferous tubules. Seminiferous tubules drains into epididymis → stores sperms Epididymis continue as the va...

Male Hormonal System  Functional Anatomy of Testis Testis is the primary sex organ in males. Consists of 200 – 300 lobules. Each lobule contains coiled tubules known as the seminiferous tubules. Seminiferous tubules drains into epididymis → stores sperms Epididymis continue as the vas deferens.  Seminiferous Tubules Thread like convoluted tubular structures. Consists of three types of cells: 1. Germ cells: Formation of sperm (spermatogenesis) 2. Sertoli cells: Support & nourish spermatogenic cells Forms blood-testis barrier; prevents immune cells to form antigens against genetically unique sperm cells. 3. Leydig cells Located in the interstitium of the testis → interstitial cells of Leydig. Secretes testosterone.  Spermatogenesis Spermatogonia are immature germ cells lie in the inner surfaces of the seminiferous tubules. At puberty they begin to undergo mitotic division and continually proliferate and differentiate to form sperm. Spermatogenesis is the process of formation of sperms (takes about 74 days). i.e. transformation of spermatogonia (epithelioid cells)– to → sperm cells The two testes of the human adult form up to 120 million sperm each day. It is initiated at puberty, continues throughout a man’s life. Wall of seminiferous tubules is the main site for production of sperms, while maturation takes place in the epididymis. It requires lower temperature (about 32 ◦c); achieved by a) Location of the testes outside of the abdominal cavity. b) The countercurrent system between spermatic arteries and veins. This system also maintains high concentration of testosterone within the testes.  Steps of Spermatogenesis Type A spermatogonia (epithelioid-like cells) Spermatogonia are immature germ cells, at Proliferate by mitotic division Type B spermatogonia puberty they begin to undergo mitotic division and continually proliferate. 1) Spermatogonia migrate toward the central Primary spermatocytes (46 ch) lumen, enlarged to form 2)primary 1st meiotic division spermatocytes (46ch) which undergoes 2 Secondary spermatocytes (23ch) meiotic division to form 3)secondary 2nd meiotic division spermatocytes (23ch) then 4)spermatids that Spermatids modified to become spermatozoa (sperm) (23). Spermiogenesis Spermatocytes Immature sperm cells Mature Sperm  Maturation of Sperms Sperms in the seminiferous tubules are nonmotile, they acquire the motility in the epididymis within 18 to 24 hours. Most of sperms are stored in the epididymis, (small quantity is stored in the vas deferens).2 Their fertility is maintained for at least a month. They are kept suppressed by inhibitory substances. After ejaculation, they become motile and capable of fertilization, a process called maturation. Sertoli cells and the epithelium of the epididymis secrete fluid during ejaculation contains hormones (testosterone and estrogens), enzymes, and special nutrients that are essential for sperm maturation.  Hormonal Factors in Spermatogenesis 2 1. Testosterone Secreted by the Leydig cells. Essential during the 1st stage in forming sperm → growth and division 2. Luteinizing hormone Secreted by the anterior pituitary gland. Stimulates the Leydig cells to secrete testosterone. 3. Follicle-stimulating hormone Secreted by the anterior pituitary gland. Stimulates Sertoli cells to produce; 1) androgen-binding protein (ABP) 2) inhibin. Important for conversion of spermatids to sperm (spermiogenesis). 4. Estrogens Formed from testosterone. Probably also essential for spermiogenesis. 5. Growth hormone Controls metabolic functions of the testes → promotes division of spermatogonia. Pituitary dwarfs → deficient spermatogenesis → infertility.  Structure of Spermatozoon Composed of a head and a tail. The head comprises the condensed nucleus, with a thin cytoplasmic layer. The thick anterior two thirds is called acrosome, formed mainly from the Golgi apparatus. It contains several enzymes, allow the sperm to enter the ovum, including: a) Proteolytic enzymes (digest proteins). b) Hyaluronidase (digest proteoglycan filaments of tissues).  Structure of Spermatozoon The tail of the sperm, (flagellum), has three components: 1. Axoneme A central skeleton constructed of 11 microtubules. 2. A thin cell membrane covering the axoneme 3. A collection of mitochondria surrounding the axoneme in the proximal portion of the tail The tail has a back-and-forth movement (flagellar movement), at a velocity of 1 to 4 mm/min. Male Sexual Act  Semen The male sexual act is the process that culminates in ejaculation of several hundred million viable sperm. The sperm cells are contained in a mixture of fluids called semen that produced by the male reproductive organs. The average volume of semen is about 3.5 milliliters, it includes the following: A. Sperm cells. ▪ Each milliliter of semen contains approximately 120 million sperm cells. ▪ For normal fertility, the sperm count per milliliter must be greater than 20 million. B. Seminal vesicle fluid, ➔ makes up 60 percent of the semen. ▪ It contains mucoid, prostaglandin E2, fructose, and fibrinogen. → nutrient for sperms. C. Prostatic fluid, ➔ makes up 20% of the semen volume ▪ Contains NaHCO3 (pH 7.5; optimum pH for the motility of sperms), clotting enzyme, calcium, and profibrinolysin.  Male Sexual Act The sexual act takes place in three stages: A. Erection and lubrication. ▪ Erection is the process of filling the erectile tissue of the penis with blood at a pressure level near that of the arterial pressure. ▪ Mechanism; parasympathetic post ganglionic fibers release acetylcholine to activate muscarinic receptors on endothelium to release nitric oxide on the arterial smooth muscle → dilatation of the arteries to the erectile tissue. ▪ Norepinephrine & endothelin cause vasoconstriction and penis relaxation after orgasm.  Male Sexual Act B. Emission ▪ The process of stimulating the smooth muscle surrounding the seminal vesicles, vas deferens, and prostate gland, to empty their contents into the internal urethra. ▪ This process is elicited by sympathetic reflexes from L1 and L2. C. Ejaculation ▪ A reflex elicited in response to distention of the internal urethra, results in contraction of the ischiocavernosus, bulbocavernosus and pelvis muscles causing compression in the internal urethra and propulsion of the semen out of the urethra. Male Sex Hormones  Testosterone Secreted by the Leydig cells of the testes. A steroid hormone formed from cholesterol (lipid-soluble). Carried in plasma bound to: a) 65% bound to a β-globulin called gonadal steroid– binding globulin (GBG). b) Albumin Mechanism of action: Enters the cytoplasm by diffusion, converted by 5α-ketoreductase to its biologically active form dihydrotestosterone, which then binds with a cytoplasmic receptor protein, migrates to the nucleus, binds with a nuclear protein to induce DNA-RNA transcription. Metabolism: Removed from the blood within 30 to 60 minutes of secretion. It is metabolized to: a) Dihydrotestosterone (the biologically active androgen) in target tissues b) Estrogen in adipose tissue.  Actions of Testosterone It has effects on reproductive and nonreproductive organs. A. Reproductive 1. Fetal life: stimulate formation of male sex organs and to cause descent of the testes. Genital ridge and testes are stimulated by the hormone hCG to secret testosterone. 2. Pubertal: development of primary and secondary sexual characteristics. 3. In adult men for maintenance & normal function of the primary sex organs. B. Non-reproductive 1. Anabolic effect → ↑growth, proliferation of bone & muscles, ↑ basal metabolic rate. 2. Decreases the growth of hair on the top of the head; → male pattern baldness. 3. ↑ synthesis of clotting factors. 4. ↓high-density lipoprotein ↑and low-density lipoprotein levels &↑ hepatic lipases. 5. Stimulate production of erythropoietin→ ↑hematocrit & hemoglobin concentrations. Testosterone – Regulation of secretion Hypothalamic gonadotropin-releasing hormone (GnRH) increases release of LH and FSH from the anterior pituitary gland. LH stimulates testosterone formation by the Leydig cells, FSH stimulates spermatogenesis by Sertoli cells. Inhibin (from Sertoli cells) and testosterone (Leydig cells) inhibit FSH secretion. Inhibin formation increases as the rate of sperm cell production increases. Testosterone is inhibited as well as LH & GnRH. References 1. John E. Hall. Pocket companion to Guyton and Hall textbook of medical physiology. 13th ed. 2016. Elsevier. 2. John E. Hall. Guyton and Hall textbook of medical physiology. 13th ed. 2016. Elsevier. 3. Kim E. Barret, Susan M. Barman. Ganong’s Review of medical physiology. 25th ed. 2016. McGraw-Hill Education, Lang. 4. T. H. Merghani. The core of Medical Physiology. 4th ed.