Male Reproductive System Physiology Final PDF

RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn Physiology of Reproductive Glands: The Male Reproductive System Module Endocrine and Breast Lecturer Brona Murphy - [email protected] Ebrahim Rajab – [email protected]  LEARNING OUTCOMES 1....

RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn Physiology of Reproductive Glands: The Male Reproductive System Module Endocrine and Breast Lecturer Brona Murphy - [email protected] Ebrahim Rajab – [email protected]  LEARNING OUTCOMES 1. Outline reproduction 2. Understand the male reproductive system 3. Describe the physiological functions of the male reproductive system with particular emphasis on the gonads 4. Understand the factors that control male gonad function 5. Understand the physiological effects of testosterone and to appreciate the factors in control of testosterone secretion  REPRODUCTION Depends on union of male and female gametes to form new individual Male and female reproductive systems designed to enable union of genetic material MALE REPRODUCTIVE SYSTEM Male reproductive system consists of the penis, testes, epididymis, ejaculatory ducts, prostate and accessory glands. Essential functions of male reproductive system – Produce sperm (spermatogenesis) – Delivery semen from the testes via ejaculation.  MALE REPRODUCTIVE SYSTEM Reproductive organs Reproductive tract – System of specialized ducts that transport or house gametes after they are produced (epididymis, ductus/vas deferens, ejaculatory duct) Accessory sex glands – Empty supportive secretions into reproductive tract (prostate, seminal vesicles, bulbourethral/Cowper’s glands) External genitalia – Externally visible portions of reproductive system (penis, scrotum, testicles) Secondary sexual characteristics – External characteristics not directly involved in reproduction that distinguish males and females Body configuration and hair distribution OVERVIEW OF MALE REPRODUCTIVE ORGANS AND FUNCTIONS Organs Function 2 Testes (=male gonads) – produce sperm and sex Spermatogenesis hormones. Hormones influence sperm production and Delivery of semen to female secondary sex traits. 2 Epididymides – sperm maturation and concentration 2 Vas/ductus Deferentia –storage of sperm 1 Penis – sexual intercourse organ MALE REPRODUCTIVE SYSTEM Testes – Primary reproductive paired organs – Sperm-producing and testosterone- secreting – Suspended outside abdominal tract in skin-covered sac (scrotum) – Descent into scrotum is usually complete by seventh month of gestation Location provides cooler environment essential for spermatogenesis Descent of testis. A, Fifth week. B, Eighth to ninth weeks. Kidney reaches adult position. C, Seventh month. Testis at internal inguinal ring; gubernaculum (in inguinal fold) thickens and shortens. D, Postnatal life. Testis in scrotum; processus vaginalis closed, and gubernaculum (vestigial). MALE REPRODUCTIVE SYSTEM – REPRODUCTIVE TRACT Sperm exit each testis through the male reproductive tract, consisting on each side of – Epididymis Long coiled duct that is continuous with ductus/vas deferens Function – storage and maturation of spermatozoa – Propulsion of spermatozoa into the ductus deferens During passage through epididymis – spermatozoa mature » maturation enhanced by testosterone – concentration of spermatozoa increases a 100-fold FIG. 9.8 Diagram of male reproductive tract, including the intratesticular portion of the tract. Redrawn from Stevens A, Lowe J: Human Histology, 3rd ed., Philadelphia, 2005, Mosby. MALE REPRODUCTIVE SYSTEM – REPRODUCTIVE TRACT (CONT’D) – Ductus (vas) deferens transports spermatozoa from the epididymis to the ejaculatory duct provides fructose to the spermatozoa – Ejaculatory duct Formed by the ductus/vas deferens and seminal vesicle ducts Function – propel spermatozoa with seminal fluid into urethra – These pairs of reproductive tubes empty into a single urethra, the canal that runs the length of the penis and empties to the exterior FIG. 9.8 Diagram of male reproductive tract, including the intratesticular portion of the tract. Redrawn from Stevens A, Lowe J: Human Histology, 3rd ed., Philadelphia, 2005, Mosby.  VASECTOMY Common sterilization procedure* in which a small segment of each ductus deferens is removed Blocking exit of sperm from testes but does not interfere with testosterone activity *sterilization procedure = permanent method of birth control MALE REPRODUCTIVE SYSTEM - ACCESSORY SEX GLANDS Seminal vesicles, prostate gland and bulbourethral (Cowper’s) glands Provide secretions that constitute the bulk of semen to support viability of spermatazoa inside female reproductive tract – Semen Mixture of accessory sex gland secretions, spermatazoa and mucus Seminal vesicles Ejaculatory – Paired glands that connect with the ductus ducts deferens to form ejaculatory ducts Secrete alkaline fluid that makes up more than 50% of semen Supply fructose as energy source for ejaculated spermatozoa Secrete prostaglandins which help transport spermatozoa to site of fertilization by stimulating smooth muscle in male and female reproductive tracts Secrete fibrinogen MALE REPRODUCTIVE SYSTEM - ACCESSORY SEX GLANDS Prostate gland – Secretes alkaline fluid that aids spermatozoa viability in acidic vaginal secretions – Provides clotting enzymes and fibrinolysin Enzymes act on fibrinogen to “clot” semen to keep sperm in female reproductive tract during penis withdrawal Fibrinolysin breaks down clot to aid spermatozoa motility Bulbourethral/Cowper’s glands – secretes mucus for lubrication during ejaculation for sexual intercourse MALE REPRODUCTIVE SYSTEM Penis – Function Urination Organ used to deposit semen in female – Consists nearly entirely of erectile tissue Composed of three columns of sponge-like vascular spaces extending length of organ – In absence of sexual excitation, erectile tissues contain little blood Penis remains small and flaccid – During sexual arousal arterioles that supply vascular chambers dilate Erectile tissue fills with blood Penis enlarges in width and length Fig. 74.3 The male external genitalia. The skin of the abdomen and parts of the – Capable of penetrating skin of the scrotum have been removed, and the body of the penis has been vagina transected revealing the internal structure of the penis. The layers of the spermatic cord and the coverings of the testis have been dissected on the right. Sobotta Atlas of Human Anatomy © Elsevier GmbH, Urban & Fischer, Munich. SPERMATOZOA Consist of four parts – Head Consists primarily of the nucleus (contains DNA) – Acrosome Enzyme-filled vesicle that caps tip of the head Used to penetrate ovum – Midpiece Area where mitochondria are concentrated – Tail Provides mobility for spermatozoan SPERMATOGENESIS Yields an abundance of spermatozoa. Complex process by which undifferentiated diploid primordial germ cells (spermatogonia) are converted into haploid spermatozoa (sperm) – Includes the processes and events in which spermatogonia give rise to spermatocytes, then to spermatids, and ultimately to spermatozoa – Occurs in the seminiferous tubules of the testes – Begins in puberty – Requires testosterone – Duration: ∼ 2 months SPERMATOGENESIS Spermiogenesis – Particular stage of spermatogenesis in which spermatids differentiate into spermatozoa – Formation of the acrosome – Loss of cytoplasmic content – Condensation of genetic material – Development of the flagellum After spermiogenesis, the spermatozoa leave the seminiferous tubule to reach the epididymis. TESTES Sertoli cells and Germ cells – located within the seminiferous tubules where spermatogenesis occurs Germ cells – various stages of sperm development so that up to several hundred million sperm reach maturity daily. Sertoli cells – Provide crucial support for spermatogenesis – produce androgen binding protein (ABP) ABP is released into the testicular fluid where it binds testosterone maintains a locally high concentration of testosterone for spermatogenesis Leydig cells – interstitial cells located outside the seminiferous tubules – Synthesize and secrete testosterone FIGURE 81-2 A, Cross section of a seminiferous tubule. B, Stages in the development of sperm from spermatogonia. Guyton and Hall Textbook FIGURE 81-7 Interstitial cells of Leydig, the cells that secrete testosterone, of Medical Physiology. located in the interstices between the seminiferous tubules. Guyton and Hall Textbook of Medical Physiology. SEXUAL INTERCOURSE/COITUS/COPULATION Delivers sperm laden semen into female vagina – To accomplish reproduction in humans Involves two components – Erection – Ejaculation Erection accomplished by engorgement of penis with blood – Erection reflex Ejaculation – Emission phase Emptying of sperm and accessory sex gland secretions (semen) into (penile) urethra via sympathetically-induced contraction of smooth muscle in walls of ducts and accessory sex gland – Expulsion phase Forceful expulsion of semen from urethra via motor-neuron-induced contraction of skeletal muscles at base of penis ERECTION REFLEX A spinal reflex triggered by stimulation of mechanoreceptors in glans penis – Erection-generating centre lies in lower spinal cord – Stimulation of glans triggers, via this centre increases parasympathetic vasodilator activity & decreases sympathetic vasoconstrictor activity to penile arterioles – Efficient vasodilation of arterioles and ensuing erection Erectile dysfunction inability to achieve or sustain an erection sufficient in rigidity or duration for sexual intercourse which is present for a minimum of ∼ 6 months – Most common sexual disorder in men SPERM IN EJACULATION/SEMEN Volume and sperm content of ejaculate depend on length of time between ejaculations Average volume of semen is 2.75 ml, ranging from 2-6 ml Average ejaculate contains approx. 180x10 6 sperm (66x 106/ml) Man considered to have a low sperm count if sperm concentration falls below 15 x 106/ml of semen  HYPOTHALAMUS & PITUITARY: CONTROL OF TESTICULAR FUNCTION Testes controlled by two gonadotropic hormones secreted by anterior pituitary: Leutinizing hormone (LH) and Follicle- stimulating hormone (FSH) – LH acts on Leydig cells to regulate testosterone secretion – FSH acts on Sertoli cells to enhance spermatogenesis Secretion of LH and FSH stimulated by a single hypothalamic hormone: Gonadotropin-releasing hormone (GnRH) Secretory rate of LH and FSH also influenced by other hormones – Testosterone acts in negative feedback fashion to inhibit LH secretion Decreases GnRH release by acting on hypothalamus Reduces responsiveness of AP to GnRH – Inhibin acts in negative feedback fashion to inhibit FSH secretion FIGURE 81-10 Feedback regulation of the hypothalamic-pituitary- Acts directly on AP testicular axis in males. Stimulatory effects are shown by plus signs, and negative feedback inhibitory effects are shown by minus signs. CNS, Central nervous system; FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone. Guyton and Hall Textbook of Medical Physiology. PHYSIOLOGICAL EFFECTS OF TESTOSTERONE Testosterone is a steroid hormone derived from cholesterol precursor molecule that has many effects Effect on reproductive system before birth – Before birth, testosterone from the testes (Leydig cells) masculinises the reproductive tract and external genitalia and promotes descent of scrotum – After birth, testosterone secretion ceases and the testes remain small and non-functional until puberty GnRH activity is inhibited Effect on sex-specific tissues after birth –Responsible for growth and maturation of male reproductive system –Pubertal process is initiated by an increase in GnRH activity –Resulting in testosterone secretion by Leydig cells once more Testes enlarge and sperm production commences Accessory sex gland enlarge and become secretory FIGURE 81-2 A, Cross section of a seminiferous tubule. B, Stages in the development of sperm Penis and scrotum enlarge from spermatogonia. Guyton and Hall Textbook Sexual libido is developed of Medical Physiology. PHYSIOLOGICAL EFFECTS OF TESTOSTERONE (CONT’D) Reproduction related effects - helps maintain sex drive in adult male - negative feedback control of gonadotropin- releasing hormone Effect on secondary sexual characteristics - All depend on testosterone for their development and maintenance - necessary for development of male pattern of hair growth, deep voice, thick skin and male body configuration Non-reproductive actions - General protein anabolic effects and promotes bone growth - Contributing to more muscular physique of males and pubertal growth spurt - Oil secretion by stimulating sebaceous FIG. 9.5 Actions of testosterone (T), dihydrotestosterone (DHT), gland and estradiol (E2) in men. From Koeppen B, Stanton B: Berne - Contributing to acne at puberty and Levy Physiology, updated 6th ed., Philadelphia, 2010, Mosby. Note that Testosterone is converted to estradiol in adipose tissue and to dihydrotestosterone in the genital skin and prostate. Endocrine and Reproductive Physiology. 5th Edition. White, Harrison and Mehlmann.  ANDROGEN DEFICIENCY IN AGING MALES Ongoing testosterone secretion required for spermatogenesis and maintaining male reproductive tract. Once initiated at puberty, testosterone production and spermatogenesis occur continuously throughout male’s life Testicular efficiency decreases at 45-50 years. – Gradual reduction in circulating testosterone levels and sperm production Probably due to aging-related degeneration of small testicular blood vessels – androgen deficiency in ageing males (ADAM) Aversa, A., Morgentaler, A. The practical management of testosterone deficiency in men. Nat Rev Urol 12, 641–650 (2015). https://doi.org/10.1038/nrurol.2015.238  MULTIPLE CHOICE QUESTIONS 1. Spermatogenesis is regulated by a negative feedback control system in which follicle- stimulating hormone (FSH) stimulates the steps in sperm cell formation. What is the negative feedback signal associated with sperm cell production that inhibits pituitary formation of FSH? A. Testosterone B. Inhibin C. Estrogen D. Luteinizing hormone E. Dihydrotestosterone Answer: B 2. A “birth control” compound for men has been sought for several decades. Which of the following would provide effective sterility? A) Substance that mimics the actions of luteinizing hormone B) Substance that blocks the actions of inhibin C) Substance that blocks the actions of follicle-stimulating hormone D) Substance that mimics the actions of gonadotropin-releasing hormone Answer: C. Blocking the action of follicle stimulating hormone on the Sertoli cells of the seminiferous tubules interrupts the production of sperm. Choice C is the only option that is certain to provide sterility.  Recommended Reading Medical Sciences. Jeannette Naish. Chapter 10. Endocrinology and the Reproductive System. Or, Endocrine and Reproductive Physiology. Bruce White, John Harrison, Lisa Mehlmann. Chapter 8. Life Cycle of the Male and Female Reproductive Systems. Or, Master Medicine: Physiology. J McGeown. Chapter 8. Endocrine physiology.