Male RS

• Male reproductive system


  Endocrine function of the testis
• Male phenotype


  • The testes of gonadal males secrete antimüllerian hormone and testosterone
  • Testosterone stimulates the growth and differentiation of the wolffian ducts, which develop into the male internal genital tract
  • Antimüllerian hormone causes atrophy of the müllerian ducts (which would have become the female internal genital tract)
• Biosynthesis of testosterone


  1. Cholesterol in the Leydig cells

  2. 17α-hydroxylase pregnenolone is hydroxylated in the 17 position and then subjected to side chain cleavage to form dehydroepiandrosterone

  3. Androstenedione is also formed via progesterone and 17-hydroxyprogesterone, but this pathway is less prominent in humans

  4. Dehydroepiandrosterone and androstenedione are then converted to testosterone
• Regulation of the testis/hypothalamic-pituitary-seminiferous tubular axis

  1. Hypothalamic control—GnRH

  2. Anterior pituitary—FSH and LH

  3. Negative feedback control—testosterone and inhibin
• GnRH


  Arcuate nuclei of the hypothalamus secrete GnRH into the hypothalamic–hypophysial portal blood. GnRH stimulates the anterior pituitary to secrete FSH and LH
• FSH


  Acts on the Sertoli cells to maintain spermatogenesis. The Sertoli cells also secrete inhibin, which is involved in negative feedback of FSH secretion
• LH


  Acts on the Leydig cells to promote testosterone synthesis. Testosterone acts via an intratesticular paracrine mechanism to reinforce the spermatogenic effects of FSH in the Sertoli cells
• Testosterone


  Inhibits the secretion of LH by inhibiting the release of GnRH from the hypothalamus and by directly inhibiting the release of LH from the anterior pituitary
• Inhibin


  Produced by the Sertoli cells, inhibits the secretion of FSH from the anterior pituitary
• Actions of testosterone


  • Differentiation of epididymis, vas deferens, and seminal vesicles
  • Pubertal growth spurt
  • Cessation of pubertal growth spurt (epiphyseal closure)
  • Libido
  • Spermatogenesis in Sertoli cells (paracrine effect)
  • Deepening of voice
  • Increased muscle mass
• Actions of dihydrotestosterone


  • Differentiation of penis, scrotum, and prostate
  • Male hair pattern
  • Male pattern baldness
  • Sebaceous gland activity
  • Growth of prostate
• Spermatogenesis


  The process of male gamete formation. It includes formation of a spermatocyte from a spermatogonium, meiotic division of the spermatocyte, and transformation of the four resulting spermatids into spermatozoa
• Spermatogenesis


  1. Spermatozoa leaving the testes are not fully mobile. They continue their maturation and acquire motility during their passage through the epididymis

  2. Activation of CatSper cation channel proteins from the CatSper family, which are localized to the principal piece of the sperm tail, helps the sperms to be propelled forward

  3. Once ejaculated into the female, the spermatozoa move up the uterus to the isthmus of the uterine tubes, where they slow down and undergo capacitation
• Capacitation


  A maturation step to enable spermatozoa to fertilize an oocyte. It involves destabilization of the acrosomal sperm head membrane, chemical changes in the tail that allow greater mobility, and calcium influx leading to increased cAMP and motility. It is facilitated by the removal of sterols and epididymal/seminal glycoproteins and controlled by a fertilization promoting peptide from the prostate gland
• Acrosomal reaction


  Takes place at the ampulla of the Fallopian tube. First step is penetration of corona radiata by releasing hyaluronidase from the acrosome to digest cumulus cells surrounding the oocyte and exposing acrosin attached to the inner membrane of the sperm. Acrosin then digests the zona pellucida and the membrane of the oocyte. Part of the sperm cell membrane then fuses into the egg cell's membrane and the contents of the head sink into the egg
• Blood-testis barrier (BTB)


  • A physical barrier between blood and the lumen of the seminiferous tubules formed by tight junctions between adjacent Sertoli cells. It prevents many large molecules from passing from the interstitial tissue to the lumen, protecting highly immunogenic material from leaking out. It is however permeable to testosterone and some proteins which act in a paracrine manner. Anything that destroys the BTB will lead to an impairment of meiosis and spermatogenesis
• Orgasm and ejaculation


  1. Climax (orgasm) is a 15 second reaction that includes the discharge of semen

  2. Emission = sympathetic nervous system stimulates peristalsis in smooth muscle of the ductus deferens which propels sperm

  3. Expulsion = semen in urethra activates muscular contractions that lead to expulsion. Sympathetic reflex constricts the internal urethral sphincter so urine is unable to enter the urethra and semen cannot enter the bladder
• Semen or seminal fluid

  Fluid expelled during orgasm (2-5ml), composed of 60% seminal vesicle fluid, 30% prostatic fluid, and 10% sperm. Normal sperm count is 50-120 million/mL. Prostate contributes a thin, milky white fluid containing Ca, citrate, phosphate ions, clotting enzymes, and serine protease (PSA). Seminal vesicles contribute a yellowish fluid containing fructose, carbohydrates, prostaglandins, and a protein called proseminogelin
• Semen stickiness


  An adaptation that promotes fertilization. The clotting enzyme from the prostate activates proseminogelin, converting it to seminogelin which entangles the sperm and makes it stick to the inner wall of the vagina and cervix, preventing loss. After 30 minutes the serine protease (prostate) breaks down the seminogelin, allowing the sperm to become active and begin crawling up the mucosa of vagina and uterus
• Requirements for sperm motility

  • Elevated pH - the prostatic fluid buffers the spermatic ducts and vagina raising pH to 7.5, thus activating the sperm
  • Synthesis of ATP - energy from the fructose and other sugars contributed by the seminal vesicles