ch. 27 - reproductive

• Testes


  Sperm-producing male gonads that lie within the scrotum

  
• Sperm delivery to body

  1. Epididymis

  2. Vas deferens

  3. Ejaculatory duct

  4. Urethra

  
• Accessory sex glands


  • Seminal glands
  • Prostate
  • Bulbo-urethral glands
• The scrotum


  • Sac of skin and superficial fascia
  • Hangs outside abdominopelvic cavity at root of penis
  • 3°C lower than core body temperature is necessary for sperm production
  • Midline septum divides scrotum into two compartments
  • Affected by temperature changes - Dartos muscle and Cremaster muscles
• The testes


  • Septa divide testes into ~250 lobules, each containing one to four seminiferous tubules (site of sperm production)
  • Sperm travels from seminiferous tubules to straight tubule → rete testis → efferent ductules → epididymis
  • Epididymis is made up of the head, the body, and the tail (sperm are stored in the tail until ejaculation)
  • Blood supply - Testicular arteries and veins (pampiniform venous plexus to keep testes cool)
  • Spermatic cord encloses nerve fibers, blood vessels, and lymphatics that supply testes

  
• Epididymis


  Sperm mature here, pseudostratified columnar epithelial cells with microvilli (stereocilia) absorb excess testicular fluid and pass nutrients to stored sperm

  
• Ejaculation


  1. Epididymis contracts, expelling sperm into vas deferens

  2. Vas deferens and ejaculatory duct expand to form ampulla, smooth muscle propels sperm from epididymis to urethra
• Urethra


  Conveys both urine and semen (at different times), has three regions - prostatic, intermediate, and spongy
• Penis


  • Male copulatory organ, consists of root, shaft, and glans penis, prepuce (foreskin), corpus spongiosum, and corpora cavernosa
• Circumcision


  Surgical removal of prepuce (foreskin), 60% reduction in HIV risk and reduced risk for other reproductive infections
• Seminal glands


  Contains smooth muscle that contracts during ejaculation, produces viscous alkaline seminal fluid (70% of semen volume)
• Prostate


  Consists of smooth muscle that contracts during ejaculation, secretes milky, slightly acidic fluid (one-third of semen volume)
• Bulbo-urethral glands


  Produce thick, clear mucus during sexual arousal to lubricate glans penis and neutralize traces of acidic urine in urethra
• Semen


  Milky-white mixture of sperm and accessory gland secretions, 2–5 ml containing 20–150 million sperm/ml, alkaline fluid that neutralizes acidity and enhances motility
• Erection


  Enlargement and stiffening of penis, caused by parasympathetic activation leading to vasodilation and engorgement of erectile tissues
• Ejaculation


  Propulsion of semen from male duct system, initiated by sympathetic nerves causing contraction of vas deferens, prostate, and seminal glands, followed by contraction of bulbospongiosus muscles to expel semen
• Erectile dysfunction


  Inability to achieve erection, caused by inadequate nitric oxide release or problems with blood vessels or nervous system (often due to diabetes)
• Seminiferous tubules


  • Contain sustentocytes (Sertoli cells), spermatogenic cells, myoid cells, and interstitial endocrine cells (Leydig cells)
• Spermatogenesis


  Mitosis of spermatogonia to form spermatocytes, meiosis of spermatocytes to form spermatids, spermiogenesis to form mature sperm

  
• Hormonal regulation of male reproductive function

  • Hypothalamus
  • Anterior pituitary gland
  • Testes
• Meiosis I


  Undergoes meiosis I, forming two secondary spermatocytes (n)
• Meiosis II


  Secondary spermatocyte (n) rapidly undergoes meiosis II to become two spermatids (n)
• Spermatids


  • Small, round cells with large nuclei found close to lumen of tubule
  • Nearly all genes are turned off and DNA compacted into dense pellets
• Spermiogenesis


  1. Spermatids to sperm

  2. Streamlining process where spermatid elongates, loses excess cytoplasm, and forms a tail
• Spermatids


  • Contain correct haploid chromosome number needed for fertilization (n)
  • Are still nonmotile
• Hormones involved in regulation of testicular function and male reproductive anatomy

  • GnRH
  • FSH
  • LH
  • Testosterone
  • Inhibin
• Hormonal regulation of testicular function

  1. Hypothalamus releases GnRH

  2. GnRH binds to anterior pituitary gonadotropic cells, causing them to secrete FSH and LH

  3. FSH stimulates Sertoli cells to release androgen-binding protein (ABP), keeping testosterone concentration high near spermatogenic cells

  4. LH binds to Leydig cells, causing them to secrete testosterone

  5. Rising testosterone levels trigger spermatogenesis

  6. Testosterone entering blood stimulates sex organ maturation, development/maintenance of secondary sex characteristics, and libido

  7. Rising testosterone levels feedback on hypothalamus to inhibit GnRH and pituitary to inhibit gonadotropin release

  8. Inhibin released by Sertoli cells when sperm count high inhibits GnRH and FSH release
• Before birth, male infant has testosterone levels two-thirds of adult
• After brief rise in early infancy, blood testosterone levels recede and remain low through childhood
• Activation of the HPG Axis at Puberty

  1. Before puberty, low levels of circulating steroidal sex hormones enough to suppress secretion of GnRH

  2. As puberty approaches, hypothalamus becomes less sensitive to inhibition by sex hormones and releases GnRH in pulse like manner

  3. Anterior pituitary releases FSH and LH in response to increased GnRH levels

  4. FSH and LH stimulate gonads to release more sex hormones

  5. Threshold for inhibition of GnRH continues to rise, resulting in more and more release of sex hormones

  6. Sex hormones are released until adult pattern of hormone interaction is achieved
• Without GnRH and gonadotropins, testes atrophy and sperm and testosterone production ceases
• Testosterone


  Synthesized from cholesterol, transformed at some target cells into dihydrotestosterone (DHT) in prostate and estradiol in some brain neurons
• Effects of testosterone deficiency


  • Atrophy of accessory organs
  • Semen volume declines
  • Erection/ejaculation are impaired
• Male secondary sex characteristics


  • Appearance of pubic, axillary, and facial hair
  • Enhanced growth of hair on chest or other areas
  • Larynx enlargements causes deepening of voice
  • Skin thickens and becomes oily
  • Bones grow, increase in density
  • Skeletal muscles increase in size and mass
  • Boosts basal metabolic rate
  • Basis of sex drive (libido) in males
• Reproductive role of female more complex because of pregnancy
• Ovaries


  Female gonads
• Ovaries


  • Paired structures flanking the uterus, almond shaped and about twice as large
  • Each ovary is held in place by several ligaments (ovarian ligament, suspensory ligament, mesovarium)

  
• Tunica albuginea


  Fibrous layer surrounding each ovary

  
• Ovary structure


  • Outer cortex
  • Inner medulla
• Ovarian follicles


  Structures in which immature eggs develop