REPRODUCTIVE SYSTEM

• Reproductive System


  Function: producing offspring, propagation of the species
• The reproductive system is the only major system that doesn't work continuously, it is only activated at puberty
• Mammals only reproduce sexually, humans are dieocious (separate sexed)
• Differentiation of gonads


  Occurs in the 7th week of embryonic development
• Major Organs of Male Reproductive System


  • External: penis and scrotum
  • Internal: testes, epididymis, vas deferens, ejaculatory duct, urethra
  • Accessory: seminal vesicles, prostate gland, bulbourethral glands
• Penis


  Transfer organ, contains erectile tissues that fill with blood during sexual arousal
• Scrotum


  Keeps testes at cooler temperature, as sperm can only be produced at several degrees below normal body temp
• Testes


  • Primary reproductive organ of male, contain seminiferous tubules for spermatogenesis, and interstitial cells that secrete testosterone
• Epididymis


  Highly coiled tube where sperm mature and are stored until needed
• Vas Deferens


  Muscular tube that transports sperm from epididymis to ejaculatory duct
• Ejaculatory Duct


  Connects vas deferens to urethra
• Urethra


  Transports sperm and urine out of the body
• Accessory Glands


  • Seminal vesicles
  • Prostate gland
  • Bulbourethral glands
• Seminal Vesicles


  Secrete fluid that makes up 60% of semen, providing nutrients for sperm
• Prostate Gland


  Secretes fluid that makes up 30% of semen, helps protect and buffer sperm
• Bulbourethral Glands


  Secrete fluid that lubricates the penis and helps neutralize acidity in the urethra
• External Female Reproductive Organs


  • Vulva
  • Mammary glands
• Vulva


  Group of structures at the external opening of the vagina, including the mons pubis, labia majora, labia minora, clitoris, and Bartholin's glands
• Mammary Glands


  Produce nutrient-rich milk for nursing infants
• Internal Female Reproductive Organs


  • Ovaries
  • Oviducts
  • Uterus
  • Vagina
• Ovaries


  • Contain follicles with partially developed egg cells, perform oogenesis and hormone secretion
• Uterine Tubes


  Also called oviducts or fallopian tubes, receive the egg at ovulation and transport it to the uterus
• Uterus


  Thick, muscular organ that receives the egg and holds the embryo/fetus during pregnancy
• Vagina


  Muscular tube that leads to the outside of the body, secretes lubricating fluid during sexual arousal
• Spermatogenesis


  Process of sperm production in the seminiferous tubules of the testes, takes 70-80 days
• Sertoli Cells


  Specialized cells in the seminiferous tubules that facilitate spermatogenesis
• Anterior pituitary gland


  Serves as the primary control of reproductive function, secreting FSH and LH at puberty to stimulate testicular development and sperm production
• Testosterone


  Main male hormone, secreted by the interstitial cells of the testes, has local effects on sperm development as well as systemic effects on protein synthesis, muscle development, secondary sexual characteristics, and behavior
• Androgens are also produced in women, but at relatively weak levels, promoting protein synthesis and growth without masculinizing effects
• High testosterone levels


  Inhibit LH secretion, maintaining a constant level of testosterone in the blood
• Androgens


  • Stimulate general protein synthesis
  • Promote muscular development, bone growth, thickening of skin and growth of facial and body hair
  • Promote development and maintenance of secondary sexual characteristics
  • Cause behavioral changes (e.g. sex drive, aggression, courtship behaviors)
• Androgens are also produced in women, but relatively weakly, and promote protein synthesis and growth without masculinizing effects
• Negative feedback loop


  High testosterone levels inhibit LH
• Spermatogenesis


  1. Primordial germ cells colonize embryonic gonad and become spermatogonia

  2. Spermatogonia remain dormant in childhood

  3. At puberty spermatogonia begin to divide (mitosis)

  4. Some spermatogonia begin moving away from the wall of the tubule and enlarge to become primary spermatocytes

  5. Primary spermatocyte undergoes meiosis I to produce secondary spermatocytes

  6. Secondary spermatocytes undergo another division to produce spermatids

  7. Spermatids mature into sperm cells
• Sertoli Cells


  • Produce a blood-testes barrier that protects developing sperm cells
  • Nourish developing sperm cells by secreting fluid rich in proteins, enzymes and testosterone
  • Phagocytize any damaged sperm cells
• The blood-testis barrier formed by Sertoli cells prevents antibodies and other large molecules in the blood and intercellular fluid from getting to the germ cells
• A young adult male produces around 300,000 sperm per minute, or 400 million per day
• Spermatozoan Structure


  • Head (with acrosome containing enzymes and enzyme inhibitors)
  • Midpiece (containing mitochondria to produce ATP for propulsion)
  • Tail (flagellum for locomotion)
• Semen


  Mixture of sperm and glandular secretions, typically 3-5 ml in volume
• Sperm count in healthy young males averages around 60 million sperm per ml, ranging between 40-120 million per ml