Reproductive System

• Testes


  Golf ball-sized, approximately 4 cm long and 2.5 cm wide, connected to the trunk via the spermatic cord
• Testes


  • Fibrous connective tissue capsule (tunica albuginea) surrounds each testis
  • Extensions of this capsule (septa) divide the testis into wedge-shaped lobules
  • Each lobule contains 1-4 tightly coiled seminiferous tubules, the "sperm-forming factories"
  • Seminiferous tubules empty sperm into the rete testis, which leads to the epididymis
• Interstitial cells


  Cells in the soft connective tissue surrounding the seminiferous tubules that produce androgens, the most important of which is testosterone
• Male duct system


  • Epididymis
  • Ductus deferens
  • Urethra
• Epididymis


  • Highly convoluted tube about 6 m long that hugs the posterior side of the testis
  • Provides temporary storage site for immature sperm
  • Sperm mature and develop ability to swim as they travel through the epididymis
• Ductus deferens


  • Runs upward from the epididymis via the spermatic cord, arches over the urinary bladder, and descends along the posterior bladder wall
  • Expands as the ampulla and empties into the ejaculatory duct, which passes through the prostate to merge with the urethra
  • Propels live sperm from the epididymis and distal part of the ductus deferens into the urethra
• Urethra


  • Extends from the base of the urinary bladder to the tip of the penis
  • Has three regions: prostatic urethra, membranous urethra, and spongy (penile) urethra
  • Carries both urine and sperm to the body exterior
• Urine and sperm never leave the body at the same time. When ejaculation occurs and sperm enter the prostatic urethra, the bladder sphincter constricts to prevent urine from passing into the urethra and sperm from entering the urinary bladder.
• Accessory glands


  • Seminal vesicles
  • Prostate
  • Bulbourethral glands
• Seminal vesicles


  • Large hollow glands that produce about 60% of seminal fluid, the fluid portion of semen
  • Their secretion is rich in sugar, vitamin C, prostaglandins, and other substances that nourish and activate sperm
• Prostate


  • Single doughnut-shaped gland about the size of a peach pit that encircles the upper part of the urethra
  • Prostate fluid plays a role in activating sperm and enters the urethra during ejaculation
• Hypertrophy of the prostate, an increase in its size, affects nearly every older man and strangles the urethra, making urination difficult and enhancing the risk of bladder infections and kidney damage.
• Prostatitis, inflammation of the prostate, is the single most common reason for a man to consult a urologist, and prostate cancer is the third most prevalent cancer in men.
• Bulbourethral glands


  Tiny, pea-sized glands inferior to the prostate that produce a thick, clear mucus that cleanses the urethra and serves as a lubricant during sexual intercourse
• Semen


  • Milky white, somewhat sticky mixture of sperm and accessory gland secretions
  • The liquid portion acts as a transport medium for nutrients and chemicals that protect the sperm and aid their movement
  • Fructose in the seminal vesicle secretion provides energy for the sperm
  • The relative alkalinity of semen helps neutralize the acidic environment of the female's vagina, protecting the delicate sperm
  • Semen also contains antibiotic chemicals, the hormone relaxin, enzymes that enhance sperm motility, and substances that inhibit an immune response in the female reproductive tract
• Semen dilutes sperm; without such dilution, sperm motility is severely impaired. The amount of semen propelled out during ejaculation is 2 to 5 ml, but there are 50 to 150 million sperm in each milliliter.
• Male infertility may be due to obstructions of the duct system, hormonal imbalances, environmental estrogens, pesticides, excessive alcohol, or many other factors. Semen analysis is one of the first tests done when a couple has been unable to conceive.
• Scrotum


  • Divided sac of skin with sparse hairs that hangs outside the abdominal cavity, between the legs at the root of the penis
  • Provides a temperature about 3°C lower than body temperature, which is necessary for the production of healthy sperm
• Penis


  • Skin-covered organ that delivers sperm into the female reproductive tract
  • Consists of a shaft ending in an enlarged tip, the glans penis
  • The skin folds downward to form the prepuce or foreskin around the proximal end of the glans penis
• Frequently in the United States, the foreskin is surgically removed shortly after birth, in a procedure called circumcision.
• Erection


  The penis enlarges and becomes rigid due to the filling of its erectile tissue with blood during sexual excitement, helping the penis serve as the male organ of copulation
• Spermatogenesis


  • Sperm production that begins during puberty and continues throughout life
  • Sperm are formed in the seminiferous tubules of the testis, starting with primitive stem cells called spermatogonia
  • Meiosis occurs as the dividing cells are pushed toward the lumen of the tubule, resulting in spermatids
  • Spermatids undergo further changes in spermiogenesis to become mature, streamlined sperm cells
• The entire process from the formation of a primary spermatocyte to release of immature sperm in the tubule lumen takes 64 to 72 days. Sperm in the lumen are still unable to "swim" and are moved by peristalsis through the tubules of the testes into the epididymis.
• Sperm development


  1. Spermatocytes pushed toward lumen of tubule

  2. Spermatids produced by meiosis

  3. Spermiogenesis - excess cytoplasm stripped, tail formed

  4. Mature sperm - streamlined cell with high metabolism and means of propulsion
• Sperm


  • Head is nucleus with compacted DNA
  • Acrosome - enzyme-containing structure that helps penetrate egg
  • Midpiece contains mitochondria that provide ATP for tail movement
  • Tail propels sperm
• Sperm development from primary spermatocyte to release of immature sperm takes 64-72 days
• Sperm in lumen are still unable to swim and fertilize egg
• Sperm maturation in epididymis

  Increased motility and fertilizing power
• Testosterone


  Most important hormonal product of testes
• Testosterone production


  1. Interstitial cells produce testosterone

  2. Activated by LH from pituitary

  3. Produced continuously after puberty
• Effects of testosterone


  • Stimulates adolescent growth spurt
  • Develops reproductive organs
  • Underlies sex drive
  • Causes male secondary sex characteristics
• If testosterone not produced, secondary sex characteristics do not appear and reproductive organs remain childlike (sexual infantilism)
• Castration or inability to produce testosterone results in decreased size and function of reproductive organs and decreased sex drive
• Testosterone is necessary for final stages of sperm production
• Ovaries


  Primary female reproductive organs that produce eggs and hormones
• Ovulation


  1. Egg released from mature follicle

  2. Follicle becomes corpus luteum
• Ovulation generally occurs every 28 days
• Uterine tubes


  Receive ovulated egg and provide site for fertilization
• Fertilization usually occurs in uterine tube
• Uterine tubes not continuous with ovaries, placing women at risk of pelvic inflammatory disease