repro

• Sexual reproduction


  Combination of male and female gametes to form a zygote
• Male gamete


  • Sperm (spermatozoon)
  • Has motility
• Female gamete


  • Egg (ovum)
  • Contains nutrients for developing embryo
• Male


  • Parent producing sperm
  • Has a Y chromosome
• Female


  • Parent producing eggs
  • Lacks a Y chromosome
• Male reproductive system


  • Produces sperm and introduces them into the female body
  • Has a copulatory organ (penis) for introducing gametes into the female reproductive tract

  
• Female reproductive system


  • Produces eggs, receives sperm, provides for gametes' union, harbors fetus, and nourishes offspring
  • Has a copulatory organ (vagina) for receiving sperm

  
• Reproductive system components


  • Primary sex organs (gonads)
  • Secondary sex organs
• Primary sex organs


  Produce gametes; testes in male, ovaries in female
• Secondary sex organs


  • Organs other than gonads that are necessary for reproduction
  • Male - system of ducts, glands; penis delivers sperm cells
  • Female - uterine tubes, uterus, and vagina receive sperm and harbor developing fetus

  
• Reproductive organ locations


  • External genitalia - located in the perineum
  • Internal genitalia - located in the pelvic cavity

  
• Secondary sex characteristics


  • Features that distinguish the sexes and influence mate attraction
  • Develop at puberty
  • Both sexes - pubic and axillary hair, associated scent glands, pitch of voice
  • Male - facial hair, coarse and visible body hair, muscular physique
  • Female - distribution of body fat, breast enlargement, finer body hair
• Chromosomes


  23 pairs, including 22 pairs of autosomes and 1 pair of sex chromosomes (XY males, XX females)
• Sex determination


  1. X-carrying sperm fertilizes egg: female

  2. Y-carrying sperm fertilizes egg: male

  
• Prenatal sexual differentiation


  1. Initially sexually undifferentiated

  2. Gonads develop as gonadal ridges

  3. In males, mesonephric ducts develop into reproductive tract, paramesonephric ducts degenerate

  4. In females, paramesonephric ducts develop into reproductive tract, mesonephric ducts degenerate

  
• SRY gene


  Sex-determining region of Y chromosome, codes for testes-determining factor (TDF) that initiates testes development
• Presence of SRY gene


  Testes develop and secrete testosterone, stimulating mesonephric duct development and causing paramesonephric duct degeneration
• Absence of androgens


  Results in female development
• Intersex


  Disconnect between genes, gonads, and genitals; individual has "male" and "female" characteristics
• Gender


  Psychological sense of masculine, feminine, or other sexual identity and social role
• Androgen insensitivity syndrome (AIS)


  Individual is XY with testes that secrete testosterone, but shows feminine phenotype due to deficiency of testosterone receptors
• External genitalia of males and females develop from similar embryonic structures

  
• Penis is homologous to clitoris, scrotum is homologous to labia majora
• Descent of the gonads


  1. Gonads initially develop high in abdominal cavity and then migrate into pelvic cavity (ovaries) or scrotum (testes)

  2. Gubernaculum and vaginal process create inguinal canal pathway for testicular descent

  3. Testes accompanied by elongating arteries, veins, lymphatics, nerves, ducts, and muscle extensions

  4. Ovaries descend to lesser pelvis, gubernaculum becomes ligaments supporting ovary and uterus

  
• About 3% of boys are born with undescended testes (cryptorchidism)
• Scrotum


  • Pouch containing testes
  • Divided by median septum
  • Contains spermatic cord with ductus deferens, vessels, nerves
  • Cremaster muscle and dartos fascia regulate temperature

  
• Testes


  • Endocrine and exocrine glands that produce sex hormones and sperm
  • Oval shape, covered by tunica albuginea
  • Seminiferous tubules produce sperm, Leydig cells produce testosterone
• Temperature of testes


  Must be held at about 35°C
• Mechanisms to regulate the temperature of the testes


  1. The cremaster contracts to hold testes closer to body when cold, relaxes to hold testes further from body when warm

  2. Dartos fascia smooth muscle contracts when cold, wrinkling the scrotum and holding testes against warm body to reduce surface area and heat loss

  3. The pampiniform plexus venous plexus surrounds testicular artery, removing heat from descending arterial blood to be carried away by ascending venous blood

  
• Testes


  • Combined endocrine and exocrine glands that produce sex hormones and sperm
  • Each testis is oval and slightly flattened, 4 cm long x 2.5 cm in diameter, covered anteriorly and laterally by tunica vaginalis
  • Covered by tunica albuginea - white, fibrous capsule
  • Septa from the capsule divide testis into 250 to 300 lobules, each with 1 to 3 seminiferous tubules where sperm are produced
  • Between seminiferous tubules are interstitial endocrine cells that produce testosterone

  
• Seminiferous tubules


  • Lined with a thick germinal epithelium composed of several layers of germ cells (developing sperm) and tall nurse cells (supporting cells that protect germ cells and promote their development)
  • Nurse cells secrete proteins androgen-binding protein and inhibin, which regulate sperm production
  • Tight junctions between nurse cells form blood-testis barrier that prevents antibodies and immune cells from attacking germ cells
• Sperm flow


  1. From seminiferous tubules to rete testis, with fluid secreted by nurse cells

  2. Sperm do not swim while in the male reproductive tract

  
• Testicular artery


  • Supplies each testis
  • Low blood pressure results in poor oxygen supply to the testes
  • Sperm develop large mitochondria to cope with poor oxygen supply and help them survive hypoxic environment of female reproductive tract

  
• Blood leaving the testis


  • Through the pampiniform plexus of veins which converge to form the testicular vein
  • Right testicular vein drains to inferior vena cava, left one drains into left renal vein

  
• Testicular nerves


  • From spinal cord segments T10 and T11
  • Carry sensory fibers concerned with pain and sympathetic fibers regulating blood flow

  
• Sperm travel


  1. Through a series of spermatic ducts to reach the urethra

  2. Efferent ductules collect sperm from rete testes and transport it to epididymis

  3. Duct of the epididymis is where sperm mature and are stored

  4. Ductus deferens (vas deferens) tube between epididymis and seminal vesicle

  5. Ejaculatory duct formed where ductus deferens and duct of seminal vesicle merge, passes through prostate and empties into urethra

  
• Accessory glands in male reproductive system


  • Seminal vesicles
  • Prostate
  • Bulbourethral glands
• Benign prostatic hyperplasia (BPH)


  Noncancerous enlargement of the prostate that compresses urethra and obstructs flow of urine
• Prostate cancer


  Typically goes unnoticed until painful, diagnosed through digital rectal exam and elevated PSA and acid phosphatase levels
• Penis


  • Half is an internal root, half is an externally visible shaft and glans
  • External portion 4 in. long when flaccid, 5 to 7 in. long when erect
  • Skin over shaft loosely attaches to allow expansion, extends over glans as prepuce (foreskin) that is removed by circumcision