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Purpose of Male Organs
To produce sperm and introduce them to female body
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Primary Sex Organs (Gonads)
Testes
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Secondary Sex Organs
- Other organs needed for reproduction
- Ducts, glands and penis
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External Genitalia
- Externally visible; mostly in perineum
- Penis, scrotum
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Internal Genitalia
Not externally visible; mostly in pelvic cavity (except for testes)
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Secondary Sex Characteristics
- Develop at puberty and play a role in mate attraction
- Both sexes: pubic and axillary hair and associated with scent glands, pitch of voice
- Male: facial hair, torso and limb hair, muscle tone
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Sex Determination
- All human cells except for gametes have 23 pairs of chromosomes
- 22 pairs of autosomes
- Sex chromosomes (XY males, XX females)
- Gametes have 23 chromosomes (not paired)
- 22 Autosomes
- X or Y
- Egg always has x
- Half of sperm have x, half have y
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Sexual Differentiation
- For first month, fetus is sexually undifferentiated
- Gonads develop at 5-6 weeks as gonadal ridges with ducts
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Mesonephric Ducts
- Wolffian Ducts
- Develop into male reproductive system
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Paramesonephric Ducts
- Mullerian Ducts
- Develop into female reproductive tract
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Prenatal Hormones and Differentiation
- Y chromosomes contains the SRY gene (sex determining region of the Y chromosome)
- Codes for testis-determining factor (TDF) protein
- TDF initiates development of testes in male
- At 8-9 weeks of age, testes begin secreting testosterone and anti-mullerian hormone (AMH)
- Testosterone stimulates mesonephric ducts to develop into male reproductive system
- AMH causes paramesonephric ducts to degenerate
- Female development occurs when testosterone and AMH aren't present
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External Genitalia Development
- Homologous structures in males and females
- Genital tubercle becomes glans of the penis or clitoris
- Urogenital folds form penis and labia minora
- Labioscrotal folds become scrotum and labia major
- Genitalia formed by 12 weeks of age
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Descent of Gonads
- Gonads develop near the kidneys and migrate to pelvic cavity (ovaries) or scrotum (testes)
- Gubernaculum tissue cord extends from gonad to floor of pelvic cavity
- At about 7 months, testes pass through inguinal canal guided by gubernaculum
- Arteries, veins, nerves, vas deferens follow testes
- Ovary descent also guided by gubernaculum
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Androgen Insensitivity Syndrome
- Occasionally a mutation on the X chromosome will mutate androgen receptors
- Mutated receptors cannot bind to androgens
- AIS individuals are XY, have testes, secrete normal levels of testosterone
- External genitalia develop as female anatomy
- No uterus, no menstruation
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Congenital Adrenal Hyperplasia
- Defective enzyme to produce glucocorticoids, so androgens build up
- (Can be XX or XY but have excess androgens)
- CAH females have normal female internal genitalia, but often ambiguous external genitalia
- Enlarged clitoris that can look like small penis
- CAH females often have masculinized behavior
- More likely to be homosexual than non-CAH women
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The Scrotum
- The pouch of skin, muscle, and connective tissue containing the testes
- Left testicle usually hangs lower than the right
- Skin has sebaceous glands, some hair, lots of sensory nerve endings
- Internal median septum divides septum into left and right compartments
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Testes
- Produce sex hormones and sperm
- Tunica albuginea surrounds testes
- Tunica vaginalis membrane covers tunica albuginea
- Testes divided into 250-300 lobules
- Each lobule contains one or a few seminiferous tubules
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Histology of the Testes
- Sperm formed in seminiferous tubules
- Leydig (interstitial) cells produce androgens
- Sertoli (sustentacular) cells secrete AMH and inhibin, and nurture sperm throughout their development
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Epididymis
- Sperm leaves testes through rete testes to enter efferent ductules and epididymus
- Epididymis lies on posterior surface of testis
- Highly coiled tube divided into head, body, and tail
- Sperm mature so that they are capable of motility and fertilization
- Sperm stored in the tail until ejaculation
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Spermatic Cord
- Bundle of connective tissue containing vas deferens, blood vessels, and testicular nerve
- Testicular artery supplies each testis
- Blood leaves testis through pampiniform plexus that then forms testicular veins
- Right testicular vein drains into inferior vena cava
- Left testicular vein drains into renal vein
- Testicular nerves come from thoracic nerves
- Sensory and motor neurons
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Vas Deferens
- Muscular tube passing from scrotum to posterior surface of bladder
- Carries sperm from epididymis to urethra during ejaculation
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Temperature Regulation
- Testes have adapted to cooler environment (35 C), cant produce sperm at normal body temperature (37 C)
- Temperature regulated by two muscles and countercurrent heat exchanger
- Cremaster muscles cover the spermatic cord
- Contract in cold temps to drop testes close to body
- Relax in warm temps to suspend testes far from body
- Dartos muscle: smooth muscle under scrotal skin
- Contracts in cold to cause wrinkly scrotum
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Countercurrent Heat Exchanger
- As blood travels down testicular artery, some heat is changed with cold blood in pampiniform plexus
- Prevents arterial blood from warming testes
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