Animal Reproduction

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Production of normal sperm cannot occur at the body temperatures of most mammals. So the testes are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity.

Slide 33

Ducts

From the seminiferous tubules of a testis, mature sperm pass into the coiled tubules of the epididymis.

During ejaculation, sperm are propelled through the muscular vas deferens and the ejaculatory duct, and then exit the penis through the urethra.

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Accessory Glands

Semen is composed of sperm plus secretions from three sets of accessory glands.

The two seminal vesicles contribute about 60% of the total volume of semen.

The prostate gland secretes its products directly into the urethra through several small ducts.

The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra.

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Penis

The human penis is composed of three cylinders of spongy erectile tissue.

During sexual arousal, the erectile tissue fills with blood from the arteries, causing an erection.

The head of the penis has a thinner skin covering than the shaft, and is more sensitive to stimulation.

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The timing and pattern of meiosis in mammals differ for males and females

Gametogenesis = the production of gametes by meiosis. This differs in females and males

Sperm are small and motile and are produced throughout the life of a sexually mature male.

Spermatogenesis is production of mature sperm.

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Spermatogenesis

Epididymis

Seminiferous tubule

Testis

Cross section of seminiferous tubule

Sertoli cell nucleus

Primordial germ cell in embryo

Mitotic divisions

Spermatogonial stem cell

Mitotic divisions

Mitotic divisions

Spermatogonium

Primary spermatocyte

Meiosis I

Meiosis II

Secondary spermatocyte

Lumen of seminiferous tubule

Plasma membrane

Tail

Neck

Midpiece

Head

Mitochondria

Nucleus

Acrosome

Spermatids (at two stages of differentiation)

Early spermatid

Differentiation (Sertoli cells provide nutrients)

Sperm

2n

2n

2n

n

n

n

n

n

n

n

n

n

n

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Mature sperm

Plasma membrane

Tail

Neck

Midpiece

Head

Mitochondria

Nucleus

Acrosome

Slide 39