chapter46 - III. Mammalian Reproduction A. Human...

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III. Mammalian Reproduction A. Human reproduction involves intricate anatomy and complex behavior 1. Reproductive anatomy of the human male In most mammalian species, including humans, the reproductive system includes the external genitalia and the internal reproductive organs. - The external genitalia includes the scrotum and penis. - The internal reproductive organs consist of the gonads (testes), accessory glands, and associated ducts. The male genitalia (scrotum and penis ) aid the reproductive process in different ways. - Testes develop in the abdomen and descend into the scrotum just before birth. This is important since sperm cannot develop at normal body temperature. - By having the testes hang outside the abdominal cavity in the scrotum, the temperature is 2 o C lower and sperm production can occur. - The penis serves as the male copulatory organ. The ejaculatory duct joins the urethra (from the excretory system) which opens at the tip of the penis. - The movement of semen through the urethra during copulation results in the sperm being deposited directly in the female system. Internal male reproductive organs are the gonads and associated ducts: - The testes are comprised of highly coiled tubes surrounded by layers of connective tissue. - The tubules, or seminiferous tubules , are where sperm form. - Interstitial cells , or Leydig cells , are scattered between the tubules and produce testosterone and other androgens. - Sperm pass from the seminiferous tubules into the tubules of the epididymis . - These coiled tubules are where sperm are stored and mature (gain motility and fertilizing power). - At ejaculation , sperm are forced through the vas deferens , which is a muscular duct running from epididymis to the ejaculatory duct . - The ejaculatory duct forms by the joining of the two vas deferens ducts (one from each testis) with the duct from the seminal vesicles. - The ejaculatory duct opens into the urethra , the tube that runs through the penis and drains both the excretory and reproductive systems. There are three sets of accessory glands associated with the male system. These glands add their secretions to the semen. 1. A pair of seminal vesicles is located below and behind the bladder and empty into the ejaculatory duct. - They secrete a fluid containing mucus, amino acids (causes semen to coagulate after deposited in female), fructose (provides energy for sperm) and prostaglandins (stimulate female uterine contractions to help move semen to the uterus). - Seminal vesicle secretions make up about 60% of the total semen volume. 2. The prostate gland is a large gland that surrounds the upper portion of, and empties directly into, the urethra. - It secretes a thin, milky alkaline fluid that contains several enzymes. - Prostatic fluid balances the acidity of residual urine in the male system and the acidity of the vagina and
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This note was uploaded on 04/05/2008 for the course BIO G 006 taught by Professor Macneill,a. during the Spring '08 term at Cornell University (Engineering School).

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chapter46 - III. Mammalian Reproduction A. Human...

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