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Unformatted text preview: Chapter 26: The Reproductive System Chapter Overview Reproduction is a means to continue the species. Individuals have a finite lifespan, but their genes live on in future generations. To produce a child takes two parents who have the appropriate anatomy and physiology for reproduction. Sexual Reproduction The Two Sexes Sex is genetically determined. Females inherit two X chromosomes from their parents, whereas males inherit an X chromosome from their mother and a Y chromosome from their father. The first step of the reproductive process is gamete production. Females produce eggs that are large and nutrient-rich for the developing embryo; males produce sperm that are small and motile and equipped to travel to meet an egg. Each gamete produced by a woman or man contains a unique combination of genes with the result that no two offspring are genetically alike unless they are identical twins. In mammals, females have additional reproductive tasks. Both males and females produce gametes and engage in courtship, but females also nurture the embryo and fetus during pregnancy, and produce milk during lactation. Different reproductive roles account for sex differences between adults. Overview of the Reproductive System The male reproductive system is designed to produce sperm and introduce them into the females body. The female reproductive system produces eggs, receives sperm, accommodates pregnancy and birth, and nourishes the offspring after birth. Both sexes have primary and secondary sex organs. The primary sex organs are the gonads, either ovaries or testes, which produce gametes. The secondary sex organs in males consist of a series of ducts, glands, and the penis. In women the secondary organs are the uterine tubes, uterus, and vagina. Secondary sex characteristics develop in adolescence and play a role in mate attraction. These include pubic and axillary hair and associated apocrine glands in both sexes; facial hair, deeper voice, and increased muscle mass in boys; and distribution of fat on breasts and hips in girls. (Body fat in women also provides energy for reproduction.) Male Reproductive Anatomy The Scrotum 186 The scrotum is a skin-covered pouch that hangs down from the abdomen. It is divided into right and left portions by the internal median septum that is visible externally as a seam called the perineal raphe that extends to the margin of the anus....
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