The Human Reproductive System

► Males produce semen and deliver it into the female reproductive tract. Semen consists of sperm suspended in a fluid that nourishes them and facilitates fertilization.

► Sperm are produced in the seminiferous tubules of the testes, mature in the epididymis, and are delivered to the urethra through the vasa deferentia. Other components of semen are produced in the bulbourethral gland, seminal vesicles, and prostate gland. Review Figures 43.8, 43.9. See Web/CD Activities 43.1 and 43.2

► All components of the semen join in the urethra at the base of the penis and are ejaculated through the erect penis by muscle contractions at the culmination of copulation.

► Spermatogenesis depends on testosterone secreted by the Leydig cells of the testes, which are under the control of LH from the anterior pituitary. Spermatogenesis is also controlled by FSH from the pituitary. Hypothalamic GnRH controls pituitary secretion of LH and FSH. The production of these hormones by the hypothalamus and pituitary is controlled by negative feedback from testosterone and another hormone, inhibin, produced by the Sertoli cells of the testes. Review Figure 43.10

► Eggs mature in the female's ovaries and are released into the oviducts. Sperm deposited in the vagina during copulation move up through the cervix and uterus into the oviducts. Review Figure 43.11. See Web/CD Activity 43.3

► Fertilization occurs in the upper regions of the oviducts. The zygote becomes a blastocyst as it passes down the oviduct. Upon arrival in the uterus, the blastocyst implants in the endometrium and forms a placenta.

► The maturation and release of eggs constitute an ovarian cycle. In humans, this cycle takes about 28 days. Review Figures 43.12

► The uterus also undergoes a cycle that prepares it for receipt of a blastocyst. If no blastocyst is implanted, the lining of the uterus deteriorates and sloughs off in the process of menstruation. Review Figure 43.13. See Web/CD Tutorial 43.2

► Both the ovarian and the uterine cycles are under the control of hypothalamic and pituitary hormones, which in turn are under the feedback control of estrogen and progesterone.

Review Figure 43.14

► Childbirth is initiated by hormonal and mechanical stimuli that increase the contraction of uterine muscle. Oxytocin plays a major role in this positive feedback loop. Review Figure 43.15

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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