Hormone Regulation of the Reproductive System Homeostasis 5: Hormone Regulation of the Reproductive System

The Reproductive Systems Both male and female reproductive systems have a pair of gonads (testes/ovaries). Gonads produce reproductive cells called gametes (sperm/egg) and sex hormones which control the development and function of the reproductive system.

Structure and Function of the Male Reproductive System The Testes: held outside the body in the scrotum (regulates temperature around 35°C). Made of long, coiled tubes called seminiferous tubules (where sperm cells are made) and interstitial cells (testosterone hormone-secreting). After the seminiferous tubules make the sperm, they move to the epididymis to mature until they move to the ductus deferens. Seminal Fluid: as the sperm cells pass through the ductus deferentia, they are mixed with fluids from a series of glands (seminal vesicle, prostate gland, and Cowper’s gland). This combination od sperm and fluid is called semen. The movement of semen is the result of a series of interactions between the sympathetic, parasympathetic and somatic nervous systems.

Male Reproductive System

Male Sex Hormones Male sex hormones are known as androgens. Reproductive systems will not mature until puberty at which time a series of hormonal change events happen when the hypothalamus increases its production of gonadotopic releasing hormone (GnRH) GnRH acts on the anterior pituitary gland causing it to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which respectively cause the seminiferous tubules to begin producing sperm and the interstitial cells to release testosterone. Testosterone acts on various tissues to complete the development of sex organs and sexual characteristics. Most men experience a decline in testosterone levels at about age 40 (andropause) but do remain fertile for life.

Structures of the Female Reproductive System Female reproductive system does not mass produce its gametes like the male system. Two female gonads (ovaries) only make a limited number of eggs (ova) The ovary contains specialized cell structures called follicles. Each month a single follicle matures than ruptures, releasing an ovum into the oviduct (ovulation). The ovum then travels down the oviduct to the uterus. The uterus is a muscular organ that holds and nourishes a developing fetus. The lining is called the endometrium, which thickens in preparation for a potential zygote (sperm fertilized ovum). If fertilization does not occur, menstruation happens.

Female Reproductive System

Female Sex Hormones A girl begins puberty when the hypothalamus increases its production of GnRH which acts on the anterior pituitary to release LH and FSH, which act on the ovaries to produce estrogen and progesterone. Female reproductive systems act in a cycle called the menstrual cycle that is about 28 days long. Menstrual cycle is actually two separate but linked cycles: the ovarian cycle and the uterine cycle.

Ovarian Cycle Divided into two stages: Follicular stage: increased FSH levels cause a follicle to mature and it releases estrogen and some progesterone. This increase in estrogen acts on the ant. pituitary to stop releasing FSH and acts on the hypothalamus to secrete GnRH, which releases LH. The LH levels trigger ovulation and the follicle bursts, releasing the ovum. Luteal stage: LH causes the follicle to change into a corpus luteum, which secretes progesterone and some estrogen, which inhibit the FSH and LH production at the ant.pituitary and the corpus luteum degenerates, which lowers the estrogen and progesterone levels again. Lower levels of estrogen and progesterone trigger a release of FSH and the cycle starts again.

Uterine Cycle The timing of the uterine cycle ensures that the uterus is prepared to receive a new life. Begins on the first day of menstruation, levels of sex hormones are low, endometrium layer is thin. Lasts of 5 days. As a new follicle releases estrogen, the levels in the blood increase and causes the endometrium to thicken. After ovulation, the release of progesterone by the corpus luteum causes a more rapid thickening of the endometrium between days 15 and 23. If fertilization does not occur, the corpus luteum degenerates, level of sex hormones drops, endometrium breaks down and menstruation happens again.

Menopause The number of working follicles decrease as a woman ages, which leads to an overall decline in estrogen and progesterone. The mentrual cycle becomes disrupted and eventually stops altogether. A woman who has completed menopause no longer produces ova and is not fertile. This also disrupts the other hormones in the body causing mood changes, hot flashes, rising cholesterol, decreasing bone mass, increased risk of uterine or breast cancers and heart disease.

Practice: Page 425 # 2, 3, 5, 6, 8-10.