4.4 Lesson 4: Reproductive Hormones

The Female Reproductive System

• Human females have a pair of ovaries, which produce gametes (eggs) as well as estrogens and progestins.

• Estrogens (i.e. estradiol) are steroid hormones that are responsible for the changes that occur to a female during puberty.

• Progestins (i.e. progesterone) are steroid hormones that are responsible for maintaining the uterus for fertilization.

• Estrogens and Progestins are controlled by the release of follicle-stimulating hormones (FSH) and luteinizing hormones (LH) from the pituitary gland in the brain

• The release of FSH and LH is controlled by gonadotropin-releasing hormone (GnRH) from the hypothalamus.

• The continued release of these hormones is controlled by a negative feedback mechanism.

Ovarian Cycle

• The ovarian cycle occurs from puberty to menopause and involves events in the ovaries that leads to the release of a mature egg approximately every 28 days.

• The ovarian cycle is coordinated with the menstrual cycle.

• The beginning of the ovarian cycle is stimulated by the release of GnRH, which stimulates the release of FSH and LH.

• FSH stimulates 6 – 20 oocytes in the ovaries to begin meiosis.

• As they develop, each oocyte is surrounded by cells to form a follicle.

• This is called the follicular phase.

• As the follicle enlarges, FSH and LH stimulate the release of estrogen.

• High estrogen levels has a positive feedback effect on the hypothalamus and pituitary.

• The burst in LH production stimulates the follicle cells to enzymes that rupture the follicle walls and releases the egg.

• This event is called ovulation

• The spike in LH also causes the cells at the surface of the ovaries to enlarge, forming a structure called the corpus luteum.

• It secretes a large quantity of estrogen and progestin, as well as inhibin.

• These hormones stimulate the growth of the uterine lining to prepare for fertilization, and inhibit FSH and LH so no new follicles form

• This is called the luteal phase

• If no fertilization occurs, the corpus luteum begins to shrink.

• The shrinkage inhibits the secretion of estrogen, progestins, and inhibin.

• The absence of these hormones stimulates menstruation to begin.

• FSH and LH are no longer inhibited and a new monthly cycle begins.

• If fertilization of the egg occurs, the egg releases calcium ionsthat prevents other sperm from fertilizing.

• Once the embryo is implanted into the uterine lining, the cells release human chorionic gonadotropin, which prevents the shrinking of the corpus luteum.

• hCG in the blood and urine provides the basis of pregnancy tests

The Male Reproductive System

• Human males have a pair of testes that secrete androgens.

• Androgens (i.e. testosterone) are steroid hormones that stimulate and control the development of the male reproductive system.

• The synthesis and release of testosterone is controlled by hormones that are involved in the female reproductive system

• Testosterone also controls the process of spermatogenesis.

• The process of spermatogenesis takes 9-10 weeks.

• This process creates sperm cells from precursor cells called spermatogonia.

• The organs that produce and deliver the sperm make up the reproductive system.

• GnRH is released from the hypothalamus every 1 – 2 hours.

• This regulates the release of FSH and LH from the pituitary gland.

• FSH stimulates Sertoli cells in the testes to secrete proteins for spermatogenesis

• LH stimulates Leydig cells in the testes to secrete testosterone

• This process is controlled by a negative feedback mechanism

Performance Enhancing Substances

• In addition to its role in the male reproductive system, testosterone also controls the metabolic genes that build the proteins used for muscle development.

• Anabolic steroids are synthetic steroids that mimic the effect of testosterone to build muscle mass.

• Due to their synthetic nature, these steroids have a variety of negative side effects in both men and women.