Topic 6.6: Reproduction

16 02 2012

6.6.2: Role of hormones in the menstrual cycle:

 

Role of Hormones in the Menstrual Cycle

The menstrual cycle is a cycle of physiological changes that occur in fertile females of placental mammals.

It has three phases, the follicular phase(involves development and maturation of follicles), ovulation( release of mature ovum) and lacteal phase(the corpus luteum and its role in maintaining the proliferative endometrium thro hormonal control)

Follicle stimulating hormone(FSH) produced by the anterior lobe of the pituitary gland stimulates development of the Graafian follicle from a primary follicle. It also stimulates the follicle to start secreting estrogen.

Estrogen hormone produced by the follicle initiates the proliferation of the endometrium. It also stimulates crypts in the cervix to produce fertile cervical mucus. As the primary follicle matures, estrogen suppresses the secretion of the Luteinizing Hormone(LH) by the anterior lobe of the pituitary gland. When the Graafian follicle is nearly mature, increased level of estrogen stimulates production of LH.

Luteinizing Hormone causes the final maturation of the egg. It also initiates ovulation by causing the Graafian follicle to release its secondary oocyte which matures into an ootid then into an ovum. After ovulation LH initiates the re-organization of the remnants of the Graafian follicle to form a body called corpus luteum. This body grows and produces progesterone and estrogen hormones.

Progesterone hormone, together with estrogen, prepares the uterus for implantation by initiating the thickening of the endometrium and increase in blood supply. It also causes a rise in the basal body temperature of a woman. It also suppresses production of FSH and LH to prevent development of another follicle and subsequent ovulation. Progesterone maintains pregnancy by sustaining the proliferative endometrium(prevents it from shedding, which would result in a miscarriage).

If fertilization occurs, the embryo produces the Human Chorionic Gonadotropin Hormone(HCG) which prevents disintegration of the corpus luteum thereby maintaining production of progesterone critical in sustaining pregnancy.

If implantation does not occur within two weeks, the corpus luteum involutes(degenerates) causing a sharp decline in the level of  progesterone and estrogen. This causes the proliferative endometrium to slough off (shed) in a process known as menstruation.

(Taken from: http://gskool.com/n/node/75)

6.6.3:  A Graph showing hormone levels in the menstrual cycle

http://bcs.whfreeman.com/thelifewire/content/chp43/4302002.html

6.6.4: Role of testosterone in males

The role of testosterone

Testosterone is a male sex hormone required for sperm production, the development of male reproductive organs and the emergence of secondary male sexual characteristics such as facial hair, a deeper voice and muscles.

In men testosterone is produced in the testes and adrenal glands.

Testosterone is also produced in women’s ovaries and adrenal glands. Little is known about the exact role of testosterone in women, but scientists believe it helps maintain muscle and bone strength and contributes to sex drive or libido.

On average, men produce between 4 and 10mg of the hormone per day and overall they have about 20 times more testosterone than women.

(Taken from: http://www.bbc.co.uk/science/humanbody/sex/articles/testosterone.shtml)


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