Human Female Reproductive Organs.

Essay by cheshirestar18High School, 10th gradeA+, August 2003

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In the female reproductive system, ova are produced in the ovaries, two small organs set in the pelvic cavity below and to either side of the bellybutton. The ovaries also secrete the hormones estrogen and progesterone. The estrogen hormone causes the thickening of the lining of the uterus and vagina in the early phase of the menstrual cycle. The estrogen hormone is also responsible for female secondary sex characteristics such as pubic hair and breasts, and they affect other tissues including the genital organs, skin, hair, blood vessels, bone, and pelvic muscles. Progesterone induces secretory changes in the lining of the uterus that is very important in case the egg gets fertilized. Being a steroid, progesterone is secreted mostly by the corpus luteum, a group of cells formed in the ovary after the follicle ruptures during the release of the egg cell. If fertilization does not take place, the secretion of progesterone decreases and menstruation occurs.

If fertilization does occur, progesterone is secreted during pregnancy by the placenta and acts to prevent spontaneous abortion. The hormone also prepares the mammary glands for milk production. After an ovum matures, it passes into the uterine tube, or fallopian tube. If there are sperm from sexual intercourse (or artificial insemination) fertilization occurs . The ovum, either fertilized or unfertilized, then passes down the fallopian tube, aided by cilia in the tube, and into the womb, or uterus, a pear-shaped organ specialized for development of a fertilized egg.

An inner uterine layer of tissue, the endometrium, undergoes changes as a result of the changing levels of the hormones secreted by the ovaries. The endometrium is thickest during the part of the menstrual cycle in which a fertilized ovum would be expected to enter the uterus and is thinnest just after menstruation. If...