branches of biology and principles

May 20th, 2015
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The word biology is derived from the greek words /bios/ meaning /life/ and /logos/ meaning /study/ and is defined as the science of life and living organisms. An organism is a living entity consisting of one cell e.g. bacteria, or several cells e.g. animals, plants and fungi.

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The cyclic changes in the ovary and uterus are under the control of estrogen and progesterone hormones whose secretion is under the control of gonadotropic hormones secreted by anterior pituitary.Hormonal Control of Menstrual Cycle in Human FemaleDuring menstrual phase the levels of estrogen and progesterone falls considerably.This induces adenohypophysis to secrete FSH and LH.Increased levels of FSH stimulates the graafian follicle to mature and secrete estrogens. The rising level of estrogen, causes the endometrium to become thicker and more richly supplied with blood vessels. The level of estrogens in blood increases gradually for a few days and is at the peak on the 12thday of the cycle.The estrogen surge reduces FSH secretion and this in turn introduces LH surge within 12 hours i.e., on the 13thday of the cycle.LH causes ovulation and formation of corpus luteum.During post ovulatory phase corpus luteum secretes progesterone.Corpus luteum secretes progesterone, which performs the following functions:a) It facilitates the preparation of the endometrium of the uterus for receiving the blastocyst and its implantation. (whether fertilisation occurs or not)b) It inhibits the contraction of the uterus and any further development of a new follicle.c) If fertilisation does not occur, the rising progesterone level inhibits the release of Gonadotropin releasing hormone (GnRH), which inturn inhibits the production of FSH, LH and progesterone.d) Once the progester

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