Hormonal Control of the Female Menstrual Cycle
The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of about 28 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.
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It is controlled by the interaction of several hormones of Hypothalamus, Pituitary and gonadal hormones. The action of one hormone is used to stimulate or inhibit the production of another.
On the basis of ovarian changes the cycle can be divided into three phases: follicular phase, ovulatory phase, and the luteal phase.
- The Follicular phase - is the first part of the menstrual cycle, where one or more follicles start to develop into a mature female gamete. The follicle cells surround the oocyte (developing egg cell), and produce hormones that trigger other responses
- The Ovulatory phase - is when the oocyte is released (follicle cells remain in the ovary) from the ovary and passes down the fallopian tube and towards the uterus
- The Luteal phase - most of the follicle cells remain in the ovary after ovulation. They continue to develop and form a structure called the corpus luteum, as a result more hormones are produced.
- (i) menstrual phase (day 1 – day 3) : Due to falling level of progesterone the uterine wall contracts and extra endometrial lining is shed along with blood and mucus. Volume of blood lost varies from 40 – 150 ml.
- (ii) Proliferative phase (day 3 – day 14) :Uterine endometrium proliferates under influence of estrogen and there is formation of endometrial glands.
- (iii) Secretory phase (day 14 – day 28) : Endometrial glands secrete nutritive substances under influence of progesterone.
Frequently Asked Questions
The menstrual cycle is mainly regulated by a coordinated interaction between hormones from the hypothalamus (GnRH), anterior pituitary gland (LH and FSH), and ovaries (estrogen and progesterone). These hormones operate in a feedback system to regulate changes in the uterus and ovaries, preparing the body for a possible pregnancy each month.
The four key hormones are follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. FSH stimulates follicle growth, LH triggers ovulation, estrogen prepares the uterine lining, and progesterone maintains the lining in case of pregnancy.
FSH rises early in the cycle, stimulating follicle growth and estrogen production. Estrogen peaks before ovulation, causing an LH surge that triggers ovulation. After ovulation, progesterone levels rise, maintaining the uterine lining. If pregnancy does not occur, estrogen and progesterone levels fall, resulting in menstruation.
The menstrual cycle has distinct phases: follicular (prepares follicles, increased FSH, estrogen rises), ovulatory (LH surge, ovulation), and luteal (progesterone dominance from the corpus luteum). Each phase is regulated by specific hormonal changes.
Hormonal imbalances can disrupt the cycle's timing, cause symptoms like irregular or missed periods, excessive bleeding, or affect fertility. Conditions like stress, PCOS, thyroid disorders, or pituitary abnormalities can impact hormone levels and menstrual function.