Tag: biology

Ovaries in woman stop their action at an early age by 40 for about 2%. Ovarian failure occurs at an average age of menopause is 50 years old.

The gamete formation in females is a cyclic activity that takes about 28/29 days and involves changes in the structure and function of the entire reproductive system. It is called menstrual cycle.

Just after the menstrual phase, the proliferative phase starts that shows an increase in the level of the FSH or follicular stimulating hormone. This leads to the regeneration of the endometrium lining. The regeneration takes around 5 to 10 days. On the 14$^{th}$ day, the ovulation takes place.

Menstruation is triggered by reduced levels of the hormones estrogen and progesterone in a female's body at the end of the previous menstrual cycle. This decline in hormone levels is due to the absence of a fertilized egg implanting on the walls of the endometrium.

Menstruation starts at puberty which is known as menarche. It is the shredding of endometrial lining, ovum and some blood vessels. It ends at the age of 45 to 50 which is known as menopause. It is a cyclic process which happens every month. It includes the menstrual phase, the follicular phase, the ovulatory phase, and the luteal phase. Ovulatory phase happens because of a sudden release of LH hormone.

After ovulation, the pituitary hormones FSH and LH cause the remaining parts of the dominant follicle to transform into the corpus luteum, which produces progesterone. The increased progesterone in the adrenals starts to induce the production of estrogen. The hormones produced by the corpus luteum also suppress production of the FSH and LH that the corpus luteum needs to maintain itself. Consequently, the level of FSH and LH fall quickly over time, and the corpus luteum subsequently atrophies. Falling levels of progesterone trigger menstruation and the beginning of the next cycle.

• The menstrual cycle is a monthly cycle in which the primate females ovulate once in a month.
• Menstruation is important because it prepares the body for the fertilization and is a key process in reproduction.
• The cycle occurs in humans, chimpanzees and Orangutans, gorillas and monkeys.
• Other mammals have a similar cycle which is known as the oestrous cycle.

The functional layer of the human endometrium is a highly regenerative tissue undergoing monthly cycles of growth, differentiation, and shedding during a woman's reproductive years. Fluctuating levels of circulating estrogen and progesterone orchestrate this dramatic remodeling of human endometrium.

If fertilization does not occur, progesterone inhibits LH from pituitary.