Name: Animation E1, 4.1 Interaction of hormones in the menstrual cycle
Uploaded: 2025-04-11T13:55:03.000Z
Duration: 3 min 9 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Girls start their menstrual cycle when they enter puberty.

In each cycle, the uterine lining undergoes a pattern of thickening associated with events in the ovary.

These changes are mainly brought about by the interaction of hormones.

At the beginning of the menstrual cycle, the thickened uterine lining breaks down and menstruation occurs.

Meanwhile, the pituitary gland starts to secrete more follicle stimulating hormone, FSH.

FSH stimulates the development of several follicles in the ovary.

One of the follicles will become fully mature.

During the development of the follicles, the follicle cells are stimulated by FSH to secrete oestrogen into the blood.

This causes the uterine lining to thicken and inhibits further secretion of FSH by the pituitary gland.

The level of oestrogen continues to rise and reaches a peak just before ovulation.

A high level of oestrogen causes a sudden release of FSH and luteinising hormone (LH) by the pituitary gland.

The high level of LH triggers ovulation, which usually occurs on day 14.

Shortly after ovulation, the high level of LH stimulates the ruptured follicle to develop into a yellow body.

The yellow body secretes large amounts of progesterone and oestrogen.

The oestrogen level in blood rises again and the progesterone level reaches a peak.

The high level of progesterone together with oestrogen maintains the thickness of the uterine lining.

It also inhibits further secretion of FSH and LH by the pituitary gland.

The yellow body begins to degenerate around day 24.

Due to the degeneration of the yellow body, the levels of oestrogen and progesterone fall, the uterine lining is no longer maintained, the thickened uterine lining starts to break down, a new cycle begins.