Control of the Menstrual Cycle
The human menstrual cycle is controlled by hormones. The human menstrual cycle (also called the oestrous cycle) lasts about 28 days. The menstrual cycle involves:
A follicle (an egg and its surrounding protective cells) developing in the ovary.
Ovulation – an egg being released.
The uterus lining becoming thicker so that a fertilised egg can implant.
A structure called the corpus luteum developing from the remains of the follicle.
If there’s no fertilisation the uterus lining breaks down and leaves the body through the vagina. This is known as menstruation, which marks the end of one cycle and the start of another.
The menstrual cycle is controlled by the action of four hormones:
1. Follicle stimulating hormone (FSH) – stimulates the follicle to develop.
2. Luteinising hormone (LH) – stimulates ovulation and stimulates the corpus luteum to develop.
3. Oestrogen – stimulates the uterus lining to thicken.
4. Progesterone – maintains the thick uterus lining ready for implantation of an embryo.
FSH and LH are secreted by the anterior pituitary gland. Oestrogen and progesterone are secreted by the ovaries.
Here’s how the cycle works:
1. The menstrual cycle begins when the uterus lining is shed, along with some blood (days 1-5).
2. From day 1, the pituitary gland releases FSH into the blood which stimulates follicles in the ovary to grow and mature. Each follicle contains…