Control of the oestrous cycle Daniel Laverick| Andrew Westgarth |Andrew Watkis

Definition The Oestrus Cycle : The regular pattern of changes that takes place in the reproductive system of female mammals, which is controlled through the interaction of a number of hormones! The Menstrual Cycle : In humans and some other primates, the lining of the uterus is shed along with some blood between each cycle.

Hormonal control of the menstrual cycle There are four main hormones that control the human oestrous cycle: Follicle-stimulating hormone (FSH): Stimulates the development of follicles. Stimulates production of oestrogen. Luteinising hormone (LH): Causes ovulation to occur. Stimulates production of progesterone. Oestrogen: Causes rebuilding of uterus lining. Stimulates production of LH. Progesterone: Maintains uterus lining. Inhibits production of FSH. Oestrogen and progesterone are produced in the ovaries, while FSH and LH are produced in the pituitary gland of the brain.

The Cycle The LH then causes one of the follicles in the ovary to release its egg. (Ovulation) The menstrual cycle begins when the uterus lining is shed (along with blood) DAY 1-5 DAY 14 DAY 10 DAY 1 As the follicles grow, more oestrogen is produced. The level of oestrogen increases until, it reaches it’s critical point. This then inhibits the production of more FSH and stimulate production of LH, which is Positive Feedback The pituitary gland releases into the blood which stimulates follicles in the ovary to grow and mature. Each follicle contains an egg The growing follicles secrete small amounts of oestrogen into the blood. This low level of oestrogen causes the uterus lining to build up, and also inhibits(stops) the release of FSH and LH. This is Negative Feedback.

FSH release therefore resumes and the cycle repeats. The Cycle Continued After Ovulation, LH stimulates the now empty follicle to develop into a structure known as the Corpus Luteum, which secretes progesterone. With less progesterone, the lining of the uterus is no longer maintained and so breaks down (menstruation). Less progesterone also means that FSH release is no longer inhibited. FSH release therefore resumes and the cycle repeats. Progesterone maintains the thick lining of the uterus, and also inhibits release of FSH and LH (Negative Feedback) If the egg is not fertilised, the corpus luteum degenerates and so no longer produces progesterone.

Menstrual Cycle

Diagram