Describe the menstrual cycle in man.

The menstruation/ sexual/ oestrus cycle

This cycle found in female; ensures that female reproductive physiology events are synchronised. For the uterus prepares itself for implantation before ovulation.

 

The events that occur in the course of the cycle follow a set of regulated pattern by hormone which are produced by the pituitary gland and the ovary.  A complete cycle takes about 28 days. If pregnancy occurs the cycle is interrupted by other hormones produced by the placenta. The woman is most likely to get pregnant between 12^th and the 17^th day from the onset of menstruation.

 

 

 

Hormonal control of the cycle

Pituitary hormones secreted by the anterior lobe of pituitary gland are Follicle stimulation hormones (FSH) and luteinising hormone (LH).

 

Ovarian hormones produced by the ovary are oestrogen and progesterone.`

 

The menstrual cycle of the human female showing the events occurring in ovary together with relative levels of oestrogen and progesterone.

 

 

1. Just after menstruation, the anterior lobe of the pituitary gland starts secreting FSH.
2. FSH cause a Graafian follicle to develop in the ovary to secrete oestrogen.
3. Oestrogen

• brings about the healing and repair of the uterine endometrium following menstruation.
• inhibits production of FSH
• stimulates production of LH.

In the course of 11 days or so the amount of oestrogen in blood stream steadily increases. Then shortly before evolution takes place, LH is released.

 

4. LH

• causes ovulation
• promotes development the Graafian follicle into a corpus luteum to secrete progesterone

5. The corpus luteum secretes progesterone.
6. Progesterone

• This along with oestrogen, causes the continued thickening and vascularization of the uterine endometrium in preparation for implantation.
• Inhibits secretion of LH leading to degeneration of corpus luteum

7. For a week or so after ovulation the concentration of progesterone and oestrogen gradually increase and then suddenly decrease.
8. With the fall in the levels of the two hormones, the uterine endometrium begins to disintegrate and menstruation starts and the cycle repeats.