#114 Menstrual cycle

The menstrual cycle in women is a recurring process in which the lining of the uterus is prepared for pregnancy, and if pregnancy does not happen, the lining is shed at menstruation. The cycle lasts about 28 days.

Several hormones control this cycle:     

	FSH LH	Oestrogen, Progesterone
Secreted by	Pituitary gland (at the base of the brain)	Ovaries
Function	Control the release of egg from ovary	Change the thickness of uterus lining

1. Menstruation

• Usually, one egg is released from an ovary every month. Before the egg is released, the lining of the uterus becomes thick and spongy to prepares for a fertilised egg. It is full of tiny blood vessels, ready to supply the embryo with food and oxygen if it should arrive. 
• If the egg is not fertilised, it is dead by the time it reaches the uterus.
• Is does not sink into the spongy wall, but continues onwards, down through the vagina.
• As the spongy lining is not needed now ---> it gradually disintegrates and is slowly lost through the vagina.
• This is called menstruation, or period and it last for about 5 days.

2. Ovulation

Ovary	Pituitary gland
a follicle develops secretes oestrogen ↑↑ oestrogen in the blood. lining of the uterus grows thick, spongy	secretes LH, FSH stimulates follicle to secrete oestrogen.
When the follicle is fully developed ---> LH ↑↑↑↑ and  FSH ↑↑
follicles rupture and release fully developed ovarian cells (ovulation)
empty follicle stops secreting oestrogen becomes a corpus luteum secretes progesterone uterus lining thick, spongy, well supplied with blood in case a egg is fertilised.	↓↓ LH, FSH

If the egg is not fertilized

corpus luteum gradually disappears no more progesterone secreted uterus lining breaks down

Menstruation

a new follicle develops

If the egg is fertilized

corpus luteum does not degenerate so quickly secretes progesterone until the embryo sinks into uterus wall and a placenta develops

Placenta secretes progesterone through pregnancy

it maintains the uterus lining so that the menstruation does not happen during pregnancy