16 March 2014

#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:     

Oestrogen, Progesterone
Secreted by
Pituitary gland
(at the base of the brain)
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

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 
  • 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


  1. On the first picture of 'The Hormonal Cycle' above, the LH and FSH are labelled the wrong way around. Just FYI :)

  2. Thanks, you're so attentive! The correction has been done. Cheers!!!

  3. At the menstruation there, you did mentioned the "As the spongy lining is not needed now ---> it gradually disintegrates and is slowly lost through the vagina." is the ovum pass though outside the vagina ? sorry i'm not clear about this

  4. Check menstruation to correct spelling mistake