New News Biology #42

Menstrual Cycle & Puberty

Puberty = ‘period in which adolescents start to develop secondary sexual characteristics’

It is triggered by reproductive hormones (testosterone in men, oestrogen in women)

Menstrual Cycle has four stages, each corresponding to a different hormone. It happens in the female reproductive system, with eggs produced in the ovaries going through one of the fallopian tubes to the uterus. If it was fertilized, it will stick to the uterus lining. If not, it will break down with the thickened uterus lining.

Average is 28 days, though it may vary a lot. The graph is red (representing the uterus lining).

Stage 1: Menstruation (bleeding and breakdown of uterus lining)

Stage 2: Lining starts to build up again (prepare for fertilized egg)

Stage 3: A single egg is released from the ovaries (lasts only one day, Day 14)

Stage 4: Maintaining the lining of the uterus.

End of cycle: If no fertilized egg, the cycle will repeat, starting from Stage 1. If there is a fertilized egg, it will fully develop into fetus, and the cycle stops.

Levels of the four different hormones during a cycle:

Oestrogen (produced in ovaries) stays the same in stage 1, increases and peaks at stage 3, and lowers at stage 4.

Progesterone (produced in ovaries) stays the same level from stage 1 to stage 2, and peaks during stage 4 (maintaining the lining), if it falls at the end of stage 4, it restarts the cycle.

LH (produced in pituitary gland) stimulates the release of the egg on Day 14 aka ovulation.

FSH (produced in pituitary gland) stimulates growth of an egg.