The Menstrual Cycle
HORMONES AND PUBERTY
- During PUBERTY, the body begins to release SEX HORMONES which lead to secondary sexual characteristics.
- In MEN, TESTOSTERONE is the key hormone, produced by the TESTES. It stimulates SPERM PRODUCTION and causes physical changes like facial hair growth.
- In WOMEN, OESTROGEN is produced by the OVARIES and is responsible for eggs maturing and changes like breast development. It also plays a significant role in the MENSTRUAL CYCLE.
THE MENSTRUAL CYCLE
Hormones
There are FOUR hormones involved in the menstrual cycle:
1. OESTROGEN
- Produced in the OVARIES.
- Causes the uterus lining to GROW.
- Stimulates LH RELEASE and INHIBITS FSH.
2. PROGESTERONE
- Produced after ovulation by the OVARIES.
- MAINTAINS the uterus lining.
- INHIBITS FSH and LH.
3. FSH (Follicle-Stimulating Hormone)
- Produced by the PITUITARY GLAND.
- Causes eggs to MATURE in the ovaries.
- STIMULATES oestrogen production.
4. LH (Luteinising Hormone)
- Also produced by the PITUITARY GLAND.
- Triggers OVULATION (the release of an egg).
Stages
The menstrual cycle consists of FOUR stages:
STAGE 1: Days 1-4
MENSTRUATION begins, and the lining of the uterus breaks down for about four days.
STAGE 2: Days 4-14
The uterus lining REBUILDS itself, forming a thick layer ready for potential fertilisation.
The egg DEVELOPS in preparation to be released.
STAGE 3: Day 14
OVULATION occurs where an egg is released from an OVARY.
The uterus lining has fully REBUILT by this point
STAGE 4: Day 28
The uterus lining is MAINTAINED for about 14 days until day 28. If no fertilisation occurs, the cycle restarts.
If the egg gets fertilised by a sperm, the lining remains maintained in preparation to develop the embryo.
Here is how the levels of each of the hormones vary throughout one full cycle:
OESTROGEN levels are the HIGHEST from days 4-14 to make the uterus lining REBUILD.
PROGESTERONE levels are the HIGHEST from days 14-28, to keep the uterus lining MAINTAINED in preparation for fertilisation.
LH levels are the HIGHEST on day 14 to RELEASE the egg (OVULATION).
FSH levels remain high on day 14 and during MOST of the cycle to allow the egg to DEVELOP.