3.10 Menstrual cycle

1. Oestrogen and Progesterone are both examples of hormones. 
2. Hormones are produces in a structure called endocrine gland. 
3. Hormone will travel through the blood from the endocrine g;and to its target tissue. 
4. The hormone will have an effect on the target tissue. Some hormones such as oestrogen and progesterone will have multiple effects. 
5. The ovary is the endocrine gland for oestrogen. 
6. The oestrogen flows from the ovary through the bloodstream and into the lining of the uterus. The effects of this are: 
• In the first half of the cycle (14 days) the lining becomes increasingly thick. The oestrogen brings about the thickening of the wall of the endometrium. 
• oestrogen flows through our bloodstream to our brain. In the brain, it releases another hormone called liutenizing hormone (LH). The production of this hormone reaches its peak at about day 13 in the cycle. This causes the ovary to release an egg. The egg will come out of the ovary and will move into the oviduct where it is now possible for fertilization to occur.
• Whilst this is happening, a circular structure within the ovary known as a folicle becomes larger and larger. The egg is inside the folicle. It is the cells around the folicle which produce oestrogen.
• The folicle reaches its largest size at about day 13 when the liutenizing hormone causes the wall of the folicle to rupture to release the egg. 
• This process is known as ovulation. 
• After the completion of this process, the empty follicle has an altered function. It develops a yellow color called corpus liuteum. 
7. This yellow body is known to produce progesterone. The ovary and the corpus luteum is the endocrine gland for progesterone. 
• The progestrone flows through the bloodstream to the lining of the uterus and maintains the thickness of it for the next (16-24) 8 days of the cycle. It prevents the lining from breaking down. 
• During this period of time, there is a possibility of the fertilized egg implanting into the wall of the uterus and developing into a pregnancy. 
• However, if this does not happen, the corpus luteum breaks down and the progesterone level falls leading to the breakdown in the lining of the uterus. 
• This concludes with the release of menstrual period.
8. This is the end of one menstrual cycle.