3.10 Menstrual Cycle

understand the roles of oestrogen and progesterone in the menstrual cycle.
-oestrogen and progesterone are examples of hormones.
-hormones are produced in a structure called and endocrine gland.
-hormone will travel through the blood from the endocrine gland to target tissue.
-at the target tissue the hormone will have an effect. (may have multiple effects)
-ovary is the endocrine gland for oestrogen, it produces oestrogen which flows in the bloodstream to the lining of the uterus where it has effect no.1 which is the thickening of the endometrium. effect no.2 is that it flows to the bloodstream to the brain and it releases a second hormone known as luteinising hormone (LH) the production of luteinising hormone reaches its peak at around day 13- causes the ovary to release an egg into the oviducts where it is possible for fertilisation.

-in ovary- during the first half of the menstrual cycle the follicle becomes larger and larger- inside follicle is an egg. the cells around the follicle is producing oestrogen.
-the follicle reaches it largest point at around day 13 when the luteinising hormone causes the wall of the outside to rupture and the egg is released. - called ovulation.
-once process is complete the empty follicle changes function and colour (to yellow) gives us the name corpus lutetium (known as the yellow body) this yellow body is known to produce progesterone.
-ovary and the corpus lutetium in particular is the endocrine gland for progesterone.

-progesterone travels through the blood stream to the lining of the uterus to give effect no.3 to maintain the lining of the uterus- prevents the lining of the uterus from breaking down.
-in this condition it is possible that a fertilized egg could implant to the wall of the uterus and develop into a pregnancy.
-but if there is no implantation of an fertilized egg the corpus lutetium breaks down and progesterone levels fall.

-the fall in progesterone levels lead to effect no. 4
-which is the breakdown in the lining of the uterus- menstrual period/menstrual bleeding.
-marks end of one menstrual cycle and a start of a new menstrual cycle.
-when the lining has broken down completely the cycle and the change in hormones begins one more.