The Menstrual Cycle

Introduction This monthly cycle is called the menstrual cycle (from the Latin mensis meaning month) When females reach puberty they begin to experience a menstrual cycle This is a cycle in which changes take place in the uterus and ovaries over an approximately 28 day period. This cycle is controlled by a number of hormones

Meet the Players Female sex hormones: Oestrogen and Progesterone Uterus wall and lining Ovary and ovum Follicle: ball of fluid that holds ovum Corpus luteum: empty follicle without ovum FSH: Follicle Stimulating Hormone LH: Leutinising Hormone

Ovulation and the Menstrual Cycle The human female usually ovulates to produce one mature ovum each month from the onset of puberty (age 11-14) to the beginning of menopause (> age 45)

So What Happens? The cycle begins with the release of FSH from the pituitary gland. This causes one of the follicles in the ovary to mature and produce an ovum The ovum developing in the follicle signals the ovary to produce oestrogen Oestrogen stimulates cell division in the lining of the uterus The uterus thickens and its blood supply increases As the amount of oestrogen INCREASES, it REDUCES the production of FSH

So What Happens? As oestrogen levels drop, LH is released from the pituitary gland This triggers OVULATION by signaling the follicle to burst and release the ovum The corpus luteum remains and starts producing progesterone which stimulates the uterus lining to thicken even more If no pregnancy occurs, the corpus luteum breaks down and the production of progesterone drops This stimulates the walls of the uterus to break down again If implantation occurs, the developing embryo produces progesterone and oestrogen – maintaining the thickness of the lining. FSH is not produced, hence why there is no ovulation and menstruation during pregnancy.

So…in terms of days… Days 1-5 : At the beginning of the menstrual cycle the is a low level of female sex hormones .This causes the uterus lining to break down. As this happens, blood vessels rapture and a flow of blood and cells passes out the vagina.

So…in terms of days… Days 6-13 : The lining of the uterus thickens again under the influence of oestrogen and a new ovum starts to develop in the ovary. The ovum grows inside a ball of fluid called a follicle. As the follicle grows it moves towards the edge of the ovary, closer to the fallopian tubes.

So…in terms of days… Day 14 : Around day 14 of the cycle, the ovum is mature and ovulation takes place. The follicle bursts open to release the ovum into the fallopian tube. The empty follicle forms the corpus luteum.

So…in terms of days… Days 15-28 : The ovum travels down the oviduct towards the uterus. The oviduct is full of fluid and lined with cilia which vibrate to create currents which move the ovum along the tube. The uterus wall continues to thicken and becomes richly supplied with blood in preparation for receiving a fertilized ovum.

If Fertilization Occurs… The fertilized ovum will be implanted in the thick lining of the uterus When this happens we say the woman is pregnant

If Fertilization Does Not Occur… No pregnancy occurs The unfertilized ovum dies within 24 hours The corpus luteum breaks down in the ovary and the lining of the uterus breaks down. These pass out of the vagina during the next menstrual cycle

Animation http://www.fertilitylifelines.com/aboutyourfertility/femalebiology.jsp

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