THE MENSTRUAL CYCLE
Females release an oocyte from the ovaries every 24 to 35 days. This is part of a monthly menstrual cycle controlled by the hormones. Oestrogen levels rise due to a mid-cycle surge in luteinizing hormones. This in turn triggers ovulation and the ovary releases an egg. Progesterone levels begin to increase a few days after this occurs and the uterus lining thickens in preparation for a fertilised egg. If the egg is not fertilised, the level of progesterone and oestrogen decline, and the egg and uterus lining are shed as menstrual flow.
Hormone levels increase during pregnancy, including the production of relaxin which allows the muscles in the abdomen to stretch and accommodate the growing foetus. Pregnant women often experience other changes to their body, including increased hair growth and the appearance of large brown patches on the skin. This is largely due to the high levels of oestrogen and progesterone in the body.
The menopause signifies a two- or three-year decline in a female reproductive activity. This usually occurs between the ages of 45 and 55 when the supply of eggs has been exhausted. This causes the ovaries to shrink and fail to respond to hormones. Women going through the menopause can experience a variety of symptoms including hot flushes, headaches, depression, insomnia, increased rate of vaginal infections, loss of bone calcium, loss of skin collagen, thinning of head hair and an increase in body hair as well as a greater chance of blood clots.
The vagina is the muscular passageway that runs from the uterus to the vulva and ends in the vagina orifice. This orifice is protected by a fold of mucous called the hymen. The vagina has a number of functions, including allowing the escape of menstrual flow, receiving the penis and ejaculated sperm during intercourse, and provides an exit for the foetus during birth.
The walls of the vagina have three layers. The outer adventitia anchors the vagina to its surrounding organs and is made up of areolar connective tissue. The intermediate muscularis is a layer of longitudinal smooth muscle fibres which stretch during labour. The final layer is the inner mucosa which lies in transverse folds and secretes acidic mucous which retards microbial growth and harms sperm. An alkaline mucous produced from the cervix moistens the vagina.