Sex hormones play an important role in the development of secondary characteristics and also the menstrual cycle in women.
During puberty, FSH and LH (known as gonadotrophins) stimulate the ovaries in females to bring about the follwing effects:
In boys, the same gonadotrophins are produced and stimulate the testes to produce testosterone. The effects of this are:
In females, hormones play an important part in the preparation of the body for reproduction. The menstrual cycle which lasts approximately 28 days, can be divided into the following phases:
For the first five days or so, progesterone produce by the corpus luteum enters the blood stream and the pituitary gland responds by producing less luteinising hormone. This in turn causes the sorpus luteum to break down, thus causing the levels of progesterone to fall. The endometrium stops retaining fluid and this starts to break down also. The resulting menstrual fluid contains extra mucus secretions, the cells lining the uterus, blood from broken capillaries in the endometrium and the unfertilised ovum.
Fig. 1 Menstrual phase
For approximately seven days, follicle stimulating hormone is produced in the anterior lobe of the pituitary which stimulates the follicles of the ovaries to produce oestrogen. The oestrogen stimulates the endometrium promoting growth of new blood vessels an dmucus-producing cells. At the end of the stage, ovulation occurs and a mature Graafian follicle ruptures, releasing a single egg which then travels along the fallopian tube towards the uterus.
Fig. 2 Proliferative phase
The last phase is approximately 14 days in duration. Luteinising hormone is secreted by the anterior lobe of the pituitary gland stimulating the ruptured follicle lining to grow into corpus luteum - a temporary sturture formed as a result of this hormone on the ruptured ovaria follicle. The corpus luteum produces progesterone which stimulates the endometrium to retain fluid and produces mucus, make the passage of sperm easier through the reproductive tract. After ovulation, the egg can be fertilised within 8-24 hours. If it is not, the menstrual phase begins.
Fig. 3 Secretory phase