Chapter 3 Hormonal Cycles
Fertilisation and Early Development
The ovarian cycle
• Under the influence of follicle-stimulating hormone (FSH) and, later, luteinising hormone (LH) the Graafian follicle matures and moves to the surface of the ovary. At the same time it swells and becomes tense, finally rupturing to release the secondary oocyte into the fimbriated end of the uterine tube; this is ovulation.
• The empty follicle, known as the corpus luteum, collapses, the granulosa cells enlarge and proliferate over the next 14 days, and the whole structure becomes irregular in outline and yellow in colour.
• Unless pregnancy occurs, the corpus luteum atrophies and becomes the corpus albicans.
Ovarian hormones
Progesterone
The effects of progesterone are mainly evident during the second half of the cycle:
• It causes secretory changes in the lining of the uterus, when the endometrium develops tortuous glands and an enriched blood supply in readiness for the possible arrival of a fertilised oocyte.
• It causes the body temperature to rise by 0.5°C after ovulation and gives rise to tingling and a sense of fullness in the breasts prior to menstruation.
