Changes in the ovary

Developing the ova, which are the female reproductive cells, and releasing them from the ovary is carried out by the ovary. The changes occurring within it divide into two main phases.

Figure to be added

Figure 14.25 — the changes occurring within the ovary during the menstrual cycle: the levels of luteinising hormone and follicle stimulating hormone across days 0, 14 and 28, and below them the primary follicle, secondary follicle, Graafian follicle, ovulation, corpus luteum and corpus albicans.

1. The follicular phase

This is the initial phase. Under the influence of follicle stimulating hormone (FSH), secreted from the pituitary gland, a primary follicle within the ovary develops as far as the Graafian follicle and reaches the state of being able to release an ovum.

This takes about 14 days. During this phase, the secretion of the hormone oestrogen from the ovary also occurs.

2. The luteal phase

This is the final phase. Once the Graafian follicle has matured, under the influence of luteinising hormone (LH) secreted from the pituitary gland, it bursts and releases the ovum within it from the ovary towards the fallopian tube.

The released ovum travels forward along the fallopian tube. If fertilisation has not occurred, the remaining part of the Graafian follicle becomes the corpus luteum and then the corpus albicans, and degenerates.

This takes about 14 days. During this phase, the secretion of the hormone progesterone from the ovary also occurs.

Two hormones in, two hormones out

Keep the four straight by which organ makes them. The pituitary sends the instructions — FSH first, then LH. The ovary sends the replies — oestrogen during the first phase, progesterone during the second. Ovulation is the hinge between them, at about day 14.