Changes in the uterus

If fertilisation of the ovum has occurred, the embryo arising from it develops within the uterus. The changes occurring within the uterus can be divided into three main phases.

Figure to be added

Figure 14.26 — the changes occurring within the uterus during the menstrual cycle: the oestrogen and progesterone curves above, and below them the uterine lining through the menstrual phase (day 4), the proliferative phase (day 14), the secretory phase (day 28) and into the next menstrual phase.

1. The menstrual phase

This is the initial phase. If fertilisation has not occurred, the level of the hormone progesterone falls. Because of this, the uterine wall that had developed breaks down, and those parts pass out of the body along the vagina together with blood. This is called the menstrual flow.

It lasts about four days.

2. The proliferative phase

This is the second phase. The uterine wall that has broken down begins to develop gradually, because of the influence of the hormone oestrogen. Here, a new layer of cells forms on the inner wall of the uterus and it becomes vascularised — blood capillaries become abundant.

This takes about 10 days.

3. The secretory phase

This is the final phase. The uterine wall that has developed thickens further, the blood supply increases, and the glands of the uterine wall become active and reach a secretory state. This occurs because of the influence of the hormone progesterone.

This takes about 14 days. During this phase, body temperature also rises slightly.

Build, furnish, or clear away

The three phases are one preparation and its undoing. The proliferative phase rebuilds the wall, the secretory phase makes it ready to receive an embryo, and the menstrual phase removes it when no embryo arrived.