Page 33 - كتاب تمريض نسا الاكتروني

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The length of the menstrual cycle is typically 28 days, but it can be highly variable. In
some women it may be as short as 21 days or as long as 39 days. The menstrual cycle is
best understood if we focus first on events occurring in the ovaries, and then on events
occurring in the uterus. We are going to describe each of them in turn.

he ovarian cycle

The ovarian cycle refers to the monthly series of events in the ovaries, associated with
the maturation and release of an ovum, and the ‘just in case’ preparation for its fertilization
and implantation in the uterus. You may be wondering why the regulation of the female
reproductive system is so complicated, as shown in Figure 1. The reason is that the ovarian

cycle has to be initiated (switched on) and then suppressed (switched off) in a precisely
regulated sequence every month. In this section, we will explain how this is achieved.

The ovarian cycle consists of two consecutive phases, each of about 14 days’ duration.

Events are measured from ‘day 1’, which is the first day of the last normal menstrual
period (LNMP).

The follicular phase: days 1 to 14

The sequence shown in Figure 1 begins with the secretion of GnRH from the
hypothalamus, which stimulates the pituitary gland to produce FSH and LH, which in turn
act on the ovaries, telling the ovarian follicles to complete the maturation of an ovum.

During this period, a few ovarian follicles containing immature ova develop and mature
under the stimulation of FSH and LH. Usually by day 14, only one follicle has become

fully mature, and the ovum it contains is ready to be released. All other follicles that had
begun maturing during this phase of the ovarian cycle degenerate as soon as ovulation has
occurred.

Note that only one time interval is fairly constant in all females — the time from ovulation

to the beginning of menstruation, which is almost always 14 to15 days. However, the time
of ovulation is variable and difficult to predict accurately.

The luteal phase: days 15 to 28

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