Chapter 7 – Abnormal Uterine Bleeding and Other Disorders of the Menstrual Cycle

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The menstrual cycle: An introduction

A ‘normal’ menstrual cycle (Figure 7.1) is associated with a monthly bleed (every 21 to 35 days) with duration of seven days or less. A blood loss of 80 mls or less, per month, is regarded as being in the normal range.

A regular menstrual cycle depends on the presence of a coordinated reproductive hormone system, including the hypothalamus, anterior pituitary gland and ovaries, as well as normal uterine and vaginal anatomy. The menstrual cycle is ‘switched on’ at puberty when the hypothalamus secretes gonadotrophin-releasing hormone (GnRH). Pulses of this hormone cause the release of follicle-stimulating hormone (FSH) from the anterior pituitary. FSH in turn stimulates the growth of a cohort of ovarian follicles. The granulosa cells of the ovarian follicles produce increased amounts of the hormone oestradiol, which in turn trigger a surge of luteinising hormone (LH) causing the dominant follicle to ovulate.

As a result of stimulation by oestradiol, the endometrium thickens in preparation for implantation of an embryo should fertilisation and pregnancy occurs. The dominant follicle resolves to become the corpus luteum, which then produces the hormone progesterone as well as oestradiol. If a pregnancy does not eventuate, the corpus luteum ceases production of hormones. This causes the breakdown ... Buy now