7 Menstrual changes in adolescence

Abstract

Adolescent girls are a particularly sensitive group when any abnormality arises. The transformation from girl to woman involves fundamental changes in body shape and image, allowing the development of the fully mature and fertile woman. These pubertal changes involve growth, and the appearance of secondary sexual characteristics, subsequent to the maturation of the hypothalamo-pituitary--ovarian axis. The fact that the changes vary from person to person leads to management problems, as most girls judge their development through their peers. Failure to reach expected landmarks of development, especially the establishment of the menstrual cycle, can cause great distress and a thorough understanding of pubertal development is essential if the doctor is going to manage these problems effectively. NEUROENDOCRINOLOGY OF PUBERTY The release of the pituitary gonadotrophins is controlled by gonadotrophinreleasing hormone (GnRH) and the amplitude and frequency of its episodic secretion is controlled by the hypothalamus. The onset of puberty results from an increase in frequency and amplitude of GnRH from a centre in the hypothalamus called the pulse generator. Animal studies suggest that this is located in the arcuate nucleus of the mediobasal hypothalamus, and it is capable of functioning independently of neural connections (Plant, 1987). During fetal life, the pattern of hypothalamo-pituitary-ovarian activity is fascinating. Although data on the human are scant, animal studies suggest that GnRH, luteinizing hormone (LH) and follicle stimulating hormone (FSH) are detectable by 10 weeks gestation (Grumbach and Kaplan, 1976) and the pituitary portal system is intact by 14 weeks. The release of FSH and LH increases until mid-gestation, presumably because there is very little ovarian activity and thus no inhibitory feedback from oestradiol-17t3. The levels of FSH and LH are higher in female than male fetuses because the higher levels of circulating testosterone in the male fetus lead to negative feedback.