Endocrinology of Menopause
Secsual hormones are steroïd hormones and have a similar chemical structure and mechanism of activity. After binding to a specific receptor they change the functioning of the genomet.
Classes are corticoïsteroids en sex steroiden such as androgens, oestrogens and progestagens.
Each subgroup indicates a a series of hormonens with a similar effect. Estrogens comprise the natural hormones as oestradiol, oestrone en oestriol evenutally with slicht chemical alterations to increase solubility in water for oral administration such as ethinyl-oestradiol or oestradiolvalerianate. Animals and plants have other oestrogens sucha s in urine if pregnant mares and fyto oestrogens. Important is the confusion of the word ‘natural’: Fyto estrogens orrcur in nature but are not natural for women – oestradiol-valerianats is chmically modified but becomes a natural estrogen in bloed.
Oestrogens induce the development of breasts and the uterus and the development of the endometrium. Progesterone changes the estrogen effect on the endometrium, and stops growth while preparing for a pregnancy.
Oestrogens and progesterone originate form the ovary and are linked to the ovulation. Male hormones are made in the ovary and inthe adrenals.
Importnat is that ‘so called’ normal concentrations are a range and that concentrations in the individual woman can be much higher of lower. This explaind that individualisation of therapy is needed
The menstrual cycle
The menstrual cylc is similar to a domino cascade : a gtowing oocyte starts a cascade of event with strict timing, which explains that a menstrual cycle can be so regular at 28 days.
Estrogens increase in parllel with the growing follicle, then induce an ovulation and thereafter secretion of progesterone. In the absence of a pregnancy, progesterone secretion stops after 14 days, and this decrease induces a menstruationg uit, de menstruatie.
Important aspect to know for hormone replacement therapy
- Oestrogens stimulate the growth of the endometrium
- Progesterone stops the growth, also if given together with estrogens
- A sudden drop in oestrogens or progestagens induces a withdrawal bleeding .
- less bleeding if the endometrium is thin.
Oocytes
The secretion of estrogens en progestagens is linked to the follicular growth At 50 yearas of age few oocytes are left and ovulation and hormone production stops.
Puberty versus Menopause
At puberty starts the secreion of androgens from adrenals and ovaries inducing hair growth of the pubis and somewhat later estrogens induce breast development and menstruation.
In the absenc of dollicular growth and ovulation, menopause starts; However, the androgen secretion continues explaining that pubic hair does not disappear. Androgens can be metabolised into estrogens (e.g. in fatl)