OESTROGENS



OESTROGENS *****

• Steroid hormones synthesised from cholesterol and secreted mainly by the ovary but also by the adrenal cortex and in large quantities by the placenta *

• Three forms - Oestradiol, Oestrone and Oestriol. Oestradiol is the major oestrogen secreted by the ovary. Oestrone is mainly formed from androgens while Oestriol is an oxidative product of oestradiol and oestrone

• Oestradiol has 12 times the oestrogenic potency of oestrone and 80 times that of oestriol

• Serum oestradiol concentrations are maximal just before ovulation on day 14 of a regular 28 day cycle *

• Circulate bound loosely to plasma proteins (mainly  SHBG and albumin) *

• Conjugated by the liver into glucuronides and sulphates. 20% of these are excreted in bile and 80% in urine. The liver also converts oestradiol to oestriol.

• Inhibits FSH secretion by the anterior pituitary. Positive feed-back effect results in pre-ovulatory LH surge

• Has two known receptors located within the cytoplasm / nucleus - ER - alpha and beta

OESTROGEN - EFFECTS

• Development of secondary sexual characteristics. Pubertal hair growth is under androgenic control *

• VAGINA: Increase in size, conversion of cuboidal to stratified squamous epithelium at puberty. Vaginal epithelial cells accumulate glycogen, their nuclei shrink and they become cornified

• ENDOMETRIUM - stimulates proliferation of glandular and stromal elements. Stimulates the development of progesterone receptors in endometrial cells

• MYOMETRIUM - increases sensitivity to oxytocin *

• Increases uterine blood flow - vasodilates uterine artery *

• FALLOPIAN TUBES - proliferation of glandular tissue; increased number of ciliated cells and increased ciliary activity

• CERVIX - increased mucus production- thin, watery and clear with a ferning pattern if dried on a slide. Mucus shows increased elasticity and a drop may be stretched to 10-12cm and is easily penetrable by sperm

• BREASTS - stimulates fat deposition and growth of stroma and ducts. Devlopment of lobules and alveoli are mainly under influence of progesterone and prolactin. Inhibits milk secretion

• SKELETON - stimulates osteoblastic activity; stimulates fusion of the epiphyses of long bones

METABOLISM

• Anabolic effect; stimulates protein deposition in specific organs.

• Increases sub-cutaneous fat and blood supply to skin.

• Stimulates sodium and water retention by the kidneys

• Increases hepatic globulin synthesis: sex hormone binding globulin, thyroxine and cortisol binding globulins *

• Free thyroxine and free cortisol unchanged *

• Increased transferring concentrations *

• Serum albumin levels are usually decreased (along with the associated calcium levels). *

• Reduced serum folate concentration *

• Increase insulin resistance

• Increase HDL cholesterol

• Decrease LDL cholesterol

• Increase total cholesterol

• Increase triglycerides

• Clotting factors - increase in factors II, V, VII, IX, X, XII and especially VII; decrease of Antithrombin III. Therombogenic *

PROGESTERONE

• C21 steroid Synthesised from cholesterol by the corpus luteum *

• Acts via receptor located in the cytoplasm / nucleus

• Also secreted in large quantities by the placenta *

• Metabolised by the liver into pregnanediol, 10% of which is excreted in urine

PROGESTERONE - EFFECTS

• UTERUS - secretory changes in the endometrial glands. Inhibits uterine contractions *. Cervical mucus is thick, viscous and non-ferning

• FALLOPIAN TUBES - secretory changes in epithelium

• CERVIX - production of small quantity of viscous mucus which is less penetrable to sperm

• BREASTS - proliferation of lobules and alveoli. Secretory changes in alveoli. Does not stimulate milk secretion (Prolactin).

• RESPIRATION - increased ventilation *

• METABOLISM - catabolic hormone; thermogenic with a rise of ~0.5C in basal body temperature*; induces sodium and water retention by the kidneys. Promotes development of the lobules and alveoli of the breast

 

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