Reproductive endocrinology and menstrual cycle Flashcards
General structure of steroids
27 carbon skeleton
four fused rings
small, lipophillic molecules
What is the central core molecule of all steroids?
Cholesterol
Give 3 examples of steroid hormones
Testosterone
Progesterone
Oestrogens
What differentiates different steroid hormones
The functional groups attached to four ring structure
3 oestrogens?
Oestrone (E1)
Oestradiol (E2)
Oestriol (E3)
Which oestrogen is usually being referred to when oestrogen is mentioned?
Oestradriol
Which oestrogen is only seen in pregnancy?
Oestriol (E3)
Where is testosterone produced in men and women?
Men: Leydig cells of testes
Women: Thecal cell, adrenals, peripheral conversion in adipose
Where is DHT produced in men and women?
Men: conversion from testosterone in sertoli cells
Women: peripheral conversion from testosterone
Where is progesterone produced in men and women?
Men: Adrenals
Women: Corpus luteum, synctiotrophoblasts
Where is oestradiol produced in men and women?
Men: peripheral conversion from testosterone where aromatase is present
Women: granulosa cells, peripheral conversion from testosterone, syncytiotrophoblasts
How are steroids synthesised in men? (6 steps)
- Gonadotrophin releasing hormone stimulates FSH and LH from ant. pituitary
- LH stimulates testosterone produced by Leydig
- Testosterone and pituitary FSH mainly go to sertoli
- Enzyme 5-alpha reductase converts testosterone to DHT
- Sertoli cells secrete androgen binding protein
- Binds to testosterone and carries to seminiferous tubule to stimulate spermatogenesis
How are steroids synthesised in females? (4 steps)
- LH stimulates testosterone production by theca cells in ovarian follicle
- Testosterone enters granulosa cells, converted by aromatase to oestrogen
- Oestradiol stimulates formation of LH receptors on granulosa cells
- Enables follicles to respond to LH surge–> ovulation
3 functions of progesterone
prepare endometrium for implantation
effects cervix, vagina and breast
placental progesterone maintains endometrium in pregnancy
Are steroid hormones of glycoprotein hormones bigger molecules?
Glycoprotein
How are structures of FSH, LH, hCG and TSH similar?
Same alpha unit (29 amino acids)
How are structures of FSH, LH, hCG and TSH different?
Different beta unit
Why are LH and hCG particularly similar?
Same amino acids, stimulate same receptors
hCG has 24 extra amino acids
What structure releases gonadotrophin releasing hormone?
The hypothalamus
What stimulates release of FSH and LH?
Gonadotrophin releasing hormone
What is the effect of FSH on the body?
Stimulates growth of Graafian follicles to maturity
Enhances production of androgen binding protein by sertoli cells of testes
What is the effect of LH on the body?
Surge triggers ovulation- converts residual follicle into corpus luteum
Necessary to maintain luteal function
Stimulates thecal cells in ovary to produce testosterone for oestradiol production
Acts upon Leydig cells of testes and produces testosterone (men)
Effect of hCG on body?
maintains corpus luteum
What is benefit of peptide hormones having a half life?
Means they are fast acting and effect is not long lasting
Name 4 peptide hormones
Gonadotrophin releasing hormone
Growth hormone releasing hormone
Oxytocin
Prolactin
What are the 3 stages of the menstrual cycle?
Menstrual stage: 1-5 days
Proliferative stage: 6-14 days
Secretory stage: 15-28 days
What happens during the menstrual stage?
Endometrium collapses due to lack of oestrogen and progesterone.
Sheds with blood from ruptured arteries
Detached endometrium passes through vagina as menstrual flow
What happens during the proliferative stage?
Oestrogen from mature follicle stimulates thickening of endometrium
Glands and spiral arteries form
Oestrogen stimulates synthesis of progesterone receptors on endometrial cells
What happens during the secretory stage?
progesterone from corpus luteum acts of endometrium
stimulates enlargment of glands which secrete mucus and glycogen in prep for fertilised oocyte
What happens if fertilisation doesn’t occur?
Corpus luteum degenerates and forms corput albicans
Progesterone levels fall
Endometrium breaks down
Menstruation occurs
What happens if fertilisation does occur?
Blastrocysts implants into materal endometrium
Developing placenta secretes hCG
Corpus luteum doesn’t degenerate because of hCG
Functions of androgens? (6)
Induce male sexual characterstics Support spermatogenesis Influence sexual and aggresive behaviour Promote protein anabolism, somatic growth Induce body hair Regulate gonadotrophin secretion
What is the most potent androgen?
DHT
Functions of oestrogens? (5)
Stimulate growth of mammary gland and endometrium
Induce female secondary sexual characteristics
Prepare uterus for spermatazoa transports
Increase vascular permeability
Regulate secretion of gondotrophin
