Reproductive endocrinology and the menstrual cycle Flashcards
What are steroids
Lipids with a 27 carbon skeleton, 4 fused rings and groups attached
How to steroids pass through the cell membrane?
They are lipophilic so pass through the membrane via simple diffusion
What are the different forms of steroids receptors?
Nuclear and cytoplasmic
Name the 3 main groups of steroids. What is responsible for there differences?
Oestrogen
Progesterone
Testosterone
The different groups attached to the 4 ring structure
Name the 3 different types about oestrogen? What is the difference between the 3?
oestradiol (2 OH), oestriol (3 OH) and oestrone (1 OH)
Where is testosterone produced in males and females?
Males- leyding cells
Females- 25% theca cells
25% adrenals
50% peripheral conversion in adipose tissue
Where is Dihydrotestosterone produced in males and females?
Males- Conversion from testosterone in sertoli cells and target tissue
Females- peripheral conversion from testosterone
Where is Progesterone
produced in males and females?
Males- Adrenals
Females- Corpus luteum (ovary), syncytiotrophoblasts (placenta),adrenals
Where is Oestradiol
produced in males and
females?
Males- Peripheral conversion from testosterone
Females- Granulosa cells (ovary), peripheral conversion from testosterone, syncytiotrophoblasts (placenta)
What is the first step in the synthesis of steroids?
The conversion of cholesterol to pregnenolone
Where is GnRH produced?
Hypothalamus
What is the menstrual cycle?
A series of cyclic changes in the uterine endometrium. Occur on a monthly basis in response to changes in levels of ovarian hormones.
What are the 3 stages of the menstrual cycle?
Menstrual phase 1-5 days
Proliferative phase 6-14 days
Secretory phase 15-28 days
What happens in the menstrual phase?
Withdrawal of oestrogen & progesterone causes endometrium to collapses and shed along with blood from ruptured arteries.
Blood loss- 50-150ml
menstrual flow (endometrial tissue and blood) exits vagina
What happens in the Proliferative phase?
Oestrogen from the mature follicle stimulates thickening of endometrium
Glands and spiral arteries form.
Oestrogen stimulates the synthesis of progesterone receptors on endometrial cells
What happens in the Secretory phase ?
Progesterone from corpus luteum stimulates enlargement of glands which begin secreting mucus and glycogen in preparation for implantation of the fertilised oocyte.
If fertilisation does not occur, the corpus luteum degenerates
Progesterone levels fall and the endometrium degenerates.
The cycle starts again with the first day of menstrual flow.
What happens when fertilisation occurs?
Blastocyst implants into maternal endometrium
Developing placenta secretes human chorionic gonadotrophin (hCG)
Corpus luteum does not degenerate because of hCG
Progesterone levels do not fall because progesterone secretion is maintained by the corpus luteum
Progesterone maintains the endometrium.
What is the potency of each androgen?
DHT 100%
Testosterone 50%
Androstenedione 8%
DHEA 4%
Name 5 functions of androgens
- Induce male secondary sexual characteristics
- Support spermatogenesis
- Influence sexual and aggressive behaviour (male & female)
- Promote protein anabolism, somatic growth & ossification
- Regulate gonadotrophin secretion (testosterone)
Name 5 functions of oestrogen
- Stimulate growth of mammary gland & endometrium
- Induce female secondary sexual characteristics
- Prepare uterus for spermatozoa transport
- Increase vascular permeability
- Regulate gonadotrophin secretion
What is the potency of each type of oestrogen
17b oestradiol 100%
Oestriol 10%
Oestrone 1%
Describe the stages of steroid synthesis in males
- GnRH stimulates FSH and LH secretion via the anterior pituitary
- LH stimulates testosterone production by Leydig cells
- Testosterone and FSH target Sertoli cells
- In Sertoli cells 5α reductase converts testosterone to DHT
- Sertoli cells then secrete androgen binding protein (ABP)
- ABP binds to testosterone & carries it to the seminiferous tubule where it stimulates spermatogenesis
Describe the stages of steroid synthesis in females
- LH stimulates testosterone production by theca cells in the ovarian follicle
2, Testosterone enters granulosa cells and is converted by aromatase into oestrogen (mainly 17β oestradiol) - Oestradiol stimulates formation of LH receptors on granulosa cells
- This will enable follicle to respond to LH surge thus giving rise to ovulation
Where in the ovarian follicle are androgen precursors synthesised?
Theca cells (outer layer) They diffuse into the granulosa cells to be converted into estrogen
What type of molecule us LH. FSH and hCG?
Glycoproteins- oligosaccharide chains covalently attached to polypeptide side-chains.
Where are LH. FSH and hCG produced?
LH and FSH- anterior pituitary
hCG- Placenta (syncytiotrophoblast cells)
Describe the sturcture of gonadotrophins
2 glycosylated proteins (alpha and beta) form the glycoprotein
Alpha subunit is identical for FSH. LH and hCG
Beta subunit is different for all and is responsible for the biological action
Name the similarities and differences between LH and hCG.
Similarities- have the same sequence of amino acids and both stimulate the same receptor
Difference- hCG beta subunit contains an additional 24 amino acids
What stimulate the production of LH and FSH?
Gonadotrophin releasing hormone (GnRH)
What is the function of FSH?
- stimulates the growth of immature Graafian follicles
2. Enhances the production of androgen-binding protein by the Sertoli cells (testes)
What is the function of LH?
- surge triggers ovulation and converts the residual follicle into a corpus luteum (female)
- is necessary to maintain luteal function (female)
- thecal cells in the ovary to produce testosterone for oestradiol production (female)
- acts upon the Leydig cells of the testis and is responsible for the production of testosterone (male)
What is the function of hCG?
maintains corpus luteum in pregnancy
Where is inhibin produced in males and females?
Males- sertoli cells (production reduces sperm count
Females- Granulosa cells- (negtive control of FSH during menstrual cycle)
What is activin and its function in males and females?
- transforming growth factor beta family
increase FSH activity
enhaves LH actions in males and females
Where the function of relaxin in males and females?
Females- produced during menstruation and pregnancy (relaxation of ligaments)
Males- found in seminal fluid to enhance sperm motility
Where is prolactin produced?
Anterior pituitary
