1 - Reproductive Endocrinology and the Menstrual Cycle Flashcards
What are the 2 main groups of molecules involved in human development?
Steroids and Glycoproteins
What are 5 features of steroids?
- Lipids
- 4 fused rings
- 27C skeleton
- Small
- Central core molecule is cholesterol
What are 3 types of steroids?
- Oestrogen
- Progestagens
- Androgens
What are the 3 types of Oestrogen?
E1 - Oestrone
E2 - Oestradiol (main oestrogen)
E3 - Oestriol (only in pregnancy)
Where is testosterone synthesised?
Leydig cells of testes in males
Ovary in females
Where is DHT synthesised?
Sertoli cells of testes in males
Where is Progesterone synthesised?
Adrenals in males
Ovary/Placenta in females
Where is oestradiol synthesised?
Ovary/placenta in females
Where is androstenedione synthesised?
Leydig cells
Where is DHEA synthesised?
Leydig cells
Where are oxidative enzymes located and what is the 1st step in steroid synthesis?
- Mitochondria and endoplasmic reticulum
- Conversion of cholesterol to pregnenolone
What are the 6 steps of steroid synthesis in males?
- GnRh in the hypothalamus stimulates FSH and LH from anterior pituitary
- LH stimulates testosterone production from leydig cells
- Target of testosterone and FSH is Sertoli cells
- Sertoli cells have the enzyme 5a reductase which converts testosterone to DHT
- Sertoli cells secrete ABP
- ABP binds to testosterone and carries it to seminiferous tubule to stimulate spermatogenesis
What are the 6 steps of steroid synthesis in females?
- GnRH stimulates FSH and LH from AP
- LH stimulates testosterone by THECA cells in the ovarian follicle
- Testosterone enters GRANULOSA cells surrounding oocyte
- Converted into oestrogen by aromatase
- Oestradiol stimulates formation of LH receptors on granulosa cells
- Enables follicle to respond to LH and cause ovulation
What is the potency of DHT, Testosterone, Androstenedione and DHEA?
DHT - 100%
Testosterone - 50%
Androstenedione - 8%
DHEA - 4%
What is the action of androgens?
Maintain male somatic tissue differentiation
Induce male secondary sexual characteristics
Support spermatogenesis
Influence sexual and aggressive behaviour (male & female)
Promote protein anabolism, somatic growth & ossification
Regulate gonadotrophin secretion (testosterone)
Induce body hair (in females – pubic & axillary)
What is the potency of 17b oestradiol, oestriol and oestrone?
Oestradiol - 100%
Oestriol - 10%
Oestroine - 1%
What is the action of oestrogens?
Stimulate growth of mammary gland & endometrium
Induce female secondary sexual characteristics
Prepare uterus for spermatozoa transport
Increase vascular permeability
Mildly anabolic
Regulate gonadotrophin secretion
What are the function of progestagens?
Luteal progesterone prepares the endometrium for implantation during the secretory phase of the menstrual cycle.
Effects cervix, vagina and breast
Placental progesterone maintains the endometrium (decidua) in pregnancy (after approximately 10-12 weeks)
What is a glycoprotein?
Protein containing oligoscaccharide chains covalently attached to their polypeptide side chains
What are the gonadotrophins produced by the anterior pituitary?
- LH
- FSH
- TSH
What is the name of the gonadotrophin produced by the placenta and the cell in placenta it is from?
Human chorionic gonadotropin (HCG)
Syncytiotrophoblast
What is the funcitonal glycoprotein?
2 alpha and 2 beta subunits
What is an alpha subunit?
Identical in FSH, LH, TSH and hCG - 92 Amino acids
What is the beta subunit ?
Different in FSH, LH, hCG and gives them their specific biological action
What is the function of FSH?
Stimulates growth of immature Graafian follicles in the ovary to maturity
Enhances production of androgen binding protein by the Sertoli cells of the testes amd is needed for spermatogenesis
What is the function of LH?
Surge triggers ovulation and converts the residual follicle into a corpus luteum
Necessary to maintain luteal function
Supports thecal cells in the ovary that provide androgens and hormonal precursors for oestradiol
Acts upon the Leydig cells of the testes and is responsible for the production of testosterone
What is the function of hCG?
Maintains corpus luteum during pregnancy to ensure a constant release of progesterone to maintain the uterus lining during pregnancy
What is the function of inhibin?
Produced by males by Sertoli cells. Secreted when sperm count is high to inhibit pituitary release of FSH and hypothalamic secretion on GnRH
In females it is produced by granulosa cells and helps to exert negative control on FSH production during the menstrual cycle
What is the function of activin?
Increases FSH activity and enhances the actions of LH in both males and females
Belongs to the transforming growth factor beta family
What is the funciton of Relaxin?
Produced by females in the menstrual cycle (follicular development and oocyte maturation) and pregnancy (relaxation of ligaments and parturition)
Produced in males in seminal fluid and enhances sperm mobility
How many amino acids doe GnRh, GHRH, Oxytocin and Prolactin have?
- Gonadotrophin releasing hormone (GnRH) – 10 amino acid peptide (hypothalamus)
- Growth hormone releasing hormone (GHRH) – 44 amino acid peptide (hypothalamus)
- Oxytocin – 9 amino acid peptide (hypothalamus/posterior pituitary)
- Prolactin – 198 amino acid polypeptide (anterior pituitary)
What are the 3 stages of the menstrual cycle?
o Menstrual phase: 1-5 days
o Proliferative phase: 6-14 days
o Secretory phase: 15-28 days
How much blood is usually lost during menstruation?
50 - 150ml
What happens during the menstrual phase?
Withdrawal of oestrogen and progesterone
endometrium collapses and is shed
What happens during the proliferative phase?
o Oestrogen from the mature follicle stimulates thickening of endometrium
o Glands and spinal arteries form
o Oestrogen stimulates the synthesis of progesterone receptors on endometrial cells
What happens during the secretory phase?
o Progesterone from corpus luteum acts on endometrium
o Progesterone stimulates enlargement of glands which begin secreting mucus and glycogen in preparation for implantation of oocyte
o If fertilization doesn’t occur, the corpus luteum degenerates
o Progesterone levels fall and the endometrium degenerates
o The cycle starts again with the first day of menstrual flow
What happens if fertilisation doesnt occur?
o Corpus luteum degenerates and forms the corpus albicans
o Progesterone levels fall
o Endometrium breaks down
o Menstruation occurs
What happens if fertilisation does occur?
o Blastocyst implants into maternal endometrium
o Developing placenta secretes human chorionic gonadotrophin (Hcg)
o Corpus luteum does not degenerate because of Hcg
o Progesterone levels do not fall because progesterone secretion is maintained by the corpus luteum
o Progesterone maintains the endometrium
