1 - Reproductive Endocrinology and the Menstrual Cycle

Question 1

What are the 2 main groups of molecules involved in human development?

Answer 1

Steroids and Glycoproteins

Question 2

What are 5 features of steroids?

Answer 2

• Lipids
• 4 fused rings
• 27C skeleton
• Small
• Central core molecule is cholesterol

Question 3

What are 3 types of steroids?

Answer 3

• Oestrogen
• Progestagens
• Androgens

Question 4

What are the 3 types of Oestrogen?

Answer 4

E1 - Oestrone
E2 - Oestradiol (main oestrogen)
E3 - Oestriol (only in pregnancy)

Question 5

Where is testosterone synthesised?

Answer 5

Leydig cells of testes in males

Ovary in females

Question 6

Where is DHT synthesised?

Answer 6

Sertoli cells of testes in males

Question 7

Where is Progesterone synthesised?

Answer 7

Adrenals in males

Ovary/Placenta in females

Question 8

Where is oestradiol synthesised?

Answer 8

Ovary/placenta in females

Question 9

Where is androstenedione synthesised?

Answer 9

Leydig cells

Question 10

Where is DHEA synthesised?

Answer 10

Leydig cells

Question 11

Where are oxidative enzymes located and what is the 1st step in steroid synthesis?

Answer 11

• Mitochondria and endoplasmic reticulum

- Conversion of cholesterol to pregnenolone

Question 12

What are the 6 steps of steroid synthesis in males?

Answer 12

• 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

Question 13

What are the 6 steps of steroid synthesis in females?

Answer 13

• 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

Question 14

What is the potency of DHT, Testosterone, Androstenedione and DHEA?

Answer 14

DHT - 100%
Testosterone - 50%
Androstenedione - 8%
DHEA - 4%

Question 15

What is the action of androgens?

Answer 15

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)

Question 16

What is the potency of 17b oestradiol, oestriol and oestrone?

Answer 16

Oestradiol - 100%
Oestriol - 10%
Oestroine - 1%

Question 17

What is the action of oestrogens?

Answer 17

Stimulate growth of mammary gland & endometrium
Induce female secondary sexual characteristics
Prepare uterus for spermatozoa transport
Increase vascular permeability
Mildly anabolic
Regulate gonadotrophin secretion

Question 18

What are the function of progestagens?

Answer 18

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)

Question 19

What is a glycoprotein?

Answer 19

Protein containing oligoscaccharide chains covalently attached to their polypeptide side chains

Question 20

What are the gonadotrophins produced by the anterior pituitary?

Answer 20

• LH
• FSH
• TSH

Question 21

What is the name of the gonadotrophin produced by the placenta and the cell in placenta it is from?

Answer 21

Human chorionic gonadotropin (HCG)

Syncytiotrophoblast

Question 22

What is the funcitonal glycoprotein?

Answer 22

2 alpha and 2 beta subunits

Question 23

What is an alpha subunit?

Answer 23

Identical in FSH, LH, TSH and hCG - 92 Amino acids

Question 24

What is the beta subunit ?

Answer 24

Different in FSH, LH, hCG and gives them their specific biological action

Question 25

What is the function of FSH?

Answer 25

 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

Question 26

What is the function of LH?

Answer 26

 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

Question 27

What is the function of hCG?

Answer 27

 Maintains corpus luteum during pregnancy to ensure a constant release of progesterone to maintain the uterus lining during pregnancy

Question 28

What is the function of inhibin?

Answer 28

 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

Question 29

What is the function of activin?

Answer 29

 Increases FSH activity and enhances the actions of LH in both males and females  Belongs to the transforming growth factor beta family

Question 30

What is the funciton of Relaxin?

Answer 30

 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

Question 31

How many amino acids doe GnRh, GHRH, Oxytocin and Prolactin have?

Answer 31

* 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)

Question 32

What are the 3 stages of the menstrual cycle?

Answer 32

o Menstrual phase: 1-5 days o Proliferative phase: 6-14 days o Secretory phase: 15-28 days

Question 33

How much blood is usually lost during menstruation?

Answer 33

50 - 150ml

Question 34

What happens during the menstrual phase?

Answer 34

Withdrawal of oestrogen and progesterone | endometrium collapses and is shed

Question 35

What happens during the proliferative phase?

Answer 35

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

Question 36

What happens during the secretory phase?

Answer 36

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

Question 37

What happens if fertilisation doesnt occur?

Answer 37

o Corpus luteum degenerates and forms the corpus albicans o Progesterone levels fall o Endometrium breaks down o Menstruation occurs

Question 38

What happens if fertilisation does occur?

Answer 38

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