HPG axis

Question 1

Which two sex steroids are produced in the testis?

Answer 1

Inhibin and testosterone

Question 2

Which two sex steroids are produced in the ovary?

Answer 2

Oestrogen and progesterone

Question 3

What hormone is released by the hypothalamus?

Answer 3

GnRH - decapeptide from 92 AA prepropeptide

Question 4

What is the characteristic of GnRH secretion at puberty and what is its function?

Answer 4

Pulsatile to activate the gonads

Question 5

What happens if GnRH is continuously released?

Answer 5

Causes a downregulation and internalisation of GnRH recpetors on gonadotroph cells preventing LH/FSh release.

Question 6

How can GnRH be used in fertility treatment?

Answer 6

Can use a GnRH antagonist or a GnRH agonist as the peak causes downregulation

Question 7

What condition results from a failure of GnRH secreting neurons to migrate during development?

Answer 7

Kallmann Syndrome = infertility

Question 8

Which hormones are released in the pituitary as a result of GnRH and where are they released from?

Answer 8

GnRH stimulates the anterior pituitary indirectly via vascular beds to release gonadotrophins from the gonadotrophs to act on the gonads. They release LH and FSH

Question 9

Where is hCG produced?

Answer 9

A gonadotrophins produced by embryonic trophoblasts

Question 10

How do gonadotrophins signals?

Answer 10

Bind to cell surface receptors and signal via GPCR.

Question 11

Where does LH act?

Answer 11

On LHCGR of:
Leydig cells in testes
Theca and granulosa cells of ovary

Question 12

Where does FSH act?

Answer 12

On FSHR of:
Sertoli cells in testes
Granulosa cells of ovary

Question 13

Where does hCG act?

Answer 13

On luteal cells of the corpus luteum

Question 14

What is the difference between the structure of LH compared to FSH and hCG?

Answer 14

All have a common alpha chain, a unique beta chain. LH has 1 carb chain and the others have 2 chains.

Question 15

What is the difference between the HPG axis feedback in males and females?

Answer 15

Males always have -ve feedback where as women have both +ve and -ve.

Question 16

What are sex steroids derived from ?

Answer 16

Cholesterol via acetate.

Question 17

Where are progestagens released from?

Answer 17

Ovaries and placenta

Question 18

Where are androgens released from?

Answer 18

Testes mainly, adrenal gland and ovaires

Question 19

Where are oestrogens released from?

Answer 19

Ovaries, liver, adipose, adrenal, placenta in both males and females.

Question 20

How are sex steroids transported and where is their receptor?

Answer 20

As they are lipid soluble and act on intracellular receptors via steriod response elements, they are bound to carrier proteins such as albumin, sex hormone binding globulin (HBG) and androgen binding protein (ABP) from testes.

Question 21

Which sex steroids are produced first?

Answer 21

Progestagens then androgens then oestrogens

Question 22

What determines the potency of the steroid?

Answer 22

How well it binds to the receptor. It varies due to the chemical structure of each class.

Question 23

Some steroids can bind receptors from another class. What will result from COC binding to androgen R?

Answer 23

Causes androgeneric action resulting in acne

Question 24

What is the use of mifepristone?

Answer 24

An anti-progestagen acting as an antagonist to terminate pregnancy.

Question 25

What are the 3 types of progestagens and their functions?

Answer 25

Progesterone - Preparation and maintenance of uterus 17alpha OHP - Growth of mammary glands during pregnancy 20alpha OHP - Suppresses lactation and regulates gonadotrophins

Question 26

What are the receptors for progestagens?

Answer 26

PR-A and PR-B. Each activates different genes

Question 27

What are the 4 types of androgens and what is their function?

Answer 27

DHT - Development and maintenance of male reproductive system Testosterone - Secondary sexual characteristics Androstenedione - Sexual function and support DHEA - Spermatogenesis and regulation of gonadotrophins

Question 28

At what receptor do androgens act?

Answer 28

AR - have varying isoforms for different sensitivities to androgen levels

Question 29

Name the 3 types of oesrtogens and their fucntions.

Answer 29

Oestradiol - Puberty to menopause. Secondary sexual characteristics and mammary gland growth and activity. Oestriol - Pregnancy. Proliferation of endometrium for progesterone action Oestrone - Post menopausal. Regulates gonadotrophins.

Question 30

At which receptors do oestrogens act?

Answer 30

ERalpha and ERbeta

Question 31

How is the amount of steroid or the amount/structure of receptor controlled?

Answer 31

Via feedback loops

Question 32

What information is not gained from measuring hormone levels?

Answer 32

Structure of receptors

Question 33

What is central hypogonadism?

Answer 33

LOW FSH and LH causing low gonad function. Arises due to a problem with the hypothalamus or pituitary

Question 34

What is primary hypogonadism?

Answer 34

Failure to produce sex steroids and therefore a loss of feedback resulting in HIGH FHS and LH. Due to a problem with the gonads.

Question 35

Why is GnRH not measured when investigating fertility?

Answer 35

It has a pulsatile nature and a short half life

Question 36

What is the effect of prolactin on the HPG axis during pregnancy?

Answer 36

High prolactin levels in pregnancy and breast feeding inhibit gonad activity by suppressing GnRH release, keeping FSH and LH levels LOW.

Question 37

How is prolactin used as a contraceptive method after parturition? How effective is this method?

Answer 37

Prolactin suppresses HPG axis to induce lactational amenorrhea. It is 98% effective with contiuous breast feeding and no formula.

Question 38

What is the result of hyperprolactinaemia outside of pregnancy?

Answer 38

Galactorrhea - discharge unrelated to breast feeding.

Question 39

What is the difference between male and female gamete production?

Answer 39

Males gametogenesis is continuous bbut female is cyclic, producing one oocyte every month.

Question 40

What are the 3 stages of the menstrual cycle?

Answer 40

Follicular, ovulation and luteal/secretory (day 14)

Question 41

On which day of the cycle do menses begin and on which day is ovulation?

Answer 41

Day 1 menses | Day 14 ovulation

Question 42

On which day should the levels of LH and FSH be measured? What does the level of FSH indicate?

Answer 42

Day 2/3 | FSH shows the ovarian reserve - how many oocytes and for how long

Question 43

On which day should progesterone be measured and what does it provide an indication of?

Answer 43

Day 21/28 to show ovulation

Question 44

What is oligomenorrhea?

Answer 44

<9 cycles in 12 months

Question 45

What is amenrrhea?

Answer 45

No bleeding for 6 months. Primary = never had a period Secondary = Ceased periods

Question 46

What is menorrhagia?

Answer 46

Heavy bleeding

Question 47

What is dysmenorrhea?

Answer 47

Painful bleeding

Question 48

What happens to the hormone levels at menopause?

Answer 48

When ovarian reserve is depleted and ovulation ceases, progesterone and oestrogen production by the ovary stops. This removes the negative feedback and causes LH and FSH levels to RISE.

Question 49

How can fertility treatment be used to treat prostate cancer?

Answer 49

Use GnRH antagonists to suppress Testosterone production