Lecture 3: Reproductive endocrinology

Question 1

What is a steroid hormone?

Answer 1

a steroid hormone is a four ring structure that is derived from cholesterol. Steroid hormones are produced by the gonads and are typically hydrophobic. There are 3 main classes of steroid hormones in reproduction biology:

1. androgens
2. Oestrogens
3. Progestagens

Question 2

Draw its biosynthesis pathway: (clue for rows- Cholesterol and 3 more, cyp17 and 2 more, 4 androgens and 2 oestrogen)

Answer 2

cholesterol, pregenolone, progesterone, aldosterone

17- OH progesterone
Cortisol

Dehydroepi-androsterone,
androsteredione, testosterone, 5a dihydrotestosteone

estrone, estradiol

Question 3

What are the water soluble proteins?

Answer 3

• gonadotrophics, which are LH, FSH and oxytocin and produced by the anterior pituitary gland
• Small peptides, GnRH produced by the hypothalamus

Question 4

What are the 4 androgens made by the testes and explain their purpose?

Answer 4

1. 5a- dihydrotestosterone
2. testosterone
3. androstenedione
4. dehydro-epi-androsterone

Question 5

What are the principle actions of androgen?

Answer 5

• for secondary sex characteristics of a male (deep voice, body hair, penile growth)
• supports the process of spermatogenesis
• promotes protein anabolism, cell growth and ossification
• Testosterone contributes to the regulation of the secretion of gonadotrophin

Question 6

What are the 3 oestrogens made by the granulosa cells of a tertiary follicle and also adipose tissue?

Answer 6

1. Oestradiol (corpus luteum produces a little)
2. oestrone
3. oestriol (produced by placenta)

Question 7

What are the normal serum levels of oestrogen in females?

Answer 7

200-1100 pmol/ L

Question 8

What are the principle actions of oestrogen?

Answer 8

• for sex characteristics of females
• promote endometrial growth during the proliferative phase
• prepares the endometrium for progesterone action
• stimulates activity and growth of mammary glands
• stimulates calcification, which is why post menopausal women have higher risk of osteoporosis
• regulates the secretion of gonadotrophines

Question 9

Explain what the role of progesterone is?

Answer 9

• produced by corpus luteum and the placenta
• prepares the uterus for implantation and helps maintain pregnancy
• its the main pregnancy associated hormone

Question 10

What are the serum levels of progesterone during menstrual cycle?

Answer 10

• preovulatory phase= < 4 nmol/ L
• LH surge= < 4-10 nmol/L
• Post ovulation (around day 22)= 25-120 nmol/L

Question 11

What are the principle actions of progestagen?

Answer 11

• reduce mitotic proliferation of the endometrium
• increase water content and secretions of endometrium
• promotes the growth of the uterus during pregnancy
• inhibits cervical mucus secretion (remember that oestrogen STIMULATES this!)
• stimulates growth of mammary glands but suppresses milk production

Question 12

What are the two type of hormone receptors?

Answer 12

1. cell surface (for gonadotrophins LH and FSH) —> mediated by cAMP, intracellular calcium and PIP proteins
2. intracellular (for steroid hormones) —> mediated by receptor hormone complexes

Question 13

What does the hypothalamus do in hormone regulation?

Answer 13

• its that main homeostatic regulator for the body (repoduction, stress, hunger, body temperature)
• It receives sensory imput and translate it into neural and hormone information to be relayed back. In terms of reproduction, paricellular cells in the hypothalamus are responsible for sending hormones into the vascular route and to the anterior pituitary.
• it is influenced by the pulsatile release of the hypothalamic hormones

Question 14

What does the anterior pituitary do?

Answer 14

• Produces FSH, LH and GH

- linked to the hypothalamus via vascular route and hypophyseal portal system

Question 15

What are the two types of neurons present in the posterior pituitary?

Answer 15

• regular- releases neurotransmitters

- neurosecretory- synthesise, carry and release neurosecretory peptide hormones

Question 16

What does the posterior pituitary do?

Answer 16

store peptide hormones (such as oxytocin and antidiuretic hormone) in secretory vesicles and await a nerve impulse to elicit exocytosis and release of hormones into the blood

Question 17

What are the roles fo the peptide hormones oxytocin and ADH?

Answer 17

• oxytocin: milk ejection and contraction of uterus for childbirth
• ADH: kidney function- water retension

Question 18

Describe the pulsatile release of GnRH

Answer 18

• every 60-90 minutes, there is a release of GnRH from the hypothalamus.
• This pulsatile release is important to prevent desensitisation of its receptor.
• It is influences by oestradiol, neural influences
• endorphins
• and gonadotrophins (that are heterodimers)

Question 19

Why are GnRH analogues important?

Answer 19

sometimes, there are people who suffer from diseases that affect their homeostatic regulator. Examples include: endometriosis, fibroids, breast cancers, menorrhagia (low ostradiol)

Therefore, it is important that the administration of GnRH analogues is not continuous over a long period of time. It needs to be in a pulsative regime. Otherwise there will be an oversecretion of the gonadotrophin hormones LH and FSH and that can lead to desensitisation of the GnRH receptors (i.e. receptor saturation).