3) HPG Axis

Question 1

What are some examples of hypothalamic releasing hormones?

Answer 1

CRH, TRH, GHRH, somatostatin, gonadotropin releasing hormone, prolactin RH, dopamine

Question 2

What are the features of hypothalamic releasing hormones?

Answer 2

Secretion in pulses tied to biological clock
Act on specific receptors and through secondary messengers
Stimulate release and synthesis of pituitary hormones
Hyperplasia and hypertrophy of target cells

Question 3

Where is the pituitary gland located?

Answer 3

Beneath hypothalamus in sella turcica of sphenoid bone

Question 4

What is the anterior pituitary also known as?

Answer 4

Pars distalis or adenohypophysis

Question 5

What is the posterior pituitary also known as?

Answer 5

Pars nervosa or neurohypophysis

Question 6

How are the hypothalamus and anterior pituitary connected?

Answer 6

Superior hypophyseal artery

Question 7

What does the HPG axis regulate?

Answer 7

Development
Reproduction
Ageing

Question 8

Describe the release of GnRH:

Answer 8

Pulsatile, every 1-3 hours

Travels to pituitary in hypophyseal portal system

Question 9

What affects the intensity of the GnRH stimulus?

Answer 9

Frequency and intensity of release

Question 10

What are the main actions of FSH and LH?

Answer 10

Stimulate sex hormone synthesis and control gamete production

Question 11

Where does LH act in men and what does this do?

Answer 11

Leydig cells to cause production of testosterone

Question 12

What effect does testosterone have on the HPG axis?

Answer 12

Negative feedback on hypothalamus and AP, reducing GnRH and LH + FSH release

Question 13

Where does FSH act in men and what does this do?

Answer 13

Receptors on Sertoli cells on seminiferous tubules

Causes Sertoli cells to grow and secrete spermatogenic substances

Question 14

What is ABP and what is its function?

Answer 14

Androgen binding protein, need testosterone for Sertoli cell function so ABP binds testosterone to keep it in tubules

Question 15

What is the effect of inhibin on HPG axis?

Answer 15

Reduces FSH selectively

Question 16

Describe the release of testosterone:

Answer 16

Circadian rhythm, highest in morning

Affected by environmental stimuli

Question 17

Describe the changes in release of hormones and gonadal steroids in ageing men:

Answer 17

Testosterone falls with LH and FSH rising

Question 18

Where do LH and FSH bind in females?

Answer 18

Theca interna and granulosa cells respectively

Question 19

What is the effect of moderate titres of oestrogen on HPG axis?

Answer 19

Negative feedback (reduced GnRH)

Question 20

What is the effect of high titres of oestrogen on HPG axis?

Answer 20

Positive feedback if no progesterone

Causes LH surge

Question 21

What effect does progesterone have on the HPG axis?

Answer 21

Increases inhibitory effects of moderate oestrogen and prevents positive feedback at high oestrogen

Question 22

How do oestrogen and progesterone affect GnRH release?

Answer 22

Oestrogen reduces GnRH per pulse, progesterone frequency of pulses

Question 23

Where is inhibin released from in females?

Answer 23

Granulosa cells

Question 24

What are the effects of testosterone on the body?

Answer 24

Maintenance of male internal genitalia 
Metabolic effects (anabolic)
Behavioural effects (aggression and sexual activity)