Week 2 - HPG axis

Question 1

What is the adrenohypophysis/pars distalis?

Answer 1

-Anterior portion of pituitary

Question 2

What is the neurohypophysis/pars nervosa?

Answer 2

-Posterior portion of pituitary

Question 3

Which side of the pituitary stains darker?

Answer 3

-Anterior

Question 4

What type of tissue composes the posterior pituitary?

Answer 4

-Nervous tissue

Question 5

What is the function of the posterior pituitary?

Answer 5

-It is a neuro-secretory gland producing ADH and oxytocin

Question 6

What is the median eminence?

Answer 6

-Upper portion of neural stalk which projects into hypothalmus

Question 7

What tissue is the anterior pituitary composed of?

Answer 7

-Glandular cells

Question 8

How is the posterior pituitary connected to the hypothalamus?

Answer 8

-Hypothalamic neurones

Question 9

How is the anterior pituitary connected to the hypothalmus?

Answer 9

-Superior hypophyseal artery

Question 10

What 6 hormones are produced from the anterior pituitary?

Answer 10

• TSH
• GH
• ACTH
• Prolactin
• FSH
• LH

Question 11

How does the hypothalmus regulate the anterior pituitary?

Answer 11

-Releases Hypothalamic Releasing Hormones into the hypothalamic pituitary portal which act on specific trophic cells in the anterior pituitary to control secretion of their hormones

Question 12

How is the whole hypothalamic-pituitary-gonadal axis controlled?

Answer 12

-Negative feedback from trophic hormones

Question 13

How are hypothalamic releasing hormones characterisically secreted?

Answer 13

-Pulsatile release synchronised by external signals eg light/dark

Question 14

How do hypothalamic releasing hormones act on target cells?

Answer 14

-Bind to specific membrane receptors and transduce signals via secondary messangers which stimulate the release f stored pituitary hormones and synthesis of new ones

Question 15

Name the hypothalamic releasing hormones and their corresponding effects

Answer 15

• Corticotrophin releasing hormone -> Stimulates ACTH secretion
• Thyrotropin releasing hormone -> Stimulates TSH and prolactin secretion
• Growth hormone releasing hormone -> Stimulates GH secretion
• Somatostatin -> inhibits GH secretion
• Gonadotropin releasing hormone -> Stimulates FSH/LH secretion
• Prolactin releasing hormone -> stimulates PRL secretion
• Dopamine -> inhibits prolactin secretion

Question 16

How is GnRH characteristically released?

Answer 16

-Pulsatile -> once an hour

Question 17

What type of receptors does GnRH stimulate on gonadotrophic cells of pituitary?

Answer 17

-GPCR

Question 18

How do FSH and LH exert their effects on the gonads?

Answer 18

-Bind to GsPCR -> Gas -> Increase Adenylate Cyclase activity -> Increased cAMP -> Activation of PKA

Question 19

Which cells specifically do FSH and LH act on?

Answer 19

• Ovarian granulosa cells and theca interna in females

- FSH -> Sertoli cells and LH ->leydig cells in males

Question 20

What are the two major effects of FSH and LH regarding reproduction?

Answer 20

• Stimulate sex steroid synthesis

- Control gamete production

Question 21

What effect does testosterone have on GnRH, FSH/LH?

Answer 21

Negative feeback on the hypothalmus and pituitary causes:

• Reduces GnRH secretion
• Reduced FSH/LH

Question 22

What effect does high levels of oestrogen alone have on GnRH, FSH/LH?

Answer 22

Positive feeback on the hypothalmus and pituitary causes:
-Promotes GnRH secretion
-Promotes FSH/LH secretion
(LH surge)

Question 23

What effect do moderate levels of oestrogen have on GnRH, FSH/LH?

Answer 23

Negative feeback on the hypothalmus and pituitary causes:

• Reduced GnRH secretion
• Reduced FSH/LH secretion

Question 24

How does Progesterone influence the effect which oestrogen has on GnRH? What effect does this have on LH?

Answer 24

• Increases the inhibitory effects of moderate oestrogen -> Minimal FSH/LH production
• Prevents positive feedback of high oestrogen -> no LH surge

Question 25

What is different between the way which oestrogen and progesterone reduce GnRH secretion?

Answer 25

• Oestrogen reduced the amplitude of GnRH pulse

- Progesterone reduced the frequency of GnRH pulse

Question 26

What is the function of inhibin?

Answer 26

-Selectively reduces FSH secretion

Question 27

From where is inhibin produced?

Answer 27

-Gonads

Question 28

Which cells in the male produce testosterone?

Answer 28

-Leydig cells

Question 29

Which cells in the male produces androgen binding globulin and inhibin?

Answer 29

-Sertoli cells

Question 30

What is androgen binding globulin?

Answer 30

-A protein which binds to testosterone and keeps in within the seminiferous tubules

Question 31

What is the function of inhibin in males?

Answer 31

-Supports spermatogenesis and inhibits the production of FSH, LH and GnRH

Question 32

What are the functions of LH in the male?

Answer 32

• Promote testosterone secretion

- Promote spermatogenesis

Question 33

What happens, with regards to controlling the system,if testosterone reaches a high level in the male? What is the advantage of this

Answer 33

• Negative feedback on hypothalmus and pituitary causing decreased GnRH, LH and FSH which causing a reduction in testosterone secretion ->returns to normal
• Produces a constant level of testosterone and spermatogenesis

Question 34

What happens if spermatogenesis speeds up?

Answer 34

-more inhibin secreted -> reduces FSH secretion -> returns to normal

Question 35

In what type of rhythm is testosterone produced?

Answer 35

-Long term testosterone levels are constant but is under circadian rhythm so is highest in the morning (also effected by environmental stimuli)

Question 36

What drives secondary sexual characteristics in male puberty?

Answer 36

-Testosterone

Question 37

What is the function of inhibin in females?

Answer 37

• Inhibition of activin which stimulates GnRH

- Selective inhibition of FSH allowing LH surge

Question 38

How is the pituitary gland connected to the hypothalamus?

Answer 38

-Stalk containing nerve fibres and blood vessels