HPG Axis

Question 1

HPG Axis diagram

Answer 1

Question 2

Hypothalamus to Pituitary
structures

Answer 2

Question 3

General Kisspeptin (KISS1/Kiss1) role

what was it also known as?

Answer 3

metastin

role: gatekeeper of puberty

Controls synthesis and secretion of GnRH in GnRH neurons

Upstream of GnRH

Question 4

GNRH neurones are expressed in which two regions?

Answer 4

• Arcuate Nucleus
• Medial preoptic nucleus

Question 5

GNRH that is synthesised and secreted move through the what?
to get to the anterior pituitary

Answer 5

The hypophyseal portal system

Question 6

Where is Kisspeptin expressed?

Two spots in something*

Answer 6

In the hypothalamus:
- Arcuate Nucleus (ARC)
- Anterventral Periventricular Nucleus (AVPV)

Question 7

Kisspeptin receptor (GPR54/KISS1R)

Where is it expressed?

Answer 7

Expressed on GnRH neurons.

Question 8

Inactivating mutations of KISS1R and Kisspeptin = ?

Answer 8

failure to undergo spontaneous puberty.

Question 9

Activating KISS1R mutations = ?

Answer 9

Can lead to precocious puberty

Question 10

Kisspepetin neurons and GnRH neurons diagram interaction

Answer 10

Kisspeptin neurons send projections to GnRH neurons, and binding to KISS1R expressed on GnRH neurons.

Question 11

A bolus of Kisspeptin correlates with a…

Answer 11

peak of LH secretion

Question 12

GnRH is secreted in pulses from hypothalamus every…

Answer 12

30-120min

Question 13

Slow frequency GnRH pulse favours..

Answer 13

FSHb transcription and FSH release,

Question 14

Rapid GnrH pulse frequency favours..

Answer 14

LHb transcription and LH release

Question 15

Continuous pulsatile release results in..

Answer 15

cessation of response

Question 16

What is generating the GnRH pulse ?

Answer 16

A sub-population of Arcuate Nucleus Kisspeptin Neurons (ARNKISS)

Studies showed:
ARNKISS were all found to exhibit intermittent periods of synchronized electrical activity which had a near perfect correlation with pulsatile LH secretion.

Inhibition of ARNKISS in the mid-caudal region of the arcuate nucleus suppressed pulsatile LH secretion

Question 17

Gonadotrophin hormones: LH, FSH (and hCG)

Features and structure as themselves

Answer 17

• Glycoprotein hormones
• Heterodimeric
• Pulsatile (due to B units)

Question 18

Follicle-stimulating hormone (via FSHR) function:

Testis?

Answer 18

Regulation of Sertoli cell metabolism

Question 19

Follicle-stimulating hormone (via FSHR) function:

Testis?

Answer 19

Regulation of Sertoli cell metabolism

Question 20

Follicle-stimulating hormone (via FSHR) function:

Ovary?

Answer 20

• follicular maturation
• granulosa cell estrogen synthesis

Question 21

Luteinising-stimulating hormone (via LHR) function:

Testis?

Answer 21

Stimulation of Leydig cell androgen synthesis

Question 22

Luteinising-stimulating hormone (via LHR) function:

Ovary?

Answer 22

• theca cell androgen synthesis
• ovulation
• progesterone production of corpus luteum

Question 23

General function of gonadotrophins

Answer 23

Supports germ cell growth, development and maturation

to produce..

oocyte and sperm, competent for fertilisation

Question 24

Leydig cells?

LHR or FSH expression and why is this then crucial?

Answer 24

LHR expression
->
Androstenedione, DHEA, Testosterone production

Question 25

Sertoli cells? LHR or FSH expression and why is this then crucial?

Answer 25

FSHR expression -> Sertoli cell metabolism (important for spematogenesis) + Testosterone --> dihydrotestosterone

Question 26

Theca cells? LHR or FSH expression and why is this then crucial?

Answer 26

LHR expression ---> Testosterone and Androstenedione

Question 27

Granulosa cells? LHR or FSH expression and why is this then crucial?

Answer 27

FSHR expression --> through aromatase takes Testosterone and Androstenedione and forms Oestradiol and Oestrone

Question 28

Corpus luteum? LHR or FSH expression and why is this then crucial?

Answer 28

LHR (and FSHR) expression ---> Progesterone (and oestrogens)

Question 29

Inhibin Features and structure as themselves

Answer 29

Peptide hormones Heterodimers 2 isoforms of inhibin: A and B.

Question 30

Inhibin role

Answer 30

inhibits FSH secretion via direct negative feedback to anterior pituitary

Question 31

In males which inhibin is invovled?

Answer 31

Inhibin B

Question 32

In females which inhibin is invovled?

Answer 32

Inhibin expression is cyclical depending on the phase of the menstrual cycle. Can switch from inhibin B in the follicular phase to Inhibin A in the luteal phase.

Question 33

Summary of HPG axis in depth

Answer 33