2.1 hypothalamic-pituitary-gonadal axis: lecture

Question 1

what do the output of the hypothalamus-pituitary unit regulate the function of? (axis)

Answer 1

thyroid (hypothalamic-pituitary-thyroid) - HPT
adrenal (hypothalamic-pituitary-adrenal) - HPA
reproductive glands - HPG

Question 2

what else does the output of the hypothalamus-pituitary unit regulate (non-axis)?

Answer 2

somatic growth
lactation
milk secretion
water metabolism

Question 3

how is hypothalamic releasing hormones secreted? controlled by?

Answer 3

in pulse tied to internal biological clock

synchronised external signals e.g. light

Question 4

where do hypothalamic releasing hormones act?

Answer 4

on specific membrane receptors

Question 5

how do hypothalamic releasing hormones transduce signals?

Answer 5

via second messengers e.g. GPCR (Gs) - G alpha s

Question 6

what does hypothalamic releasing hormone stimulate?

Answer 6

release of stored pituitary hormones

synthesis of pituitary hormones

Question 7

how does hypothalamic releasing hormone affect target cells?

Answer 7

stimulate hyperplasia and hypertrophy of target cells

Question 8

how is hypothalamic releasing hormone regulated?

Answer 8

regulates its own receptor

Question 9

what does corticotropin releasing hormone (CRH)’s effect on pituitary?

Answer 9

stimulates ACTH secretion

Question 10

what is thyrotropin releasing hormone (TRH)’s effect on pituitary?

Answer 10

stimulates TSH and prolactin secretion

Question 11

what is growth hormone releasing hormone (GHRH)’s effect on pituitary?

Answer 11

stimulates GH secretion

Question 12

what is somatostatin’s effect on pituitary?

Answer 12

inhibits GH (& other hormone) secretion

Question 13

what is gonadotropin releasing hormone (GnRH)’s effect on pituitary?

Answer 13

stimulates LH and FSH secretion

Question 14

what is prolactin releasing hormone (PRH)’s effect on pituitary?

Answer 14

stimulates PRL secretion

Question 15

what is prolactin inhibiting hormone also known as?

Answer 15

dopamine

Question 16

what is the effect of prolactin inhibiting hormone (PLH) on pituitary?

Answer 16

inhibits PRL secretion

Question 17

where is the pituitary gland located?

Answer 17

immediately beneath the hypothalamus
in a depression of the base of the skull called the pituitary fossa (Turkish saddle / sella turcica)
sits at the base of brain and is roughly size and shape of a bean

Question 18

what is the pituitary gland also known as?

Answer 18

hypophysis

Question 19

what is the anterior pituitary gland also known as?

Answer 19

pars distalis

adenohypophysis

Question 20

what is the posterior pituitary gland also known as?

Answer 20

pars nervosa

Question 21

how is the anterior pituitary gland connected to the hypothalamus?

Answer 21

by the superior hypophyseal artery

Question 22

what is the anterior pituitary gland?

Answer 22

an amalgam of hormone producing glandular cells

NOT nervous tissue

Question 23

which hormones are produced by the anterior pituitary?

Answer 23

6 peptide hormones:
prolactin
growth hormone (GH)
thyroid stimulating hormone (TSH)
adrenocorticotropic hormone (ACTH)
follicle stimulating hormone (FSH)
leutinising hormone (LH)

Question 24

which are the most significant hormones in reproduction from the anterior pituitary gland?

Answer 24

FSH
LH
prolactin

Question 25

what does the HPG axis comprise of? (interactions)

Answer 25

the interaction between hypothalamus, pituitary gland and the gonads

Question 26

what does the HPG axis work together to regulate?

Answer 26

development
reproduction
ageing and many other body processes

Question 27

what does the HPG axis regulation rely upon?

Answer 27

a number of complex negative feedback loops, which when lost results in disease

Question 28

describe the organs involved in the HPG axis

Answer 28

hypothalamus –> anterior pituitary –> gonads –> reproductive tract

Question 29

what does a major share of the control of sexual functions in both male and female begin with?

Answer 29

secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus

Question 30

what does GnRH do?

Answer 30

stimulate anterior pituitary gonadatrophs to secrete 2 gonadotropic hormones: LH + FSH
(little / no FSH, LH without GnRH)
5-10% anterior pituitary cells = gonadatrophs

Question 31

what is GnRH?

Answer 31

10 amino acid peptide

Question 32

how is GnRH released?

Answer 32

pulsatile

every 1-3 hours, lasting 5-25 mins

Question 33

where does GnRH travel to?

Answer 33

anterior lobe of pituitary in hypophyseal portal systen

Question 34

what is intensity of GnRH stimulus affected by?

Answer 34

frequency of release (how often)

intensity of release (how strong)

Question 35

what does GnRH control?

Answer 35

synthesis and secretion of FSH and LH by gonadotroph cells in AP

Question 36

what controls the gonadotroph synthesis (hypothalamus) and release (AP)?

Answer 36

under positive and negative feedback by gonadal steroids (act on repro tract) and gonadal peptides

Question 37

how do gonadal hormones decrease gonadaotrophin release?

Answer 37

by decreasing GnRH release from hypothalamus and by affecting ability of GnRH to stimulate gonadotrophin secretion from anterior pituitary

Question 38

how do gonadal hormones decrease gonadotrophin release?

Answer 38

by decreasing GnRH release from hypothalamus
and by affecting ability of GnRH to stimulate gonadotrophin secretion from AP
(neg feedback on hypothalamus and AP)