physiology of the HPA axis (see notes!)

Question 1

what 2 hormones are released by the posterior pituitary gland

Answer 1

1. anti-diuretic hormone (ADH)
2. oxytocin

Question 2

is the posterior pituitary gland an endocrine gland

Answer 2

no, not a true endocrine gland -> doesn’t produce its own hormones, it just stores and releases them

Question 3

what kind of connection does the hypothalamus and posterior pit gland have

Answer 3

neural - the posterior pituitary is and extension of the hypothalamus and they communicate via nerves

Question 4

what area of the hypothalamus is responsible for oxytocin release

Answer 4

paraventricular nuclues

Question 5

what area of the hypothal is responsible for ADH release

Answer 5

supraoptic nucleus

Question 6

what is the “neck” of the pituitary gland called

Answer 6

infundibulum

Question 7

what kind of organ is the anterior pituitary gland

Answer 7

endocrine organ -> hypothal sends hormonal signals via the hypophyseal portal system to the pituitary gland

Question 8

what 5 hormones does the hypothalamus release

Answer 8

1. thyroid releasing hormone (TRH)
2. prolactin releasing hormone (PRH)
3. gonadotropin releasing hormone (GnRH)
4. corticotropin releasing hormone (CRH)
5. growth hormone releasing hormone (GHRH)

Question 9

6 hormones released by the anterior pituitary gland

Answer 9

1. Thyroid stimulating hormone (TSH)
2. prolactin
3. FSH
4. LH
5. adrenocorticotropin hormone (ACTH)
6. growth hormone (GH)

Question 10

HP-gonadal axis

Answer 10

GnRH -> LH -> ovaries/testes -> stimulates oestrogen/testosterone synthesis

Question 11

HP-Thyroid axis

Answer 11

TRH -> TSH -> thyroid gland -> stimulate thyroxine synthesis

Question 12

HP-adrenal axis

Answer 12

CRH -> ACTH -> adrenal cortex -> stimulates corticosteroid synthesis

Question 13

what is the role of the HPA axis

Answer 13

to modulate stress responses leading to the release of cortisol

Question 14

what kind of cells secrete CRH

Answer 14

small bodied neurones

Question 15

what area of the hypothalamus is CRH secreted from

Answer 15

paraventricular nucleus

Question 16

what is the short -ve feedback loop in the HPA axis

Answer 16

CRH-> anterior pit gland -> ACTH release -> ACTH inhibitsCRH release

Question 17

what cells are responsible for ACTH release

Answer 17

corticotrophs

Question 18

ACTH release cellular mechanism (draw out)

Answer 18

CRH binds to CRHR -> g protein coupled receptor causes ATP -> cAMP -> activates PKA -> PKA binds to Ca2+ receptors -> Ca2+ influx -> causes exocytosis of ACTH vesicles

Question 19

HPA axis long -ve feedback loop

Answer 19

CRH -> ant pituitary gland -> ACTH release -> adrenal glands -> cortisol synthesis -> cotrisol downregulates both CRH and ACTH release

Question 20

ACTH action on adrenal gland cells mechanism (intracellularly)

Answer 20

ACTH binds to melanocortin-2 receptor -> g coupled protein receptor causes ATP -> cAMP -> activates PKA -> increases activity of P450scc and increases enzyme synthesis

Question 21

when is cortisol secreted (2)

Answer 21

1. throughout the day in a pulsitile manner
2. in response to stress

Question 22

how does cortisol prepare the body for flight or flight response (2)

Answer 22

1. provided adequate nutrients for ATP synthesis
2. glucose sparing for the brain

Question 23

what are the 4 zones to the adrenal gland and what does each produce

Answer 23

1. medulla -> adrenaline, NA
   cortex:
2. zona Glomerulosa -> aldosterone (RAAS system)
3. zona fasiculata -> glucocorticoids (e.g. cortisol), allows energy to be provided to vital tissues
4. zona reticularis -> androstenedione -> androgens (sex hormones)

Question 24

how do hormones work (3)

Answer 24

1. enters cell and binds to the receptor in the cytoplasm
2. hormone-receptor complex enter nucleus
3. acts as a transcription factor can causes transcription/inhibition of certain genes from the DNA

Question 25

why must glucose be spared for the brain in stress response

Answer 25

the brain will pretty much only metabolise glucose and so it must be reserved for the brain as other tissues can use other metabolites e.g. fatty acids

Question 26

what is the action of cortisol on adipose tissue, the liver and extra-hepatic tissue (e.g. skeletal muscle)

Answer 26

1. adipose tissue - increased lipolysis => more free fatty acids in the blood that can be metabolised
2. liver - gluconeogenesis and glycogenolysis => increased glucose in the blood
3. extra-hepatic tissue - decreased protein synthesis, increased proteolysis => more free amino acids in the blood, these can be used for ATP release instead of glucose; increased fat oxidation (for ATP release); decreased glucose metabolism (more glucose for brain) -> i.e. shifting the metabolism of these tissues away from glucose

Question 27

what is the preferred metabolite for skeletal muscle in stress

Answer 27

fat