Catecholamines

Question 1

Label the adrenal gland

Answer 1

Question 2

What is the secretion of the adrenal medulla?

Answer 2

catecholamines:
- epinephrine/adrenaline
- norepinephrine/noradrenaline

Question 3

Describe the synthesis of epinephrine and norepinephrine

Answer 3

Question 4

What are the sources of epinephrine and norepinephrine

Answer 4

Epinephrine - adrenal medulla
Norepinephrine - adrenal medulla + postganglionic sympathetic neurons

Question 5

Describe the sympathetic control of catecholamine secretion

Answer 5

Sympathetic tone keeps arterioles constricted to 50% diameter
Increased sympathetic stimulation: more constriction
Decreased sympathetic stimulation: less constriction

Question 6

Describe the effect of resting catecholamine secretion from adrenal medulla

Answer 6

Sufficient to maintain blood pressure if nervous system lost
Dominant mechanism for maintaining vascular tone

Question 7

Describe the kinetics of catecholamines

Answer 7

Stored in secretory vesicles and released via exocytosis
Circulate freely in blood
Metabolised by liver and kidneys
Short plasma half-life (1-3 mins)
Urinary excretion of unmetabolised catecholamines

Question 8

Describe the effect of catecholamines compared to sympathetic stimulation

Answer 8

Catecholamines have same effect as direct stimulation via sympathetic nerves - but have effect on whole body simultaneously and has a longer lasting effect

Question 9

Describe neurone classification by transmitter

Answer 9

Adrenergic neurones - secrete norepinephrine (post-ganglionic sympathetic neurones)
Cholinergic neurones - secrete acetylcholine (parasympathetic or somatic)

Question 10

Describe the interaction between the SNS and adrenal medulla

Answer 10

Adrenal medulla acts as a sympathetic ganglion
Pre-ganglionic sympathetic neurons carry action potential to adrenal medulla => influx of Ca2+ => exocytosis of catecholamines

Question 11

What are the effect of catecholamines binding to alpha 1 adrenergic receptors?

Answer 11

Vasoconstriction
Pupil dilation
Intestinal relaxation
Pilomotor contraction (erects hairs)
Bladder sphincter contraction

Question 12

What is the effect of catecholamines binding to alpha 2 adrenergic receptors?

Answer 12

sedation and anaesthesia

Question 13

What is the effect of catecholamines binding to beta 1 adrenergic receptors

Answer 13

Increase HR
Increase contractility

Question 14

What is the effect of catecholamine binding to beta 2 receptors

Answer 14

Vasodilation
Bronchodilation
Glycogenolysis
Lipolysis

Question 15

Describe the action of alpha-2 adrenergic receptors in sedation and anaesthesia

Answer 15

Often has re-synaptic position and exerts a negative feedback effect on synaptic signal transmission

Question 16

What are the clinical consequences of SNS activation?

Answer 16

Question 17

Describe the adenylyl cyclase pathway in B-adrenergic receptors

Answer 17

Catecholamine binds to cell surface receptor => activates G protein => stimulated adenylyl cyclase => generates cyclic AMP (cAMP) => activates protein kinase A => phosphorylates protein => biological response

Question 18

Describe the effects of cAMP

Answer 18

Binds to protein kinase A and enters nucleus
binds to CREB (cAMP-response element binding protein) and phosphorylates it => CREB-P
CREB-P binds to CRE and changes gene expression

Question 19

Describe the phospholipase C pathway in alpha adrenergic receptors

Answer 19

Hormone binds cell surface receptor
Activates phospholipase C via G protein
Phospholipid PIP2 broken down to IP3 and DAG
DAG activates protein kinase C which phosphorylates protein => biological response

Question 20

What factors effect the tissue response to SNS activation

Answer 20

Type and density of receptors
Relative concentrations of local catecholamines

Question 21

Give an example of how different adrenergic receptors cause different responses upon sympathetic stimulation

Answer 21

Alpha receptors in intestine => vasoconstriction
Beta 2 receptors in muscle => vasodilation

Question 22

What are the metabolic effects of catecholamines?

Answer 22

Glycogenolysis and gluconeogenesis to increase amount of readily available energy
Stimulates hormone-sensitive lipase => lipolysis

Question 23

What is the clinical relevance of the metabolic effects of catecholamines?

Answer 23

Stressed animals show hyperglycaemia

Question 24

Compare the effects of epinephrine and noreinephrine

Answer 24

Epinephrine:
- greater metabolic effect
- greater effect on B-receptors (cardiac stimulation)
- causes vasodilation via B2 receptors (fight or flight)
Norepinephrine:
- causes vasoconstriction via alpha receptors (shock)