Catecholamines

Question 1

• Why do the axons of the adrenal medulla extend into the cortex?

Answer 1

To allow for activation

Question 2

• How does the synthesis of catecholamines begin?

Answer 2

Amin acid tyrosine converted to dihydroxyphenylalanine, catalysed by tyrosine hydroxylase (rate limiting step)

Question 3

• What are the sources of epinephrine and norepinephrine?

Answer 3

All the epinephrine comes from the adrenal medulla, norepinephrine also comes from the postganglionic sympathetic neurons

Question 4

• Why is sympathetic tone keeping arterioles constricted to 50% normal diameter important?

Answer 4

Allows one system (sympathetic) to cause both constriction and dilation

Question 5

• How does endocrine stimulation differ from nervous?

Answer 5

Same effect however endocrine stimulation effects last 5 to 10 times longer

Question 6

• What is the sympathetic NS reaction to stress stimulated by?

Answer 6

Preganglionic sympathetic neurons in adrenal medulla release ACh

Question 7

• What is the difference between cholinergic and adrenergic neurons?

Answer 7

Cholinergic secrete Ach, adrenergic secrete NE

Question 8

• How do adrenal neurons work?

Answer 8

Act like sympathetic ganglions, secrete ACh which stimulates secretion of epinephrine

Question 9

• What pathways are involved in signal transduction?

Answer 9

Adenyl cyclase (G protein coupled), phospholipase C, IP3 & DAG and ion channels

Question 10

• Why does the adenyl cyclase pathway exist?

Answer 10

To amplify the signal

Question 11

• What do the second messengers IP3 and DAG, of the phospholipase C pathway activate?

Answer 11

Protein kinase C

Question 12

• What do β1 receptors do?

Answer 12

Increase HR & contractility

Question 13

• What is the difference between α and β2 receptors?

Answer 13

Generally speaking, α receptors are stimulatory (constriction), β2 receptors are inhibitory (dilation)

Question 14

• With regards to energy production, what do catecholamines do?

Answer 14

Increase glycogenolysis and stimulate hormone sensitive lipase to hydrolyse adipose tissue to yield glycerol

Question 15

• What is the difference between epinephrine and NE with regards to blood vessels within muscle?

Answer 15

Epinephrine acts on β2 receptors, causing vasodilation

Norepinephrine acts on α receptors, causing strong vasoconstriction