nervous and hormonal control of vascular tone

Question 1

What is involved in intrinsic control of blood vessels

Answer 1

• myogenic response
  -paracrine & autocrine
• physical factors -temperature & shear pressure
  -regulates blood flow to organs and tissues
  -vasodilators-inflammation , local metabolites ( nitric oxide, prostaglandin, endothelin, potassium and hydrogen ions )

Question 2

What is involved in extrinsic control of blood vessels

Answer 2

• parasympathetic , sympathetic and sensory vasodilator nerves
  -sympathetic vasoconstrictor nerves
  -brain Function selectivity alters blood flow to organs according to need

In the nerves
Vasoconstrictor- noradrenaline
Vasodilators - Ach, nitric oxide

In hormones
Vasoconstrictor- adrenaline, angiotensin II
Vasodilator- atrial natriuretic peptide (ANP)

Question 3

Steps for constriction in sympathetic vasoconstrictor nerves

Answer 3

• action potential moves down axon and arrive at varicosity
• depolarisation at the varicosity activating voltage gated calcium channels
• entrance of calcium causes release neurotransmitters- mainly noradrenaline
• noradrenaline diffuses to vascular smooth muscle cells binds to mainly alpha one , some alpha two and beta two

-noradrenaline is taken up again and recycled or broken down

Question 4

What is the release of noradrenaline modulated by

Answer 4

Angiotensin II acting on AT1 receptor

Question 5

what is varicosity

Answer 5

veins that are bulging and swollen

Question 6

what happens when noradrenaline is released in the varicosity detail

Answer 6

noradrenaline is released which causes vasodilation via alpha 1 receptors

alpha 2 receptors provide negative feedback so that the noradrenaline doesnt continuously lead to constriction

Question 7

what is the rostal ventrolateral medulla controlled by and its role

Answer 7

caudal ventrolateral medulla and hypothalamus and provides central control of blood flow and blood pressure

Question 8

how is the sympathetic nerve activity described as

Answer 8

tonic, 1 action potential per second

Question 9

in sympathetic vasoconstrictor nerves what does noradrenaline activate and cause

Answer 9

activates alpha 1 adrenoreceptors on vascular smooth muscle cells causing vasoconstriction

Question 10

main roles of sympathetic vasoconstrictor nerves

Answer 10

-distinct sympathetic pathways ( switching on vasoconstriction in some vessels )

-control resistance arterioles (produces vascular tone allows vasodilation or vasoconstriction , maintains arterial blood pressure and blood flow to brain myocardium

-precapillary vasoconstriction ( downstream capillary pressure drop so increased absorption of interstitial fluid into blood plasma to maintain blood volume)

-control venous blood volume ( venoconstriction leads to decreased venous blood volume increasing venous return , increases stroke volume via starlings law

Question 11

when does vasodilation usually occur

Answer 11

when vascular tone produced by sympathetic vasoconstrictor nerves is inhibited

Question 12

are specific vasodilator nerves sympathetic or parasympathetic

Answer 12

parasympathetic

Question 13

in vasodilator nerves what are blood vessels innervated by

Answer 13

parasympathetic cholingeric fibres , they release acetylcholine which binds to muscarinic receptors on the smooth muscle or endothelium

Question 14

example of parasympathetic vasodilators

Answer 14

-salivary glands- release ach and VIP

-pancreas and intestinal mucosa - release VIP , both need high blood flow to maintain fluid secretion.

male gentalia - erectile tissue , release nitric oxide by sympathetic nerves causes production of cGMP which leads to vasodilation

Question 15

examples of sympathetic vasodilators

Answer 15

-skin -sudomotor fibres, release Ach , VIP causing vasodilation via nitric oxide associated with sweating

Question 16

what does sympathetic activity vasoconstriction

Answer 16

-reduces blood flow , limit sweat production and limit cooling

Question 17

what is the lewis triple response

Answer 17

inflammation
-redness caused by capillary vasodilation

-flare-redness in surrounding area due to arteriolar dilation mediated by axon reflex

-wheal- exudation of extracellular fluid from capillaries and venules

Question 18

hormones involved in vasoconstriction

Answer 18

-adrenaline
-angiotensin II
-vasopressin - ADH

Question 19

hormone involved in vasodilation

Answer 19

-ANP - atrial natriuretic peptide

Question 20

where is adrenaline released from and when

Answer 20

adrenal medulla via action of acetylcholine on nicotinic receptors
during
-exercise
-flight-fight-fear response
-hypotension
-hypoglycaemia

Question 21

main role of adrenaline (epinephrine)

Answer 21

-glucose mobilisation

-stimulation of heart rate & contractility during normal exercise

-vasodilation of coronary and skeletal muscle arteries

Question 22

action of noradrenaline on resistance vessels

Answer 22

-activate alpha 1 Gq
-leads to phospholipase c
-leads to PIP2 converting to IP3 and DAG
-calcium ions are released
-smooth msucle contraction

Question 23

action of adrenaline on resistance vessels

Answer 23

-activates beta 1 and beta 2 Gs
-leads to adenylate cyclase
-converts ATP to cAMP
-leads to beta 1 heart contraction
-beta 2 smooth muscle relaxation vasodilation

Question 24

what does adrenaline have a higher affinity for

Answer 24

higher affinity for beta over alpha , mainly acts at beta 2 to dilate vessels

Question 25

what does noradrenaline have a higher affinity for

Answer 25

higher affinity for alpha, mainly acts at alpha 1 to constrict vessels

Question 26

role of beta 1 on heart

Answer 26

increases rate and force of contraction

Question 27

role of alpha 2

Answer 27

inhibits adenylate cyclase , reduces calcium ions , inhibits release of noradrenaline from varicosity

Question 28

steps in renin angiotensin aldosterone system (RAAS)

Answer 28

-low sodium load , detected at macula densa
-decreased pressure at juxtagomerular cells
-leads to renal sympathetic activity
-renin released
-conversion of angiotensinogen to angiotensin I
-occurs in lung vascular endothelium
-angiotensin 2 is produced from angiotensin 1
-aldosterone released
-central effects eg thirst
-vasoconstriction raises TPR
-release of vasopressin (ADH)
-Aldosterone leads to renal sodium chloride and water retention -raised blood volume

Question 29

how are vasopressin stimulated to be released

Answer 29

-dehydration/ haemorrhage NTS inhibition is switched off and CVLM stimulates vasopressin

Question 30

when there is an increase in osmolarity what does this lead to

Answer 30

-vasopressin synthesised in hypothalamus
-released from vesicles in posterior of pituitary gland
-leads to insertion of water aquaporin channels into apical membrane of renal collecting tubule
-collecting duct epithelial cells allowing water to move out of the nephron and back into the blood stream
-reabsorption of fluid by kidney and vasoconstriction both maintain blood pressure

Question 31

what is ANP released and secreted by

Answer 31

-released by atrial myocytes

-secreted by increased filling pressures which stimulate stretch receptors

Question 32

where does ANP act

Answer 32

acts at ANP receptors on vascular smooth muscle cells increasing cGMP pathway (like nitric oxide)

Question 33

what does systemic vasodilation oppose

Answer 33

action of noradrenaline, RAAS, ADH