regulation of blood flow

Question 1

why do organs need to regulate their blood flow (4)

Answer 1

to match blood supply to metabolic rate; to allow for efficient delivery of nutrients/removal of waste; increase/decrease heat loss; ensure blood flow to vital organs is maintained in the case of major haemorrhage

Question 2

how is blood flow controlled (vascular level)

Answer 2

change in vascular tone

Question 3

structure of non-striated vascular smooth muscle

Answer 3

single nucleus; membrane has Caveolae (similar to t tubules); dense bodies of a-actin (origin of actin + myosin filaments, similar to sarcomere); unorganised

Question 4

what extrinsic factors affect vascular tone

Answer 4

circulating hormones; autonomic stimulation

Question 5

what is the ion most important in sm contraction

Answer 5

Ca2+; intracellular levels govern contraction; L-type Ca2+ channels are found on vascular smooth muscle -> CCBs can affect contraction

Question 6

what needs to occur to vsm myosin in order for it to form cross bridges with actin

Answer 6

phosphorylation of the light chain

Question 7

light chain phosphorylation pathway

Answer 7

intracellular Ca2+ levels increase -> binds to calmodulin-> Ca2+-calmodulin activates myosin light chain kinase -> MLCK phosphorylates myosin - allows cross bridges to form

Question 8

what happens to Ca2+ post contraction

Answer 8

binds with Calsequestrin in the sarcoplasmic reticulum and is stored there; or is transported out of the cell via Na+/Ca2+ exchanger etc.

Question 9

an upregulation of what 2 molecules causes VSM to relax?

Answer 9

c-AMP (inhibits MLCK) and c-GMP (activates myosin phosphatase)

Question 10

resistance equation (ohms law)

Answer 10

R = flow (V)/pressure (I)

Question 11

what is autoregulation (blood flow)

Answer 11

intrinsic ability of an organ to maintain constant blood flow changes in perfusion pressure in the absence of external neural/hormonal stimuli i.e. constant flow is maintained despite changes in the perfusion pressure

Question 12

what is the myogenic theory of autoreg

Answer 12

stretch receptors in the bv walls are activated -> influx of Ca2+ -> sm contraction -> decreased radius -> flow remains the same despite greater transient blood flow; bayliss myogenic response

Question 13

what is the metabolic theory of autoreg

Answer 13

decrease in blood flow leads to an increase in waste product accumulation -> waste products activate receptors which cause vasodilation (Ca2+ influx etc.) -> blood flow increased back to desired rate

Question 14

examples of vasodilatory metabolites (9)

Answer 14

↓ PO2; ↓pH; ↑ pCO2; ↑ temp; ↑K+; ↑ lactate; ↑osmolality; ↑histamine; ↑ products of ATP breakdown (adenosine, inorganic phosphate)

Question 15

what is the effect of vasodilatory (waste) metabolites on the lungs

Answer 15

vasoconstriction

Question 16

how does adenosine cause muscle relaxation

Answer 16

binds to AT2 receptors -> activates c-AMP -> inhibits MLCK binding -> vasodilation

Question 17

what does eNOS activation lead to

Answer 17

brachial artery vasodilation

Question 18

what is endothelin

Answer 18

a powerful vasoconstrictor; there are 3 isoforms coded for by different genes; produced as pro-hormone big endothelians, converted by endothelian converting enzyme

Question 19

what are prostoglandins synthesised by?

Answer 19

vascular endothelium from arachidonic acid

Question 20

what types of prostoglandins are vasoconstrictors and which are vasodilators

Answer 20

VC - F series, serotonin;
VD - E, I series, PGE2/4

Question 21

what can be given to raynauds patients to ease symptoms

Answer 21

prostacyclin (PGI2) - vasodiliator

Question 22

what hormones are vasodilators (3)

Answer 22

kinins (bradykinin, lysylbradykinin); adrenomedullin; atrial natiuretic peptide (ANP)

Question 23

kinin precursors

Answer 23

kininogens

Question 24

how do kinins work

Answer 24

act on B2 receptors on endothelial cells, causing a release of NO in endothelial cells

Question 25

role of kinins in clotting

Answer 25

plasma kallikrenin acts on HMW kininogen to make bradykinin

Question 26

action of adrenomedullin

Answer 26

a depressor polypeptide that inhibits alodsterone; releases NO and increases c-AMP in cells; exerts action through calcitonin receptor like recptor and RAMP2/3

Question 27

action of ANP & BNP (3)

Answer 27

secreted from the heart (ANP from atria and BNP from ventricles); lowers BP by antagonising various vasocontrictors - released when the heart is stretched; inhibits renin secretion;

Question 28

circulating vasoconstrictors (4)

Answer 28

angiotensin/renin; noradrenaline; urotensin II; vasopressin

Question 29

pre ganglionic NT (ANS)

Answer 29

Ach

Question 30

post ganglionic sympathetic NT

Answer 30

NA

Question 31

post ganglionic parasympathetic NT

Answer 31

Ach

Question 32

what does NA exist alongside in NT vesicles

Answer 32

ATP; neuropeptide Y

Question 33

what is the neural mechanism of blood flow regulation

Answer 33

regulation of BF that depends on cardiovascular centres in the medulla oblongata

Question 34

what does baroreceptor firing cause (neural mech of BF)

Answer 34

reflex via the medullary cardiovascular centre - decreased symp to heart, arterioles, veins; increase parasymp to heart

Question 35

RAAS pathway

Answer 35

renin –> angiotensin – (liver)–> angiotensin I – (ACE) –> angiotensin II –> vasoconstriction (↓GFR, ↓urine output); adrenal gland stimulaton –> aldosterone –> ↑Na+ retention, ↑ water retention –> ↑ BP