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Physiology > Local regulation of blood flow > Flashcards

Local regulation of blood flow Flashcards

1
Q

what are the physical determinants of blood flow within the vascular system?

A

viscosity of blood
pressure difference
vessel radius
length of vessel

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2
Q

what is the most important factor in local regulation of blood flow?

A

vessel radius

in the equation radius is raised to the power of 4

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3
Q

what determines vessel radius?

A

vascular smooth muscle tone

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4
Q

a change in vascular tone of which vessel type is most influential in regulating local blood flow?

A

arterioles

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5
Q

how is blood flow regulated?

A

neurologically
humorally
locally

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6
Q

neurological regulation of blood flow

A

autonomic nervous system

alpha 1 adrenoreceptors - sympathetic NS

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7
Q

humoral regulation of blood flow

A

angiotensin 2
vasopressin
adrenaline
atrial natriuretic peptide

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8
Q

local regulation of blood floq

A

autoregulation and active hyperaemia - metabolic hypothesis

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9
Q

what is hyperaemia?

A

excess of blood in the vessels supplying an organ

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10
Q

flow

A

Q

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11
Q

how to calculate flow

A

Q ∝ pressure change x r^4 / n x L
L = vessel length
n = blood viscosity

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12
Q

what is the name of the formula used to calculate flow?

A

Poiseuille’s formular

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13
Q

what are the main sites of resistance to blood flow?

A

arterioles, they are the control valves into capillary beds

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14
Q

structure of arterioles

A

thick layer of smooth muscle in walls - tunica media

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15
Q

normal arteriolar tone

A

normal blood flow

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16
Q

vasoconstriction of arterioles

A

increases resistance

decreases blood flow

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17
Q

vasodilation of arterioles

A

decreases resistance

increases blood flow

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18
Q

what does local regulation of blood flow do?

A

controls regional/ organ blood flow

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19
Q

humoral factors

A

vasoactive hormones

20
Q

neurogenic factors

A

sympathetic nerves

21
Q

local factors

A

active hypereamia

autoregulation

22
Q

how do humoral factors regulate vascular tone?

A

adrenaline - beta 2 receptors on vascular smooth muscle and natriuretic peptides - ANP and BNP cause vasodilation

Angiotensin II, vasopressin/ ADH and adrenaline at alpha 1 receptors cause vasoconstriction

23
Q

how do neurogenic factors regulate vascular tone?

A

release of noradrenline via sympathetic NS bind to alpha 1 receptors on vascular smooth muscle and cause vasoconstriction

24
Q

what metabolic changes occur during exercise/ in active tissue?

A 
cell respiration and metabolic demand increase
pO2 decreases
pCO2 increases
lactate increases
pH decreases
Adenosine/ K+ increases
temperature increases 
there are chemical and physical changes in extracellular fluid
25
Q

what happens when pCO2 increases in active tissue?

A

cause release of nitric oxide from vascular endothelium
causes relaxation of underlying vascular smooth muscle
vasodilation and increased blood flow
supply meets demand

26
Q

what is active hyperaemia?

A

local/ intrinsic mechanism of increasing blood flow to tissues/ organs to meet metabolic demand

27
Q

what happens during tissue injury?

A

histamine, bradykinins, prostaglandins released

cause vasodilation

28
Q

what do vascular endothelial cells

A

provide low resistance protective lining to blood vessels
release nitric oxide
release endothelin
release vascular endothelial growth factor

29
Q

what causes nitric oxide release?

A

local chemical and physical changes due to increased metabolic demand
increased shear stress on endothelium

30
Q

release of endothelin

A

stimulated by angiotensin II and vasopressin

inhibited by nitric oxide

31
Q

what is endothelin?

A

potent vasoconstrictor

32
Q

what does the release of vascular endothelial growth factor do?

A

promotes angiogenesis

long term adaptation in response to decreased blood flow to a tissue

33
Q

increased blood flow to skeletal muscle during exercise

A

blood flow to active skeletal muscle increases by as much as 1000% compared to resting
supplying arterioles vasodilate
increase in blood flow brought on by local/intrinsic factors in response to metabolic changes within tissue extracellular fluid

34
Q

what else can influence arteriolar vascular tone?

A

fluctuations in mean arterial pressure and blood supply to a tissue/ organ

35
Q

what happens when there is an increase in mean arterial pressure or blood supply?

A

increased stretch of arteriolar smooth muscle
increased Ca2+ influx into smooth muscle
smooth muscle contract
causing increased vascular tone and vasoconstriction
blood flow to tissue/ organ returned to normal

36
Q

what happens when there is a decrease in mean arterial pressure or blood supply?

A

decreased stretch of arteriolar smooth muscle
no Ca2+ influx to smooth muscle
smooth muscle relaxes
causing decreased vascular tone and vasodilation
blood flow returned to normal

37
Q

what is autoregulation?

A

intrinsic myogenic response to changes in mean arterial pressure or blood supply to a tissue or organ

38
Q

active hyperaemia

A

responds to changes in demand

39
Q

autoregulation

A

responds to changes in supply

40
Q

where is local metabolic control of blood flow most important?

A

cerebral, coronary, renal, pulmonary and exercising skeletal muscle vascular beds

41
Q

control of blood flow in skeletal muscle

A

active hyperaemia most influential during exercise due to large increase in metabolic demands - lactate, adenosine and K+
autoregulation contributes in exercise
nerves/ hormones are most influential at rest
sympathetic innervation via alpha 1 adrenoreceptors and circulating adrenaline via beta 2 adrenoreceptors

42
Q

control of cerebral blood blow

A

active hyperaemia contributes - sensitive to increases in pCO2 and H+
autoregulation contributes to maintain constant blood flow to brain
nerves and hormones have little influence as cerebral vascular smooth muscle has no alpha 1 receptors

43
Q

control of coronary blood flow

A

active hyperaemia is most influential as coronaries are sensitive to hypoxia and adenosine
autoregulation contributes to maintain constant blood flow to heart
nerves and hormones have little influence

44
Q

control of blood flow to skin

A

active hyperaemia has little influence except when there is damage and release of histamine
autoregulation has little influence
nerves and hormones had varied sympathetic innervation via alpha 1 adrenoreceptors in response to changes in temperature

45
Q

control of pulmonary circulation

A

active hyperaemia but there is vasoconstriction in response to low pO2 - hypoxic vasoconstriction
autoregulation and nerves and hormones have little influence

Physiology (46 decks)

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