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BDS1 BAMS human systems > factors affecting blood blow > Flashcards

factors affecting blood blow Flashcards

1
Q

what does blood contain?

A
  • erthrocytes (RBS)
  • leukocytes (WBC)
  • platelets
  • plasma proteins
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2
Q

what is the name for the proportion of RBS to total volume of blood?

A

haematocrit

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3
Q

what does increased haematocrit indicate?

A

dehydration- risk of deep vein thrombosis

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4
Q

what does decreased haematocrit indicate?

A

anaemia

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5
Q

what happens to blood at the lungs?

A
  • oxygenated
  • CO2 removed
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6
Q

what does blow flow vary according to?

A

the metabolic demands of the organs

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7
Q

when does skeletal muscle have a greater demand for blood?

A

during exercise

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8
Q

when does the gastrointestinal system have a greater demand for blood?

A

following ingestion of food

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9
Q

why are there differences in blood flow within individual organs?

A

due to alterations in vascular resistance

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10
Q

what are the different categories for blood flow regulation?

A
  • local (intrinsic)
  • neural/hormonal (extrinsic)
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11
Q

describe local control of blood flow

A

Matches blood flow to metabolic requirement of tissue system
Direct action of metabolites on arteriolar resistance

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12
Q

describe neural/hormonal control of blood flow

A

Action of sympathetic nervous system on vascular smooth muscle
Action of vasoactive substances (histamine, bradykinin, prostaglandins)

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13
Q

what are specific needs of the tissues for blood flow (local control BF)?

A
  • Delivery of oxygen to tissues and nutrients (glucose, amino acids, fatty acids)
  • Removal of carbon dioxide and hydrogen ions
  • Maintenance of ion concentrations in tissues
  • Transport of hormones
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14
Q

what are the three mechanisms through which intrinsic control (local) of blood flow can occur?

A
  • autoregulation
  • active hyperemia
  • reactive hyperemia
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15
Q

what is autoregulation (LCBF)?

A
  • maintaining constant blood flow while arterial pressure changes

eg decrease in arterial pressure gives vasodilation to decrease resistance and maintain constant blood flow

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16
Q

what is active hyperemia (LCBF)?

A
  • Blood flow to tissues is proportional to its metabolic activity.
  • Increased blood flow when metabolic activity increases (exercising skeletal muscle increased O2 consumption / ATP demand)
  • Increased arteriolar dilation.
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17
Q

what is reactive hyperemia (LCBF)?

A
  • Increase in blood flow in response to a prior period of decreased blood flow.

e.g., following period of arterial occlusion, an O2 dept accumulates – longer the arterial occlusion, greater O2 debt, greater the increase in blood flow (above pre-occlusion levels) until the O2 dept reversed.

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18
Q

what are factors which determine resistance to blood flow?

A
  • vessel diameter
  • vessel length
  • viscosity of blood
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19
Q

how does vessel diameter change?

A

with vasoconstriction and vasodilation- contraction and relaxation of vascular smooth muscle

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20
Q

what does poiseuille’s equation rely on?

A
  • flow is through a uniform straight pipe
  • flow is non-pulsatile
  • flow is smooth (laminar)
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21
Q

what does poiseuille’s equation describe?

A

how flow is related to perfusion pressure, radius, length and viscosity

22
Q

what do veins have that’s larger than arteries?

A

cross-section

23
Q

why are venous valves orientated towards the heart?

A

to maintain flow in one direction

24
Q

what aids the venous system?

A

the action of working skeletal muscles intermittently contracting to compress the veins

25
Q

how is venous return aided during exercise?

A

as intrathoracic pressure becomes more negative

26
Q

which activation via noradrenaline constricts veins and increases venous return?

A

sympathetic

27
Q

what is preload?

A

venous return to the right ventricle

28
Q

what happens if preload increases?

A

the heart will have to work harder to pump blood out- problem in angina and heart failure

29
Q

what does coronary circulation do?

A
  • Facilitates perfusion of myocardium- blood to heart
  • Maintains high basal rate of O2 supply to cardiac muscle
30
Q

what does skeletal muscle circulation do?

A

Adapted to meet metabolic demand of skeletal muscle during exercise

31
Q

what does cerebral circulation do?

A

regulation to maintain cerebral perfusion (brain)

32
Q

what supplies blood to the heart?

A

the left and right coronary arteries- which originate at the root of the aorta (behind the cusps of the aortic valve)

33
Q

which coronary artery supplies which side of the heart?

A

right supplies right, left supplies left

34
Q

what does the left coronary artery divide into?

A
  • The left anterior descending artery branches off the left coronary artery and supplies blood to the front of the left side of the heart.
  • The circumflex artery branches off the left coronary artery and encircles the heart muscle. This artery supplies blood to the outer side and back of the heart.
35
Q

what is the function of the segments which branch off from the coronary arteries?

A

Coronary arteries branch into segments dividing into capillary networks that facilitate O2 diffusion into cardiac myocytes that have a high ATP requirement.

36
Q

what happens to blood once it has passed through coronary capillaries?

A

it collects in venules that drain to form the epicardial veins which transport blood to the coronary sinus which empties blood into the right atrium

37
Q

what are thesbian veins?

A

thesbian veins drain deoxygenated blood from capillary network in ventricular wall directly into the cardiac chambers

38
Q

what is coronary blood flow in a human at rest?

A

70-80 ml/min/100g

39
Q

when does perfusion of the myocardium from coronary arteries occur?

A

during early diastole

40
Q

what does exercise training do?

A

increases the number of arterioles and capillaries

41
Q

what is blood flow regulated by at rest?

A

its sympathetic innervation

42
Q

what is blood flow to skeletal muscle regulated by during exercise?

A

local control

43
Q

what are examples of local vasodilators in skeletal muscle?

A

lactate, adenosine and potassium ions (K+)

44
Q

what does alpha-1-adronoreceptor activation cause?

A

vasoconstriction

45
Q

what does beta-2-adrenoreceptor activation cause?

A

vasodilation

46
Q

what does adrenaline cause?

A

vasodilation

47
Q

what % of vascular resistance does cerebral arteries account for?

A

50%

48
Q

what is the circle of willis?

A

the joining area of several arteries at the bottom (inferior) side of the brain- can help to preserve cerebral perfusion if carotid artery obstruction occurs

49
Q

describe cerebral autoregulation

A
  • Cerebral resistance vessels dilate to maintain perfusion when arterial Blood Pressure falls.
  • Below arterial blood pressure of ~60mmHg, cerebral blood flow steeply declines.
  • Severe hypotension can lead to mental confusion and syncope
50
Q

what are cerebral resistance vessels highly sensitive to?

A

local hypoxia and arterial CO2

51
Q

what does hypERcapnia cause?

A

cerebral vasodilation, mediated by endothelial NO
(also caused by local hypoxia)

52
Q

what does hypOcapnia cause?

A

cerebral vasoconstriction. Hyperventilation can reduce cerebral perfusion (dizziness)
(also caused by systemic hypoxia)

BDS1 BAMS human systems (47 decks)

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