CVS 4 - factors affecting blood flow

Question 1

What does whole blood contain?

Answer 1

erythrocytes (RBCs), leukocytes (WBCs), platelets, plasma proteins

Question 2

What is haematocrit?

Answer 2

proportion of erythrocytes to total volume

Question 3

How is haematocrit assessed?

Answer 3

by measuring the Packed Cell Volume (RBC component of whole blood)

Question 4

What may an increased haematocrit indicate?

Answer 4

dehydration (impacts viscosity and velocity of blood)

Question 5

What may a decreased haematocrit indicate?

Answer 5

anaemia

Question 6

What are the layers of centrifuged blood?

Answer 6

plasma (contains plasma proteins), buffy coat, red blood cells

Question 7

What is the buffy coat?

Answer 7

thin pale layer between plasma and RBCs containing leukocytes and platelets

Question 8

Appearance of solution containing intact RBCs

Answer 8

cloudy, red appearance (intact erythrocytes disperse light)

Question 9

Appearance of solution containing haemolysed (ruptured) erythrocytes

Answer 9

transparent, red solution (haemoglobin released - red pigment absorbs but does not disperse light)

Question 10

What happens when blood is added to 0.9% NaCl (saline) solution?

Answer 10

cloudy mix - no haemolysis as saline is isotonic to RBCs

Question 11

What happens when blood is added to distilled water?

Answer 11

solution goes red and transparent - haemolysis occurred. Distilled water is hypotonic to erythrocytes (gain water, swell, rupture)

Question 12

What happens when blood is added to 0.9% NaCl + detergent?

Answer 12

solution turns red and transparent - haemolysis. Detergent dissolves phospholipid membrane

Question 13

What happens when blood is added to 0.5ml isosmotic sucrose solution (300mosmol/L)?

Answer 13

cloudy mix - no haemolysis. Similar osmolarity to saline and sucrose too large to cross erythrocyte plasma membrane

Question 14

What happens when blood is added to 0.5ml isosmotic urea solution (300mosmol/L)?

Answer 14

red and transparent - haemolysis. Urea undergoes facilitated diffusion into RBC and water follows. solution is hypotonic to erythrocytes

Question 15

What happens when blood is added to 0.9% NaCl + urea crystals?

Answer 15

solution goes cloudy - no haemolysis. solution isotonic to erythrocytes

Question 16

Difference in haemolysis between fresh and stored blood

Answer 16

stored blood undergoes more haemolysis

Question 17

Why does blood flow vary between organs?

Answer 17

each organ has different metabolic demands

Question 18

Which organ system is the only exception to blood flow not depending on the metabolic demand?

Answer 18

pulmonary system - blood flow is entire CO as all blood must undergo gas exchange

Question 19

Examples of blood flow to organs increasing according to a greater metabolic requirement

Answer 19

during exercise, blood flow to skeletal muscle increases due to greater oxygen demand. Following ingestion, blood flow to GI system increases due to greater oxygen demand.

Question 20

What is the cause of interorgan blood flow differences?

Answer 20

alterations in vascular resistance

Question 21

How can mechanisms that regulate blood flow be categorised?

Answer 21

local (intrinsic) control and neural/hormonal (extrinsic) control

Question 22

What is the function of local control of blood flow?

Answer 22

to match blood flow to metabolic requirement of tissue system

Question 23

How is blood flow controlled locally?

Answer 23

direct action of metabolites on arteriolar resistance

Question 24

How does neural control of blood flow act?

Answer 24

via action of sympathetic NS on vascular smooth muscle

Question 25

How does hormonal control of blood flow act?

Answer 25

via action of vasoactive substances (histamine, bradykinin, prostaglandins)

Question 26

What needs of the tissues are supplied by blood flow?

Answer 26

transport oxygen and nutrients (glucose, amino acids, fatty acids), removal of carbon dioxide and hydrogen ions, maintain ion concentrations, transport hormones

Question 27

Which three mechanisms can local/intrinsic control of blood flow occur by?

Answer 27

autoregulation, active hyperemia, reactive hyperemia

Question 28

What is autoregulation?

Answer 28

maintenance of constant blood flow while arterial pressure changes e.g. if coronary arterial pressure decreases, compensatory vasodilation occurs to decrease resistance which maintains constant blood flow

Question 29

What is active hyperemia?

Answer 29

blood flow to tissues is proportional to its metabolic activity

Question 30

What happens as a result of active hyperemia when metabolic activity increases?

Answer 30

increased arteriolar dilation which increases blood flow

Question 31

What is reactive hyperemia?

Answer 31

an increase in blood flow in response to prior period of decreased blood flow

Question 32

What is the purpose of reactive hyperemia?

Answer 32

to reverse the oxygen debt that has accumulated during the arterial occlusion

Question 33

What factors determine resistance to blood flow?

Answer 33

vessel diameter (vasoconstriction/vasodilation), vessel length, viscosity of blood

Question 34

Viscosity of blood usually remains within a narrow range except in which circumstance?

Answer 34

when haemocrit changes (RBC count can impact viscosity)

Question 35

What can cause an increase in blood viscosity?

Answer 35

dehydration and immobility (so blood flow is reduced)

Question 36

Which medical condition does an increase in blood viscosity increase the risk of developing?

Answer 36

Deep Vein Thrombosis (DVT)

Question 37

How can the risk of deep vein thrombosis (DVT) be reduced?

Answer 37

hydration, movement, compression socks

Question 38

What is vessel resistance (R) directly proportional to?

Answer 38

vessel length (L) and blood viscosity (n). R proportional to nL

Question 39

What is vessel resistance (R) inversely proportional to?

Answer 39

radius to the power of 4 (R proportional to 1/r4)

Question 40

What is the equation to calculate blood flow (Q)?

Answer 40

Q= change in pressure (deltaP) / resistance (R)

Question 41

Which equation describes how flow is related to perfusion pressure, radius, length and viscosity?

Answer 41

Poiseuille's equation

Question 42

What is Poiseuille's equation?

Answer 42

Q is directly proportional to r^4 delta P / nL

Question 43

What are the limitations of Poiseuille's equation?

Answer 43

assumes 1. flow is through a uniform straight pipe (no branching, bending) 2. flow is non-pulsatile 3. flow is laminar (smooth)

Question 44

Where in the blood vessel is velocity of flow greatest?

Answer 44

at the centre (furthest from resistance of wall)

Question 45

If flow in a tube (vessel) had negligible resistance, how would this affect velocity?

Answer 45

velocity would be the same across the tube

Question 46

How do pressure differences within the venous system compare with the arterial system?

Answer 46

pressure differences within the venous system are small (graph tapers)

Question 47

What is the orientation of valves in veins?

Answer 47

venous valves are oriented towards the heart

Question 48

How is venous return aided?

Answer 48

contraction of skeletal muscles compressing veins, more negative intrathoracic pressure during exercise, sympathetic activation

Question 49

How is venous return to the heart aided during exercise?

Answer 49

intrathoracic pressure becomes more negative due to frequent respirations which increases the pressure gradient between abdominal and thoracic veins

Question 50

How does sympathetic activation increase venous return?

Answer 50

sympathetic activation releases noradrenaline which constricts veins

Question 51

What is venous return to the right ventricle termed?

Answer 51

preload

Question 52

Define afterload

Answer 52

pressure heart is contracting against to expel blood into the arterial system

Question 53

According to Starling's Law, what happens if preload increases?

Answer 53

an increased preload equates to an increased EDV which greater stretches the myocardium leading to increased contraction force (up to a point)

Question 54

Which diseases when paired with an increase in preload can result in a problem?

Answer 54

coronary artery disease (angina) or heart failure

Question 55

Function of coronary circulation

Answer 55

perfusion of myocardium to maintain high basal rate of oxygen supply

Question 56

Function of skeletal muscle circulation

Answer 56

meet metabolic demand of skeletal muscle during exercise

Question 57

Function of cerebral circulation

Answer 57

maintain cerebral perfusion

Question 58

What percentage of the resting cardiac output does the heart receive?

Answer 58

5%

Question 59

What percentage of the body weight does the heart represent?

Answer 59

<0.5%

Question 60

Which arteries is the blood supply to the entire myocardium derived from?

Answer 60

left and right coronary arteries

Question 61

Where do the coronary arteries originate?

Answer 61

At the root of the aorta behind cusps of the aortic valve

Question 62

What portion of the heart is generally supplied by the left coronary artery?

Answer 62

left ventricle and atrium

Question 63

What portion of the heart is generally supplied by the right coronary artery?

Answer 63

right ventricle and atrium

Question 64

Which arteries does the left coronary artery divide to form?

Answer 64

left circumflex artery and left anterior descending artery

Question 65

Where does the left circumflex artery branch to supply?

Answer 65

LA and LV

Question 66

Where does the left anterior descending artery branch to supply?

Answer 66

descends to the apex and branches to supply the interventricular septum and portion of the right and left ventricles

Question 67

How is blood returned once it passes through coronary capillaries?

Answer 67

blood collects in venules that drain to form epicardial veins which transport blood to the coronary sinus

Question 68

Name the largest epicardial vein

Answer 68

great cardiac vein

Question 69

Where is blood emptied from the coronary sinus?

Answer 69

into the right atrium

Question 70

Name an alternative pathway for blood drainage from the coronary circulation, other than the coronary sinus

Answer 70

thesbian veins (very small) drain deoxygenated blood directly into cardiac chambers

Question 71

What is the rate of coronary blood flow at rest?

Answer 71

70-80 ml/min/100g

Question 72

When does the perfusion of the myocardium from the coronary arteries occur?

Answer 72

during early diastole

Question 73

Why can perfusion of the myocardium not occur during systole?

Answer 73

contraction of myocardium constricts the vessels

Question 74

What percentage of left coronary blood flow occurs during diastole?

Answer 74

80%

Question 75

What is the coronary blood flow during exercise?

Answer 75

300-400 ml/min/100g

Question 76

What physiological adaptations occur in an athletic heart?

Answer 76

increased number of arterioles and capillaries, exercise induced hypertrophy (different from pathological hypertrophy)

Question 77

Which circulation is a major influence of total peripheral resistance (TPR)?

Answer 77

skeletal muscle vascular resistance

Question 78

How is the blood flow in skeletal muscle circulation regulated at rest?

Answer 78

sympathetic innervation

Question 79

How is blood flow in skeletal muscle circulation regulated during exercise?

Answer 79

by local (intrinsic) control mechanisms

Question 80

Name local vasodilators in skeletal muscle

Answer 80

lactate, adenosine and potassium ions (K+)

Question 81

Activation of which receptors causes vasoconstriction in skeletal muscle circulation?

Answer 81

alpha-1 adrenoreceptor

Question 82

Activation of which receptors causes vasodilation in skeletal muscle circulation?

Answer 82

beta-2 adrenoreceptors

Question 83

Effect of adrenaline on skeletal muscle circulation

Answer 83

cause vasodilation by binding to beta-2 adrenoreceptors

Question 84

How is MAP maintained when skeletal muscle has an increased metabolic demand (e.g. during exercise)?

Answer 84

sympathetic vasoconstriction continues in feed arteries and proximal resistance vessels which prevents an excessive decrease in TPR

Question 85

Which circulation accounts for ~50% of vascular resistance?

Answer 85

cerebral arteries

Question 86

Name the anastomotic arterial ring at the base of the brain

Answer 86

circle of Willis

Question 87

Which arteries anastomose to form the circle of Willis?

Answer 87

basilar and internal carotid arteries

Question 88

What is the function of the circle of Willis?

Answer 88

preserves cerebral perfusion if carotid artery obstruction occurs

Question 89

What is the effect of cerebral autoregulation when arterial blood pressure falls?

Answer 89

cerebral resistance vessels dilate to maintain perfusion

Question 90

Below what arterial blood pressure does cerebral blood flow steeply decline (cerebral autoregulation stops)?

Answer 90

~60mmHg

Question 91

What are the consequences of severe hypotension?

Answer 91

mental confusion and syncope (loss of consciousness)

Question 92

What is a high carbon dioxide level in the blood termed?

Answer 92

hypercapnia

Question 93

What is a low carbon dioxide level in the blood termed?

Answer 93

hypocapnia

Question 94

What is the effect of hypercapnia on cerebral circulation?

Answer 94

hypercapnia causes cerebral vasodilation

Question 95

What substance mediates cerebral vasodilation?

Answer 95

endothelial NO

Question 96

What is the effect of hypocapnia on cerebral circulation?

Answer 96

hypocapnia causes cerebral vasoconstriction

Question 97

How can hyperventilation affect cerebral perfusion?

Answer 97

hyperventilation can reduce cerebral perfusion (dizziness) as hypocapnia occurs which triggers cerebral vasoconstriction

Question 98

What is the effect of local hypoxia on cerebral circulation?

Answer 98

local hypoxia leads to cerebral vasodilation

Question 99

Why can systemic hypoxia lead to cerebral vasoconstriction?

Answer 99

systemic hypoxia triggers increased ventilation which results in hypocapnia. This causes cerebral vasoconstriction

Question 100

Aside from coronary, skeletal muscle and cerebral circulations, name other circulations with specialised local control

Answer 100

pulmonary circulation, skin circulation (for thermoregulation), renal circulation

Question 101

Which practical investigates cardiovascular reflexes?

Answer 101

tilt table test

Question 102

What is the initial effect on blood pressure when returning to an upright position after laying down?

Answer 102

decrease in arterial BP

Question 103

Describe the cardiovascular reflex that occurs when the subject returns to an upright position

Answer 103

- decrease in arterial BP - detected by baroreceptors in aortic arch and carotid sinus - decreased baroreceptor firing - detected by medullary CV centre - increased sympathetic discharge - decreased parasympathetic discharge - increased venous tone and pressure - increased venous return - EDV preserved - CO and MAP maintained