Control of Blood Flow and Nutrient Exchange

Question 1

What physiological principle explains the need for blood flow?

Answer 1

Fick’s principle.

Question 2

What is Fick’s principle?

Answer 2

Oxygen consumption = Blood flow x (arterio-venous oxygen difference)
O2 Consumption = Blood Flow x (aO2 - vO2)

Question 3

What component of Fick’s principle is affected by cardiovascular system function?

Answer 3

Blood flow

Question 4

Which systems in the body affect the aO2 component of Fick’s principle?

Answer 4

1. Respiratory system

2. Hematological system (Hb)

Question 5

What symptoms result from decreased oxygen supply?

Answer 5

Dizziness, fainting, and shortness of breath.

Question 6

What are the 3 determinants of blood flow (cardiac output)?

Answer 6

1. Changes in pressure gradients
2. Changes in resistance
3. Changes in stroke volume and heart rate

Question 7

What are the 5 determinants of stroke volume?

Answer 7

1. Preload (Frank-Starling)
2. Contractility
3. Blood volume
4. Afterload
5. Venous return

Question 8

How is blood flow calculated?

Answer 8

Blood flow = Pressure gradient / resistance of conduit

F = (P1-P2)/R

Question 9

How does resistance affect upstream and downstream pressures?

Answer 9

Increased resistance always causes higher pressures upstream and lower pressures downstream.

Question 10

How is the pressure gradient calculated?

Answer 10

Pressure gradient = Flow x Resistance

Question 11

What is right atrial pressure normally?

Answer 11

0 mmHg

Question 12

How is MAP calculated?

Answer 12

MAP = DBP + ⅓(SBP-DBP)

Diastolic blood pressure plus ⅓ pulse pressure

Question 13

How is pulse pressure calculated?

Answer 13

SBP - DBP

Question 14

How is cardiac output calculated?

Answer 14

CO = SV x HR

Question 15

What is MAP minus right atrial pressure equivalent to?

Answer 15

MAP - RAP = CO x TPR (= cardiac output x total peripheral resistance)

Question 16

What are some of the extrinsic factors that cause vasoconstriction?

Answer 16

1. ANS - SNS - NA (alpha-1 receptors)

2. Circulating Angiotensin II

Question 17

What are some of the extrinsic factors that cause vasodilation?

Answer 17

1. ANS - SNS - Na (beta-2 receptors)

2. ANS - PNS - Ach-NO

Question 18

What are some of the intrinsic (local) factors that cause vasoconstriction?

Answer 18

• Endothelial factors: endothelin
• Local metabolites: oxygen
• Prostaglandins
• Myogenic responses

Question 19

What are some of the intrinsic (local) factors that cause vasodilation?

Answer 19

• Endothelial factors (NO)
• Local metabolites - adenosine & carbon dioxide
• Prostaglandins
• Histamine

Question 20

What are determinants of stroke volume based on?

Answer 20

Frank-Starling effects

Question 21

Determinants of stroke volume: What is the effect of postural changes?

Answer 21

Results in changes in gravity which affect venous return

Question 22

Determinants of stroke volume: What are some things that affect intra-thoracic pressure?

Answer 22

• Breathing
• Holding breath
• Valsalva maneuver

Question 23

Determinants of stroke volume: What is the effect of increased intra-thoracic pressure?

Answer 23

Decreases venous return = decreased filling volumes = decreased stroke volume

Question 24

Determinants of stroke volume: What is the effect of the skeletal muscle pump?

Answer 24

Increases venous return = increased filling volumes = increased stroke volume

Question 25

Determinants of stroke volume: What is the effect of changes in blood volume?

Answer 25

Increased blood volume = increased stroke volume and vice versa

Question 26

Determinants of stroke volume: What is the effect of constriction or dilation of capacitance vessels (veins)?

Answer 26

If capacitance vessels constrict they hold less blood, therefore more blood returns to the heart = increased filling volumes = increased stroke volume

Question 27

Determinants of stroke volume: What is the effect of decreased blood ejected from ventricle (leaves more blood behind)?

Answer 27

Blood left behind adds to filling volume = increased stroke volume.

Question 28

Determinants of stroke volume: What is the effect of restriction of cardiac filling by fluid in the pericardial space or stiff wall of the heart?

Answer 28

Restrict expansion of ventricle = decreased filling = decreased stroke volume

Question 29

Determinants of stroke volume: What is the effect of a heart rate exceeding 180 beats per minute?

Answer 29

Does not allow enough time for heart to adequately fill = decreased filling = decreased stroke volume

Question 30

What causes increased contractility?

Answer 30

SNS effects, beta-agonists, increased cAMP (PDEI)

Question 31

What causes decreased contractility?

Answer 31

Decreased oxygen, cell death, pharmacological depressants

Question 32

How is tension calculated (afterload)?

Answer 32

(Pressure x Radius) / (2 x wall thickness)

Question 33

What are the results of an increased afterload?

Answer 33

Increased O2 demand

= Reduced systolic function

Question 34

To maintain blood flow, what two things are needed?

Answer 34

1. A well functioning pump (heart)

2. Low resistance

Question 35

What results in oedema?

Answer 35

1. Increased capillary hydrostatic pressure

2. Decreased capillary oncotic pressure

Question 36

What are the three causes of decreased oxygen delivery to tissues?

Answer 36

1. Decreased blood flow (cardiac output)
2. Decreased oxygenation of blood (resp)
3. Decreased oxygen carrying capacity (haem)

Question 37

What are the causes of decreased cardiac output?

Answer 37

1. Increased resistance (vasoconstriction)
2. Decreased blood pressure (heart failure, shock)
3. Decreased heart rate (ANS)
4. Decreased stroke volume (decreased venous return, decreased blood volume, decreased contractility, increased afterload, decreased filling)