25 - Vascular Function and Control

Question 1

Proportion of blood in systemic veins

Answer 1

65%

Question 2

Proportion of blood in systemic arteries

Answer 2

13%

Question 3

Proportion of blood in systemic capillaries

Answer 3

5%

Question 4

Proportion of blood in the lungs

Answer 4

10%

Question 5

Proportion of blood in the heart

Answer 5

7%

Question 6

Is the pressure in veins or arteries more sensitive to volume changes?

Answer 6

In arteries

Question 7

Examples of things that increase amount of blood in the venous system 1) 2)

Answer 7

1) Decreasing cardiac output puts less blood into arteries 2) Decreasing TPV forces less blood into arteries

Question 8

Mean circulatory filling pressure

Answer 8

When there is no blood being pumped, blood leaves arteries for veins until pressure stabilises. This pressure is 7mmHg

Question 9

What is autotransfusion?

Answer 9

When blood is lost, there is a drop in blood pressure. This increases venoconstriction, which pushes blood into arteries.

Question 10

What is a vascular function curve?

Answer 10

Describes what happens to venous pressure when cardiac output varies

Question 11

What does a vascular function curve look like?

Answer 11

Question 12

Effect on vascular function curve of increasing vasoconstriction or blood volume

Answer 12

Greater venous pressure with cardiac output

Question 13

Effect on vascular function curve of decreasing TPR

Answer 13

Question 14

What is ‘zero pressure’ on vascular function curves?

Answer 14

When venous pressure=atmospheric pressure.

Question 15

What occurs at zero pressure of vascular function curves?

Answer 15

Veins of the periphery collapse under atmospheric pressure (veins in neck, limbs, etc)

Question 16

Effect of increasing TPR

Answer 16

Increases blood pressure NOT by squeezing blood, but by keeping blood in larger vessels. Doesn’t affect compliance of vessels

Question 17

Central venous pressure

Answer 17

Pressure in the great veins just outside the heart (IVC, SVC) 1-5mmHg Slightly higher than right atrial pressure Pressure required to fill heart (needs to be enough to maintain CO) Rising central venous pressure is a sign of heart failure

Question 18

How is central venous pressure assessed clinically?

Answer 18

Jugular venous pressure (JVP). Lie patient at 45 degrees, see if jugular vein visible

Question 19

Cardiac function curve

Answer 19

Describes what happens to cardiac output when venous pressure varies

Question 20

Cardiac function curve appearance

Answer 20

Question 21

Cardiac function curve when blood volume increases or vasoconstriction

Answer 21

Increased venous pressure for a given cardiac output

Question 22

Increase in heart contractility does what to CO and venous pressure

Answer 22

Increase CO, decrease venous pressure

Question 23

Effect of increasing TPR on cardiac output and venous pressure

Answer 23

Increased venous pressure increases the amount of blood filling the heart. Increased venous pressure, increased CO

Question 24

Substances produced by endothelium that affect smooth muscle contraction 1) 2) 3)

Answer 24

1) Nitric oxide (vasodilation) 2) Endothelin (extremely potent vasoconstrictor) 3) Prostaglandins (vasoconstrictors)

Question 25

Vessels dilated by NO

Answer 25

Arteries. Veins much less so.

Question 26

Circulating vasoactive substances mediated by endothelium 1) 2) 3)

Answer 26

1) Angiotensin (vasoconstrictor) 2) Thrombin (vasoconstrictor) 3) Bradykinin (vasodilator

Question 27

Factors modulating NO release 1) 2) 3) 4)

Answer 27

1) Physical stimuli (EG: hitting back of hand) 2) Hypoxia 3) Circulating vasoactive factors 4) Paracrine vasoactive factors (adjacent cells, blood cells)

Question 28

Vasoactive compounds released by leukocytes 1) 2) 3)

Answer 28

1) NO 2) Histamine 3) Cytokines

Question 29

Vasoactive factors released by platelets 1) 2) 3)

Answer 29

1) Thrombine 2) ADP 3) Thromboxane A2