Session 5

Question 1

What is velocity in relation to blood vessels?

Answer 1

Rate of movement of blood passing along a vessel

Question 2

What is laminar flow?

Answer 2

Flow where there is a gradient of velocity from the middle to the edge of the vessel: velocity is highest in the centre and fluid is stationary at the edge

Question 3

What is turbulent flow?

Answer 3

Layers of fluid move past eachother too fast so the velocity gradient breaks down and fluid tumbles over causing resistance to increase

Question 4

What is viscosity?

Answer 4

The extent to which fluid layers resist sliding over each other

Question 5

What effect does diameter of a vessel have on flow rate?

Answer 5

Increasing diameter increases velocity so flow rate increases: mean velocity is proportional to cross sectional area

Question 6

What effect does viscosity have on resistance?

Answer 6

As viscosity increases resistance increases

Question 7

What effect does radius have on resistance?

Answer 7

As radius increases resistance decreases

Question 8

What is the effect of combining flow resistances in series?

Answer 8

The resistances of the individual tubes summate

Question 9

What is the effect of combining flow resistances in parallel?

Answer 9

The reciprocal of the total resistance is equal to the sum of the reciprocal of the resistances of the individual tubes

Question 10

What is the pattern of flow resistance in the systemic circulation?

Answer 10

• Arteries are low resistance
• Arterioles are high resistance
• Venules and veins are low resistance

Question 11

What is the pattern of pressure through the systemic circulation?

Answer 11

• Pressure drop in the arteries is small
• Pressure drop in the arterioles is large due to the high resistance
• Pressure drop in the venules and veins is small

Question 12

What is the relationship between arteriolar resistance and arterial pressure at a constant flow?

Answer 12

As arteriolar resistance increases, arterial pressure also increases

Question 13

What are the advantages of having distensible blood vessels?

Answer 13

Transmural pressure across the vessel walls allow a them to stretch so resistance falls and flow increases, making it easier for blood to flow through them

Question 14

How does vessel distensibility produce capacitance?

Answer 14

As vessels widen more blood flows in and out and vessels can store more blood; capacitance. Veins have the highest capacitance as they are most distensible

Question 15

What factors affect systolic pressure?

Answer 15

• How hard the heart pumps
• Total peripheral resistance
• Compliance of arteries

Question 16

What factors affect diastolic pressure?

Answer 16

• Systolic pressure

- Total peripheral resistance

Question 17

What is the pulse pressure and what is its typical value?

Answer 17

• The difference between systolic and diastolic pressure

- Typically 40mmHg

Question 18

How is average pressure calculated?

Answer 18

Diastolic pressure plus 1/3rd pulse pressure

Question 19

What is total peripheral resistance?

Answer 19

The sum of the resistance of all the peripheral vasculature in the systemic circulation

Question 20

What property of arteries acts to reduce arterial pressure fluctuations between systole and diastole?

Answer 20

Elasticity: walls can distend in systole so pressure doesn’t rise too much, and recoil in diastole to allow flow to continue until the next period of systole

Question 21

What factors affect vasomotor tone?

Answer 21

• Sympathetic innervation of alpha1 adrenergic receptors produces vasomotor tone
• Tone is antagonised by vasodilator factors
• Actual tone is determined by the balance between each factor

Question 22

How do metabolites modify vasomotor activity and why?

Answer 22

• Metabolically active tissues produce metabolites that act as vasodilator a (e.g. Hydrogen, potassium and adenosine)
• Metabolites act to relax smooth muscle in the vessels so resistance lowers and blood flow increases
• Increased blood flow provides metabolically active tissues with more blood to remove toxic metabolites

Question 23

What is reactive hyperaemia?

Answer 23

• If a tissue has had blood supply cut off then restored a large amount of blood will enter the tissue
• Tissue will continue producing metabolites to dilate vessels so maximum blood flows to the vessels when perfusion is restored

Question 24

How can vasodilation be auto-regulated?

Answer 24

• Increased metabolite concentration causes vasodilation
• Increased vasodilation increases blood flow so metabolites are removed at a faster rate
• When the tissue metabolism decreases less metabolites are produced so vessels become less dilated

Question 25

What is central venous pressure?

Answer 25

The pressure in the great vessels supplying the heart

Question 26

What is venous return?

Answer 26

The rate of blood flow back to the heart, it acts to limit cardiac output

Question 27

What is flow in relation to blood vessels?

Answer 27

Volume of blood passing a given point in a vessel per unit time