Blood Vessels and Blood Flow

Question 1

What divisions of blood vessels has the largest cross-sectional area?

Answer 1

Capillaries

Question 2

How does the amount of blood stored in the veins change during exercise?

Answer 2

Exercise causes VENOCONSTRICTION leading to a decrease in the amount of stored blood, so there is more venous return.

Question 3

State the equation relating blood flow, pressure difference and resistance.

Answer 3

Blood Flow = pressure difference/resistance

Question 4

Where does the biggest drop in blood pressure take place?

Answer 4

In the arterioles

Question 5

What three variables determine resistance to blood flow?

Answer 5

Fluid viscosity
Vessel radius
Length of tube

Question 6

Describe how blood normally flows in vessels.

Answer 6

Normal blood flow is laminar - blood flows fastest in the middle and slowest around the outside.

Question 7

What is shear rate?

Answer 7

The velocity gradient at any time

Question 8

What is shear stress?

Answer 8

Velocity gradient x viscosity

Question 9

What are the effects of a) high, and b) low shear stress?

Answer 9

High = promotes endothelial survival

Low (turbulent) = promotes endothelial proliferation, which affects vasoconstriction, platelet aggregation, coagulation

Question 10

What are the equations for pulse pressure and mean arterial blood pressure?

Answer 10

Pulse Pressure = SBP - DBP

Mean Arterial Blood Pressure = DBP + 1/3 PP

Question 11

How do aortic and ventricular pressure differ and what is the reason for this difference?

Answer 11

Once the aortic valves close, ventricular pressure falls but aortic pressure only falls slowly during diastole because the elasticity of the aorta buffers the pressure.

Question 12

What is the name given to the dampening effect of the aorta?

Answer 12

Windkessel Effect

Question 13

What are the consequences of a decrease in arterial compliance?

Answer 13

Pulse pressure will increase

Question 14

State the Law of Laplace.

Answer 14

When the pressure within a vessel is kept constant, tension is directly proportional to the radius.
T = PR

Question 15

What does circumferential stress equal?

Answer 15

Circumferential stress = tension/wall thickness

Circumferential stress = PR/h

Question 16

What is compliance?

Answer 16

Change in volume of the vessel per unit change in pressure.

Question 17

Describe how aneurysms are linked to the Law of Laplace.

Answer 17

The vessel radius increases meaning that greater wall tension is needed to withstand the internal pressure. If the structure of the wall is damaged and it can’t have the required tension, then the vessel will continue to dilate.

Question 18

How do the compliance of arteries and veins differ?

Answer 18

Veins are a lot more compliant

Question 19

What is the difference between the blood pressure in the ankle compared to the hand?

Answer 19

Blood pressure in the ankle is much greater than in the hand

Question 20

Why don’t we faint every time we stand up due to blood pooling in our leg veins?

Answer 20

Standing causes activation of the sympathetic nervous system, which stiffens and constricts the veins resulting in greater venous return to the heart.
Constricted arteries means there is an increase in TPR to maintain blood pressure.
There is also a slight increase in heart rate and force of contraction.

Question 21

What are the two pumps that facilitate the movement of venous blood back to the heart?

Answer 21

Skeletal muscle pump

Respiratory pump