Control Of Blood Flow

Question 1

What does TPR stand for?

Answer 1

Total peripheral resistance

Question 2

What does TPR control?

Answer 2

Blood flow and blood pressure- increase in resistance means need to increase pressure to keep the same flow

Question 3

What is TPR controlled by?

Answer 3

• Darcy’s and poiseuilles laws
• myogenic response
• blood viscosity

Question 4

What is conductance in relation to resistance?

Answer 4

Conductance is the opposite of resistance

Question 5

What is hypertension in the arterioles?

Answer 5

Overconstriction of arterioles

Question 6

What happens when the arterioles dilate?

Answer 6

Decrease in TPR. Means decreased blood pressure upstream but greater flow

Question 7

What happens when the arterioles constrict?

Answer 7

Increase TPR. Means there’s an increased blood pressure upstream, but less flow

Question 8

What are the features of blood flow in the common iliac and superior mesenteric arteries when sedentary?

Answer 8

Superior mesenteric is dilated
Increased flow to intestines
Common iliac constricted
Decreased flow to legs

Question 9

What are the features of common iliac and superior mesenteric arterioles when exercising?

Answer 9

Superior mesenteric is constricted
Decreased flow to intestines
Common iliac dilated
Increased flow to less

Question 10

What does poiseuilles law describe?

Answer 10

The parameters that govern TPR

Question 11

What is resistance related to?

Answer 11

Blood viscosity
Radius of vessel
Vessel length

Question 12

What does increased distension of vessel do?

Answer 12

Makes it constrict

Question 13

What does the Baylis myogenic response do?

Answer 13

Maintains blood flow at the same level during changing arterial pressures

Question 14

What does stretching of the vessel cause?

Answer 14

Ion channels to open, which then depolarise, leading to smooth muscle contraction

Question 15

What is viscosity?

Answer 15

A measure of the internal friction opposing the separation of the lamina

Question 16

What are four factors in viscosity?

Answer 16

Haematocrit, tube diameter, red cell deformability, velocity of blood

Question 17

What do veins do when there is very little pressure?

Answer 17

Fold up

Question 18

What is Bernoulli’s theory?

Answer 18

Mechanical energy of flow is determined by pressure, kinetic and potential energies

Question 19

What does stimulation of sympathetic nerves cause in the CVS?

Answer 19

Vasoconstriction, which shifts blood centrally. This increases venous return as CVP and EDP is increased. CVP increases preload so increases stroke volume

Question 20

What effect does cardiac output have on venous return?

Answer 20

The circulation is a closed system so the heart pushes the blood further through the vascular system via the arterial side of the capillary system into the veins in the direction of the right side of the heart

Question 21

What effect does breathing have on venous return?

Answer 21

The pressure in the chest is negative on inhalation at the same time intra-abdominal pressure rises as the diaphragm moves downwards. This causes the venous valves in the pelvic veins to close, and the blood moves into the thorax. On exhalation, the intra-abdominal pressure decreases and the pelvic veins and inferior vena cava refills

Question 22

What effect does muscle pump have on venous return?

Answer 22

The deep venous system is embedded in muscles. Due to this, every muscle contraction squeezes the veins to push the column of blood in them in the direction of the heart. When the muscle relaxes, the venous valves prevent the retrograde flow of blood towards the capillaries

Question 23

What effect does venous tone have on venous return?

Answer 23

The blood in the veins exerts pressure on the veins wall, which generates tension and maintains pressure. Furthermore, sympathetic vasoconstriction can mobilise more blood back to the heart