Vasculature

Question 1

Describe laminar fluid flow

Answer 1

The fluid molecules touching the wall move slowly due to friction, the next layer slips over these fluid molecules but is partially effected by the friction but not to the same extent. Therefore the middle layer of fluid molecules move the most rapid

Question 2

What accurse as a result of turbulence?

Answer 2

Flow is disrupted and resistance is increased. So posieuille equation doesn’t hold true

Question 3

What is used to indicate if flow is laminar or turbulent

Answer 3

Reynold’s number (Re). For a given system there will be a critical value for Re, above which turbulence is highly likely

Question 4

What causes the Re number to increase and make turbulence more likely

Answer 4

High velocity flow, large diameter vessels, low blood viscosity and abnormal vessels wall.

Question 5

Describe how flow effects viscosity?

Answer 5

Increased blood velocity, decreases the viscosity. Faster the blood flows the thinner it gets

Question 6

Describe how the blood pressure cuff makes artificially generated turbulence

Answer 6

When blood travels via laminar flow, no sound can be heard. The BP cuff is inflated to pressure above patient systolic so no sound is heard as it occludes the artery. When the pressure in the cuff is equal to patients systolic pressure 1st korotofff sound is heard. The blood in the vessels flows in spirts as the pressure in the artery rises above pressure in the cuff and then drops beyond the cuffed region resulting in turbulence, this produces an audible sound.

Question 7

What is LaPlace’s Law

Answer 7

Tension = Pressure x Radius. The tension in the vessel walls is what is required to prevent the pressure from the blood rupturing the vessel walls

Question 8

What are the sites of tissue blood flow regulation

Answer 8

The smooth muscle control of arteriole and precapillary sphincters

Question 9

Why is low tension required to appose the pressure in arterioles?

Answer 9

Because arterioles have a small radius, the smaller the radius then the lower the tension required as the blood pressure is decreased

Question 10

Describe the formation of an aneurysm

Answer 10

There is a weakened point in a vessel wall which cannot produce the required tension to appose the blood pressure. So the pressure stretches the wall, increasing the radius and therefore increasing the tension required to withstand the internal pressure. So high risk of rupture.

Question 11

How to arterioles regulate blood flow

Answer 11

Control regional distribution (The arteriole controls the supply of blood in the area where it is situated)

Question 12

How do metarterioles regulate blood flow?

Answer 12

They link arterioles directly to venules.

Question 13

How do precapillary sphincters regulate blood flow?

Answer 13

They vasodilate in response to local factors, increasing the blood flow to the capillary

Question 14

What are the ways of regulating tissue blood flow?

Answer 14

Active and reactive hyperemia, flow autoregulation, vasomotion and response to injury

Question 15

Describe what is meant by active and reactive hyperaemia

Answer 15

Active - If tissue is highly metabolically active, the rate of flow will increase
Reactive - Blood flow increases after a tissue has been deprived of blood for a period of time

Question 16

Describe flow autoregulation of tissue blood flow?

Answer 16

This occurs in response to changes in arterial pressure. If pressure is increased then arterioles restrict to reduce flow but if pressure is decreased then arterioles dilate to increase flow. It can also be in response to myogenic response (stretch activated calcium channels)

Question 17

How does vasomotion regulate tissue blood flow?

Answer 17

Spontaneous oscillating contraction of blood vessels. (it is random)

Question 18

Describe how response to injury can regulate tissue blood flow

Answer 18

Endothelial cells release endothelin-1 which causes vasocontriction so, for example if there is damage to an artery you are not loosing lots of blood.

Question 19

Describe the neural, hormonal and local effectors of vasocontriction

Answer 19

Neuronal - Sympathetic nerves.

• Hormonal - Adrenaline, angiotesin 2 and vasopressin.
• Local - Myogenic response and endothelian-1

Question 20

Describe the neural, hormonal and local vasodilator effectors

Answer 20

Neural - Nitric oxide releasing nerves.
Hormonal - Adrenaline and atrial-natriuretic peptide.
Local - Decreased oxygen, adenosine, potassium, CO2 and hydrogen, nitric oxide and bradykinin

Question 21

Describe acute and long term regulation of local blood flow

Answer 21

Acute - Rapid changes within seconds or mins due to local factors (adenosine, increased H+ and increased histamine)
Long term - Change in physical size or number of blood vessels

Question 22

Explain the pressure of blood flow through capilaries.

Answer 22

There is a low pressure and low velocity which allows time for diffusion and exchange of nutrients and waste. The volume passing through the capillaries is still the same as there are so many capillaries and therefore they have a large cross-sectional area.