Physiology 5 - Vasculature

Question 1

What is the effect of a small change in vessel radius on blood flow and to what degree?

Answer 1

Huge increase - to the power of 4

Question 2

What is Reynold’s number used to determine?

Answer 2

Whether flow is likely to be laminar or turbulent

Question 3

What is the relationship between distending pressure (P), tension in the vessel wall (T) and radius of the vessel (R)?

Answer 3

T = PR

Question 4

The loss of what in the artery wall leads to aneurysm?

Answer 4

Tensile strength

Question 5

Why do arterioles constrict before blood enters the capillaries?

Answer 5

To reduce the pressure and hence reduce the possibility of damage occurring to the capillaries

Question 6

As a response to injury, endothelin-1 can sometimes be released from damaged endothelial cells. What does the release of endothelin-1 cause?

Answer 6

Potent vasoconstriction

Question 7

What is the difference between active hyperaemia and reactive hyperaemia?

Answer 7

Active hyperaemia is a response where blood flow will increase to a certain area where activity is heightened (resulting in more waste build up) (20x increase).
Reactive hyperaemia is a response to a temporary blockage in blood flow being alleviated (4-7x increase)

Question 8

Parabolic velocity profile flow is referred to as what type of flow?

Answer 8

Laminar

Question 9

What are 4 factors that increase the chance of flow being turbulent?

Answer 9

High velocity flow
Large diameter vessels
Low blood viscosity
Abnormal vessel wall

Question 10

How is Reynold’s number calculated?

Answer 10

(velocity of flow x radius of vessel) / viscosity

Question 11

If a value is calculated that is above the Reynold’s number, what does this suggest?

Answer 11

Turbulence will occur

Question 12

Decreasing velocity of blood flow has what effect on the blood viscosity?

Answer 12

Increases the blood viscosity

Question 13

What are Korotkoff sounds, with reference to turbulence?

Answer 13

Artificially generated turbulence - auscultations upon BP measurement with a sphygmomanometer

Question 14

What does LaPlace’s Law state?

Answer 14

Distending pressure (P) produces an opposing force or tension (T) in the vessel wall, proportional to the radius (R) of the vessel: T = P x R

Question 15

With regard to the parameters present in LaPlace’s Law, what happens in aneurysm and haemorrhage?

Answer 15

Radius increases but pressure remains the same. Therefore, tension increases. Since the area of the wall is damaged it cannot withstand the tension

Question 16

What is the function of a metarteriole?

Answer 16

Links arterioles to venules - capillaries branch from metarterioles

Question 17

What is vasomotion?

Answer 17

Spontaneous oscillating contraction of blood vessels, which seems to happen for no reason

Question 18

What is the molecule released from endothelial cells in response to injury causing potent vasoconstriction?

Answer 18

Endothelin-1

Question 19

What is the difference between active and reactive hyperaemia?

Answer 19

Active hyperaemia: rate of flow increase by up to 20x if tissue is highly active
Reactive hyperaemia: rate of flow increase to 4-7x the original when blood supply is blocked

Question 20

What is released by endothelial cells causing relaxation of smooth muscle cells and increasing blood flow?

Answer 20

Nitric Oxide (NO)

Question 21

What neural communicates cause vasoconstriction?

Answer 21

Sympathetic nerves

Question 22

What neural communicates cause vasodilation?

Answer 22

NO releasing nerves

Question 23

What hormones cause vasoconstriction?

Answer 23

Adrenaline
Angiotensin II
Vasopressin

Question 24

What hormones cause vasodilation?

Answer 24

Adrenaline

Atrial-natiuretic peptide

Question 25

What local factors cause vasoconstriction?

Answer 25

Endothelin-1

Myogenic response

Question 26

What local factors cause vasodilation?

Answer 26

Decrease in O2
K+, H20, H
Adenosine
NO
Bradykinin

Question 27

How is acute regulation of blood flow achieved?

Answer 27

Rapid changes within seconds or minutes (vasomotion)

Vasodilator theory widely accepted (‘local factors’): e.g. ↓P02, ↑PCO2, ↑H+, ↑ K+, ↑lactic acid, ↑ adenosine, ↑ H2

Question 28

How is long term regulation of local blood flow achieved?

Answer 28

Change in physical size or number of blood vessels