L08-Peripheral circulation-Capillaries and veins

Question 1

What is the structure of a capillary?

Answer 1

It is a single cell thick with no elastin or smooth muscle so it cannot dilate or constrict
Its small diameter restricts the velocity of flow.

Question 2

What is ficks law of diffusion?

Answer 2

The rate of diffusion = permeability coefficient x area x concentration gradient

Question 3

What are the three main mechanisms of exchange through capillaries?

Answer 3

Diffusion
Vesicular transport
Bulk flow (through capillary fenestrations)

Question 4

How does the branching of capillaries effect diffusion?

Answer 4

It increases diffusion as it greatly iincreases the cross sectional area.

Question 5

What determines the flow to capillaries?

Answer 5

The dilation or constriction of the arterioles

Question 6

What substances tend to be moved across capillaries by vesicular transport?

Answer 6

Large charged molecules

Question 7

What is the change in blood pressure along a capillary?

Answer 7

Blood enters the capillary with a hydrostatic pressure of 35mmHg and leaves with around 15mmHg, this results in a difference of around 20mmHg

Question 8

How do veins differ from arteries?

Answer 8

They have less smooth muscle in the tunica media
Floppy rather than ridgid
Have valves
Capacity to hold large volumes

Question 9

What are the three layers of veins and arteries?

Answer 9

Outermost - tunica adventitia
tunica media
innermost - tunica intima

Question 10

What is meant by veins being capacitance vessels?

Answer 10

They can hold large volumes - 60-80% of blood found here

Question 11

What determines venous return?

Answer 11

Venous compliance as if the veins do not recoil the blood will not be returned.

Question 12

How does the compliance curve for veins appear?

Answer 12

The curve is steepest at low pressures as this is when the veins are most compliant and then it becomes more levelled out at higher pressures as it becomes less compliant.

Question 13

How does sympathetic control affect veins compliance?

Answer 13

They cause a constriction of smooth muscle that causes a fall in compliance. This causes a fall in capacitance and hence an increased venous return

Question 14

What are the main factors that affect central venous pressure?

Answer 14

Blood volume
Gravity
skeletal muscle pump 
venous capacitance
respitritory pump