Clin Phys Week 11 FINISHED

Question 1

What does the microcirculation consist of?

Answer 1

Vascular shunts

True capillaries

Question 2

What are vascular shunts?

Answer 2

Metarterioles - thoroughfare channel connecting in an arteriole directly with a post capillary venule

Question 3

What are true capillaries?

Answer 3

10 to 100 per capillary bed, capillaries branch off the met arteriole and return to the thoroughfare channel at the distal end of the bed

Question 4

Describe capillary walls

Answer 4

Approximately 4-9micrometres in diameter

Single layer of endothelial cells with clefts and vesicles.
-Clefts control water and small substance diffusion

Endothelial and basement layers control flow

Endothelial wall is thinner than in artery or vein.

Question 5

What is vasomotion? What is it regulated and controlled by?

Answer 5

Motion of blood through the capillary beds.

Regulated by:
-degree of opening of the arterioles, met arterioles and pre capillary sphincters.
Controlled by:
-local factors (metabolic products - CO2, H+
-neural stimulation

Question 6

How do substances move through the capillaries?

Answer 6

Filtration
Diffusion
Osmosis

Question 7

What does diffusion depend on?

Answer 7

Concentration gradient
Surface area
Size of the molecule
Lipid solubility
Distance

Question 8

What are the 2 forces inside capillaries that move fluid?

What determined which one moves the fluid at any given tome?

Answer 8

Hydrostatic pressure
Osmotic pressure

Whichever is the strongest determines the direction of fluid movement

Question 9

What are the 2 Starling Forces which determine the flow of fluid ****

Answer 9

1 - Capillary hydrostatic pressure
2 - Interstitial hydrostatic pressure
3 - Plasma colloid osmotic pressure
4 - Interstitial colloid osmotic pressure

Question 10

What is capillary hydrostatic pressure?

Answer 10

Hydrostatic pressure gradient created by the heart (BP)

The hydrostatic pressure gradient in capillaries is a net outward force, moving water through pores into the capillary wall.

The capillary pressure is protected from large changes in MAP, but is sensitive to changes of venous pressure including the central venous pressure

Question 11

What is central venous pressure?

Answer 11

The pressure in the right atrium

Question 12

What is interstitial hydrostatic pressure?

Answer 12

Pressures range from -8mmHg in the lungs to -2mmHg in the subcut tissue, +2mmHg in the liver and +6mmHg in the brain

Created by drainage of lymph and external compression force

Question 13

What is interstitial fluid? What does it comprise of? Where is the fluid contained?

Answer 13

The fluid contained within the interstitial space. Derived via filtration from the capillaries.

It has the same constituents as plasma except it has a lower protein concentration.

Fluid is generally entrapped in the proteoglycan filaments as a gel. Fluid mainly diffuses rather than flows.

Question 14

What is plasma colloid osmotic pressure? What is its average pressure?

Answer 14

Due to the plasma proteins (mainly albumin) creating osmotic pressure in the capillary.

Usually around 28mmHg (between 25-30mmHg)

Question 15

What is interstitial fluid colloid osmotic pressure? What is its average pressure?

Answer 15

Created by the leaking of small amounts of proteins into the interstitium.

Average around 8mmHg

Question 16

What is hydrostatic pressure?

Answer 16

Pressure on the inside of the capillary forcing out into the interstitial space because of force from the heart contractions etc

Question 17

What is osmotic pressure?

Answer 17

Pressure on the outside of the capillary forcing fluid into the capillary due to a higher solute concentration inside the the capillary.

Question 18

What can go wrong with pressure in the capillaries?

Answer 18

Increased capillary Hydrostatic pressure:

• arterial end (due to increase in BP)
• venous end (due to heart failure)

Decreased capillary osmotic pressure:
- decreased albumin plasma concentration due to starvation, liver or kidney disease)

Blockage lymphatic vessels