Lecture Topic 14: Capillary exchange

What main 3 design of capillaries that makes them perfectly for 2-way exchange?

Short diffusion distance / slow blood flow / large SA

What are the 3 structures of capillary?

Continuous / fenestrated / sinusoid

What are the function for fenestrated capillaries?

Water filled pores → rapid exchange of water and solutes

Where are fenestrated capillaries located?

Endocrine organs, intestine, kidneys

What are the function for sinusoid capillaries?

Large clefts between endotherlial cells and incomplete BM → free exchange of water and larger solutes

What are all the principal transport mechanisms involved?

Diffusion / Bulk flow / transcytosis

What is bulk flow?

When substances are moving down a pressure gradient

What substances are exchanged via (all types of) diffusion?

Lipid-soluble / ions / small water-soluble

What substances are exchanged via transcytosis?

Macro molecules

What part of an endothelial cell can substances move through via bulk flow?

Clefts / pores

What is determined by the net pressure difference across capillary walls?

Bulk flow between capillaries and interstitial fluid

What is blood colloid osmotic pressure?

The plasma osmotic pressure ‘pulling’ fluid IN

What is capillary hydrostatic pressure?

Blood pressure exerted on capillary walls ‘pushing’ fluid out

What is interstitial fluid hydrostatic pressure?

The pressure exerted on the outer capillary walls by the IF ‘pushing’ fluid in

What is the interstitial fluid colloid osmotic pressure?

The osmotic pressure of the interstitial fluid ‘pulling’ fluid out

What is the equation for the net filtration pressure?

Net filtration pressure = net hydrostatic pressure - net osmotic pressure

How would you work out the net hydrostatic pressure? (give abbreviations)

CHP - IHP

What is CHP?

Capillary hydrostatic pressure

What is IHP?

Interstitial fluid hydrostatic pressure

How would you work out the net osmotic pressure? (give abbreviations)

BCOP - ICOP

What is BCOP?

Blood colloid osmotic pressure

What is ICOP?

Interstitial fluid colloid osmotic pressure

What must the net filtration pressure be for filtration?

+ve

What must the net filtration pressure be for reabsorption?

-ve