Lecture 14-Capillary Exchange Flashcards
How do the capillaries provide a short distance for diffusion
thin walls-Thin walls (1µm)
Small diameter (8µm)
Close proximity to cells
why does blood flow slowly in capillaries
large cross-sectional area of capillary network
how does the capillary have a large surface area for exchange
10+ billion capillaries
600m^2
what are the 3 types of capillaries
continuous
fenestrated
sinusoid
which is the most common capillary
continuous
where are fenestrated capillaries found
endocrine organs, intestine and kidneys
features of fenestrated capillaries
water-filled pores to allow rapid change of water and solutes
where are sinusoid capillaries found
endocrine organs, liver, bone marrow, spleen
features of sinusoid capillaries
large clefts between endothelial cells and incomplete BM to allow free exchange of water and larger solutes e.g. plasma proteins
what are the transport mechanisms in capillary exchange
diffusion (down conc gradient)
bulk flow (down pressure gradient)
transcytosis (by vesicular transport; through endothelial cells)
what substances travel through endothelial cells via diffusion in capillary exchange
-lipid soluble gases and molecules e.g. O2, CO2, Fatty Acids
-ions e.g. Na+, K+, Ca2+,Cl- (via ion channels in the ECs)
what substances travel between endothelial cells in capillary exchange
small water-soluble molecules e.g water, ions, glucose, urea, amino acids
what substances travel via transcytosis in capillary exchange
macromolecules e.g glycoproteins in vesicles
where does bulk flow occur during capillary exchange
down pressure gradients between gaps and pores
what is bulk flow associated with in capillary exchange
filtration and reabsorption
what determines bulk flow between capillaries and interstitial fluid
the net pressure difference across capillary walls
what 4 forces influence fluid and solute movement
-capillary hydrostatic pressure
-interstitial fluid hydrostatic pressure
-blood colloid osmotic pressure
-interstitial fluid colloid osmotic pressure
capillary hydrostatic pressure
the blood pressure exerted on capillary walls ‘pushing’ fluid out
interstitial fluid hydrostatic pressure
the pressure exerted on the outer capillary walls by the IF pushing fluid in
blood colloid osmotic pressure
the plasma osmotic pressure pulling the fluid in
interstitial fluid colloid osmotic pressure
the osmotic pressure of the interstitial fluid pulling fluid out
net filtration pressure formula
net filtration pressure= net hydrostatic pressure - net osmotic pressure
net hydrostatic pressure formula
capillary hydrostatic pressure (decreases along capillary) - interstitial fluid hydrostatic pressure (generally negligible- 0)
what does net hydrostatic pressure favour
favours pushing fluid from capillary to IF
