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21 Cards in this Set
- Front
- Back
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What is the function of capillaries?
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Exchange
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What is the structure of capillaries?
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comprised only of endothelium
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What is the blood flow through it like?
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Intermittent
can be more or less continuous due to changes in arteriolar diameter |
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What does arteriolar constriction do to the blood flow through capillaries? Why?
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Decreases it
Pressure capillary opening low, RBC more likely to block, flow cannot continue until RBC unblocks |
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What is the velocity of the blood in capillaries like?
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V low
0.07 cm/sec |
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What is the resistance like in the capillaries?
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significant - pressure drops as blood travels along
resistance, however, cannot be changed in capillaries |
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What are the 2 types of exchange across capillaries?
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Diffusion
Filtration |
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How do you work out rate of diffusion?
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P x (C1 - C2) x A
P = permeability of capillary endothelium C1 and C2 are concentrations of substance across endothelium A is the cross sectional area available for diffusion |
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What does permeability depend on?
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The type of capillary -
continuous is less permeable than fenestrated |
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What are all capillaries impermeable to?
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plasma proteins
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How can permeability be increased?
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Bradykinin = increases permeability in salivary and sweat glands during functiona/active hyperaemia
Bradykinin + histamine etc = increase permeability in tissues during inflammation/allergy Generally, permeability is constant |
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How does diffusion rate meet metabolism of tissue cells?
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Function hyperaemia
Increase SA Increase blood flow maintains higher concentration gradient (C1-C2) |
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What is filtration?
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The process by which fluid moves across the capillary endothelium
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What does filtration depend on?
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The balance between hydrostatic and osmotic forces across the wall of the capillary
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Define hydrostatic and oncotic pressure
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Fluid pressure
osmotic pressure mainly exerted by proteins |
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How do you work out the net osmotic pressure of plasma?
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plasma oncotic pressure - tissue osmotic pressure
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What happens to the net fluid into capillaries when the arterioles dilate?
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Decreases
functional hyperaemia opposite for constriction haemorrage |
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What happens to net fluid into capillaries when plasma protein concentration increases?
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increase
dehydration opposite for a drop in plasma proteins malnutrition, liver failure |
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What could cause an increase in tissue oncotic pressure?
What is a consequence of this |
Vascular permeability is increased, plasma proteins leak out
increase net fluid out inflammation/allergy |
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How many liters are filtered in and out of capillaries in 24 hours?
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20L out
16L in 4L out every 24 hours |
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What is the importance of the lymphatic system?
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Returns excess fluid to blood circulation
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