Physiology and Pharmacology
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| Two main functions of capillaries | show 🗑
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| Classes of capillaries | show 🗑
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| Intercellular cleft | show 🗑
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| show | Blocks protein access to the intercellular cleft
Transmembrane proteins conjugated to sugar molecules
Water and small molecules can move
Proteins are repelled - 4-5nm gaps too small
Hyaluronidase (released by macrophages) destroys this in inflammation
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| show | Allows slow permeation of proteins across the capillary wall
Transcytosis
Proteins cannot cross junctions so rely on vesicles
Can visualise by dinitrophenol conjugated albumin
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| Types of solutes | show 🗑
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| show | Solute flux is proportional to diffusion coefficient, surface area and conc difference but inversely proportional to thickness
Permeability is the diffusion flux/(area of membrane x conc difference)
Diffusion flux = Permeability x area x conc difference
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| show | Increased blood flow
Reduced interstitial concentration
Reduce capillary permeability e.g. in response to shear stress
Recruitment of capillaries
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| show | Less steep decay in luminal concentration - faster replenishment
Lower interstitial conc
Maintains concentration difference
Increased flow increases shear stress that increases permeability
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| Recruitment of capillaries | show 🗑
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| Oedema | show 🗑
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| Fluid absorption | show 🗑
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| Starling principle of fluid exchange - evidence | show 🗑
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| What affects flow | show 🗑
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| show | Flow = LpA[(Pc-Pi)-sigma(Pip-Pii)]
Lp = hydraulic conductance of endothelium
A = wall area
Sigma = osmotic reflection coefficient (capillary is leaky so only a fraction of osmotic pressure is exerted)
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| Medical importance of sigma | show 🗑
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| show | Usually favour filtration and formation of lymph
Increased imbalance causes oedema e.g. pulmonary oedema or mitral stenosis (due to increase in Pc or decrease in Pip)
If blood pressure falls e.g. haemorrhage these favour absorption (Pc reduced)
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| Causes of excessive capillary filtration | show 🗑
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