TISSUE FLUID & OEDEMA
Oedema (dropsy) = Increase in fluid in extracellular spaces of tissue.
Extracellular fluid volume is largely dependent on total amount of Na+ in ECF compartment;
therefore, need to regulate Na+.
Tissue fluid is mainly produced in capillaries (microcirculation). Blood pressure coming into
the microcirculation is controlled by metabolic factors and sympathetic nervous system.
Capillary = approx. 6 micrometres in diameter. Capillary also has a single layer of permeable
endothelium.
3 TYPES OF CAPILLARY:
1. Continuous Capillary
Most common type of capillary.
Have tight junctions (held closely together).
Limiting factor = contains pores and size of pores limits the size of substance
coming through.
2. Fenestrated Capillary
Contain large pores.
No tight junctions and more permeable than continuous capillary.
Therefore, because of these features, found in kidney and gut for larger
molecules to get through.
3. Sinusoid Capillary (Discontinuous)
Wide spaces and allow proteins/RBC’s to pass through.
Found in the liver and spleen.
In terms of least leaky to most leaky: Continuous capillary < Fenestrated capillary < Sinusoid
capillary.
Solute permeability = dependent on pore size.
Plasma proteins can’t cross capillary wall.
Some solutes pass through endothelial cells (lipid solutes) whereas, some solutes pass
between endothelial cells via pores (Na+, K+, glucose and amino acids). However, pores are
quite small so limits rate and size of molecules that can get through.
Fluid flows in a unidirectional manor across the capillary wall.
Fluid flow from plasma to interstitial space is known as ultrafiltration.
Fluid flow from interstitial space to plasma is known as reabsorption.
Hydrostatic pressure = drives water out of capillaries.
Osmotic pressure = opposes hydrostatic pressure to do with solutes and drives water to a
high solute concentration.
Oedema (dropsy) = Increase in fluid in extracellular spaces of tissue.
Extracellular fluid volume is largely dependent on total amount of Na+ in ECF compartment;
therefore, need to regulate Na+.
Tissue fluid is mainly produced in capillaries (microcirculation). Blood pressure coming into
the microcirculation is controlled by metabolic factors and sympathetic nervous system.
Capillary = approx. 6 micrometres in diameter. Capillary also has a single layer of permeable
endothelium.
3 TYPES OF CAPILLARY:
1. Continuous Capillary
Most common type of capillary.
Have tight junctions (held closely together).
Limiting factor = contains pores and size of pores limits the size of substance
coming through.
2. Fenestrated Capillary
Contain large pores.
No tight junctions and more permeable than continuous capillary.
Therefore, because of these features, found in kidney and gut for larger
molecules to get through.
3. Sinusoid Capillary (Discontinuous)
Wide spaces and allow proteins/RBC’s to pass through.
Found in the liver and spleen.
In terms of least leaky to most leaky: Continuous capillary < Fenestrated capillary < Sinusoid
capillary.
Solute permeability = dependent on pore size.
Plasma proteins can’t cross capillary wall.
Some solutes pass through endothelial cells (lipid solutes) whereas, some solutes pass
between endothelial cells via pores (Na+, K+, glucose and amino acids). However, pores are
quite small so limits rate and size of molecules that can get through.
Fluid flows in a unidirectional manor across the capillary wall.
Fluid flow from plasma to interstitial space is known as ultrafiltration.
Fluid flow from interstitial space to plasma is known as reabsorption.
Hydrostatic pressure = drives water out of capillaries.
Osmotic pressure = opposes hydrostatic pressure to do with solutes and drives water to a
high solute concentration.
