How do capillaries modify the blood coming into them
Pre-capillary sphincter - it is not actually a physical structure but the arterioles leading up to capillaries have a lot of SM
Processes allowing transfer materials from blood to tissue
Diffusion
Filtration
Pinocytosis
Factors affecting quantity of substance diffused across capillaries per unit time
Capillary permeability to substance
Capillary SA
Concentration in and outside (not as relevant)
Filtration/Reabsorption
Movement of a volume of protein-free fluid out of the capillary (filtration) and back (reabsorption)
Net fluid transfer creates bulk flow
Important in determining distribution of ECF
Driving forces affecting movements of fluid (filtration/reabsorption)
Role of hydrostatic pressure in filtration/reabsoprtion
Capillary hydrostatic pressure pushes fluid out via filtration (Pc)
Interstitial fluid hydrostatic pressure works to push fluid back into capillary via reabsorption (Pi)
Role of osmotic pressure in filtration/reabsoprtion
Presence of proteins like albumin in capillary draws water into it via filtration as it cannot leave (πc)
Presence of proteins in interstitium that draw water out of capillary
What happens to pressure upstream and downstream of an arteriolar constriction
Increase pressure upstream
Decrease pressure downstream
- Hydrostatic pressure decreases in capillary and driving force of fiiltration is reduced
What happens to pressure upstream and downstream of a venular constriction
Hydrostatic pressure increases upstream
- Capillary filtration is favoured
Pressure decreases downstream
Which pressures are more significant in terms of regulating filtration/reabsorption
Capillary Hydrostatic Pressure
- Increase favours filtration
Plasma colloid osmotic pressure
- Increase favours reabsorption
Effect of liver damage on filtration/reabsorption
There will be less albumin produced, affecting osmotic pressure and reducing reabsorption
Effect of lymphatics on hydrostatic pressure during microcirculation
Effective drainage affects inerstitial fluid hydrostatic pressure so if there is poor lymphatic drainage, filtration will be favoured
Describe the changes in capillary hydrostatic pressure (Pc) & capillary colloid osmotic pressure (πc) from arteriole to venule
Pc drops across a capillry
πc remains about constant
Describe relationships between capillary hydrostatic pressure (Pc) and capillary colloid osmotic pressure (πc) for filtration/reabsorption
If Pc > πc, net filtration
If Pc < πc, net reabsorption
Describe the bulk flow at arterioles, capillaries and venules
Kf is filtration coefficient
Describe the changes that would occur to this graph with an increase in pre-capillary vasoconstriction
Describe the changes that would occur to this graph with an increase in venous pressure
Microcirculatory causes of oedema
Lymphatic Obstruction
Increased venous pressure (greater filtration)
Changes in protein levels
Hypervolaemia (increased fluid in vascular system)
Inflammation (vasodilatation & increased permeability)
