Fluid Shift & Pulmonary and Systemic Oedems Flashcards
What is the purpose of the interstitial fluid?
it acts as a go-between the blood and the body cells
What is the purpose of the capillaries?
to allow rapid exchange of gases, water & solutes with interstitial fluid, they deliver nutrients and O2 to the cells and remove the metabolites
What effects the blood flow in the capillaries?
The contractile state of the arterioles
What vessels regulate regional blood flow to the capillary bed (CB) in most tissues?
Terminal arterioles
What regulates flow in a few tissues such as the mesentery?
Precapillary Sphincters
What speed does blood flow through the capillaries and why this speed?
It is very slow to allow adequate time of exchange with the interstitial fluid
How doe exchangeable proteins move across the capillary wall?
Through vesicular transport
What gradient does fluid movement follow?
The pressure gradient (Fick’s Law of Diffusion)
How do lipid soluble substances move through the capillary wall?
Through the endothelial cells
How do water soluble substances move through the capillary wall?
substances go through the water-filled pores
How is transcapillary fluid flow driven?
by the pressure gradient across the capillary wall
What is ultra-filtration?
exchange across the capillary wall of essentially protein-free plasma
Net filtration pressure (NFP) is directly proportional to
Forces favouring filtration - Forces opposing filtration
What coefficient affects net fluid filtration?
Filtration coefficient Kf
What are the 2 forces which favour filtration in transcapillary flow?
Pc - capillary hydrostatic pressure
- interstitial fluid osmotic pressure
What are the 2 forces which oppose filtration in transcapillary flow?
- capillary osmotic pressure
Pi - interstitial fluid hydrostatic pressure (-ve in some tissues)
What are the names of the forces which determine transcapillary fluid flow?
Starling forces
What movement of fluid do starling forces favour?
They favour filtration at the arteriolar end of the capillary bed and the venular end of the capillary bed
What substance in the plasma generally cannot cross the capillary bed?
The plasma proteins
NFP =
(Pc + interstitial fluid osmotic pressure) - (Pi + capillary osmotic pressure)
By how much does the filtration of fluid exceed re absorption each day?
2-4 L this excess is returned to circulation in the lymphatics
What is the definition of oedema (edema)?
accumulation of fluid in interstitial space
What are the causes of oedema?
- raised capillary pressure
- reduced plasma osmotic pressure
- lymphatic insufficiency
- changes in capillary permeability
What raises capillary pressure?
- arteriolar dilation
- raised venous pressure possibly due to (LV failure - pulmonary oedema, RV failure - peripheral oedema (ankle, sacral) and prolonged standing
What is the resistance in the pulmonary capillaries?
The pulmonary capillary hydrostatic pressure is low, the osmotic
What causes a reduced osmotic pressure?
- malnutrition
- protein malabsorption
- excessive renal excretion of protein
- hepatic failure
(reduced plasma proteins)
What causes lymphatic insufficiency?
Lymph node damage
filariasis - elephantiasis
What causes changes in capillary permeability?
inflammation
histamine increases leakage of proteins
What can left ventricular failure result in?
Pulmonary oedema as there is fluid accumulation in the interstitial and intraalveolar lung spaces
How does pulmonary oedema manifest clinically?
varying degrees of shortness of breath
crepitations in the lung bases
What is seen through pitting oedema?
Oedema is caused by the increased hydrostatic pressure sign of heart failure rather than lymphatic problem
