Fluid Shift Across the Capillary Wall Flashcards
What is the function of interstitial fluid?
Bathes the body cells
Acts as a go-between blood and body cells
How are lipid soluble (e.g. O2, CO2) substances transported across the capillary wall?
Through endothelial cells
How are small, water soluble substances (e.g. Na+, K+, glucose, amino acids) transported across the capillary wall?
Through the pores between endothelial cells
How are exchangeable proteins transported across the capillary wall?
Vesicular transport
How are plasma proteins transported across the capillary wall?
Generally cannot cross the capillary wall
What is the net filtration pressure?
Forces favouring filtration - forces opposing filtration
Also affected by net fluid filtration
Which forces favour filtration in transcapillary fluid flow?
Capillary hydrostatic pressure
Interstitial fluid osmotic pressure
Which forces oppose filtration in transcapillary fluid flow?
Capillary osmotic pressure
Interstitial fluid hydrostatic pressure
What happens to the capillary hydrostatic pressure as you move down a capillary?
Decreases from the arteriole to venule end
What are the significant forces involved in transcapillary fluid flow?
Capillary hydrostatic pressure
Capillary osmotic pressure
What is the net filtration pressure at the arteriolar and venular end of a capillary?
Arteriolar = +10mmHg Venular = -8mmHg
What overall affect do the Starling Forces have on fluid shift in a capillary?
Favours filtration at the arteriolar end (fluid is forced out of the capillary into the interstitium)
Favours reabsorption at the ventral end (fluid is forced into the capillaries from the interstitium)
How is excess fluid returned to the circulation?
Via lymphatics as lymph
Why dos excess fluid accumulate in the interstium?
Filtration rate exceeds reabsorption (10 out 8 in)
What is oedema?
Accumulation of fluid in the interstitial space
How does pulmonary oedema affect the lungs?
Diffusion distance increases -> compromised gas exchange
Compliance of the lungs is restricted -> breathlessness
What are the main causes of oedema?
Raised capillary pressure
Reduced plasma osmotic pressure
Lymphatic insufficiency
Changes in capillary permeability
What can cause a raised capillary pressure?
Arteriolar dilatation
Raised venous pressure =
LVF, RVF, prolonged standing
What form of oedema is caused by left ventricular failure?
Pulmonary oedema
What form of oedema is caused by right ventricular failure?
Peripheral oedema
i.e. ankle, sacral etc.
What form of oedema is caused by prolonged standing?
Swollen ankles
What can cause a reduced plasma osmotic pressure?
Malnutrition
Protein malabsorption
Excessive renal excretion of protein
Hepatic failure
How does a reduced plasma osmotic pressure cause oedema?
The forces opposing filtration and drawing the fluid back into the capillaries are lost
What can cause lymphatic insufficiency?
Lymph node damage
Filariasis - elephantiasis
Why do you not see pitting oedema in lymphatic insufficiency?
Pitting oedema is caused by fluid moving back into the lymphatics
Fluid cannot move if lymphatics are not working correctly
What can cause changes in capillary permeability?
Inflammation
Histamine increases leakage of protein
