Fluid shifts across the capillary wall: pulmonary & systemic oedema Flashcards
what percentage of body weight does total body water occupy in a young man?
60% of body weight
what fraction of body water is extra-cellular and what percentage of this is interstitial?
1/3rd of body water is extra-cellular
75%
what does the interstitial fluid act as?
as the go between blood and body cells
what are capillaries composed of?
= single layer of endothelial cells
What is the function of the capillaries?
= allows rapid exchange of gases, water & solutes with interstitial fluid
Consequently;
= delivering nutrients & O2 to cells
&
= removes metabolites from cells
what does blood flow in capillaries depend on?
depends on contractile state of arterioles
what do terminal arterioles regulate?
regulate regional blood flow to capillary beds (CB) in most tissues
what other thing regulates flow in few tissues (e.g. mesentery)
pre-capillary sphincters
describe the flow of blood in capillary beds?
blood flows slowly to allow adequate time for exchange
what do capillaries form when they unite?
venules
how are exchangeable proteins moved across the capillary wall?
by vesicular transport
what does fluid movement follow?
follows pressure gradient (bulk flow)
what do the movement of gases and solutes follow?
follows Fick’s Law of diffusion (i.e. downhill)
where do lipid soluble (lipophilic) substances go?
go through the endothelial cells
where do water soluble (hydrophilic) substances go?
go through the water field pores
Yes of No.
Can large molecules (e.g. plasma proteins) cross the capillary wall)?
No they CANNOT cross the wall
what is trans-capillary fluid flow driven by?
PASSIVELY driven by pressure gradients across capillary wall. (ultra-filtration)
what is ultra-filtration?
exchange across capillary wall of essentially protein free plasma
What is the relationship between net filtration pressure =?
NFP = Forces favouring Filtration - Forces Opposing Filtration
what also affects net fluid filtration?
= filtration co-efficient (Kf)
what forces are involved in trans-capillary fluid flow?
starling forces
what force FAVOURING FILTRATION n in trans-capillary fluid flow?
capillary hydrostatic pressure (MAIN) = Pc
and
interstitial fluid osmotic pressure
what force OPPOSE FILTRATION?
capillary osmotic pressure (main)
and
interstitial fluid hydrostatic pressure = Pi
describe the relationship between NFP, Pc, Pi and Pii and PiC?
NFP = (PC + Pii) - (Pic + Pi)
where does starling force favour filtration and re-absoprtion?
Favours filtration = at arteriolar end
Favours re-absoprtion = at venular
during a day, how does filtration exceed re-absoprtion?
filtration exceeds re-absoprtion by 2-4litres
how is excess fluid is returned to circulation?
via lymphatics as lymph
how much does pulmonary resistance comprise of the systemic circulation?
only 10%
Is pulmonary capillary hydrostatic pressure low?
YES (8-11mmHg)
what is capillary osmotic pressure?
25mmHg
what does efficient lymphatic drainage remove?
removes any filtered fluid thus preventing accumulation of interstitial fluid
what is oedema?
accumulation of fluid in interstitial space
in pulmonary oedema, describe the effect of diffusion and gas exchange in the lungs?
1) diffusion distance increases
2) gas exchange compromised
what are 4 cause of oedema?
1) raised capillary pressure
2) reduced plasma osmotic pressure
3) lymphatic insufficiency
4) changes in capillary permeability
what 2 things cause raised capillary pressure?
1) arteriolar dilation
2) raised venous pressure
- left ventricular failure = pulmonary oedema
- right ventricular failure = peripheral oedema (ankle, sacral)
- prolonged standing = swollen ankles
describe the plasma osmotic pressure in normal people and oedema patients?
Normal = 65-80g/l
Oedema if < 30g/l = malnutrition = protein malabsorption = excessive renal excretion of protein = hepatic failure
what 2 things cause lymphatic insufficiency?
1) lymph node damage
2) filariasis = elephantiasis
what 2 things cause changes in capillary permeability?
1) inflammation
2) histamine increases leakage of protein
where in particular does fluid accumulate in pulmonary oedema?
1) interstitial
2) intra-alveolar lung spaces
what is a symptoms of pulmonary of pulmonary oedema?
shortness of breath
in pulmonary oedema, what might you find clinically?
= crepitations in auscultation of lung bases
in pulmonary oedema, what might a chest X-ray show?
= haziness in perihilar region
where might you find pitting oedema?
1) ankles
2) sacrum
