Pathology- Oedema Flashcards
what is the role of interstitial fluid
acts as a go between blood and body cells
what does blood flow in the capillaries depend on
the contractile state of the arterioles
describe the structure of capillaries and their purpose
single layer if endothelial cells- allow rapid exchange of gases, water and solutes with interstitial fluid
-delivery of oxygen and nutrients and removal of metabolites
other than terminal arterioles what regulates blood flow in the capillary bed
precapillary sphincters, smooth muscle
why is blood flow in the capillaries slow
to allow adequate time for exchange
what do capillaries unite to form
venules
what substances are able to pass through the endothelial cells in a capillary wall
lipid-soluble substances (O2, CO2)
what substances pass through the pores of a capillary wall
small, water soluble substances (e.g Na+, K+, glucose, amino acids)
what substances are moved through the capillary wall by vesicular transport
exchangeable proteins
what substance cannot generally pass through the capillary wall
plasma proteins (large molecules)
what law does the movement of gases and solutes follow
ficks law of diffusion
‘blood flow is proportional to the difference in concentration of a substance in the blood as it enters and leaves an organ’
what drives trans-capillary fluid
pressure gradients across the capillary wall
describe what is meant by transcapillary fluid being ‘ultra-filtration’
it is the exchange across the capillary wall of essentially protein free plasma
what is net filtration pressure (NFP) inversely proportional to
forces favouring filtration - forces opposing filtration
what does a filtration coefficient show? (Kf)
how easily permeable a membrane is to fluid
what are the two forces favouring filtration (which is the most important)
Pc- capillary hydrostatic pressure (MVP)
PieI(i)- interstitial fluid osmotic pressure
(when these pressure rise they force fluid out of the capillaries)
what is capillary hydrostatic pressure a result of
blood pressure
what are the two forces opposing filtration and which is the most important
PieC- capillary osmotic pressure (MVP)
Pi- interstitial fluid hydrostatic pressure
what is the difference between hyrdostatic and osmotic pressure
hydrostatic (pushing fluid out)
osmotic (pulling fluid in)
what is usually the capillary osmotic pressure and why is it important
25mmHg, important due to plasma protein
how do you calculate net filtration pressure
(capillary hydro static pressure + interstitial fluid osmotic pressure) - (capillary osmotic pressure + interstitial fluid hydro static pressure)
describe the net filtration pressures in arteriolar end and venular end
arteriolar end positive (10mmHg)
venular end negative (favouring absorption of fluid into vessels)
what happens to the capillary hydrostatic pressure as you go from arterioles to venules
decreases
which exceeds the other during a day; filtration or re-absorption
filtration (by 2-4 litres)
what happens to excess fluid
returns to circulation via the lymphatics as lymph
what are the starling forces
osmotic and hydrostatic pressures
is pulmonary resistance high or low
low
is pulmonary capillary hydrostatic pressure low or high
low (8- 11mmHg)
is pulmonary capillary osmotic pressure low or high
high (25mmHg)
what prevents the accumulation of interstitial fluid (oedema)
efficient lymphatic drainage removes any filtered fluid
low pressure of pulmonary capillaries allowing absorption of water
what is oedmea
accumulation of fluid in interstitial and intraalveolar lung spaces
what happens to gas exchange in pulmonary oedema
compromised as diffusion distance increases
what are the causes of oedema
raised capillary pressure,
reduced plasma osmotic pressure, lymphatic insufficiency,
change in capillary permeability,
what can cause raised capillary pressure
arteriolar dilatation,
raised venous pressure
what can cause raised venous pressure
left ventricular failure,
right ventricular failure,
prolonged standing
how does raised venous pressure affect pulmonary capillaries
back pressure in pulmonary capillaries
what type of oedema does left ventricular failure cause
pulmonary oedema
what type of oedema does right ventricular failure cause
peripheral oedema (ankle, sacral)
what type of oedema does prolonged standing cause
peripheral- swollen ankles
how does heart failure affect the frank-starling curve
shifts it to the right
what causes reduced plasma osmotic pressure
malnutrition, protein malabsorption, excessive renal excretion of protein, hepatic failure
what causes lymphatic insufficiency
lymph node damage, filariasis (parasitic worms) (a.k.a elephantiasis)
what causes changes in capillary permeability
inflammation, histamine increases leakage of protein
how is pulmonary oedema manifested clinically
dyspnoea (difficulty breathing), orthopnoea (shortness of breath), pink frothy sputum, crepitations in auscultation of lung bases, haziness in peripheral region in CXR
where does pitting oedema occur
ankles, sacrum
what usually causes pitting oedema
right sided heart failure
