Fluid shift across capillary wall Flashcards
What % of weight is body water?
60% of body weight
What proportion of body water is extracellular?
1/3rd
What percentage of body water is interstitial?
75%
What is the function of interstitial fluid?
acts as the go-between blood and body cells
What is the roll of capillaries in terms of metabolites?
remove metabolites from cells
What does blood flow in the capillaries depends upon?
the contractile state of the arterioles
In which tissue are precapillary sphincters present?
mesentery
What is the rate of blood flow through the capillary bed?
slow (like a lake)
What do capillaries unite to form?
Venule
How do water soluble substances pass through capillaries?
through water filled capillary pores
How do lipid soluble substances pass through capillaries?
gasses can pass through endothelial cells
How are exchangeable proteins moved across the capillary walls?
vesicular transport
How do plasma proteins pass across capillary walls?
They can’t
What gradient does fluid follow?
Pressure gradient
What gradient do gasses and solutes follow?
Fick’s law of diffusion
What is transcapillary flow driven by?
Pressure gradients
What is ultra-filtration?
exchange of protein-free plasma across capillary walls
What are the forces favouring filtration?
capillary hydrostatic pressure (Pc) interstitial fluid osmotic pressure (πi)
What are the forces opposing filtration?
capillary osmotic pressure (πc)
Interstitial fluid hydrostatic pressure (Pi)
What is the normal value for Pc?
35mmHg at arteriolar end
17mmHg at venular end
What is the normal value for πi?
1mmHg
What is the normal value for πc?
25mmHg
What is the normal value for Pi?
1mmHg
Where to starling forces favour absorption and filtration?
Favour filtration at the arteriolar end
Absorption at the venular end
How is excess fluid returned to the circulation?
Via the lymphatics as lymph
What is pulmonary resistance in comparison to systemic resistance?
10%
What is pulmonary capillary hydrostatic pressure?
Low (8-11mmHg)
What is capillary osmotic pressure?
25mmHg
Why is lymphatic drainage so important?
Prevents accumulation of interstitial fluid
What is oedema?
Accumulation of fluid in the interstitial space
What factors are affected by pulmonary oedema?
Diffusion distance increases so gas exchange is compromised
Compliance is affected
What are the causes of oedema?
Raised capillary pressure
Reduced plasma oncotic pressure
Lymphatic insufficiency
Changes in capillary permeability
LVF
What are the causes of raised venous pressure?
Left ventricular failure (pulmonary oedema)
Right ventricular failure (peripheral oedema, sacral)
Prolonged standing (swollen ankles- damage the valves in the lower limb veins)
What will heart failure do to the frank starling curve? and why?
Shift it right
you will have less stroke volume per pre-load, causing pooling of blood in the heart and creating back-pressure
What is the normal plasma protein pressure?
65-80g/l
What are the causes of raised capillary pressure?
arteriolar dilatation
raised venous pressure
When does reduced plasma protein cause oedema?
When it is <30g/l
What are the causes of reduced plasma oncotic pressure?
Malnutrition
Protein malabsorption
Excessive renal excretion of protein (proteinuria)
Hepatic failure (liver is not manufacturing proteins in the first place)
What are the causes of lymphatic insufficiency?
Lymph node damage
Filariasis-elephantiasis
What kind of oedema will lymphatic deficiency cause?
Non-pitting oedema
What are the causes of change in capillary permeability?
Inflammation
(histamine increases leakage of proteins)
What is the pathogenesis of LVF in oedema?
accumulation of fluid in the interstisital and intra-alveolar lung spaces, manifested by varying degrees of SOB.
What are the clinical manifestations of LVF?
Clinically there may be crepitation’s in auscultation of lung bases.
chest x ray shows haziness in perihilar region
