Interstitial fluid formation

Source region and uptake · Starling forces 2-4 L/day

Net capillary filtration governed by the Starling forces leaves more fluid in the interstitium each day than the venules take back. Lymphatics are the only route home, and the only route by which escaped plasma protein is recovered.

Detail

Filtered per day
About 20 L
Reabsorbed by venules
About 17 L
Returned as lymph
2-4 L/day
Starling equation
Jv = Kf[(Pc - Pi) - sigma(pi c - pi i)]
Protein handling
Interstitial protein can leave only by lymph

When it goes wrong

Raised capillary hydrostatic pressure in right heart failure

Pitting peripheral oedema once lymph flow can rise no further

Hypoalbuminaemia in nephrotic syndrome or liver failure

Low plasma oncotic pressure with generalised oedema and ascites

Increased permeability in sepsis or burns

Protein-rich interstitial fluid and intravascular volume depletion

Practise this structure

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