Edema is due to-
Increased capillary osmotic pressure
Decreased lymph flow
Decreased hydrostatic pressure in capillaries
Both of the above
Pathogenesis of edema
Following conditions can cause edema :-
1) The increased hydrostatic pressure of capillaries, e.g. in CHF or DVT.
2) Decreased plasma osmotic pressure of capillaries: It results from Hypoproteinemia. When total plasma protein is below 5 gm/dl (normal 6-8 gm/dl) or albumin is below 2-5 gm/dl (normal 3.5-5 gm/dl) edema takes place. Conditions causing hypoproteinemia are nephritic syndrome, liver cirrhosis, protein-losing enteropathy, and PEM.
3) Defective removal of interstitial fluid by lymphatics: It is due to lymphatic obstruction, which may be inflammatory, neoplastic, post-surgical and post-irradiation.
4) Increased vascular permeability: It occurs in acute and chronic inflammation, and during angiogenesis (new vessels are leaky).
5) Sodium (salt) and water retention: The conditions responsible for this type of edema are ARF, acute glomerulonephritis, renal hypoperfusion, and increase renin angiotensin aldosterone system
(RAAS) activity.