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What is Edema, causes and formation

Edema is increased fluid in the interstitial tissue spaces or it is a fluidaccumulation in the body cavities in excessive amount.Depending on the site, fluid accumulation in body cavities can be variously designated as:
a) Hydrothorax – fluid accumulation in pleural cavity in a pathologic amount.
b) Hydropericardium – pathologic amount of fluid accumulated in the pericardial cavity.
c) Hydroperitoncum (ascites) – fluid accumulation in peritoneal cavity.
d) Ancsarca – is a severe & generalized edema of the body with profoundsubcutaneous swelling.

Mechanism of edema formation:

Approximately 60% of the lean body weight is water, two-thirds of which is intracellular withthe remainder in the extracellular compartment.The capillary endothelium acts as a semipermeable membrane and highly permeable towater & to almost all solutes in plasma with an exception of proteins. Proteins in plasmaand interstial fluid are especially important in controlling plasma & interstitial fluid volume.Normally, any outflow of fluid into the interstitium from the arteriolar end of themicrocirculation is nearly balanced by inflow at the venular end. Therefore, normally, thereis very little fluid in the interstitium.
Edema is increased fluid in the interstitial tissue spaces or it is a fluidaccumulation in the body cavities in excessive amount

Edema formation is determined by the following factors:
1) Hydrostatic pressure
2) Oncotic pressure
3) Vascular permeability
4) Lymphatic channels
5) Sodium and water retention





1) Hydrostatic and oncotic pressures:

The passage of fluid across the wall of small blood vessels is determined by the balancebetween hydrostatic & oncotic pressures.There are four primary forces that determine fluid movement across the capillary membrane.Each of them can be listed under the above two basic categories, the hydrostatic pressure &the oncotic pressure. These four primary forces are known as Starling forces & they are:
a. The capillary hydrostatic pressure (Pc)
This pressure tends to force fluid outward from the intravascular space through thecapillary membrane to the interstitium.

b. The interstial fluid hydrostatic pressure (Pif)

This pressure tends to force fluid from the interstitial space to the intravascularspace.

c. The plasma colloid osmotic (oncotic) pressure (Пp)

This pressure tends to cause osmosis of fluid inward through the capillarymembrane from the interstitium. The plasma oncotic pressure is caused by thepresence of plasma proteins.

d. The interstial fluid colloid osmotic (oncotic) pressure (Пif)

This pressure tends to cause osmosis of fluid outward through the capillarymembrane to the interstitium.In addition, some fluid is normally derained by the lymphatic channels.Usually, excess fluidwill accumulate in the interstitium (i.e. edema is formed) when the capillary hydrostaticpressure is increased or when the plama oncotic pressure is decreased or when thelymphatic drainage is blocked.
What is Edema, causes and formation What is Edema, causes and formation Reviewed by gafacom on September 02, 2019 Rating: 5

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