In this article, we will discuss Edema. So, let’s get started.


Edema is also known as fluid retention or swelling, is the excessive collection of tissue fluid in the interstitial space. The generation of interstitial fluid is regulated by the forces of the Starling equation. The hydrostatic pressure within blood vessels tends to cause water to filter out into the tissue. This leads to a difference in the protein concentration between blood plasma and tissue. As a result, the colloidal or oncotic pressure of the higher level of protein in the plasma tends to suck (draw) water back into the blood vessels from the tissue. Starling’s equation states that the rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance.

Factors contributing to the formation of edema or Causes of edema

  • Increased hydrostatic pressure and tissue colloidal or oncotic pressure.
  • Reduced colloidal or oncotic pressure within blood vessels.
  • Increased blood vessel wall permeability.
  • Obstruction of fluid clearance in the lymphatic system.
  • Change in the water-retaining properties of the tissue. Raised hydrostatic pressure often reflects retention of water and sodium by the kidneys.


  • Pitting edema: Watery low protein content.
  • Inflammatory edema: Thick fluid with high protein content.




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