Lymphatics and Edema Formation

The role of the lymphatic system

The lymphatic system prevents the accumulation of excessive interstitial fluid especially in the lung. In the absence of lymphatic obstruction, lymph flow can increase 20 to 50 times to remove excess fluid accumulation.

Lymph fluid is carried into the thorax and enters the subclavian veins to flow into the cranial vena cava and right atrium.

These vessels continuously remove interstitial fluid and prevent its excessive accumulation.

How is lymph formed?

It forms as a result of Starling Forces that promote a net efflux of fluid from the vascular compartment into the interstitial spaces. Plasma protein is also deposited into the interstitial spaces by pinocytosis. This fluid and protein accumulation is removed continuously by lymphatics.

Factors promoting the flux of fluid

Into the lymphatic vessels:

• Excessive production of interstitial fluid

Out of the lymphatic vessels:

• Excessive hydrostatic pressure in the right side of the heart
• Overwhelmed lymphatic flow
• Lymphatic obstruction

Edema Formation

Edema is excessive fluid accumulation in interstitial spaces. It can develop in any organ or collect as free fluid in body cavities (such as ascites, pleural effusion, pericardial effusion).

Factors promoting the development of edema

Edema may occur because of: 

1. Excessive fluid filtration out of capillaries, which can be due to :
   • Elevated hydrostatic pressure usually due to heart failure (see Starlings Forces) or over-hydration
   • Reduced plasma colloid osmotic pressure (hypoproteinemia) which itself can be due to:
     • Excessive protein loss from the kidneys or GI tract
     • Reduced production from the liver
   • Increased capillary membrane permeability
2. Lymphatic obstruction