Formation of Tissue Fluid and Lymph

Tissue fluid, also known as interstitial fluid, surrounds our body cells, providing them with oxygen and nutrients, and removing waste products.
It’s formed from plasma, a component of blood, which leaks out of the capillaries into the surrounding tissues.
The process is driven by hydrostatic pressure, the force exerted by blood against the walls of the capillaries, which is higher at the arterial end.
At the arterial end of a capillary, the hydrostatic pressure is greater than the osmotic pressure, causing fluid to move out of the capillary and into the surrounding tissues.
As the blood moves along the capillary, the hydrostatic pressure decreases and the osmotic pressure remains relatively constant. Thus, near the venous end, the osmotic pressure is greater than the hydrostatic pressure, and some fluid moves back into the capillary.
The leftover fluid that does not return to the capillary becomes tissue fluid, allowing the exchange of gasses and nutrients between cells and the bloodstream.

Lymph is the tissue fluid that doesn’t get reabsorbed into the blood stream and instead is collected in the lymphatic system.
The tissue fluid enters the lymph capillaries through small spaces between their cells due to pressure gradients.
From the lymph capillaries, fluid is transported to larger vessels, then to lymph nodes, then to lymph trunks, and finally to the veins where it re-enters the bloodstream.
Lymph nodes, positioned along the lymph vessels, contain lymphocytes - a type of white blood cell - which play a vital role in the body’s immune response. Pathogens, foreign particles, and cellular debris transported by lymph are detected and destroyed here.
The lymphatic system hence acts as a drainage system, preventing fluid from building up in tissues, and a defence system, offering immunity by detecting and destroying pathogens.
To maintain fluid balance in the body, it’s essential that all these systems - the blood vessels, tissue fluid, and the lymphatic system work in harmony.