What is lymph? How is the composition of lymph different from the blood plasma? What is the direction of its flow?

Lymph is a clear fluid that circulates throughout the lymphatic system, which is a part of the immune system. It is derived from the interstitial fluid that surrounds cells in tissues and organs.

The composition of lymph differs from blood plasma in several ways:

Cellular Elements: While blood plasma contains red blood cells, white blood cells, and platelets, lymph primarily contains white blood cells (lymphocytes), but lacks red blood cells and platelets.

Proteins: The concentration of proteins in lymph is lower compared to blood plasma. Plasma proteins such as albumin and globulins are usually not present in high concentrations in lymph.

Nutrients and Waste Products: Lymph contains nutrients, waste products, and other substances that diffuse from the interstitial fluid into the lymphatic vessels. However, the concentrations of these substances may differ from those found in blood plasma due to the selective permeability of lymphatic capillaries.

The direction of lymph flow is primarily from the peripheral tissues towards the heart. Lymphatic vessels have one-way valves that prevent backflow, ensuring that lymph flows in the right direction. Lymph is eventually returned to the bloodstream via the thoracic duct (which drains lymph from the lower body and the left side of the upper body) or the right lymphatic duct (which drains lymph from the right side of the upper body). These ducts empty into the venous circulation near the heart.