Lymph

LYMPH

Lymph is a clear to pale white fluid that circulates through the lymphatic system. It is mainly composed of white blood cells, especially lymphocytes, which help in defending the body against bacteria, viruses, and other harmful organisms.

Lymph bathes the body tissues, helps maintain fluid balance, and removes waste materials and microorganisms from tissues. It enters the bloodstream through lymphatic vessels and ducts.

Lymph contains water, proteins, glucose, oxygen, and white blood cells. It is formed from the excess interstitial fluid that is not reabsorbed back into blood capillaries.

COMPOSITION OF LYMPH

Lymph is a clear, colourless fluid whose composition is similar to blood plasma but contains less protein.

Cellular Part

• Lymphocytes
• T-cells
• B-cells

These cells play a vital role in immunity.

Non-Cellular Part

• Water (about 94%)
• Solids (about 6%)

Solid Components

• Proteins
• Fats
• Carbohydrates
• Urea
• Creatinine
• Inorganic and non-protein nitrogenous substances

Chemical Composition of Lymph

FUNCTIONS OF THE LYMPH

Fluid and Protein Balance

During blood circulation, a large amount of fluid filters out of blood capillaries into tissue spaces. About 1–2 litres (nearly 10%) of body fluid remains as interstitial fluid. This fluid contains essential proteins and nutrients.

The lymphatic system collects this excess fluid and proteins and returns them to the bloodstream, preventing tissue swelling and maintaining fluid balance.

Transportation of Nutrients

The lymphatic system works together with the circulatory system to transport nutrients. It plays a major role in carrying:

• Fats
• Fat-soluble vitamins (A, D, E, K)

These substances are absorbed from the intestine and transported to the bloodstream through lymph.

It also helps in distributing oxygen, hormones, and other nutrients to body cells indirectly through blood circulation.

Digestion

The lymphatic system assists digestion by helping in the absorption of dietary fats. Specialized lymphatic vessels present in the intestinal lining absorb fats and transport them as lymph.

Proper functioning of the lymphatic system is essential for fat assimilation. Failure of this system may lead to malnutrition. By ensuring proper fat transport, the lymphatic system also helps prevent unhealthy fat accumulation.

Excretion

The lymphatic system removes:

• Dead blood cells
• Excess tissue fluid
• Waste materials
• Cellular debris

It also helps in eliminating toxins, pathogens, and abnormal cells such as cancer cells from tissues and intercellular spaces.

Protection

The lymphatic system provides immunity through B-cells and T-cells.

• B-cells provide humoral immunity by producing antibodies
• T-cells provide cell-mediated immunity by destroying infected or abnormal cells

When harmful pathogens enter the body, these cells identify them, become activated, and destroy them, thereby protecting the body from diseases.

FORMATION OF LYMPH

The formation of lymph occurs through five important steps:

• Collection of excess fluid
• Entry into lymphatic capillaries
• Transport through lymphatic vessels
• Filtration in lymph nodes
• Return to bloodstream

Collection of Excess Fluid

The first step is the collection of interstitial fluid from tissue spaces. This fluid is formed when water and small molecules leak out of blood capillaries due to pressure differences.

Interstitial fluid supplies nutrients to cells and removes waste products. Excess fluid collects in tissue spaces and resembles plasma but contains less protein.

Entry into Lymphatic Capillaries

Lymphatic capillaries are thin-walled vessels present in most tissues except the central nervous system and bone marrow.

The entry of interstitial fluid into lymphatic capillaries occurs due to:

• Pressure gradients
• Anchoring filaments

Anchoring filaments pull open the capillary walls when tissues move, allowing fluid to enter. Once inside, the fluid is called lymph.

Transport through Lymphatic Vessels

After entering capillaries, lymph flows into larger lymphatic vessels. These vessels resemble veins and contain:

• One-way valves
• Smooth muscle in the walls

Lymph movement is aided by:

• Muscle contraction
• Arterial pulsation
• Body movements

Lymph passes through several lymph nodes during transport.

Filtration in Lymph Nodes

Lymph nodes are small, bean-shaped structures located along lymphatic vessels. They filter lymph by removing:

• Bacteria
• Viruses
• Foreign particles
• Cancer cells

Lymph enters through afferent vessels and exits through efferent vessels. Inside the node, immune cells identify and destroy harmful substances.

Return to Bloodstream

After filtration, lymph enters larger vessels and finally drains into two major ducts:

• Thoracic duct
• Right lymphatic duct

These ducts empty purified lymph into the subclavian veins, returning it to the bloodstream.