Lymphatic system
Lymph is a clear and colorless fluid; the word "lymph" comes from the Latin word lympha, which means "connected to water, or clear water.
The lymphatic system has three main functions:
It maintains the balance of fluid between the blood and tissues, known as fluid homeostasis.
It forms part of the body’s immune system and helps defend against bacteria and other intruders.
It facilitates absorption of fats and fat-soluble nutrients in the digestive system.
Anatomy
The lymphatic system consists of lymph vessels, ducts, nodes, and other tissues.
Around 2-3 liters of fluid leak from the cardiovascular system into body tissues every day. The lymphatic system is a network of vessels that collect these fluids, or lymph. Lymph is a clear fluid that is derived from blood plasma.
Lymphatic vessels
The lymphatic vessels are found everywhere in our body.
The smaller lymphatic vessels, which take up the fluids, are called lymph capillaries.
The lymph vessels form a network of branches that reach most of the body’s tissues. They work in a similar way to the blood vessels. The lymph vessels work with the veins to return fluid from the tissues. Lymph vessels take the lymph back to the lymph nodes (there are about 700 of these in total),
The fluid that arrives in the lymph nodes is checked and filtered.
Unlike blood, the lymphatic fluid is not pumped but squeezed through the vessels when we use our muscles. Like veins, lymphatic vessels have valves inside them to stop fluid from flowing back in the wrong direction.
Lymph nodes
The vessels branch through junctions called lymph nodes. In the lymph nodes, immune cells assess for foreign material, such as bacteria, viruses, or fungus.
Lymph nodes are not the only lymphatic tissues in the body. The tonsils, spleen, and thymus gland are also lymphatic tissues.
What do the tonsils do?
In the back of the mouth, there are tonsils. These produce lymphocytes, a type of white blood cell, and antibodies.
What is the spleen?
The spleen is not connected to the lymphatic system in the same way as lymph nodes, but it is lymphoid tissue. This means it plays a role in the production of white blood cells that form part of the immune system.
The thymus gland
The thymus gland is a lymphatic organ and an endocrine gland that is found just behind the sternum. It secretes hormones and is crucial in the production, maturation, and differentiation of immune T cells.
The bone marrow
Bone marrow is not lymphatic tissue, but it can be considered part of the lymphatic system because it is here that the B cell lymphocytes of the immune system mature
Function
Fluid balance
The fluid is found in tissue spaces and cavities, in the tiny spaces surrounding cells, known as the interstitial spaces. These are reached by the smallest blood and lymph capillaries.
Around 90 percent of the plasma that reaches tissues from the arterial blood capillaries is returned by the venous capillaries and back along veins. The remaining 10 percent is drained back by the lymphatics.
Loss of the lymphatic system would be fatal within a day. Without the lymphatic system draining excess fluid, our tissues would swell, blood volume would be lost and pressure would increase.
Absorption
Most of the fats absorbed from the gastrointestinal tract are taken up in a part of the gut membrane in the small intestine that is specially adapted by the lymphatic system.
The immune system
The third function is to defend the body against unwanted organisms. Without it, we would die very soon from an infection.
The body’s first line of defense involves:
• physical barriers, such as the skin
• toxic barriers, such as the acidic contents of the stomach
• “friendly” bacteria in the body
However, pathogens often do succeed in entering the body despite these defenses. In this case, the lymphatic system enables our immune system to respond appropriately.

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