Lymphatic system: Components and Functions

Contents:

The lymphatic system is a major part of the body’s immune system.
The lymphatic system is a subset of the circulatory system, with a number of actions.
The lymphatic system is a network of organs, lymph nodes, lymph ducts, and lymph vessels that make and move lymph from tissues of the bloodstream.
A lymphatic system is a specialized form of reticular connective tissue that consists of tissues and organs that produce, mature, and store lymphocytes and macrophages, for the body’s defense purposes.
It acts as a transport channel that carries white blood cells to and from the lymph nodes into the bones and antigen-presenting cells to the lymph nodes.
Lymphatic capillaries reabsorb excessive tissue fluid and transport the fluid through the lymphatic pathway and ultimately dispose of it into the blood.
Lymphatic vessels carry lipid and lipid-soluble vitamins absorbed by the gastrointestinal tract to blood.

Lymph
Lymphatic vessels
- Lymph trunks and ducts
- Thoracic (Left lymphatic) duct
- Right lymphatic duct
Lymphatic tissue
- Lymph nodes
- Tonsils
- Spleen
- Thymus gland

The excess interstitial fluid which drains into the lymphatic capillaries is called as lymph.
It is a clear watery fluid, similar in composition to plasma, with the exception of plasma proteins.
Lymph transports the plasma proteins that seep out of the capillary beds back to the bloodstream.
It also carries away bacteria and cell debris from damaged tissues, which are then filtered out and destroyed by the lymph nodes.
Lymph contains lymphocytes, which circulate in the lymphatic system allowing them to patrol the different regions of the body.
In the small intestine, fats absorbed from the lymphatics capillaries called as lacteals give the lymph, a milky appearance.

Chemical composition:

Blood capillaries (blood)

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Interstitial spaces (interstitial fluid)

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Lymphatic capillaries (lymph)

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Lymphatic vessels (lymph)

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Lymphatic ducts (lymph)

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Junction of the internal jugular and subclavian veins (blood)

The lymphatic flow is regulated by means of movements of skeletal muscles and through breathing movements.
This movement compresses the lymphatic vessels and forces the lymph flow towards the subclavian veins.
Lymphatic vessels contain a one-way valve that prevents the backflow of lymph.

These are tiny thin-walled vessels.
These are closed at one end.
The main purpose is to drain the excess of interstitial fluid from around the cell to the venous circulation.
The wall of lymphatic capillaries is made up of endothelium.
These are larger in diameter.
The anchoring filaments hold the endothelial cells to the nearby tissues.

A lacteal is a lymphatic capillary present in the mucosa of the small intestine
It absorbs dietary fats and lipid-soluble vitamins from the small intestine.
A special type of lymph, known as chyle, is produced in the digestive system as lymph absorbs triglycerides from the intestinal villi.
The chyle has a milky while coloration due to the presence of triglycerides.

Lymphatic capillaries combine together to form lymphatic vessels.
These are thin-walled structures that carry lymph.
Lymph vessels are lined by endothelial cells.
A lymph vessel pushes lymph from lymph capillaries to the lymphatic trunk and ducts.
Lymphatic vessels resemble small veins.

The oval or bean-shaped organs located along the length of lymphatic vessels are called as lymph nodes.
They range from 1 to 25 mm in length.
They are greyish pink in color.
These are scattered throughout the body, usually in groups.
These groups are arranged in two sets; superficial and deep.
Each node is covered by a dense connective tissue called as capsule.
The capsular extensions are called as trabeculae.
Internally node has two parts: the outer cortex and the inner medulla.
The outer cortex contains densely packed lymphocytes arranged in masses called as follicles.
The outer rim of each follicle contains T-lymphocytes and macrophages.
In the medulla, the lymphocytes are arranged in strands called as medullary rays.
Internal to the capsule is a supporting network of reticular fibres and fibroblasts.
Along with capsule, trabeculae, reticular fibres and fibroblasts constitute the stroma of the lymph node.
Each node has a concave surface called as hilum.
Four or five afferent lymph vessels may enter a lymph node while only one efferent vessel carries lymph away from the node.

Functions:

The lymph node filters foreign substances from lymph as it moves back to the cardiovascular system.
These substances along with microbes are trapped by the reticular fibres within the node.
Then lymphocytes and macrophages destroy the foreign substance by phagocytosis.

It is a flattened oval organ located in the upper part of the abdomen, under the diaphragm, and behind the stomach.
It is covered by dense connective tissue called a capsule.
The capsular extensions are called trabeculae.
Internal to the capsule is a supporting network of reticular fibres and fibroblast.
Along with capsule, trabeculae, reticular fibres, and fibroblast form the stroma (supporting network) of the spleen.
The spleen consists of two different kinds of tissue:
- White pulp: It consists of masses of lymphocytes and macrophages
- Red pulp: It consists of blood sinuses.
Spleen has a concave surface called as hilum.
The structure entering and leaving the spleen at the hilum are;
- Splenic artery
- Splenic vein
- Lymph vessels
- Nerves

Functions:

It plays an important role in the phagocytosis of bacteria, damaged RBC’s and platelets.
During early fetal devolvement, the spleen participates in the blood cell formation.
Spleen stores and releases blood in times of demand such as during hemorrhage.
The spleen contains T and B-lymphocytes which are activated by the presence of antigen to fight off infection.