Lymphatic system: Components and Functions


  • 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.

Parts of the Lymphatic system

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

Lymphatic system


  • 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.

Lymphatic system

Chemical composition:

  • Proteins (g/100 ml): 2.6
  • Chloride (m.eq/lit): 116
  • Calcium (m.eq/lit): 4.6
  • Urea (mg/100 ml): 23.5

Flow of Lymph:

  • The sequence of lymph flow:

Blood capillaries (blood)

Interstitial spaces (interstitial fluid)

Lymphatic capillaries (lymph)

Lymphatic vessels (lymph)

Lymphatic ducts (lymph)

Junction of the internal jugular and subclavian veins (blood)

Lymphatic system

  • 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.

Lymphatic Vessel

  • 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.

Lymphatic system

  • 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 system

Lymphatic Capillaries

  • 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.

Lymphatic system

Lymph Nodes

  • 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.


  • 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.

Lymphatic system


  • 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


  • 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.

Lymphatic system

Lymphatic system

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