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Renin Angiotensin Mechanism.

Lymphatic System.

 Lymphatic System:

Introduction:

  • Within the spaces between the cells the tiny vessels are present called lymphatic capillaries. 

  • These capillaries drain water and some particles from the intestinal spaces. 

  • The fluid which is present in the lymphatic capillaries is called as lymph (LIMF-clear fluid). 

  • Normally 3 litres of lymph is produced and drained into lymphatic capillaries per day. 

  • Lymph is clear watery fluid similar in composition to blood plasma without plasma proteins. 

  • The lymphatic system consists of lymphatic capillaries, lymphatic vessels, lymph nodes and lymph fluid.

Functions of the lymphatic system:

1) Lymphatic vessels drain excess interstitial fluid from tissue spaces and return it to the blood.

2) Lymphatic vessels carry lipids and lipid soluble vitamins which are absorbed by the gastrointestinal tract to the blood.

3) Lymphatic system is concerned with the production and maturation of lymphocytes responsible for immunity.

Lymph circulation:

  • The lymphatic capillaries located in the spaces between the cells unite to form larger lymphatic vessels. 

  • At interval between the lymphatic vessels lymph flows through lymph nodes. 

  • All the lymphatic vessels come out from the lymph nodes and unite to form lymph trunks. 

  • From the lymph trunks, lymph flows into two important ducts i.e. the thoracic duct and the right lymphatic duct.

  • The thoracic duct is about 38-45 cm long and begins as dilation called the cisterna chyli present anterior to the second lumbar vertebra. 

  • The thoracic duct is the main duct which receives lymph from the left side of the head, neck, chest, left upper limb and the entire body below the ribs.

  • The right lymphatic duct is about 1.2 cm long and receives lymph from the upper right side of the body. 

  • The right lymphatic duct and the thoracic duct empties its lymph into right subclavian vein and left subclavian vein respectively.

Lymph nodes:

  • There are about 600 bean shaped lymph nodes present along the length of lymph vessels. 

  • They occur in groups, mainly present near the mammary glands, axillae and groin region.

  • Four to five afferent vessels enters into the lymph node while only one efferent vessel carries lymph away from the node. 

  • Outer capsule is made up of fibrous tissue that goes into the node which forms the partitions called trabeculae. 

  • The lymph node consists of reticular and lymphatic tissue containing many lymphocytes and macrophages.

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Fig.6.1-L.S.of Lymph node

Lymphatic organs and tissues:

1) Spleen:

  • The spleen is oval in shape and it is the largest lymphatic tissue in the body.

  •  It measures about 12 cm in length. 

  • The spleen is present at the left side in between the stomach and diaphragm. 

  • The spleen varies in size and shape between people, but it’s commonly fist-shaped, purple, and about 4 inches long. 

  • Because the spleen is protected by the rib cage, you can’t easily feel it unless it’s abnormally enlarged.

  • Spleen consists of hilum. 

  • The splenic artery, splenic vein and efferent lymphatic vessels pass through the hilum. 

  • It is surrounded by a capsule of dense connective tissue. 

  • Trabeculae go inward from the capsule. 

  • Splenic pulp is present between the trabeculae which consist of lymphocytes and macrophages.

Functions of spleen:

1) Old and abnormal erythrocytes are destroyed in the spleen.

2) Breakdown products, bilirubin and iron are transported to the liver via splenic and portal vein.

3) Phagocytosis of microorganisms takes place in the spleen.

4) The spleen consists of up to 350 ml of blood and act as blood reservoir in case of haemorrhage.

5) The lymphocytes of the spleen carry out immune function.

6) The fetal blood cells are produced in the spleen and liver.

2) Thymus 

  • The thymus is present in between the sternum and the aorta. 

  • T-lymphocytes migrate from red bone marrow to the thymus where they start to mature. 

  • Thymus is large in infants weighing about 70 gm. 

  • After puberty the thymus tissue are replaced by areolar and connective tissue and in old age the thymus weighs about 3 gm.

QUESTIONS

  1. Define lymph. Give its composition.

  2. Give the functions of the lymphatic system.

  3. Describe lymphatic system.

  4. What are lymph nodes? Give their functions.

  5. Draw a well labelled diagram of lymph node.

  6. What is spleen? Describe its structure and functions.

  7. Explain lymph circulation in short.
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