Lymphatic System: Definition, Functions & Structure

Lymphatic System: Do you know the name of one system in our body that is a part of the circulatory system and the immune system? The lymphatic system (or lymphoid system) in our body contains white blood cells that provide immunity to fight against diseases. The lymphatic system refers to a network of tissues and organs that help get rid of the toxins, waste, and other unwanted materials from the body.

To score high in the exam, students must have an idea about the Lymphatic system, Lymphatic drainage, Lymphatic system function, Lymphatic vessels, Lymphatic organs, etc. Embibe has a separate team of experts who constantly work for students to provide them with the best study materials. Read on to know more about Lymphatic System.

Lymphatic System Definition: Lymphatic System Function

The lymphatic system is an elaborate network of vessels that collects the interstitial fluid (or tissue fluid) along with some protein molecules and drains it back into the major veins. It is also defined as a network of tissues and organs that help to get rid of the toxins, waste and other unwanted materials from the body.

Lymphatic System Structure or Anatomy: Lymphatic Organs

1. The lymphatic system comprises lymph, lymphatic capillaries, lymphatic vessels, lymphatic nodes, and lymphatic ducts. 
2. It also consists of other organs and tissues like the spleen, thymus, tonsils, Peyer’s patches, etc.

Fig: Human Lymphatic System

Lymphatic System Components

A. Lymph

1. Lymph is a fluid connective tissue that flows inside the specialised vessels known as lymphatic vessels. 
2. It is a colourless fluid that is a part of the tissue fluid, that in turn, is a part of the blood plasma. 
3. The lymph contains very small amounts of nutrients and oxygen but contains abundant carbon dioxide and other metabolic wastes as compared to the tissue fluid.
4. It also has a high concentration of WBCs (specialized lymphocytes) and contains all the ions present in blood plasma.
5. It is devoid of RBCs, platelets, and some plasma proteins and has less calcium and phosphorus content compared to blood.

B. Lymphatic Capillaries

1. These capillaries are thin-walled, small, and are composed of a single layer of endothelial cells.
2. They lie close to the blood capillaries but differ from the capillaries to the extent that they end blindly.
3. The lymphatic capillaries of intestinal regions, which absorb the digested fats are called lacteals.

Fig: Lymph and Lymphatic capillaries

C. Lymphatic Vessels

1. The lymphatic capillaries combine to form large lymphatic vessels.
2. They are formed of an outer coat of fibrous tissue, a middle coat of muscular tissue and an inner lining of endothelial cells. 
3. They have numerous valves.
4. They are present in all tissues except the central nervous system and cornea.

Structure ofLymphatic vessel

D.  Lymphatic Nodes

1. They are small oval or bean-shaped structures located along the length of lymphatic vessels and are 1-25 nm long.
2. They are covered by a capsule of dense connective tissue through which the lymph gets filtered.
3. They produce the B-lymphocytes that change to plasma cells to produce antibodies against invading antigens and T-lymphocytes that directly attack the foreign particles.
4. They also contain macrophages that remove bacteria, foreign materials, and cell debris from the lymph.

Structure of Lymphatic Node

Lymphatic Ducts

The lymphatic ducts are of the following two kinds:

1. Thoracic Duct

1. The lymphatic vessels of the left side unite to form a thoracic duct which begins at the cisterna chyli (a sac-dilation situated in front of the first and second number vertebrae).
2. The thoracic duct contains several valves that discharge its lymph into the left subclavian vein.

2. Right Lymphatic Duct

1. The lymphatic vessels of the thorax (right side), head and neck combine to form the right lymphatic duct.
2. This duct is about 1 cm in length and discharges its lymph into the right subclavian vein.

Fig showing the types of Lymphatic Ducts

Lymphoid Organs

There are three types of lymphoid organs in our body which are as follows:
1. Primary lymphoid organs
2. Secondary lymphoid organs
3. Tertiary lymphoid organs

1. Primary Lymphoid Organs

1. Primary lymphoid organs are those organs where B and T-lymphocytes mature and acquire antigen-specific receptors.
2. These organs are the sites of origin and proliferation of lymphocytes.
3. After the maturation of lymphocytes, they migrate to the secondary lymphoid organs.
4. Primary lymphoid organs include bone marrow and thymus.
   a. Bone marrow: It is the main lymphoid organ where all blood cells including lymphocytes are formed. Maturation of B-lymphocytes occurs here only.

Fig showing bone marrow

Thymus

1. The Thymus is also a lymphatic organ that lies in the upper chest near the neck.
2. It is prominent in children but begins to degenerate in early childhood.
3. It teaches the lymphocytes in the foetus to distinguish the body cells (self) from foreign cells (non-self).

Structure of Thymus

2. Secondary Lymphoid Organs

1. Secondary lymphoid organs are the sites where B and T-lymphocytes interact with the antigen, and then proliferate and differentiate to become effector cells.
2. These organs include lymph nodes, spleen, tonsils, Peyer’s patches of the small intestine, and Mucosal associated lymphoid tissues (MALT).
   a. Spleen
   i. The spleen is the largest component of the lymphatic system. It is a large, bean-shaped, vascular, dark-red organ located in the abdomen just below the diaphragm at the tail of the pancreas behind the stomach.
   ii. Spleen is composed of red pulp rich in RBCs having small patches of white pulp (lymphatic nodules) scattered in it.
   iii. The red pulp is enclosed by a capsule of white fibrous tissue that sends trabeculae into the pulp and is surrounded by the visceral peritoneum.
   iv. The functions of the spleen include destruction of worn-out RBCs, a reservoir for RBCs, production of antibodies, erythropoiesis, etc.
   

Fig showing Anatomy of Spleen

b. Tonsils
i. Tonsils too are lymphatic tissues that are located in the throat.
ii. They do not filter lymph and protect against infection.

Fig showing types of Tonsils

c. Peyer’s Patches
i. These are clusters of lymph nodes found in the small intestine, especially along the ileum. 
ii. They produce lymphocytes.

Fig showing Peyer’s Patches

d. Mucosal-Associated Lymphoid Tissues (MALT)
i. MALT is aggregations of lymphoid tissues located within the lining of the major tracts like respiratory, digestive, and urogenital tracts.
ii. It constitutes about \(50\% \) of the lymphoid tissues in the human body. They are the centres of lymphocyte production.
iii. Apart from lymphocytes, phagocytic macrophages and dendritic cells are also present.

Mucosal Associated Lymphoid Tissues (MALT)

3.Tertiary Lymphoid Organs 

1. Tertiary lymphoid organs usually contain very few numbers of lymphocytes which assume their role when they encounter the antigens that cause inflammation.
2. These organs also play an important role in the immune response to cancer.

Tertiary lymphoid structure in cancer

Lymphatic Circulation

1. The lymph flows at extremely low pressure in the lymphatic vessels that get filtered through the lymph nodes to remove bacteria, abnormal cells and other matter.
2. The fluid that is forced out of the blood capillaries sets up some pressure in the tissue fluid. This establishes a pressure gradient in the lymphatics that causes the flow of lymph into the lymphatic ducts.
3. Movements of the viscera and the contractions of the body muscles help considerably in squeezing the lymph along.
4. The valves present in lymphatic vessels prevent the backflow of lymph.
5. Movement of villi assists flows of lymph in the lacteals.
6. Gravity helps in moving the lymph down the lymphatic vessels of the head and neck. Lymph only moves in one direction, i.e., towards the heart.

Fig showing Lymphatic Circulation

Lymphatic System Functions

The functions of the lymphatic system are as follows:

1. It helps in draining excess tissue fluid from the extracellular spaces back into the blood.
2. The lymphatic vessels store the fluid absorbed from the digestive tract temporarily and release it gradually so that the kidneys do not face a sudden pressure of urine excretion.
3. It transports carbon dioxide and nitrogenous waste materials that diffuse into the tissue fluid to the blood.
4. It transports lymphocytes and antibodies from the lymphatic nodes to the blood.
5. It transports the digested and absorbed fats from the intestine to the blood in the form of chylomicron droplets.
6. It kills the invading microorganisms and foreign particles in the lymphatic nodes.
7. It helps to maintain the quality and quantity of the blood by restoring the fluid and solutes that leave it.
8. The plasma protein macromolecules synthesised in the liver cells and hormones produced in the endocrine glands are brought by the lymphatic system to the blood. 

Lymphatic System Diseases

Following are the diseases in which the lymphatic system stops working properly:

1. Lymphoma: It is the cancer of the lymphatic system.
2. Lymphadenitis: It is the swelling of the lymph node due to infection.
3. Lymphedema: It results due to the blockage in the lymphatic system due to the swelling of the tissues causing oedema.

Summary

Thus, the lymphatic system comprises an extensive network of vessels that passes through almost all our tissues to allow the movement of lymph. There are about 600 lymph nodes in the body. The lymphatic system plays a key role in the immune system, fluid balance, and absorption of fats and fat-soluble nutrients. If the nodes, ducts, vessels, or lymphatic tissues become blocked, infected, inflamed, or cancerous, then the lymphatic system can stop working properly.

FAQs on Lymphatic System

Q.1. What is a Lymphatic System?
Ans: Lymphatic system is an elaborate network of vessels that collects the interstitial fluid (or tissue fluid) along with some protein molecules and drains it back into the major veins.

Q.2. What are the 6 lymphoid organs?
Ans: The names of 6 lymphoid organs are the spleen, thymus, tonsils, bone marrow, mucous membranes, and lymph nodes.

Q.3. What are the functions of the lymphatic system?
Ans: The functions of the lymphatic system are as follows:
a. It helps in draining excess tissue fluid from the extracellular spaces back into the blood.
b. The lymphatic vessels store the fluid absorbed from the digestive tract temporarily and release it gradually so that the kidneys do not face a sudden pressure of urine excretion.
c. It transports carbon dioxide and nitrogenous waste materials that diffuse into the tissue fluid to the blood.
d. It transports lymphocytes and antibodies from the lymphatic nodes to the blood.

Q.4. Does Apple Cider Vinegar help the Lymphatic System?
Ans: Apple cider vinegar contains potassium that helps to break the mucus in the body and clean the lymph nodes. It also binds to the toxins that help in removing the toxins.

Q.5. What happens when your lymphatic system malfunctions?
Ans: Following diseases are caused when the lymphatic system malfunctions:
a. Lymphoma: It is the cancer of the lymphatic system.
b. Lymphadenitis: It is the swelling of the lymph node due to infection.
c. Lymphedema: It results due to blockage in the lymphatic system.

Q.6. How do you tell if your lymphatic system is blocked?
Ans: When the lymphatic system gets blocked, the fingers get swollen, hands and feet get cold, increase in weight, depression, and fatigue.

Q.7. How does the lymphatic system protect your body?
Ans: The lymphatic system is formed of various lymphoid organs that produce phagocytic WBCs, macrophages, B, and T-lymphocytes that help to fight against the invading antigens as well as to produce antibodies.

Q.8. How do you manually drain your lymphatic system?
Answer: Manually lymphatic system can be drained by lymphatic massage which involves two steps, i.e., clearing and reabsorption.

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