Organs of the Immune System or Lymphoid Organs : Types and their Function

Organs of the Immune System | Biotechnology

Throughout our body, many organs play an important role in the immune system. These organs are referred to as the organs of the Immune System or the lymphoid organs.

Today, we will be getting answers to many basic questions which come up with the topic. These are:

·        What are the organs of Immune System ?

·        Why they are known as lymphoid organs ?

·        What are the types of  Organs of the Immune System ?

·        How lymphoid organs work in Immunological system ?

·        In which way, is lymphatic system associated with the Organs ?

·        How cells of Immune system are different from the Lymphoid organs or Organs of the Immune System ?

 So, let’s just start the learning…

Our Immune System is composed of various organs and vessel shaped structure like our much known lymphatic system.

They all work together to defend or protect our body against pathogens and viral infected cells.

Organs are positioned throughout our body and lymphoid organs play an important role in producing, housing and in maturation of lymphocytes.

The movement of lymph between tissues and blood stream include the lymph, nodes and vessels are known as Lymphatic System.

The Lymphatic System produces antibodies and functions the immune processes or immune response.

Types of  Lymphoid Organs :

Here, we will highlight two main types of lymphoid organs. They are

1.     Primary Lymphoid Organs

2.     Secondary Lymphoid Organs

1.     Primary Lymphoid Organs :

Ø These organs are also known as Central Lymphocyte Organs.

Ø It is the place of lymphocyte maturation.

Ø Stem cells divide in primary lymphoid organs and become immunocompetent (ability of cells to evoke immune response).

Ø Largest part of the lymphocyte development occurs in primary lymphoid organs.

Ø The major primary lymphoid organs are:

a.     Thymus

b.     Bone marrow

a.     Thymus :

The most specialized organ of the immune system is thymus. It is placed in front of heart and behind the sternum.

T cells develop from hematopoietic cells (stem cells) and mature in thymus, so the cells are referred to as ‘T’.

The tolerancy of T cells to the body cells takes place in thymus only.

Thymus, being the largest immune organ is most active in newborn and during pre adolescent period.

Thymus slows down during teen period, but the production of lymphocytes is carried out throughout adult life.

b.    Bone marrow :

Bone marrow is a tissue present in hollow bones and mainly makes new blood cells.

Bone marrow is mainly categorized into two types : Red marrow and Yellow marrow.

Red marrow is mainly composed of myeloid tissue. Red blood cells, majority of White blood cells and platelets are produced in red marrow only.

Red marrow is present nearly in every bone in a child.

In adults, Red marrow is present in skull, ribs, sternum, vertebrae, a part of pelvic girdle and proximal heads of humerus and femur.

Yellow marrow  is mainly made up of fat cells. Most of the blood cells and capillaries are there in Yellow marrow.

Yellow marrow is present in adults only and produces no blood.

Yellow marrow is majorly found in medullary cavity of long bones.

The word ‘B’ in B cells is taken from bone marrow, because it is the site of B cell development and maturation.

2.     Secondary Lymphoid Organs :

Ø They initiate Adaptive immune response.

Ø These organs provide space or site for interaction of lymphocytes with antigen.

Ø The lymphocyte – antigen interaction then multiplies to become effector cells.

Ø The secondary lymphoid organs increase in size with age.

Ø These lymphoid organs comprises of :

a.     Spleen

b.    Lymph nodes

c.      Tonsils and Adenoids

d.    Peyer’s patches

e.      Appendix

a.     Spleen :

This organ i.e. spleen is a part of the lymphatic system and in humans; it is on the left side of the body, under the heart.

The spleen fights against infections, and make sure to keep the body cells healthy.

The spleen clear up old blood cells from the blood, and restores iron and amino acids from the old blood cells.

The spleen carries a stock of extra blood, if needed by the body.

It works in co-ordination with the circulatory system.

The spleen acts as a reservoir which carries over half the body’s monocytes.

The immunity mechanism works as,

Monocytes ----à Injured tissue --à Dendritic cells and Macrophages --à Tissue healing

b.    Lymph nodes :

Lymph node is an organ comprising of many types of cell and is an integral part of the lymphatic system.

Lymph nodes are found throughout the body and contain white blood cells.

They are responsible for the proper working of Immune system.

Lymph Nodes are mostly found in neck, underarm and groin region.

The lymph nodes swell up in the area of infected body part which keeps away the spreading of infection.

They refrain or reduce the pathogens to go through general body circulation and thus preventing the reach of pathogens to other parts of the body.

c.      Tonsils and Adenoids :

Tonsils are referred to as the lymphoid tissue areas present on the either side of the throat.

Infection of tonsils is called tonsillitis.

The word ‘tonsil’ is mostly referred to the palantine tonsils that are seen in the back of throat.

Tonsils’ are being a part of immune system, helps to protect against infection.

They basically fight off pharyngeal and upper respiratory tract infection.

Adenoids are also referred to as pharyngeal tonsils or nasopharyngeal tonsils which are present at the very back of the nose.

They are present in that part of nose which joins the mouth.

In children, sometimes they make a soft bump in the top and back section of the nasal air passage.

Removal of adenoids with surgery is called Adenoidectomy.

d.    Peyer’s patches :

Peyer’s patches are commonly referred as “tonsils of intestine”.

These patches are found in the wall of ilium region of small intestine where they capture and destroy bacteria present in the intestine.

Peyer’s patches are round and oval in shape which can be seen with naked eye.

They play a defined role in evoking immunologic response, as they contain both B cells and T cells.

These cells are similar to those found in peripheral lymph node.

Peyer’s patches work in the following manner :

Take up foreign material or bacteria ----> submucosal  macrophages----à macrophage processing ----à T cells and B cells.

e.      Appendix :

The ‘appendix’ is a pouch present at the beginning of large intestine.

It is a blind ended tube shape structure which helps immune system by supporting the growth of beneficial gut flora.

Appendix acts as a ‘safe house’ for bacteria which help in digestion.

Appendicitis is the swelling of appendix and one of the main causes of abdominal pain worldwide.

So, the above discussion gives us an insight about the various organs which are associated with the Immune System.

To know more about our immune system, its types and the cells involved in the immunogenic process, you can go through my Previous blogs to get more understanding on the Immune System basics and previously explained topics as below,

1.     ImmuneSystem Basic Concepts: Your Natural Defense and Body Cleanser

2.     Innate/Natural Immunity (OUR BODY’S FIRST LINE OF DEFENCE)

3.     CellsOf Immune System

4.  Adaptive Immune System or Acquired ImmuneSystem

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