Primary lymphoid organs

This presentation clearly explains you about the types and functions of primary lymphoid organs

1. PRIMARY LYMPHOID ORGANS By S.Gangashri, Biotechnology

2. LYMPHOID SYSTEM The lymphoid system, is an organ system in vertebrates that is part of the  circulatory system  and the immune system. It is made up of a large network of lymph, lymphatic vessels, lymph nodes, lymphatic or lymphoid organs, and lymphoid tissues. The vessels carry a clear fluid called lymph (the Latin word  ” lympha”   refers to the deity of fresh water) towards the heart. Unlike the cardiovascular system, the lymphatic system is not a closed system.

3. DISCOVERY The lymphatic system was first described in the 17th century independently by  Olaus Rudbeck  and  Thomas Bartholin

4. FEATURES Lymph is very similar to blood plasma, in that it contains waste products and  cellular debris , together with bacteria and proteins. The cells of the lymph are mostly  lymphocytes. Associated lymphoid organs are composed of lymphoid tissue, and are the sites either of lymphocyte production or of lymphocyte activation. These include the  lymph nodes , the  spleen , the  thymus , and the  tonsils. Lymphocytes are initially generated in the  bone marrow. The lymphoid organs also contain other types of cells such as stromal cells for support. Lymphoid tissue is also associated with mucosas such as  mucosa-associated lymphoid tissue (MALT)

5. FUNCTIONS The human circulatory system processes an average of 20 litres of blood per day through capillary filtration, which removes plasma from the blood. Roughly 17 litres of the filtered plasma is reabsorbed directly into the blood vessels, while the remaining three litres are left in the interstitial fluid. One of the main functions of the lymphatic system is to provide an accessory return route to the blood for the surplus three litres. The other main function is that of immune defense.

6. TYPES OF LYMPHOID SYSTEM Primary lymphoid system Secondary lymphoid system

7. PRIMARY LYMPHOID ORGANS The lymphatic system is composed of Primary lymphoid organs. These organs include the bone marrow and the thymus. They create special immune system cells called lymphocytes.

8. BONE MARROW Bone marrow is a sponge-like tissue found inside the bones. That is where most immune system cells are produced and then also multiply. These cells move to other organs and tissues through the blood. At birth, many bones contain red bone marrow, which actively creates immune system cells. Over the course of our life, more and more red bone marrow turns into fatty tissue. In adulthood, only a few of our bones still contain red bone marrow, including the ribs, breastbone and the pelvis. The bones of the skeletal system serve many important functions for the body, from giving your body support to allowing you to move. They also play an important role in blood cell production and fat storage.

9. TYPES Bone marrow is the spongy or viscous tissue that fills the inside of your bones. There are actually two types of bone marrow: Red bone marrow  helps produce blood cells Yellow bone marrow  helps store fat.

10. FUNCTIONS Red bone marrow is involved in hematopoiesis. This is another name for blood cell production. Hematopoietic stem cells that are found in red bone marrow can develop into a variety of different blood cells - Red blood cells, Platelets, White blood cells. Yellow bone marrow is involved in the storage of fats. The fats in yellow bone marrow are stored in cells called adipocytes. This fat can be used as an energy source as needed. Yellow bone marrow also contains mesenchymal stem cells. These are cells that can develop into bone, fat, cartilage, or muscle cells.

11. THYMUS The thymus is a little-known organ in the body, it does some very important things. It is part of the lymphatic system, along with the tonsils, adenoids and spleen, and it's also part of the endocrine system. 

12. SIZE & SHAPE The thymus is located just below the breast bone. It is relatively large in infants and grows until puberty. In adulthood, it starts to slowly shrink and become replaced by fat, according to the National Institute of Neurological Disorders and Stroke. It can weigh only 5 grams in elderly adults. As it grows smaller, it seems the organ becomes less important. "Removal of the organ in the adult has little effect, but when the thymus is removed in the newborn, T-cells in the blood and lymphoid tissue are depleted, and failure of the immune system causes a gradual, fatal wasting disease.

13. FUNCTIONS The thymus produces progenitor cells, which mature into T-cells (thymus-derived cells). The body uses T-cells help destroy infected or cancerous cells. T-cells created by the thymus also help other organs in the immune system grow properly.  These cells are so vital, they are often donated to those in need. "It (the thymus) is the primary donor of cells for the lymphatic system, much as bone marrow is the cell donor for the cardiovascular system," according to a paper, "The Thymus: A Forgotten, But Very Important Organ," published by the U.S. National Library of Medicine (NLM).

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