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Immune System Anatomy: Organs and Tissues

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Terms you will need

  • bone marrowBone marrow is a soft tissue inside bones where blood cells are made. It helps create different types of blood cells, including those that fight infections.
  • thymusThe thymus is an organ where T cells, a type of immune cell, mature. It helps train these cells to fight infections and not attack the body's own tissues.
  • spleenThe spleen is an organ that filters blood, removes old red blood cells, and helps fight infections by making antibodies and storing immune cells.

How this topic runs

  1. 1Start here
  2. 2How it works
  3. 3At competition depth

The immune system is a complex network of organs, tissues, and cells that defends the body against harmful pathogens and diseases. Key components include the bone marrow, thymus, and spleen, which play vital roles in the development and function of immune cells. The bone marrow produces blood cells, including lymphocytes, which are crucial for immune responses. The thymus is where T cells mature, ensuring they can recognize and respond to foreign invaders without attacking the body's own tissues. The spleen acts as a filter for the blood, removing old or damaged red blood cells and supporting immune functions. Together, these organs form the foundation of the immune system, enabling the body to mount effective defenses against infections and maintain overall health.

Figures (10)

A 3D medical animation still of spleen structure and exact location
Visceral surface of the spleen
Micrograph of splenic tissue showing the red pulp (red), white pulp (blue nuclei in lighter background) and a thickened inflamed capsule (mostly pink – top of image). H&E stain.
The spleen contains two different tissues, white pulp (A) and red pulp (B). The white pulp functions in producing and growing immune and blood cells. The red pulp functions in filtering blood of antigens, microorganisms, and defective or worn-out red blood cells.
Thalassemia-enlarged spleen taken after splenectomy
Laparoscopic view of a horse's spleen (the purple and grey mottled organ)
Scheme showing development of branchial epithelial bodies from the thoracic cavity of the fetus. I, II, III, IV. Branchial pouches.
Bone marrow aspirate showing normal "trilineage hematopoiesis": myelomonocytic cells (an eosinophil myelocyte marked), erythroid cells (an orthochromatic erythroblast marked), and megakaryocytic cells
Hematopoietic precursor cells: promyelocyte in the center, two metamyelocytes next to it and band cells from a bone marrow aspirate
A Wright's-stained bone marrow aspirate smear from a patient with leukemia

The immune system has special organs and tissues that help protect the body from germs. Three main parts are the bone marrow, thymus, and spleen. Bone marrow is inside certain bones and makes all blood cells, including immune cells.

It starts the process of making T cells and B cells, which are key for immune responses. These cells then travel to other parts of the body to do their work. The thymus is a small organ in the chest.

It removes old or damaged red blood cells and helps immune cells respond to germs. It also stores some immune cells and blood, ready to use if the body needs them quickly.

Key Points

  • Bone marrow is a semi-solid tissue found within the spongy portions of bones and is the primary site of new blood cell production in birds and mammals.
  • The thymus is a specialized primary lymphoid organ of the immune system located in the upper front part of the chest, where T cells mature.
  • The spleen is an organ found in almost all vertebrates that acts primarily as a blood filter, removing old red blood cells and participating in immune functions.
  • The red bone marrow is a key element of the lymphatic system, being one of the primary lymphoid organs that generate lymphocytes from immature hematopoietic progenitor cells.

Terms

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