Lesson 1: Organs and Cells of the immune system

The immune system is a complex network of organs, tissues, cells, and molecules working together to defend the body against infections and diseases.

Organs and components of the immune system and their functions

1. Bone Marrow:
   • Function: Bone marrow is the primary site of blood cell production, including white blood cells (leukocytes). It houses hematopoietic stem cells that differentiate into various immune cells.
2. Thymus:
   • Function: The thymus is crucial for the maturation of T cells, a type of white blood cell important for cell-mediated immunity. T cells that mature in the thymus are then released to various tissues in the body.
3. Spleen:
   • Function: The spleen filters blood and acts as a reservoir for immune cells. It plays a role in removing old or damaged blood cells and initiating immune responses by presenting antigens to white blood cells.
4. Lymph Nodes:
   • Function: Lymph nodes are small, bean-shaped structures distributed throughout the body. They filter lymph (a fluid containing white blood cells) and provide a site for immune cells to interact, initiating an immune response.
5. Tonsils and Adenoids:
   • Function: Tonsils and adenoids are lymphoid tissues located in the throat. They help trap pathogens entering through the mouth and nose, initiating an immune response.
6. Appendix:
   • Function: While the exact function of the appendix is not fully understood, it is believed to play a role in immune function, particularly during early life.
7. Peyer’s Patches:
   • Location: Found in the small intestine.
   • Function: Peyer’s patches are collections of lymphoid tissue in the intestinal lining. They contribute to the immune response in the digestive system.
8. Lymphatic System:
   • Function: The lymphatic system is a network of vessels, nodes, and organs that transport lymph throughout the body. It is essential for the circulation of immune cells, antibodies, and fluids.
9. Mucosa-Associated Lymphoid Tissue (MALT):
   • Location: Found in mucous membranes of various organs (e.g., respiratory, digestive, urogenital).
   • Function: MALT is involved in immune surveillance at mucosal surfaces, providing protection against infections.

Cell of the immune system and their functions

The immune system consists of various types of cells, each with specific functions aimed at protecting the body against pathogens and maintaining overall health. Here are some key immune cells and their functions:

1. White Blood Cells (Leukocytes):
   • Neutrophils:
     • Function: Phagocytosis (engulfing and digesting pathogens), particularly bacteria.
     • Role: Main responders during acute bacterial infections.
   • Monocytes:
     • Function: Transform into macrophages, which phagocytize pathogens and debris.
     • Role: Involved in long-term defense, presenting antigens to activate other immune cells.
   • Eosinophils:
     • Function: Defense against parasitic infections and involvement in allergic reactions.
     • Role: Release substances to destroy parasites and modulate allergic responses.
   • Basophils:
     • Function: Release histamine and other mediators involved in allergic reactions.
     • Role: Promote inflammation and immune responses.
2. Lymphocytes:
   • T Cells:
     • Helper T Cells (CD4+ T Cells):
       • Function: Coordinate immune responses by activating other immune cells.
       • Role: Essential for the adaptive immune system.
     • Cytotoxic T Cells (CD8+ T Cells):
       • Function: Kill infected or abnormal cells directly.
       • Role: Combat viral infections and eliminate cancerous cells.
   • B Cells:
     • Function: Produce antibodies (immunoglobulins) that recognize and neutralize pathogens.
     • Role: Essential for humoral immunity in the adaptive immune system.
   • Natural Killer (NK) Cells:
     • Function: Recognize and kill infected or abnormal cells.
     • Role: Provide rapid response against virus-infected cells and cancer cells.
3. Dendritic Cells:
   • Function: Capture, process, and present antigens to T cells, initiating adaptive immune responses.
   • Role: Bridge the innate and adaptive immune systems.
4. Macrophages:
   • Function: Phagocytosis, antigen presentation, and activation of immune responses.
   • Role: Key players in the innate immune system, clearing debris and initiating immune responses.
5. Mast Cells:
   • Function: Release histamine and other mediators during allergic reactions.
   • Role: Involved in inflammatory responses, especially in allergies and asthma.
6. Granulocytes:
   • Function: Release granules containing enzymes and other substances to destroy pathogens.
   • Types: Neutrophils, eosinophils, and basophils are examples of granulocytes.