The immune system is the body's defence mechanism against infections, diseases, and foreign invaders like bacteria, viruses, fungi, and parasites. It works through a complex network of cells, tissues, and organs that collaborate to recognise and eliminate harmful substances. Here’s what cause a weak immune system and how it works:
1. First Line of Defense: Physical and Chemical Barriers
- Skin and Mucous Membranes: The skin acts as a physical barrier to block pathogens. Mucous membranes in the nose, mouth, and respiratory tract trap and expel invaders.
- Chemical Barriers: Sweat, tears, saliva, and stomach acid contain enzymes and other substances that destroy or inhibit pathogens.
2. Second Line of Defense: Innate Immune System
- White Blood Cells (Leukocytes): These cells patrol the body for invaders. Key types include:
- Neutrophils and Macrophages: These cells engulf and digest pathogens through a process called phagocytosis.
- Natural Killer (NK) Cells: These cells target and kill infected or cancerous cells.
- Inflammatory Response: When tissues are injured or infected, the body releases chemicals that cause inflammation, attracting immune cells to the site to fight the infection.
- Complement System: A group of proteins in the blood that work together to destroy pathogens by puncturing their cell membranes.
3. Third Line of Defense: Adaptive Immune System
- Lymphocytes: The adaptive immune system relies on specialized white blood cells called lymphocytes, primarily B cells and T cells.
- B Cells: Produce antibodies that bind to specific antigens (proteins on the surface of pathogens), marking them for destruction.
- T Cells: Different types of T cells have various roles:
- Helper T Cells: Activate other immune cells, including B cells and other T cells.
- Cytotoxic T Cells: Directly kill infected cells or cancer cells.
- Regulatory T Cells: Help control the immune response to prevent it from being too strong.
- Memory Cells: After an infection, some B and T cells become memory cells. They "remember" the pathogen, allowing the immune system to respond more rapidly and effectively if the same pathogen is encountered again.
4. Communication and Coordination
- The immune system cells communicate through signaling molecules called cytokines. These chemicals help coordinate the immune response, directing cells to sites of infection, enhancing their activity, or regulating the intensity of the response.
5. Vaccination and Immunity
- Vaccines: Work by exposing the immune system to a harmless part of a pathogen (like a protein or a killed virus). This triggers the production of memory cells without causing the disease, providing immunity.
- Immunity: Once the immune system has successfully fought off a pathogen, it can often prevent future infections by the same pathogen through faster and stronger responses.
6. Immune System Disorders
- Autoimmune Diseases: The immune system mistakenly attacks the body's own cells, as seen in conditions like rheumatoid arthritis and lupus.
- Allergies: The immune system overreacts to harmless substances, such as pollen or pet dander.
- Immunodeficiency Disorders: Conditions like HIV/AIDS weaken the immune system, making the body more susceptible to infections.
In summary, the immune system is a highly sophisticated defense network designed to protect the body from harm. It distinguishes between self and non-self, remembers past encounters, and adapts to new threats, ensuring the body remains healthy.