Describe how the own defence system can provide natural immunity from diseases?
The body's own defence system, also known as the immune system, provides natural immunity to protect the body from infections caused by pathogens such as bacteria, viruses, fungi, and parasites. Here are some key mechanisms by which the immune system provides natural immunity:
1. Physical Barriers: The first line of defence is physical barriers, which include the skin and mucous membranes. These barriers prevent pathogens from entering the body. The skin acts as a protective layer that prevents the entry of microorganisms, while mucous membranes in the respiratory, digestive, and urogenital tracts trap pathogens and produce antimicrobial substances.
2. Innate Immune Responses:
- Phagocytosis: Specialized cells called macrophages and neutrophils engulf and destroy pathogens through a process called phagocytosis. These cells recognize foreign substances and engulf them, digesting and eliminating them.
- Inflammation: When tissues are damaged or infected, inflammation occurs. This response involves increased blood flow, leading to the accumulation of immune cells and molecules that help neutralize and eliminate pathogens.
- Natural Killer Cells: Natural killer (NK) cells are a type of cytotoxic lymphocytes that play a crucial role in innate immunity. They recognize and destroy infected or cancerous cells without prior sensitization.
3. Adaptive Immune Responses:
- Humoral Response: The humoral immune response involves the production of antibodies by B cells. Antibodies bind to specific antigens (foreign substances) and neutralize them, marking them for destruction by other immune cells or complement proteins.
- Cell-Mediated Response: The cell-mediated immune response involves the activation of T cells. Cytotoxic T cells (also known as killer T cells) directly destroy infected or abnormal cells, while helper T cells coordinate immune responses and activate other immune cells.
- Memory Cells: After an infection, memory cells are formed. These cells "remember" the specific pathogen and can rapidly mount a strong immune response if the same pathogen is encountered again, providing long-term immunity.
4. Cytokines and Interferons: Cytokines are signalling molecules produced by immune cells that regulate and coordinate immune responses. They help in communication between different immune cells and tissues. Interferons are a type of cytokine that have antiviral effects and help protect uninfected cells from viral infections.
5. Microbiota: The body's natural microbiota, consisting of trillions of microorganisms residing in various body sites, also plays a role in natural immunity. Beneficial bacteria in the gut, for example, can help prevent the colonization and growth of harmful pathogens, providing competition for resources and promoting a balanced immune response.
Overall, the body's own defence system, through its physical barriers, innate immune responses, adaptive immune responses, and other mechanisms, provides natural immunity to protect against a wide range of pathogens, helping to maintain health and prevent or combat infections.