How does the body defend itself from bacteria entering?

The body has multiple layers of defense mechanisms to protect itself from invading bacteria:

1. Physical Barriers:

- Skin: The outermost layer of the skin acts as a physical barrier, preventing bacterial entry.

- Mucous Membranes: Line the respiratory, digestive, and urogenital tracts, trapping bacteria and preventing their entry.

2. Innate Immune Responses:

- Phagocytes: Specialized white blood cells (neutrophils, macrophages) that engulf and destroy bacteria.

- Natural Killer (NK) Cells: Recognize and kill cells infected with bacteria or those with abnormal surface markers.

- Inflammation: A localized response to injury or infection, characterized by increased blood flow, which brings immune cells and nutrients to the affected area.

- Fever: Increased body temperature inhibits bacterial growth and enhances immune activity.

- Interferons: Proteins produced by virus-infected cells that spread to neighboring cells to prevent further viral replication.

3. Humoral Immune Responses:

- Antibodies: Y-shaped proteins produced by B cells that bind to specific antigens on bacteria, marking them for destruction by other immune cells.

- Complement System: A group of proteins activated by antibodies; this leads to the formation of membrane attack complexes, which puncture bacterial cell walls.

4. Cell-Mediated Immune Responses:

- Cytotoxic T Cells (Killer T Cells): Recognize and destroy infected cells by releasing toxic chemicals.

- Helper T Cells: Coordinate immune responses, activating B cells, cytotoxic T cells, and macrophages.

- Memory Cells: Remain after an infection and enable a faster and stronger immune response in case of future exposure to the same bacterium.

5. Microbiota:

- The body is home to trillions of beneficial bacteria (microbiota) that reside on the skin, in the gut, and on other surfaces. They compete with harmful bacteria for resources and can produce antimicrobial substances.

Working together, these defense mechanisms form a multi-layered defense system to protect the body from bacterial infections. If any harmful bacteria manage to breach these defenses, specialized immune cells and proteins target and eliminate them through various mechanisms.