How does the body defend against bacterial infections?

The body defends against bacterial infections through its immune system, which includes physical barriers, immune cells, and antibodies.

The human body has a complex and efficient defence system against bacterial infections, known as the immune system. This system is composed of various components that work together to protect the body from harmful bacteria. The first line of defence is the physical barriers, such as the skin and mucous membranes, which prevent bacteria from entering the body. The skin is a tough, waterproof barrier that bacteria cannot easily penetrate, while mucous membranes in the nose, throat, and lungs trap bacteria and other foreign particles.

If bacteria manage to bypass these physical barriers, the body's second line of defence comes into play: the innate immune system. This includes white blood cells, such as neutrophils and macrophages, which can engulf and destroy bacteria. These cells are part of the body's non-specific defence mechanisms, meaning they attack any foreign substance without specificity. The innate immune system also includes proteins called complement proteins, which can directly kill bacteria or make them easier for immune cells to destroy.

The third line of defence is the adaptive immune system, which is specific and memory-based. This system involves lymphocytes, including B cells and T cells. B cells produce antibodies, proteins that can recognise and bind to specific bacteria, marking them for destruction by other immune cells. T cells, on the other hand, can directly kill infected cells or help B cells produce antibodies. Once the body has encountered a specific bacterium, the adaptive immune system 'remembers' it, allowing for a faster and more effective response if the same bacterium infects the body again.

In addition to these immune responses, the body also uses fever as a defence mechanism. A higher body temperature can inhibit bacterial growth and stimulate the immune system. Moreover, the body has a variety of chemical defences, such as stomach acid, which can kill bacteria, and antimicrobial peptides, small proteins that can destroy bacteria by disrupting their cell membranes.

In summary, the body's defence against bacterial infections is a multi-layered process involving physical barriers, various immune cells, antibodies, and chemical defences. Each component plays a crucial role in preventing and fighting bacterial infections, ensuring the body's health and survival.