Defending Against Pathogens

The body’s first line of defence against pathogens is the skin and the mucous membranes lining the respiratory, digestive, and reproductive tracts.
Skin acts as a physical barrier, blocking pathogens from entering the body. It also contains sebaceous glands that release substances toxic to many bacteria.
The mucous membranes battle pathogens through the production of mucus, which can trap microorganisms. Some mucous membranes also possess cilia capable of pushing mucus away from the body.

When pathogens bypass initial defences, the body activates its immune response, which includes the innate immune response and the adaptive immune response.
The innate immune response is the body’s initial, non-specific defence against pathogens. This includes physical barriers, phagocytosis by white blood cells, inflammation, and fever.
Phagocytosis is a process where specialised white blood cells, such as neutrophils and macrophages, engulf and destroy pathogens.
The adaptive immune response is activated if the innate immune response fails to eliminate the pathogen. This response is specific, slower, and involves components such as T cells, B cells, and antibodies.

T cells are involved in cell-mediated immunity. Some T cells release substances that kill infected cells, while others stimulate B cells to produce antibodies.
B cells produce and release antibodies into the bloodstream. Antibodies lock onto antigens on the surface of pathogens, marking them for destruction.

An antibody is a protein produced by B cells. Each antibody can recognise a specific antigen on a pathogen.
An antigen is a molecule that is recognised by the immune system and can trigger an immune response. Antigens are usually found on the surfaces of microorganisms or viruses.
When an antibody locks onto an antigen, it either neutralises it directly or marks it for destruction by other cells.

Immunisation is a method used to boost the body’s specific immune response to a particular pathogen. It works by introducing dead or weakened forms of the pathogen to stimulate the production of memory cells.
Memory cells are long-lived B and T cells that recognise a specific antigen from a previous infection. These cells facilitate a faster and more effective response when the body encounters the same antigen in the future.
Immunisation can help to prevent the spread of infectious diseases within a population, contributing to herd immunity.

The lymphatic system plays a crucial role in defending against pathogens. It transports and stores lymphocytes, which are types of white blood cells that help the body fight off disease.
Lymphatic tissues, such as lymph nodes, tonsils, and the spleen, help filter out harmful substances and are sites where immune responses can be initiated.