Non-specific internal defences

​Phagocytosis

When pathogens are able to penetrate our external defences they are attacked by phagocytes. Phagocytes are specialised white blood cells, or leucocytes that engulf and digest micro-organisms and cell debris.

are granulated leucocytes and are most abundant. Neutrophils are often first to move to tissues to destroy pathogens via phagocytosis. They have a short lifespan and die after a few days, the dead cells make up pus.

Neutrophils

Monocytes leave the bloodstream and differentiate into macrophages, which are large cells capable of removing pathogens and dying cells

Monocytes and macrophages

They then use this information to assist in specific immunity.

characterised by their projections of cytoplasm they are slightly different from neutrophils and macrophages. These cells can detect, engulf and process foreign particles.

​Dendritic cells

​The inflammatory response

Inflammation is a response to any damage to the body's tissues. The purpose of inflammation is to reduce the spread of pathogens, destroy pathogens, remove damaged tissue and cell debris and begin repair of damaged tissue.
Inflammation has four main signs, redness, heat, swelling and pain.

​Steps in the inflammatory response

1. When body tissues are damaged by physical, chemical or pathogens special leucocytes called mast cells to release histamine and heparin into the tissue fluids.

2. Histamine causes the vasodilation of local capillaries increasing blood flow to the area, it also makes the walls of the capillaries more permeable allowing fluids to move from the blood vessels into the tissues.

3. Histamine and other chemicals released by mast cells attract phagocytes, particularly neutrophils to the immediate area via chemotaxis.

4. Heparin prevents clotting in the immediate area.

5. Phagocytes engulf pathogens and damaged cells via phagocytosis

6. When pathogen and damaged cells/debris are cleared mast cells stop releasing histamine and tissue repair begins. New cells are produced via mitosis.