Mammalian blood possesses a number of defensive functions

Skin is composed of dead cells containing the indigestible protein keratin

Sebum produced by the skin lowers the pH to inhibit growth of pathogens

Lysozymes in salvia, sweat and tears are anti-bacterial enzymes

Many ingested bacteria in the stomach are destroyed by acid (HCl)

A sticky substance, mucus, traps pathogens in the respiratory tract

Cilia moves away mucus towards the throat to protect gas exchange surfaces

The immune system targets foreign materials and pathogens

Inflammatory response

Histamine is released into the wound by white cells

This increases vasodilation and increases vascular permeability

Vasodilation increases the local blood flow → area becomes red, warm

Increased permeability allows escape of tissue fluid into the tissues

Tissue fluid contains plasma proteins (antibodies) and may cause swelling

Phagocytosis

White cells (phagocytes) contain digestive enzymes within lysosomes

Neutrophils primarily engulf bacteria

Macrophages engulf larger particles; including old and infected red blood cells

Found in blood, lymph systems and tissues

Squeeze through gaps in the walls of venules to enter tissues

This allows them to move faster to tissues infected with pathogens

Phagocytes are attracted by chemotaxis

Opsonisation by antibodies (bacteria becomes coated with antibody)

As a result, binding between bacteria and phagocytes is improved

Phagocytes form pseudopodia around the particle

This positions the particle into a phagocytic vacuole (also called phagosome)

Lysosome fuses with the phagosome

Intracellular killing by digestive enzymes from the lysosome

Pus if formed at the site of infection if no extensive vasculature is present

Principle of immunology

Antigen

Molecule that stimulates an immune response

Usually proteins (polysaccharides, nucleic acid, lipids can also act as antigens) and other inorganic molecules important for self-recognition

Self-antigen

Only found on the host's own cells and does not trigger an immune response

As these are proteins, their structure...