Blood Cells

White Blood Cells Phagocytes - Neutrophils - Macrophages Lymphocytes

Phagocytes Produced throughout life by the bone marrow. Scavengers – remove dead cells and microorganisms.

Neutrophils 60% of WBCs ‘Patrol tissues’ as they squeeze out of the capillaries. Large numbers are released during infections Short lived – die after digesting bacteria Dead neutrophils make up a large proportion of puss.

Macrophages Larger than neutrophils. Found in the organs, not the blood. Made in bone marrow as monocytes, called macrophages once they reach organs. Long lived Initiate immune responses as they display antigens from the pathogens to the lymphocytes.

Macrophages

Innate Immune Responses Innate immune mechanisms nonspecifically eliminate pathogens that invade internal tissues before they become established Phagocytes Complement Inflammation Fever

Innate Immunity Innate immune responses involve a set of general, immediate defenses against invading pathogens Innate immunity includes phagocytic white blood cells, plasma proteins, inflammation, and fever

Phagocytes Macrophages Large phagocytes that patrol interstitial fluid and engulf and digest pathogens Secrete cytokines when receptors bind to antigen Cytokines attract more macrophages, neutrophils, and dendritic cells to infection site

Phagocytosis If cells are under attack they release histamine. Histamine plus chemicals from pathogens mean neutrophils are attracted to the site of attack. Pathogens are attached to antibodies and neutrophils have antibody receptors. Enodcytosis of neutrophil membrane  phagocytic vacuole. Lysosomes attach to phagocytic vacuole  pathogen digested by proteases

Phagocytosis Stages in phagocytosis Phagocyte detects chemicals released by a foreign intruder (e.g. bacteria) Phagocyte moves up the concentration gradient towards the intruder The phagocyte adheres to the foreign cell and engulfs it in a vacuole by an infolding of the cell membrane. Lysosomes (organelles which are rich in digestive enzymes & found in the phagocytes cytoplasm) fuse with the vacuole & release their contents into it.

Phagocytosis During infection, hundreds of phagocytes are needed. The bacterium is digested by the enzymes, and the breakdown products are absorbed by the phagocyte. During infection, hundreds of phagocytes are needed. Pus is dead bacteria and phagocytes!

Phagocytosis

Pus An accumulation of : - dead phagocytes destroyed bacteria dead cells