Blood Cells White Blood Cells Phagocytes Neutrophils Macrophages

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 1. Phagocyte detects chemicals released by a foreign intruder (e. g. bacteria) 2. Phagocyte moves up the concentration gradient towards the intruder 3. The phagocyte adheres to the foreign cell and engulfs it in a vacuole by an infolding of the cell membrane. 4. Lysosomes (organelles which are rich in digestive enzymes & found in the phagocytes cytoplasm) fuse with the vacuole & release their contents into it.

Phagocytosis 5. The bacterium is digested by the enzymes, and the breakdown products are absorbed by the phagocyte. l During infection, hundreds of phagocytes are needed. l Pus is dead bacteria and phagocytes!

Phagocytosis

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