phagocytosis

define phagocytosis

Phagocytosis is the digestion of microbes and other foreign bodies by phagocytes: neutrophils, monocytes and macrophages.

define a phagocyte

Phagocytes are large, irregularly-shaped white blood cells with a complex cytoskeleton that allows them to move and change shape.

Neutrophils

• The most abundant white blood cells in the blood

• granulocytes

• Act as phagocytes that engulf and digest pathogens

• Usually die after phagocytosis, forming pus

Monocytes

• Large white blood cells found in the blood

• Not very active while circulating

• They differentiate into macrophages once they leave the blood and enter tissues

Macrophages

• Formed from monocytes in tissues

• Long-lived phagocytes

• Engulf pathogens and present antigens on their cell surface to lymphocytes, linking the non-specific and specific immune responses

step 1

In phagocytosis, phagocytes are attracted to the area of invasion by chemical products of the microorganism, phospholipids release by injured mammalian cells.

step 2

The Phagocytes crawl through the blood and tissue fluid in response to chemicals released by microbes or other white blood cells and move into the area of invasion and then attach to the microorganism. The attachment is mediated by variety of surface receptors including anitbody’s and lipopolysaccharide and complement receptor

step 3

The microorganism is then engulfed by the phagocyte into a vacuole known as a phagosome

step 4

vesicles in the cytoplasm called lysosomes fuse with the phagosome releasing digestive enzymes such as lysozyme and protease into the phagosome. The structure resulting from this fusion is called a phagolysosome.

step 5

inside the phagolysosome the lysozymes (digestive enzymes) such as proteases, carbohydrase’s and lipases hydrolyse the proteins, carbohydrates and lipids that make up the microbe, so killing it

finally the digested contents of the phagolysosome are eliminated from the phagocyte by exocytosis