Q.Diapedesis is performed by _________.

Leucocytes (white blood corpuscles) are the blood's defence cells — colourless, nucleated, larger than RBCs, and capable of amoeboid movement, letting them squeeze out of capillaries into tissue by diapedesis wherever they're needed. A healthy adult has 5000-11000 WBCs per mm3; a drop below 4000 is leucopenia (seen in HIV/AIDS, TB, radiation exposure or shock), a temporary rise is leucocytosis (from infection, pregnancy, or in newborns), and an uncontrolled sustained rise is leukemia, a blood cancer.

WBCs split into granulocytes (about 72%, granular cytoplasm, lobed nucleus, formed from myeloid stem cells, don't divide once formed) and agranulocytes (about 28%, no visible granules, large non-lobed nucleus, formed from lymphoid stem cells, can still divide). Granulocytes further split by staining behaviour into neutrophils (~70% of all WBCs, fine granules, 2-7 lobed nucleus, amoeboid and phagocytic — destroy pathogens; dead neutrophils plus damaged tissue and dead microbes make up pus), basophils (~0.5-1%, few large granules, twisted nucleus, non-phagocytic, secrete heparin/histamine/serotonin, active in infection and allergy), and eosinophils (~1-3%, bilobed nucleus, red-staining lysosomal granules, destroy anti …