Page 51 - Concise Pathology for Exam Preparation ( PDFDrive )

36 SECTION I General Pathology

Chemoattractants

1. Exogenous—bacterial products
2. Endogenous—C5a, leukotrienes and cytokines
Mechanism of chemotaxis (Flowchart 2.3; Fig. 2.3)

Binding of chemoattractants to specific transmembrane G protein–coupled receptors (GPCRs) on the
surface of leukocytes

Recruitment of G protein due to signals from GPCRs

Activation of phospholipase C (PLC), phosphoinositol 3 kinase (PI3K) and protein tyrosine kinases
(effector molecules)

PLC + PI3K act on membrane phospholipids

Generation of lipid second messengers

↑ Cytosolic calcium

Activation of GTPases and numerous kinases

Polymerization of actin

Locomotion
FLOWCHART 2.3. Mechanism of chemotaxis.

FIGURE 2.3. Mechanism of chemotaxis.

Q. Write briefly on phagocytosis.
Ans. Phagocytosis is defined as leukocytic engulfment of microorganisms, foreign particles
and cellular debris. The two most important phagocytic cells are:
1. Polymorphs
2. Circulating monocytes or macrophages

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