Paper I
Question
(
- (a) Define inflammation. ( 3 mark(s)
- (b) Describe the cellular events that take place in acute inflammation. ( 7 mark(s)
- (c) Describe the morphological patterns of acute inflammation. 5 mark(s)
Answer
(a) Definition of inflammation
- Inflammation is a protective, localized response of vascularized living tissue to injury (caused by infection, trauma, chemical or physical agents), aimed at delivering leucocytes and plasma proteins (antibodies) to the site of injury to eliminate the offending agent and initiate tissue repair
(b) Cellular events in acute inflammation
- Margination: Leucocytes shift from the central axial column of flowing blood to the periphery along the endothelial surface, aided by vascular dilatation and slowed blood flow (stasis)
- Rolling: Leucocytes loosely and transiently adhere to and roll along the endothelium, mediated by selectins (E-selectin, P-selectin on endothelium; L-selectin on leucocytes) binding to their sialylated carbohydrate ligands
- Adhesion (firm adhesion): Integrins on leucocytes (activated by chemokines) bind firmly to ICAM-1/VCAM-1 on endothelium, arresting the leucocyte
- Transmigration (diapedesis): Leucocytes squeeze between endothelial cells (mediated by PECAM-1/CD31) and migrate through the vessel wall into the interstitium
- Chemotaxis: Leucocytes migrate along a chemical gradient toward the site of injury, guided by chemoattractants (bacterial products, complement C5a, leukotriene B4, chemokines)
- Phagocytosis: Recognition and attachment of the offending agent (aided by opsonins — IgG, C3b), engulfment (forming a phagosome), and killing/degradation (via reactive oxygen species, lysosomal enzymes, nitric oxide)
- Leucocyte-mediated tissue injury: Release of lysosomal enzymes and reactive oxygen species can also damage normal host tissue
(c) Morphological patterns of acute inflammation
- Serous inflammation: Outpouring of thin, protein-poor fluid — e.g., skin blister from a burn, viral pleuritis
- Fibrinous inflammation: Vascular permeability increases sufficiently to allow large molecules like fibrinogen to pass, forming a fibrinous exudate — e.g., fibrinous pericarditis
- Purulent (suppurative) inflammation: Production of pus — an exudate rich in neutrophils, necrotic cells, and oedema fluid — e.g., acute appendicitis, abscess formation
- Ulcers: Local defect/excavation of the surface of an organ or tissue produced by sloughing of inflamed necrotic tissue — e.g., peptic ulcer