Page 49 - Concise Pathology for Exam Preparation ( PDFDrive )

34 SECTION I General Pathology

(c) Caused by thermal injury, X-rays, UV radiation and bacterial toxins, which lead to
delayed endothelial damage by apoptosis or cause endothelial retraction by releasing
cytokines.
4. Leukocyte-mediated endothelial injury
(a) Leukocytes adhere to endothelium, release toxic oxygen species and proteolytic
enzymes, which cause endothelial injury and increased permeability.
(b) Largely restricted to venules, pulmonary and glomerular capillaries where leukocytes
adhere for prolonged periods.
5. Increased transcytosis across the endothelial cytoplasm
(a) Occurs across interconnected channels made of vesicles and vacuoles called
vesiculovacuolar organelles.
(b) Certain factors, eg, vascular endothelial growth factor (VEGF), appear to cause
vascular leakage by increasing the number and size of the vascular channels.
6. Leakage from new blood vessels
New vessels formed during angiogenesis remain leaky until endothelial cells mature
and form intracellular junctions.

Q. Write briefly on the cellular events involved in acute inflammation.
Ans. The two main cellular events involved in acute inflammation are
1. Extravasation of leukocytes (movement from vessel lumen to interstitial space;
Flowchart 2.2; Fig. 2.2).

Normal axial flow
(RBCs confined to a central column with WBCs oriented peripherally as the latter are heavier)
Inflammation leading to stasis
Margination and pavementing of WBCs

Adhesion

Emigration and diapedesis
FLOWCHART 2.2. Sequence of cellular events in acute inflammation.

Neutrophil “Adhesion ” “Rolling” “Stcking” “Extravasation ”

Selectins
Integrins Neutrophil
in tissue
PECAM–1

FIGURE 2.2. Mechanism of extravasation of leukocytes.

2. Phagocytosis (leukocytic engulfment of microbes, foreign particles, and cellular debris).
Extravasation of leukocytes has the following steps:
(a) In the lumen: margination (peripheral orientation of leukocytes), rolling (weak
attachment of leukocytes to endothelium, detachment and binding again, causing
a rolling movement), pavementing or adhesion (activation of leukocytes and firm
binding of leukocytes to endothelium)

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