Page 77 - Concise Pathology for Exam Preparation ( PDFDrive )

62 SECTION I General Pathology

Vasculogenesis

Angioblasts Primitive
vasculogenic network

Angiogenesis

Capillary Sprouting Microvessels
FIGURE 3.3. Mechanism of formation of new blood vessels.

Growth Factors Involved in Angiogenesis
1. VEGFs
(a) Family of growth factors that include VEGF isoforms–A, B, C, D
(b) Hypoxia, PDGF, TGF-b and TGF-a induce release of VEGFs
(c) VEGFs bind to a family of receptors with tyrosine kinase activity and stimulate
both proliferation and motility of endothelial cells
2. FGFs
(a) Family with more than 20 members
(b) Best characterized are FGF1 (acidic FGF) and FGF2 (basic FGF)
(c) FGFs bind to a family of receptors with tyrosine kinase activity and stimulate pro-
liferation of endothelial cells and promote migration of macrophages and fibro-
blasts to the damaged area

Q. Write briefly on scar formation.
Ans. There are two major steps in scar formation:
1. Migration of fibroblasts to the damaged area followed by proliferation.
2. Deposition of ECM by the same cells. Deposition of ECM involves the following:
(a) Recruitment and stimulation of fibroblasts which is driven by many growth factors,
eg, PDGF, FGF2, TGF-b (elaborated by endothelium and macrophages).
(b) Macrophages clear extracellular debris and fibrin and also elaborate a host of me-
diators that induce fibroblast proliferation and ECM production.
(c) As healing progresses, the number of proliferating fibroblasts and new vessels de-
crease and collagen synthesis and ECM deposition increases.
(d) Decreased collagen degradation rather than increased collagen synthesis is
responsible for net collagen accumulation.
(e) Ultimately, the granulation tissue scaffold is converted into scar tissue composed of
fibroblasts, dense collagen, fragments of elastic tissue and other ECM components.

Q. Write briefly on healing by primary or first intention.

Ans. Primary union is seen in incised wounds with opposed edges (clean and uninfected
wound). The steps in healing by primary intention are summarized in Flowchart 3.5 and
Fig. 3.4A.

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