Page 76 - Concise Pathology for Exam Preparation ( PDFDrive )

3 Healing and Repair 61

Q. Write briefly on repair by connective tissue.

Ans.
• Repair by connective tissue occurs when:
• There is severe injury so that parenchymal tissue as well as connective tissue frame-
work of the organ is destroyed.
• Nondividing cells are injured.
• Repair begins within 24 hours; by 3–7 days, a special type of tissue called granulation
tissue (so-called because of the pink, soft and granular-gross appearance) is formed.
• Repair by connective tissue deposition consists of four main stages:
1. Formation of new blood vessels (angiogenesis)
2. Migration and proliferation of fibroblasts
3. Deposition of ECM
4. Remodelling of fibrous tissue

Q. Write briefly on angiogenesis.
Ans. Two processes assemble blood vessels (Fig. 3.3):
1. Vasculogenesis: Involves formation of primitive vascular structures from angioblasts
(endothelial cell precursors) in a manner resembling embryonal development of the
vascular system.
2. Angiogenesis: Neovascularization in which pre-existing vessels send out capillary
sprouts to produce new vessels with or without pericytes and smooth muscle cells
(mostly seen during repair of damaged tissue).
Steps in angiogenesis are shown in Flowchart 3.4.

Activation of receptors on endothelial cells in pre-existing vessels by angiogenic growth factors

Release of endothelial proteases that degrade the basement membrane to allow endothelial cells to escape from
the original (parent) vessel wall into the surrounding matrix

Migration of endothelial cells towards area of angiogenic stimulus

Proliferation of endothelial cells behind the migrating cells

Remodelling of endothelial cells into capillary tubes

Recruitment of pericytes and smooth muscle cells to form mature vessels
FLOWCHART 3.4. Steps in angiogenesis.

Structural ECM proteins: Participate in the process of vessel sprouting through interactions
with integrin receptors.
Nonstructural proteins: Contribute to angiogenesis by destabilizing cell–ECM interactions
to facilitate continued cell migration or degrade the ECM to permit remodelling and in
growth of vessels.

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