Inflammation

Question 1

What is CHRONIC INFLAMMATION?

Answer 1

“chronic” = process has extended over a long period of time

• the inflammatory process in which lymphocytes, plasma cells and macrophages predominate. As in acute inflammation, granulation and scar tissue are also formed, but in chronic inflammation they are usually more abundant
• usually the primary, sometimes called “chronic inflammation ab initio,” but does occasionally follow acute inflammation

Question 2

Progression from acute inflammation:

Answer 2

Most cases of acute imflammation do not develop into the chronic form, but resolve completely. Most common variety of acute inflammation: the suppurative type.

• if he pus forms an abscess cavity that is deep-seated, and drainage is delayed or inadequate, then by the time that drainage occurs, the abscess cavity becomes organised by th ingrowth of granulation tissue, eventually to be replaced by a fibrous scar.
• e.g. of such chronic abscesses: abscess in the bone marrow cavity (OSTEOMYELITIS), which is notroiously difficult to eradicate
• another feature that favours progression to chronic inflammation is the presence of indigestible material which is inert, and is resistant to the action of lysosomal enzymes.
  - the most indigestible forms of material are foreign body materials
  - chronic suppuration will not cease without surgical removal of the material. Foreign bodies have in common the tendency to provoke a special type of chronic inflammation called “granulomatous inflammation” and to cause macrophages to form multinucleate giant cells, called “foreign body giant cells”

Question 3

MACROSCOPIC APPEARANCE OF CHRONIC INFLAMMATION: CHRONIC ULCER

Answer 3

• a chronic peptic ulcer of the stomach with breach of the mucosa, a base lined by granulation tissue and with fibrous tissue extending through the muscle layers of the wall

Question 4

CHRONIC ABSCESS CAVITY

Answer 4

• osteomyelitis

Question 5

THICKENING OF THE WALL OF A HOLLOW VISCUS

Answer 5

Created by fibrous tissue in the presence of a chronic inflammatory cell infiltrate, e.g. Crohn’s disease, chronis cholecystitis

Question 6

GRANULOMATOUS INFLAMMATION

Answer 6

with caseous necrosis as in chronic fibrocaseous tuberculosis of the lung

Question 7

FIBROSIS

Answer 7

may become the most prominent feature of the chronic inflammatory reaction when most of the chronic inflammatory cell infiltrate has subsided

Question 8

MICROSCOPIC FEATURES OF CHRONIC INFLAMMATION

Answer 8

• the cellular infiltrate consists of: lymphocytes, plasma cells and macrophages. Neutrophil polymorphs are scarce. Some of the macrophages may form multinucleate giant cells.
• exudation of fluid is not a prominent feature, but there may be production of new fibrous tissue from granulation tissue
• there may be evidence of continuing destruction of tissue at the same time as tissue regeneration and repair
• tissue necrosis may be a prominent feature, especially in granulomatous conditions, such as tuberculosis
• healing involves regeneration and migration of specialised cells, while the predominant features in repair are angiogenesis (new blood vessel formation) followed by fibroblast proliferation and collagen synthesis resulting in granulation tissue. These processes are regulated by growth factors.

Question 9

FIBROSIS VS. FIBRIN

Answer 9

• Fibrin is deposited in blood vessels and tissues or on surfaces (e.g. in acute inflammation) as a result of the action of thrombin on fibrinogen
• Fibrosis describes the texture of a non-mineralised tissue of which the principal component is collagen (e.g. scar tissue)

Question 10

MACROPHAGES IN CHRONIC INFLAMMATION

Answer 10

• macrophages are relatively large cells, that move by amoeboid motion through the tissues
• they have considerable phagocytic capabilities for the ingestion of microorganisms and cell debris
• when neutrophil polymorphs ingest microorganisms, they usually bring about their own destruction and thus have a limited lifespan of up to about three days
• macrophages can ingest a wider range of materials than can polymorphs and being, long-lived, they can harbour viable organisms if they are not able to kill them by their lysosomal enzymes
  - examples of organisms that can survive inside macrophages : mycobacteria, such as: Mycobacterium tuberculosis and M. leprae
  - when macrophages participate in the delayed-type hypersensitivity response to these types of organism, they often die in the process, contributing to the large areas of necrosis by release of their lysosomal enzymes.

Question 11

SPECIALISED FORMS OF MACROPHAGES AND GRANULOMATOUS INFLAMMATION

Answer 11

A granuloma is an aggregate of epithelioid macrophages

Epithelioid histiocytes:
- resemble epithelial cells and tend to be arrange in clusters
- little phagocytic activity, more secretory
- may cause necrosis
- may form multinucleate giant cells