chronic inflammation

General pathology
Chronic inflammation:
It is a slowly progressing inflammatory process that persists for weeks, months or years after initial injury.
Differences from acute infection.
1- Chronic inflammation associated with more tissue destruction.
2- The main inflammatory cells are lymphocytes, plasma cells and macrophages.
3- It associated with granulation tissue formation and fibrosis rather than exudates fluid formation.

Causes of chronic inflammation:
1- Progressive from acute inflammation, like chronic abscess due to inadequate drainage of the pus, as in abscess of the bone, or associated with inflammation induced by foreign material like surgical suture, implant, piece of wood, ...
2- Recurrent episodes of acute inflammation and best example for this is chronic cholecystitis induced by repeated acute cholecystitis that associated with gall stones, and also in case of osteomyelitis.
3- Primary chronic inflammation (ab initio):
This type of inflammation do not preceded by acute inflammation and this inflammation seen in the follow conditions:
a- Exposure to potentially toxic, non-degradable substances like Silica, and Asbestoses.
b- Exposure to certain infectious agents like (T.B., Leprosy, and fungal infections).
c- In certain diseases that result from immune system abnormality, like rheumatoid arthritis and Crohn s disease.

Macroscopical appearance of chronic inflammation:
A- Chronic ulcer like chronic peptic ulcer of the stomach.
B- Chronic abscess like in osteomyelitis.
C- Thickening of the wall of hallow viscus by fibrosis like in chronic cholecystitis.
D- Granulomatous inflammation.
Granulomatous inflammation:
It is a distinctive pattern of inflammation characterized by aggregation of activated and modified macrophages called epitheliod cells exhibit vesicular nuclei, and eosinophillic cytoplasm that arranged in small clusters or nodular collection cuffed by rim of lymphocytes, and sometimes fibroblasts, this aggregate called granuloma. In T.B. granuloma there is caseous necrosis formation characterized by soft, whitish, cheese-like material, the T.B. granuloma also characterized by formation of Langhan s giant cell that arise by fusion of many macrophages, in which their nuclei arranged at the periphery of the giant cell giving characteristic horse shoe appearance.
Causes of granulomatous inflammation:
1- T.B., 2- Syphilis, 3- Leprosy, 4- fungal infection, 5- Sarcoidosis, and 6 reaction to foreign bodies like suture, or any indigestible substances .

Tissue repair &wound healing:
Healing is a tissue response to wound, inflammation and necrosis, and it’s consist of variable proportion of two distinct processes (Regeneration & scar formation).
1- Regeneration : replacement of damaged tissue by proliferation of adjacent surviving specialized parenchymal cells, like in healing of superficial skin wound that affect only the skin epidermis, so the tissue can completely reconstituted after injury.
2- Scar formation : replacement of damaged tissue by granulation tissue formation and then mature into fibrous tissue, like in healing of deep wound that affect the dermis, and also in healing of internal organs like in scar formation in the heart at site of myocardial infarction.
The type of process for healing influenced by:
1- Type of tissue affected.(hepatocytes can regenerate while neurons cannot).
2- Severity and duration of injury. (superficial and small skin wounds heal by regeneration, while deep and sever wounds heal by scar formation).


The cells in the body divide into three types according to proliferation ability:
1- Labile cells: these cells are in continuous division and death, (surface epithelial cells, and stem cells of the bone marrow).
2- Stable cells: these cells have low level of replication capacity in normal state, but they can undergo rapid division in response to injury like parenchymal cells of liver and kidney.
3- Permanent cells: these are specialized non-dividing cells, so they can not replaced by identical cells after injury, like neurons and cardiac muscles).

Role of Extacellular Matrix (ECM), in healing process:
1- provides scaffolding for tissue renewal.
2- Provide mechanical support for the cells.
3- Determine cell orientation (polarity of the tissue).
4- Regulate cell growth and differentiation.

Fibrosis: indicates repair by connective tissue. Its involves the following steps:
1- Angiogenesis, (formation of new blood vessels).
2- Migration and proliferation of fibroblasts.
3- Deposition of extacerlualr matrix.
4- Maturation and remodeling of the tissue.

Orderly phenomenon of wound healing involving the following processes:
1- Induction of an acute inflammatory process by the initial injury
2- Regeneration of parenchymal cells
3- Migration and proliferation of both parenchymal and connective tissue cells
4- Synthesis of extracellular matrix ( ECM )proteins
5- Remodeling of connective tissue and parenchymal components
6- Collagenizaton and acquisition of wound strength