Chronic inflammation Flashcards
What is chronic inflammation?
can follow on from an unresolved acute inflammation, or be chronic from the outset
composed of cellular infiltration and proliferation of local connective tissue
the principal cells involved are
1. lymphocytes,
2. plasma cells,
3. macrophages,
4. fibroblasts, and
5. vascular endothelium
Lymphocytes in chronic inflammation?
formed in bone marrow, spleen, thymus, lymph nodes and the mucosal surface associated lymphoid follicles e.g. Peyer’s patches in the intestine and the tonsils of the oropharynx
circulate between the blood, tissues and lymphatic system
life span up to 200 days
round cells with a densely staining nucleus and a thin, often indistinct, rim of cytoplasm
Plasma cells in inflammation?
Derived from B-lymphocytes at the area of tissue damage and/or arrive in efferent lymph from sites of differentiation in lymph nodes
Presence of plasma cells in a tissue indicates the body is producing an antibody response against an antigen
Round to oval shaped cells with an eccentric round nucleus and abundant plum/purple cytoplasm
Macrophages in inflammation?
large round cells with central to eccentric round nucleus and abundant clear, often vacuolated (foamy) cytoplasm
normally present in tissues as fixed histiocytes e.g. sentinel macrophages in the lung
in inflammation most are derived from circulating monocytes, which leave blood vessels and enter tissue
functions: phagocytosis, antigen presentation, stimulation of fibroplasia and fibrosis
Macrophage accumulation in tissues
inability to lyse irritants (foreign material)
antigen-antibody complexes forming around infectious agents forming ‘tissue grains’
survival of infectious agents within macrophages (e.g. acid-fast bacilli)
Macrophage subtypes
A. Epithelioid cells - look like squamous epithelial cells with a pink cytoplasm and indistinct borders, may be binucleate
- primarily secretory rather than phagocytic
B. Giant cells - multinucleated cells formed by the fusion of macrophages or epithelioid cells
Seen in tissues in association with stable foreign material or intracellular bacteria
What is granulomatous inflammation?
An important type of chronic inflammation usually caused by organisms of low virulence but great persistence in the tissues or by implanted foreign bodies. The macrophage is the main effector cell.
Microscopic structure of a granuloma
a. central core containing agent or irritant
b. surrounding chronic inflammatory cells
macrophages (often as ‘epithelioid’ cells), lymphocytes and plasma cells
eosinophils in parasitic granulomas
necrosis in mycobacterial and fungal granulomas
calcification in mycobacterial granulomas in some species
c. outer fibrous capsule
Process of tissue repair
- Removal of necrotic debris
- Ingrowth of immature blood vessels (granulation tissue)
- Production of immature scar tissue
- Production of mature scar tissue (fibrosis)
Fibroblasts and endothelial cells
Fibroblasts - derived from local connective tissue cells and involved in the organisation of damaged tissue (fibroplasia)
Endothelial cells - in conjunction with fibroplasia there is a proliferation of the vascular endothelium into the organising tissue (granulation tissue).
Granulation tissue formation
vascular connective tissue
capillary loops
fibroblasts - collagen production
leukocytes - granulocytes & macrophages
extremely resistant to infection
supports migration of epithelium
its contraction reduces the amount of tissue to be replaced
What is fibrosis?
Granulation tissue is replaced by immature then mature fibrous tissue
The formation of immature fibrous tissue is fibroplasia
The formation of mature scar tissue is fibrosis
The mature fibrous scar is as strong or stronger than the original tissue
Factors affecting healing
- the species affected
- age
- the nature of the tissue damaged
highly specialised tissue rarely repairs successfully unless the injury was mild e.g. fibrocartilaginous embolism in the spinal cord of dogs - the extent of tissue damage
If there is substantial fibrosis in the tissue, progressive destruction of the tissue continues due to further injury to adjacent normal tissue from the fibrous tissue as it matures and contracts, e.g. the liver in cirrhosis and the kidney in chronic renal disease
Regeneration vs repair
Repair is the process of replacement of damaged tissue by fibrous scar tissue (fibrosis), does not retain the same characteristics
Regeneration is the process of replacement of damaged tissue by normal tissue of the same type, the functional status of the tissue is restored
Regeneration vs repair tissue types
- labile - constantly replenishes its tissue cells throughout life
- skin and mucous membranes which normally desquamate their outer layer of cells during life
- bone marrow and fat are other examples - stable – able to regenerate in response to damage: e.g. liver, some endocrine glands and renal tubular epithelium
or able to respond to an increased demand on function: e.g. skeletal and smooth muscle - permanent - poor or no regenerative capacity: highly specialised tissues whose cells generally have only one function
neuronal cell bodies in the central nervous system, the retina of the eye, and the cells responsible for hearing in the ear
axons in the peripheral nervous system, when severed, can regenerate to a limited extent
-cardiac muscle myofibres have very poor regenerative capacity, and undergo repair by fibrosis or fat replacement
