Flashcards in 3. Acute and chronic inflammation Deck (39)
The host response to tissue damage
– to remove/ contain cause, initiate repair and reinstate useful function
Stops when injurious agent is eliminated
Essential for healing.
Triggers of Inflammation
Rapid host response - vascular and cellular reaction
Vascular changes to maximise movement of plasma proteins to site of injury:
Vasodilation - increased blood flow to the area of injury, redness and heat (ERYTHEMA). induced by histamine and nitric acid.
Increased permeability follows, - to fluid leaking into the extravascular tissue. This leads to swelling (OEDEMA)
Together this creates blood stasis, pooling the blood at site of inflammation
Endothelial cells of vessel wall contract
Endothelial cells of vessel wall contract
increasing inter-endothelial spaces, triggered by histamine, bradykinin, leukotriens, substance P etc. It is the Immediate transient response
leading to endothelial cell death, vessel wall is damaged and there is immediate extravascular leakage
leading to increased transport of fluids/proteins through cell channels. Promoted by specific factors triggered by inflammation eg VEGF
Together these mechanisms cause leakage of intravascular fluid into the extravascular spaces.
Main aim of inflammation is to recruit leucocytes to area of damage. by adhering them to vessel wall
Neutrophils and macrophages ingest and kill bacteria and necrotic cells, as well as promoting repair.
These white blood cells need to be recruited from the vessel lumens.
Red blood cells flow in centre of vessel lumen and WBCs flow peripherally. In stasis, more wcc fall into peripheral flow.
This leads to an increased amount of leucocytes to roll along then edge of the damaged endotehlium. Mediated by selectins.
The leucocytes finally stop and adhere to the endothelium. Cytokines secreted by by injured cells encourage the adhesion of the leucocytes.
Leucocyte is then encouraged to pass through endothelium to extravascular space
stimulate migration and leucocyte move towards the chemical concentration gradient
(towards site of injury where the chemokines are being produced)
PECAM-1 – platelet endothelial cell adhesion molecule
Exogenous (bacteria ) and endogenous (cytokines/complement) substances attract the leucocytes towards the area of injury.
appear at 6-24 hours, monocytes appear at 24-48hours. Neutrophils are more common in circating blood and respond to chemokines.
Function of leucocytes
Receptors on the leucocytes recognise foreign microbes
like receptors present on cell surface of leucocytes and attach to bacteria products
coupled receptors recognise N-formymethionyl of bacteria as well as chemokine breakdown
recognoze microbes that have been coated with proteins ( antibodies/complement) or opsonins, thus called opsonization. This targets them for phagocytosis
are present on leucocytes respond to the cytokines produced in response to microbes.
Through these receptors the leucocyte recognises and attaches itself to bacteria or damaged cell
leucocytes - engulfs the cell/particle
leucocyte - kills and degrades the offending agent, removing its harmful effects.
This continues until all foreign and damaged products are removed, so healthy cells remain and healing and repair can begin.
Healing with connective tissue replacement (fibrosis)
Following substantial tissue destruction, some cells cannot regenerate.
Connective tissue replaces area or damage.
Progression to chronic inflammation
- Acute problem is not resolved due to persistent injury or interference with healing.
Persistent infection: microorganisms difficult to remove e.g. parasite, mycobacteria.
Immune mediated inflammation: reaction against host tissue leading to auto-immune diseases.
Prolonged exposure to toxic agent : silica, asbestos, lipids (atherosclerosis)
Predominantly show infiltration of mononuclear cells: macrophages, lymphocytes and plasma cells.
( Macrophages destroy damaged cells and promote repair)
Tissue destruction following prolonged inflammatroy reaction
Signs of attempts at healing: connective tissue repair, increased growth of small blood vessels and fibrosis
Cellular attempt to contain offending agent it cannot eradicate
Strong activation of macrophages and T lymphocytes, leading to injury of normal tissues.
e.g Tuberculosis which leads to caseating lesions in the lungs.
Loss of function
Signs and Symptoms (1)
Signs and Symptoms (2)
Weight loss (chronic inflammation)
Sepsis- large amount of toxins stimulate cytokines, can lead to cardiovascular failure (septic shock)
Aim is complete resolution