Pathology Flashcards
What is inflammation?
The local physiological response to tissue injury.
What is acute inflammation?
The initial and often transient series of tissue reactions to injury.
What is chronic inflammation?
The subsequent and often prolonged tissue reactions following the initial response.
Steps of acute inflammation
- Vascular component - blood vessels dilate
- Exudative component - protein-rich fluid leaks from vessels (oedema)
- Cellular component - neutrophil polymorphs attracted to site of injury by chemotaxins and begin phagocytosis of pathogens
Outcomes of acute inflammation
- Complete resolution - total repair and destruction of the pathogen
- Suppuration - pus discharge leading formation of an abscess
- Organisation - growth of new capillaries and fibroblasts into damaged tissue –> fibrosis and scar formation
- Chronic inflammation - from a persisting injury
Causes of acute inflammation
- microbial infections (bacteria, viruses) - tissue damage as a result of cell death, endotoxins, hypersensitivity reactions
- hypersensitivity reactions (parasites, bacteria) - excessive immune reaction damages tissue
- physical agents (trauma, ionising radiation, temperature related)
- chemicals (corrosives, acids) - gross tissue damage, chemical irritants
- bacterial toxins
- tissue necrosis (ischaemic infarction) - death of tissues from lack of oxygen
What are the 5 cardinal signs for acute inflammation?
Rubor - redness of skin due to blood vessel dilation in damaged area
Calor - increase in temperature of peripheral body parts due to increased blood flow (hyperaemia)
Tumor - swelling due to oedema and also from the migration of inflammatory cells to the area
Dolor - pain due to distortion of tissues from oedema and pus under pressure in abscess cavity, chemical mediators can also induce pain
Loss of function - movement inhibited by pain, severe swelling may immobilise tissues
What is the role of histamine and thrombin in the inflammatory response?
To cause up-regulation of adhesion molecules on the surface of endothelial cells which results in firm neutrophil adhesion to the endothelial surface.
Stages of neutrophil polymorph emigration
- Margination - migrate to edge of blood vessels
- Adhesion - selectins bind neutrophil; cause “rolling” along blood vessels margin
- Emigration + Diapedesis - movement out of blood vessels, through or in between endothelium, other inflammatory cells follow
- Chemotaxis - neutrophils travel to the site of inflammation
Action of neutrophils at the site of inflammation
- Phagocytosis
- Phagolysosome + bacteria killing
- Macrophages clear debris
Systemic effects of inflammation
- pyrexia (fever)
- constitutional symptoms (anorexia, weight loss, night sweats, headache, pain)
- reactive hyperplasia (overgrowth of cells)
- haematological changes
- amyloidosis (build of amyloid in tissues - can lead to organ failure)
What cells are involved in inflammation?
- neutrophil polymorphs (cytoplasmic granules full of enzymes that kill bacteria)
- macrophages (phagocytic, remove debris, antigen-presenting)
- lymphocytes (produce chemicals which attract other inflammatory cells, immunological memory)
- endothelial cells (allow adherence of inflammatory cells, become porous to enable emigration of inflammatory cells, grow into damaged tissue to form new capillaries)
- fibroblasts (form collagen in areas of chronic inflammation and repair)
What are granulomas?
Small area of chronic inflammation caused by an aggregation of epitheloid histocytes (specialised macrophages).
- Caseating = central region of necrosis, usually in lungs, response to infection
- Non-caseating - no central region of necrosis, response to contact with foreign material, sarcoidosis, vasculitis, crohn’s
Sequence of Chronic Inflammation
- Either progresses from acute inflammation or starts as ‘chronic’ inflammation such as infectious mononucleosis
- no or very few neutrophils
- macrophages and lymphocytes, then usually fibroblasts
- can resolve if no tissue damage but often ends up with repair and formation of scar tissue
What are resolution and repair?
Resolution = initiating factor removed, tissue undamaged or able to regenerate
Repair = initiating factor still present, tissue damaged and unable to regenerate, damaged tissue is replaced by fibrous tissue
Which cells regenerate?
- hepatocytes
- pneumocytes
- all bloods cells
- gut epithelium
- skin epithelium
- osteocytes
Which cells don’t regenerate?
- myocardial cells
- neurones
Healing by 1st intention
Healing of a wound in which the edges are closely re-approximated so there is minimal granulation and scar formation.
Healing by 2nd intention
Healing of a wound where the wound is left open and left to heal by itself, filling in and closing up naturally.
What is thrombosis
The formation of a solid mass from blood constituents in an intact vessel in a living person.
What is an embolism
When a solid mass in the blood (embolus) is carried through the circulation to a place where it gets stuck and blocks the vessel.
Why are clots rare?
- Laminar flow - cells travel in the centre of arterial vessels and don’t touch the sides
- Endothelial cells which line vessels are not ‘sticky’ when healthy
How is a thrombus formed?
- Damage to endothelial cells in the vessel causes cells to lift from vessel wall, exposing collagen
- Platelets then begin to stick to this exposed collagen, and release the chemicals which cause platelet aggregation. Platelet aggregation also starts off the cascade of clotting proteins in the blood.
- Red blood cells then get trapped within the aggregating platelets.
- Clotting factors join the red blood cells and platelets, and the clotting cascade forms a large protein molecule fibrin, which then gets deposited and forms the clot.
- Positive feedback loop –> can end up causing a thrombus, blocking the artery
What is granulation tissue?
Tissue composed of small blood vessels in a connective tissue matrix with myofribroblasts. It is important in healing and repair.
Give an example of a granulomatous disease
TB. leprosy, Crohn’s disease, sarcoidosis
Which enzyme in the blood can act as a marker for granulomatous disease when active?
Angiotensin converting enzyme (ACE)
What 3 factors can lead to thrombosis formation?
- Change in vessel wall
- Change in blood constituents.
- Change in blood flow.
Define ischaemia
Decreased blood flow
Define infarction
Decreased blood flow with subsequent cell death.
Why are tissues with an end arterial supply more susceptible to infarction?
They only have a single arterial supply and so if this vessel is interrupted infarction is likely.
Give 3 examples of organs with a dual arterial supply.
- Lungs (bronchial arteries and pulmonary veins)
- Liver (hepatic arteries and portal veins)
- Some areas of the brain around the circle of wilis)
What can happen if ischaemia is rectified?
Re-perfusion injury can occur due to the release of waste products
What are the consequences of an arterial embolus?
Stroke, MI, gangrene etc.
What are the consequences of a venous embolus?
An embolus in the venous system will go onto the vena cava and then through the pulmonary arteries and become lodged in the lungs causing a pulmonary embolism. This means there is decreased perfusion to the lungs.
Through which blood system would an embolus have travelled if it resulted in a pulmonary embolism?
venous system
What drug can be used to prevent thrombosis?
Aspirin
Define atherosclerosis
Thickening or hardening of arteries as a result of plaque build up in the inner lining of an artery
What are 5 risk factors for atherosclerosis?
- Hypertension
- Smoking
- Obesity
- High cholesterol
- Type 1 Diabetes
Is atherosclerosis more common in the systemic or pulmonary circulation?
More common in the systemic circulation because the pressure is higher
What are the 3 main constituents of an atheromatous plaque?
- Lipids
- Fibrous tissue
- Lymphocytes
What is the primary cause of atherosclerosis?
Endothelial cell damage