T3 Acute Inflammation

Question 1

List a range of situations in which an acute inflammation can occur.

Answer 1

• Physical agents - burns, frostbite etc.
• Infections
• Hypersensitivity
• Chemical
• Tissue necrosis - for example in MI

Question 2

What are the main stages of acute inflammation?

Answer 2

1. Increase in vessel calibre - there is and transient initial vasoconstriction but then a vasodilation of the capillaries. Mediated by histamine and nitrous oxide in vascular smooth muscle to increase blood flow.
2. Increased vascular permeability and formation of fluid exudate
3. Formation of cellular exudate

Question 3

What are the main characteristics of an acute inflammatory response? (5)
Why do these occur?

Answer 3

Calor - Hot to touch - due to hyperaemia resulting in vasodilation and the delivery of warm blood to the area. Systematic fever also contributes to this.

Rubor - Red - due to vasodilation.

Dolor - Pain - due to stretching and situation of the tissues due to inflammatory oedema and the pressure from the exudate in an abscess cavity. Cytokines such as bradykinin, prostoglandins and serotonins cause pain.

Tumour - Swelling due to oedema and to a much lesser extent the mass of inflammatory cells.

Functio lasea - Loss of function - This is conscious and reflexly inhibited by pain. Severe inflammation may also immobilise the tissue.

Question 4

What is the role of neutrophil polymorphs in acute inflammation?

Answer 4

• Movement towards the source
• Adhesion to microorganisms - this is through opposition by C3b and antibodies
• Phagocytosis
• Intracellular killing of microorganisms by oxygen dependent and oxygen independent pathways (bleach)
• Release of lysosomal products attracting other leucocytes to the area

Question 5

What is an exudate?

Answer 5

Extracellular fluid with high protein concentration, containing cellular debris. Its presence implies inflammation.

Question 6

What are the clinical effects and sequelae of acute inflammation?

Answer 6

Resolution
Repair
Regeneration
Suppuration - formation of pus, a mixture of living and dead neutrophils, cellular debris.

Question 7

Define transudate.

Answer 7

Low protein fluid with little or no cellular component.

Question 8

What is oedema?

Answer 8

Excess fluid in the interstitial tissue/serous cavities. It can be either exudate or transudate.

Question 9

How does fluid exudate form?

Answer 9

Increased permeability of microvasculature results in escape of protein rich fluid into tissue. These proteins include immunoglobulins, coagulation factors and fibrinogen.

Causes include:

• Chemical mediators such as histamine, nitrous oxide and leukotriene
• Direct vascular injury e.g. trauma
• endothelial injury - bacteria and toxins

Question 10

How does cellular exudate form?

Answer 10

1. Margination of neutrophils - normally cells are confined to the central stream (axial) and do not flow in the peripheral (plasmatic zone) near the endothelium. Loss of intravascular fluid and increase in viscosity means neutrophils move in the plasmatic zone.
2. Adhesion of neutrophils - this is known as pavementing.
3. Neutrophil emigration - leukocytes move by active ameboid movement through the walls of venules and small veins. They can insert puesodpodia between endothelial cells and migrate the through gap.
4. Diapedesis - red cells escape by diapedesis. This is and passive process and depends on hydrostatic pressure.

Question 11

What is the effects of fluid exudate?

Answer 11

• Dilution of toxins
• Entry of antibodies
• Transport of drugs
• Fibrin formation
• Delivery of nutrients and oxygen
• Stimulation of the immune response
• High turnover

Question 12

Give examples of cell derived mediators of acute inflammation.

Answer 12

• Histamine
• Prostaglandins
• Lysosomal components
• Leukotrienes
• Cytokines

Question 13

Give examples of plasma derived mediators of acute inflammation.

Answer 13

• Complement system
• Coagulation system
• Fibrinolytic system
• Kinin System

Question 14

What are possible harmful affects of acute inflammation?

Answer 14

· Digestion of normal tissues e.g. abscess cavities
· Swelling e.g. acute epiglottitis - inflammation of the epiglottis is potentially dangerous
Inappropriate inflammatory response e.g. hay fever - type I hypersensitivity reaction.

Question 15

What are general effects of inflammation?

Answer 15

• Pyrexia
• Lymph node enlargement - due to reactive hyperplasia of the reticular endothelial reticulum. Local and systemic enlargement is very common. Some can even get splenomegaly.
• Nausea, malaise, anorexia - non-specific side effects
• Leukocytosis - raised white cells. In allergic disorders and parasitic infections you get raised eosinophils. In chronic such as tuberculosis, you get lots of lymphocytes. Increase in neutrophils is seen in pyogenic infections and acute inflammation.
• Amyloidosis - long standing chronic inflammation by elevation of serum amyloid A protein may cause amyloid to deposit in various tissue resulting in secondary amyloidosis.
• Increased erythrocyte sedimentation rate

Question 16

What is pyrogenic bacteria?

Answer 16

Pyogenic bacteria - pus forming bacteria.

Question 17

What is the role of fibrin in inflammation?

Answer 17

Fibrin is very important as it traps and facilitates phagocytosis and impedes the movement of microorganisms. It also acts as a scaffold for granulation tissue. It is therefore very important in inflammation.