3. Acute inflammation Flashcards
What is inflammation?
The response of living tissue to injury
What are the aims of inflammation?
Its purpose is to deliver defensive materials (white blood cells and fluid containing plasma proteins) to a site of injury.
It aims to protect the body against infection, particularly bacterial infection, and to clear damaged tissue and initiate tissue repair.
What are the features of acute inflammation?
- Immediate
- Short duration
- Innate
- Limits damage
- Stereotyped (always same ie non specific)
What are the major causes of acute inflammation?
• Foreign bodies (splinters, dirt, sutures)
• Immune reactions
• Infections (bacterial, viral, parasitic) and microbial toxins
• Tissue necrosis (any cause)
• Trauma (blunt and penetrating)
• Physical and chemical agents (e.g., thermal injury, e.g., burns or
frostbite, irradiation, environmental chemicals).
What are the two phases of acute inflammation?
vascular phase
cellular phase
What is acute inflammation controlled by?
Chemical mediators
What is the disadvantage of acute inflammation?
Can cause local and systemic complications
What is the goal of the vascular and cellular phase of inflammation?
Vascular = accumulation of exudate (through changes in blood flow)
Cellular = delivery of neutrophils
What are the clinical signs of acute inflammation?
Rubor - redness Tumor - swelling Calor - heat Dolor - pain Loss of function
Describe the changes in blood flow seen in the vascular phase?
1) Trigger
2) Vasoconstriction (seconds)
3) Vasodilatation (minutes ie more prolonged)—-> calor+rubor
4) Increased permeability (leaky) - fluid/proteins/cells escape
What is Starling’s Law in relation to movement of fluid?
Movement of fluid is controlled by the balance of hydrostatic and oncotic pressure. These pressures exist in the vessels and interstitum
What is interstitium?
Fluid outside blood vessels and between cells
What is the difference between hydrostatic and oncotic pressure
Hydrostatic = pressure exerted on a vessel wall BY FLUID. Pushes fluid away. Oncotic = pressure exerted BY PROTEINS. Draws fluid towards proteins.
What is the function of vasodilation?
- increased blood flow so increased capillary hydrostatic pressure
- forces fluid out into interstitium
- Also increases the delivery of fluid and leucocytes to the area of injury
what is the function of increased vessel permeability?
- Plasma proteins move into interstitium
* Increased interstitial oncotic pressure
what is the combined result of vasodilation and increased vessel permeability?
- Fluid movement OUT of vessel INTO interstitium
* OEDEMA (swelling/tumor)
Describe the role that histamine has in inflammation
- Histamine is a vasoactive mediator.
- It’s already present within cells and tissues in around the damage site.
- Histamine is stored in granules of mast cells, basophils and platelets.
- It is released in response to many stimulation e.g physical damage, immune reactions and complement components.
- In acute inflammation histamine is used to produce pain, arteriolar dilation and venule leakage ( increased permeability).
- The fluid leakage occurs as histamine causes endothelial cells to contract and pull apart, this then creates the gaps through which plasma proteins can get through.
Describe the role that Serotonin has in inflammation
Serotonin is very similar to histamine.
It’s also a vasoactive mediator and is stored in the granules of platelets.
It also causes pain, arteriolar dilation and venular leakage
Provide the function of prostaglandins and bradykinins in acute inflammation
- Prostaglandins are produced in inflammation from the phospholipids in cell membranes. These are also used to cause vasodilation.
- They also make the skin more sensitive to pain and cause fever.
- The production of prostaglandins can be inhibited by NSAIDs and aspirin. This can then reduce swelling and pain.
• Bradykinin is also a vasoactive mediator, it’s used to produce pain and increased vascular permeability.
What are the consequences of fluid moving out of the vessels?
The movement of fluid out of the vessels and into tissues will mean that the blood left in the vessels sill be a lot thicker, you’ll have an increased viscosity of blood.
Due to this increase viscosity blood will have difficulty in flowing causing reduced flow through vessels. This is known as stasis.
What is the advantage of increased vessel permeability and vasodilation?
As well as delivering plasma proteins to the site of injury, the abundant tissue fluid has another important
function. Excess fluid drains from the tissues in the lymphatics taking with it micro-organisms and antigens which are thus presented to the immune system within the lymph nodes
What is exudate?
- increased vascular permeability
- protein rich fluid (delivers proteins to area of injury)
- occurs in inflammation
What is transudate?
- vascular permeability unchanged
- low protein content
- fluid movement due to increased capillary hydrostatic pressure and reduced capillary oncotic pressure
- occurs in heart failure/ hepatic failure/ renal failure
What are the defensive proteins in exudate?
- Opsonins – which coat foreign materials and make them easy to phagocytose.
- Complement – a group of proteins that are assembled locally to produce a bacteria-perforating structure
- Antibodies – bind to the surface of micro-organisms and also act as opsonins.
How does a vessel wall become permeable ?
- Retraction of endothelial cells due to the action of vasoactive mediators e.g histamine, NO, bradykinin
- Direct injury to the site e.g due to burns, toxins and direct trauma.
The endothelial cells get damaged and allow proteins and vessels to escape. - Leukocyte dependent injury
Here there are enzymes/ toxic oxygen species released by activated inflammatory cells. This can then cause the increase in permeability of the vessel walls.
How is the vascular phase effective?
- Interstitial fluid
The increase in interstitial fluid dilutes the toxins from the injury and reduces the risk of damage. - The exudate
This delivers proteins to the site of injury.
One example would be fibrin which creates a mesh and limits the spread of the toxin.
As well as this it also brings immunoglobulin(released by lymphocytes) proteins to the site which allows for targeted destruction of pathogens. - Fluid drains to the lymph nodes
This means that antigens and toxins will be delivered to the lymph nodes, detected and this stimulates the adaptive immune response. Proliferation of lymphocytes in lymph nodes
What are the chemical mediators that induce vascular leakage ?
histamine and serotonin, bradykinin and the complement components C3a, C4a and C5a
Give the features of neutrophils
Neutrophils are a primary type of leucocyte (WBC) and are involved in acute inflammation.
They have a trilobed nucleus in their structure. They’re granulocytes so contain granules in their cytoplasm.
What does the presence of neutrophils in tissue indicate?
Neutrophils are usually found in the blood and the bone marrow which means that their presence in the tissue will indicate invasion by bacteria and or tissue injury.
What is the lifespan of neutrophils?
They only have life span of 12-20 hours are an end cell meaning they can’t multiply.
Each neutrophil contains about 2000 granules which themselves contain bactericidal substances.
List the 6 process that must occur to allow a neutrophil to capture and kill a bacterium in tissue space
- Be summoned to the place of injury = chemotaxis
- Switch to a higher metabolic level = activation
- Stick to the endothelial surface = margination
- Crawl through the endothelium = diapedesis
- Recognise the bacterium and attach to it = recognition-attachment
- Engulf the bacterium = phagocytosis
How do neutrophils leave blood vessels?
- Marginate to edge
- Roll - weak intermittent binding
- Adhesion - to endothelium
- Emigration/ diapedisis - escape the endothelium