Innate Immunity Flashcards
What are the three internal innate defences?
Fever
Chemical signals
Inflammation
What are neutrophils?
Most abundant WBC that self destruct after devouring pathogens
What is pus?
Neutrophils
When are neutrophils triggered?
When cells release chemicals that begin leukocytosis
True or false: neutrophils are usually used to fight viral infections
FALSE-they are used to fight bacterial infections
What are the two types of macrophages?
Free
Fixed (eg in liver)
What is the main difference between macrophages and neutrophils?
Macrophages can repeatedly engulf pathogens whereas neutrophils self-destruct after devouring one pathogen
Where are macrophages produced?
Bone marrow
What do natural killer (NK) cells do?
Kill own body cells if they become infected with a virus or become cancerous
How do NK cells carry out their function?
Normal healthy cell contains a special protein on its surface called MHC1
If the cell becomes infected, it stops making this protein
If NK cell detects a defective cell, it doesn’t swallow it like a macrophage would but instead, it pokes it with an enzyme that triggered apoptosis
What does MHC1 stand for?
Major histocompatibility complex
What are the characteristic signs of inflammation?
Rubor = redness Tumour = swelling Calor = heat Dolor = pain Loss of function
What do histamine and other inflammatory chemicals do?
Increase permeability of blood vessels, causing nearby capillaries to release protein-rich fluids. This causes swelling and the leaked protein helps to clot blood and form scabs
What is the name of the chemical released when the body detects too many pathogens?
Pyrogen
What do pyrogen chemicals do?
They stimulate the hypothalamus to increase the body temperature (systemic fever)
How does a systemic fever help fight an infection?
Increases cell metabolism so the body can heal faster and it tells the liver and spleen to hold onto all its iron and zinc so that it can’t contribute to bacterial growth
What is the oxygen-independent method of killing a pathogen?
Using hydrolytic enzymes inside lysosomes
Low pH prevents the growth of other pathogens
What is the oxygen-dependent method of killing a pathogen?
Activated phagocytes produce a number of reactive oxygen species
What are the stages of phagocytosis? (8)
- Phagocytes migrate towards site of infection
- Recognise targets
- Ingestion
- Formation of phagosome
- Formation of phagolysosome
- Digestion
- Forming residual body
- Discharge of waste
Define opsonisation
Binding of an opsonin such as antibodies and complement to a receptor on the pathogen’s cell membrane, marking it for ingestion and destruction by a phagocyte
What is a residual body?
Vesicles containing indigestible materials which are then either secreted by the cell via exocytosis or remain as fine granules within the cytosol
What are the two lines of defence of the innate immune system?
- Mechanical and chemical barriers
2. Cellular eg. Phagocytes or protein dependent eg. Complement
What does complement consist of ?
Group of serum proteins
What does complement activate?
Inflammation
Cell destruction
Opsonisation
How do the complement proteins respond and what is this called?
They respond in a sequential manner called the complement cascade
What are the two ways in which the complement cascade can be activated?
Classical pathway
Alternative pathway
What is activated in the classical pathway and when?
C1 is activated when it binds to an antigen-antibody complex
What is activated in the alternative pathway and when?
C3b is activated when it reacts with antigens such as the bacterial cell wall.
Define oedema
Accumulation of excessive amount of watery fluid in cells, tissues or serous cavities
What is lymphedema?
Swelling (especially in subcutaneous tissues) as a result of obstruction of lymphatic vessels or lymph nodes and the accumulation of large amounts f lymph in the affected region
Why does lymphedema not pit?
Lymph has a high protein content and the activation of collagen and fibroblasts makes the skin very scaly and thick so it will not pit
How does oedema form?
Increased hydrostatic pressure within blood vessels
Reduced oncotic pressure within blood vessels
Increased blood vessel permeability (inflammation)
In congestive heart failure, the right and left ventricles are not pumping properly so they dilate. Venous blood ‘dams up’ because the right ventricle cannot cope with the venous return. What will happen to the pressure in the veins?
Increases as the right side is not pumping effectively so there is a build up of hydrostatic pressure in the veins
What is a starling force?
A force that governs whether fluid moves into or out of the capillaries
What is the arteriolar capillary hydrostatic pressure?
35mmHg
What is the venular capillary hydrostatic pressure?
15mmHg
What is the blood colloid oncotic pressure?
25mmHg
Why does oedema often appear first at the ankles?
Gravity causes a vertical gradient of venous pressures
Where would you expect oedema to appear in someone who is lying/sitting in bed?
Sacral oedema (lower back)
