Barriers to Infection Flashcards
Describe physical barriers to infection.
3
The simplest (and very effective) mechanisms of immune evasion
The first line of defence
Epithelial cells
Give some examples of physical barriers
2
Skin
Mucosae (multiple mucous membranes) e.g. lining of digestive, urinary, reproductive and respiratory tracts, conjunctiva of the eyes
What are mucous membranes?
Any epithelial layer that secretes mucous
Write a note on the skins role in immunity. (structure)
7
Largest organ in the body
Good barrier to infection
Different thicknesses
5 layers - 4 layers with keratinocytes of different maturity
Stratum corneum - outermost layer of dead cells, desquamating together with adhered microbes
Waterproof, unfavourable environment for microbes, dry, salty
Cooperation with microorganism
What is the name of the outermost layer of dead skin cells?
Stratum corneum
How does the skin inactivate microorganisms?
5
Desiccation
Acids - pH of skin = 4.5-5
Skin cleaning mechanisms
Sebum - lysozyme and antimicrobial peptides
Commensals as inhibitors
What is the pH of the skin?
4.5 - 5
What is present in sebum that kills microbes
Sebum
Explain what happens during injury to the skin.
7
Tissue damage causes release of vasoactive and chemotactic factors that trigger a local increase in blood flow and capillary permeability
Mast cells become active - they rich in histamine which are vasoactive
Histamine causes blood vessels to dilate
Flow of blood slows down and vessels become leaky
Fluid leaves blood vessels and moves to tissue
White blood cells move from blood vessels to damages tissue (inflammation process begins)
White blood cells move towards site - kill bacteria
What does vasoactive mean?
Something that has an affect on blood vessels
Give three places where mucosae are present.
Respiratory system
Gastrointestinal system
Genital surfaces
In general where are mucosae found?
They line the parts of the body that are exposed to the environment at points of absorption or secretion e.g. respiratory system
Describe mucosae and their role in immunity.
4
Epithelial cells that overlie organs
Lined with goblet cells that produce sticky mucous
Over 1 L mucous produced every day
Mucous traps pathogens
Describe the role of the respiratory tract in immunity.
Large particles are trapped in nasal turbinates and sinuses
What causes a lower respiratory infection?
When particles smaller than 5uM reach alveolar structures
Explain how the mucociliary escalator works.
4
Mucous is secreted by goblet cells
Two layers of mucous - gel (top) and a sol (bottom)
Mucosa of the respiratory tract have hairs on their surface - these cilia sweep pathogen-laden mucous upwards to the mouth where it can enter the oesophagus and then enter the stomach where acid will kill pathogens
All cilia lean in one direction
How many types of tonsils are there?
Four
Name the four different types of tonsils.
Palatine tonsils
Lingual tonsil
Adenoid
Tubal tonsil
Where are the palatine tonsils?
The back of the throat (visible)
Where is the lingual tonsil?
The rear third of the tongue
Where are the adenoids?
In the nasal passage
Where is the tubal tonsil?
In the nasal passage
Explain the role of the digestive tract in immunity.
5
Stomach has pH of 1-2
Lining of stomach replaced every 2-3 days
T cells in villi - intra epithelia lymphocytes - to screen what is in the gut
Mononuclear cells in lamina propria - to ensure immune response is carried out
Colon - lymphoid aggregates - lots of B cells and T cells
What is the pH of the stomach?
pH 1-2
How often is the lining of the stomach replaced?
Every 2-3 days
What type of immune cells are found in the villi of small intestine?
T cells
What exact type of T cells are found in the villi of small intestine?
Intra epithelia lymphocytes
What is the role of the T cells in the villi of small intestine?
To screen what is in the gut
What types of cells are found in thecolon?
Lots of B cells and T cells
How does the genitourinary tract fight infection?
2
Through urination - interference of spread of bacteria to bladder and upwards
Acidic
What are commensals?
Friendly bacteria that colonise humans and compete with pathogens for resources or actively attack invading pathogens
What is our normal flora?
2
They colonise the surface of our gastrointestinal tract and compete with invaders for space and nutrients
Invaders must remove these first
Give an example of an antiviral found in body secretions.
Lactoferrin
Give two examples of antimicrobials found in body secretions.
Lysozyme
Antimicrobial peptides
What is lysozyme and how does it work?
3
An enzyme that attacks the cell walls of bacteria - especially gram positive
Found in all human secretions
Breaks down bonds in peptidoglycan
What are antimicrobial peptides?
2
Short, charged peptides that can insert in bacterial membranes disrupting their cell walls
They allow cells to be destroyed by osmosis
What is psoriasin?
3
It is a protein produced by keratinocytes
It acts as an antimicrobial peptide against E.coli by binding to Zinc required by E.coli
It acts as a chemoattractant for cells of the immune system
