Barriers to Infection

Question 1

Describe physical barriers to infection.

3

Answer 1

The simplest (and very effective) mechanisms of immune evasion

The first line of defence

Epithelial cells

Question 2

Give some examples of physical barriers

2

Answer 2

Skin

Mucosae (multiple mucous membranes) e.g. lining of digestive, urinary, reproductive and respiratory tracts, conjunctiva of the eyes

Question 3

What are mucous membranes?

Answer 3

Any epithelial layer that secretes mucous

Question 4

Write a note on the skins role in immunity. (structure)

7

Answer 4

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

Question 5

What is the name of the outermost layer of dead skin cells?

Answer 5

Stratum corneum

Question 6

How does the skin inactivate microorganisms?

5

Answer 6

Desiccation

Acids - pH of skin = 4.5-5

Skin cleaning mechanisms

Sebum - lysozyme and antimicrobial peptides

Commensals as inhibitors

Question 7

What is the pH of the skin?

Answer 7

4.5 - 5

Question 8

What is present in sebum that kills microbes

Answer 8

Sebum

Question 9

Explain what happens during injury to the skin.

7

Answer 9

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

Question 10

What does vasoactive mean?

Answer 10

Something that has an affect on blood vessels

Question 11

Give three places where mucosae are present.

Answer 11

Respiratory system

Gastrointestinal system

Genital surfaces

Question 12

In general where are mucosae found?

Answer 12

They line the parts of the body that are exposed to the environment at points of absorption or secretion e.g. respiratory system

Question 13

Describe mucosae and their role in immunity.

4

Answer 13

Epithelial cells that overlie organs

Lined with goblet cells that produce sticky mucous

Over 1 L mucous produced every day

Mucous traps pathogens

Question 14

Describe the role of the respiratory tract in immunity.

Answer 14

Large particles are trapped in nasal turbinates and sinuses

Question 15

What causes a lower respiratory infection?

Answer 15

When particles smaller than 5uM reach alveolar structures

Question 16

Explain how the mucociliary escalator works.

4

Answer 16

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

Question 17

How many types of tonsils are there?

Answer 17

Four

Question 18

Name the four different types of tonsils.

Answer 18

Palatine tonsils
Lingual tonsil
Adenoid
Tubal tonsil

Question 19

Where are the palatine tonsils?

Answer 19

The back of the throat (visible)

Question 20

Where is the lingual tonsil?

Answer 20

The rear third of the tongue

Question 21

Where are the adenoids?

Answer 21

In the nasal passage

Question 22

Where is the tubal tonsil?

Answer 22

In the nasal passage

Question 23

Explain the role of the digestive tract in immunity.

5

Answer 23

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

Question 24

What is the pH of the stomach?

Answer 24

pH 1-2

Question 25

How often is the lining of the stomach replaced?

Answer 25

Every 2-3 days

Question 26

What type of immune cells are found in the villi of small intestine?

Answer 26

T cells

Question 27

What exact type of T cells are found in the villi of small intestine?

Answer 27

Intra epithelia lymphocytes

Question 28

What is the role of the T cells in the villi of small intestine?

Answer 28

To screen what is in the gut

Question 29

What types of cells are found in thecolon?

Answer 29

Lots of B cells and T cells

Question 30

How does the genitourinary tract fight infection?

2

Answer 30

Through urination - interference of spread of bacteria to bladder and upwards

Acidic

Question 31

What are commensals?

Answer 31

Friendly bacteria that colonise humans and compete with pathogens for resources or actively attack invading pathogens

Question 32

What is our normal flora?

2

Answer 32

They colonise the surface of our gastrointestinal tract and compete with invaders for space and nutrients

Invaders must remove these first

Question 33

Give an example of an antiviral found in body secretions.

Answer 33

Lactoferrin

Question 34

Give two examples of antimicrobials found in body secretions.

Answer 34

Lysozyme

Antimicrobial peptides

Question 35

What is lysozyme and how does it work?

3

Answer 35

An enzyme that attacks the cell walls of bacteria - especially gram positive

Found in all human secretions

Breaks down bonds in peptidoglycan

Question 36

What are antimicrobial peptides?

2

Answer 36

Short, charged peptides that can insert in bacterial membranes disrupting their cell walls

They allow cells to be destroyed by osmosis

Question 37

What is psoriasin?

3

Answer 37

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