Host Defence In The Lung 2

Question 1

Function of the lungs

Answer 1

Respiration

Non-respiratory function

Question 2

Respiration

Answer 2

Ventilation and gas exchange: O2, CO2, pH, warming and humidifying

Question 3

Non- respiratory function

Answer 3

Synthesis, activation and inactivation of vasoactive substances, hormones, neuropeptides

Lung defence: complement activation, leucocyte recruitment, host defence proteins, cytokines and growth factors

Speech, vomiting, defecation.

Question 4

Airborne pathogens

Answer 4

The lung is exposed to a large number of airborne pathogens as the result of the daily inhalation of >10,000 litres of air.

This contains both pathogens and particulates

Question 5

Why are respiratory infections so comparatively rare?

Answer 5

because of mechanisms of host defence

Host defence mostly involves barriers

Question 6

Host defences

Answer 6

Intrinsic: Always present: Physical and chemical. Apoptosis, autophagy, RNA silencing, antiviral proteins

Innate defence: Induced by infection (Interferon, cytokines, macrophages, NK cells

Adaptive immunity: Tailored to a pathogen (T cell, B cells)

Question 7

Host defence functions throughout the respiratory tract (and involves the epithelium)

Answer 7

Respiratory epithelium serves to moisten and protect the airways.

It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator.

Question 8

The airway epithelium is different in distinct regions – reflecting functions –

Answer 8

Slide 18

Question 9

The airway epithelium in distinct regions contain multiple cell types and these express multiple cell specific genes

Answer 9

Slide 19 and 20

Question 10

Multiple molecules secreted from the epithelium play a role in host defence.
These are chemical epithelial barriers:

Answer 10

antiproteinases
anti-fungal peptides
anti-microbial peptides
Antiviral proteins
Opsins
Produced by most (all?) epithelial cells

Question 11

The alveolar epithelium is specialised for gas exchange but also has a host defence function

Answer 11

Host defence in the respiratory tract relies on more than epithelial cell products - physical barriers (mucus) and products of the submucosal glands are important

Question 12

Mucus

Answer 12

Airway mucus is a viscoelastic gel containing water, carbohydrates, proteins, and lipids.

It is the secretory product of the mucous cells (the goblet cells of the airway surface epithelium and the submucosal glands).

Mucus protects the epithelium from foreign material and from fluid loss

Mucus is transported from the lower respiratory tract into the pharynx by air flow and mucociliary clearance.

Question 13

Mucus clearance occurs via the escalator

Answer 13

Cilia beat in directional waves to move the mucus up the airways

Question 14

Coughing and sneezing

Answer 14

are significant non-immune defence mechanisms

Question 15

What is a cough

Answer 15

Cough is an expulsive reflex that protects the lungs and respiratory passages from foreign bodies

Causes of cough
-irritants- smokes, fumes, dust
-Diseased conditions like COPD, tumours etc
-infections (influenza)

Question 16

What causes a cough?

Answer 16

Initiated either voluntarily or by reflex

As a defensive reflex it has both affront and efferent pathways

Question 17

What is a sneeze?

Answer 17

Sneeze is defined as the involuntary explosion of air containing irritants from nose

Cause of sneeze
-Irritant of nasal mucosa
-excess fluid in airway

Question 18

Following an insult/injury the airway epithelium can in (many cases) effect a complete repair

Answer 18

This is because it exhibits a level of functional plasticity

Plasticity exists in multiple cells

This is beneficial

When the process goes wrong we get pulmonary disease
Abnormal epithelial responses to injury/insult underpin many obstructive lung diseases

Question 19

Mucus plugs/inflammation is associated with severe disease

Answer 19

Mucus and inflammatory cells blocking the airways. Hence the term obstructive lung disease is sometimes used

Mucus plugs can completely obstruct the airways and can be fatal

Question 20

Summary

Answer 20

The respiratory tract is made of a number of distinct epithelial compartments containing unique cells

Many of these epithelial cells directly contribute to the non-immune host defence functions of the lung

They provide a physical and chemical barrier to prevent infection

They exhibit a remarkable ability to repair

Aberrant repair and re-organisation underpins many lung diseases