Host defence in the lung 2

Question 1

What are the respiratory functions of the lung?

Answer 1

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

Question 2

What are the non-respiratory functions of the lung?

Answer 2

Non-respiratory functions:
- 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 3

What is the lung exposed to daily?

Answer 3

Large numbers of airborne pathogens
- Containing both pathogens and particles
E.g. Covid-19

Question 4

What does our host defence mainly involve?

Answer 4

Barriers

Question 5

What is an intrinsic host defence?

Answer 5

It is always present: physical and chemical
Apoptosis, autophagy, RNA silencing, antiviral proteins

Question 6

What is an innate host defence?

Answer 6

Induced by infection (Interferon, cytokines, macrophages, NK cells)

Question 7

What is an adaptive immunity defence?

Answer 7

Tailored to a pathogen (T cell, B cells)
- Can involve memory cells

Question 8

What is the epithelium?

Answer 8

Epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body. Many glands are also formed from epithelial tissue. It lies on top of connective tissue, and the two layers are separated by a basement membrane.

Question 9

What is a respiratory epithelium?

Answer 9

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 10

What is the epithelium like in the nasal area (head)?

Answer 10

• Respiratory mucosa, with mucous cells and the mucus escalator, lines the nasal cavity and the superior portion of the pharynx
• Cells are attached to basement membrane so pseudostratified

Question 11

What is the epithelium like in the inferior pharynx area?

Answer 11

• A stratified squamous epithelium lines the inferior portions of the pharynx, protecting the epithelium from abrasion and chemical attack

Question 12

What is the epithelium like in the lower respiratory tract area?

Answer 12

A typical mucosa lines the conducting portion of the lower respiratory tract (trachea)

Question 13

What is the epithelium like in the bronchi?

Answer 13

In the finer bronchioles, the epithelium becomes cuboidal

Question 14

What is the epithelium like in the gas exchange surfaces (alveoli)?

Answer 14

Consist of delicate simple squamous epithelium

Question 15

What are some examples of multiple cell types in the airway epithelium?

Answer 15

• Basal cell
• Ciliated cell
• Fibroblast
• Goblet cell
  etc…
  These express multiple cell specific genes to protect the alveoli as they all contribute to the cell lining

Question 16

What are chemical epithelial barriers?

Answer 16

Multiple molecules separated from the epithelium:
- Antiproteinases (pathogens use protease to invade epithelium so these block this)
- Anti-fungal peptides
- Anti-microbial peptides (proteins impact specifically bacterial pathogens)
- Antiviral proteins
- Opsins

Question 17

What is the host defence for alveolar epithelium?

Answer 17

• Alveolar type 2 cells: Alveolar type II cells secrete a lipoprotein material called surfactant, whose primary function is to reduce the surface tension in the alveoli.
• Physical barriers (mucus)
• Submucosal glands

Question 18

What is mucus?

Answer 18

• It is a viscoelastic gel containing water, carbohydrates, proteins and lipids
• It is the secretory product of the mucous cells (goblet cells of the airway surface epithelium and the submucosal glands)

Question 19

What is mucus protecting?

Answer 19

The epithelium from foreign material and from fluid loss (stops/reduces the evaporation across epithelium)

Question 20

How is mucus transported?

Answer 20

From the lower respiratory tract into the pharynx by air flow and mucociliary clearance

Question 21

What is the mucus escalator?

Answer 21

• This is how mucus is cleared
• Cilia beat in directional waves to move mucus up the airways
• coughing and sneezing are significant non-immune defence mechanisms

Question 22

What is a cough?

Answer 22

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

Question 23

What are the causes of a cough?

Answer 23

• Irritants (Smokes, fumes, dusts etc…)
• Diseased conditions (COPD, tumours etc…)
• Infections (influenza)

Question 24

How is a cough initiated?

Answer 24

• Can be voluntarily or reflexively
• As a defensive reflex it has both afferent and efferent pathways

Question 25

What are the afferent and efferent pathways of a cough?

Answer 25

Afferent limb: Includes receptors within the sensory distribution of some nerves e.g. vagus
Efferent limb: Includes the laryngeal nerve and spinal nerves

Question 26

What is a sneeze?

Answer 26

• Involuntary expulsion of air containing irritants from the nose

Question 27

What are the causes of a sneeze?

Answer 27

• Irritation of a nasal mucosa
• Excess fluid in airway

Question 28

What is the pathway of a sneeze?

Answer 28

• Receptor: nerve endings in nose
• Sensory neuron: to the integration centre (sneezing centre in the brain stem)
• Motor neuron: to the effectors (eyes, nose, lungs, diaphragm, chest muscles, parts of the mouth)

Question 29

How does the epithelium repair after an injury?

Answer 29

• Because it exhibits a level of functional plasticity (change its’ function)
• There is cell migration (cell movement)
• Then cell proliferation (growth of cells)
• Then re-differentiation (return to original form)
• Then re-generation (increase no. of cells)

Question 30

What happens when epithelium repair goes wrong?

Answer 30

Pulmonary disease
- We can also get abnormal epithelial responses to injury/insult underpin many obstructive lung diseases
An example of goblet cell metaplasia in the airway of a heavy smoker

Question 31

What is obstructive lung disease?

Answer 31

• Mucus and inflammatory cells blocking the airways
• Can be fatal