Structure and function of airways

Question 1

Describe the structure and purpose of the cartilage surrounding the trachea

Answer 1

C-shaped
Strong for support
Slightly offset to confer greater tensile strength + keep airways open
Gap to allow for expansion of the oesophagus

Question 2

What are the functions of the airway

Answer 2

Conduct and rest to airflow
Condition inspired air
Primary airway defence (mucociliary)
Homeostatic control via immune inflammatory cells

Question 3

Describe the organisation of the airways

Answer 3

Cartilage
Smooth muscle
Systemic circulation (not pulmonary)
Airway epithelium - ciliated + goblet cell
Mucus
Airway lumen

Question 4

Which cell types are found in the airway

Answer 4

lining cells, contractile cells, secretory cells, connective tissue, neuroendocrine, vascular cells, immune cells

Question 5

Which cells supply mucous to the epithelium

Answer 5

goblet cells that project into the lumen

Sub mucosal glands. Acini secrete mucus into the collecting duct which is then wafter to the lumen by the ciliated duct

Question 6

What are the functions of the epithelium

Answer 6

Secretion of mucins, water and electrolytes (components of mucus)
Movement of mucus by cilia (mucociliary clearance)
Physical barrier
Production of regulatory and inflammatory mediators e.g. NO, CO, Arachidonic acid metabolites (prostaglandins), chemokines (interleukin), cytokines (GM-CSF), proteases

Question 7

What are the functions of airway smooth muscle cells

Answer 7

Structure - (hypertrophy and proliferation during inflammation)
Tone (airway calibre) - contraction and relaxation
Secretion of mediators, cytokines and chemokines

Question 8

What occurs in the airways during inflammation

Answer 8

NO synthase upregulated
Cyclooxygenase to produce prostaglandinds upregulated
Secretion of cytokines, chemokines and adhesion mediators bring in more inflammatory cells
Hypertrophy and proliferation

Question 9

Where are serous cells found and what is their function

Answer 9

Outside and ends of mucous cells, secreting antibacterials e.g. lysozyme

Question 10

Describe the blood flow to the airway mucous

Answer 10

very high - 100-150ml/min/100g tissue

only 1-5% of cardiac output

Question 11

Describe the airway vasculature

Answer 11

Bronchial arteries arise from many sites on the aorta, intercostal arteries and others
Blood returns from the tracheal circulation via the systemic veins
Blood returns from bronchial circulation to both sides of heart via bronchial and pulmonary veins

Question 12

What is a plexus

Answer 12

vast collection of veins, capillaries and arteries found below the epithelium

Question 13

What is the function of airway vasculature

Answer 13

Gas exchange
Warming of inspired air
Contributes to humidification of inspired air
Clears inflammatory mediators
Clears inhaled drugs
Supplies airway tissue and lumen with inflammatory cells
Supplies airway tissue and lumen with proteinaceous plasma

Question 14

Explain plasma exudation

Answer 14

1. Gaps in the endothelial cells allow plasma to leak out and “bathe” the tissues
2. C-fibres (nerve) or inflammatory mediators (histamine, platelet activating factor) stimulate the endothelial cells to become more leaky

Question 15

How is airway function controlled

Answer 15

Parasympathetic (cholinergic) control

No sympathetic nerves serve the airway

Question 16

Describe what occurs when a solid is inhaled into the airways

Answer 16

1. Inhalation of a solid - shut down the airways
2. Sensed by sensory nerve fibres
3. Relayed to the brainstem via the vagus nerve
4. Impulse sent to the parasympathetic ganglion
5. Parasympathetic nervous reflex to shut/constrict the airway
6. NO is a vasorelaxant and dilates the airways + helps cilia
7. Adrenaline release also induces relaxation

Question 17

Which regulatory and inflammatory mediators are released by the airway

Answer 17

histamine
arachidonic acid metabolites
cytokines
chemokine

Question 18

Which proteinases are released by the airway

Answer 18

neutrophils and elastase

Question 19

Describe the structure of a cilium

Answer 19

apical hooks that engage with mucus at the top
Cell membrane
outer arm and inner arm linked by nexin links

Question 20

Describe mediator release from airway cells

Answer 20

Cells produce more than one mediator and they carry out more than one action

Question 21

What are the action taken during inflammation of the airways

Answer 21

Smooth muscle contraction/relaxation
Secretion
Plasma exudation
Neural modulation
Chemotaxis
Remodelling

Question 22

What percentage of the population does asthma affect

Answer 22

5%

Question 23

Describe asthma

Answer 23

A clinical syndrome characterised by increased airway responsiveness to a variety of stimuli, leading to airways obstruction
Triggered by cold air, dust, laughing, emotional upset
Dypsnoea, wheezing, cough
remodelling

Question 24

Describe the pathology of asthma

Answer 24

hyperplasia
Mucus plugs the lumen
Fragility of the epithelium
Basement membrane thickens
Increase in smooth muscle and gland size (hypertrophy)
Vasodilation of vessels
Cellular infiltration by inflammatory cells e.g. eosinophils
Bronchoconstriction (airway folds)