Structure and function of airways

Question 1

What is dichotomous branching?

Answer 1

2 branches emerging from one

Question 2

Why are the cartilages c shaped in the trachea?

Answer 2

To allow the oesophagus to pass without being affected

Question 3

Why are the cartilages not stacked neatly?

Answer 3

More tensile strength

Question 4

What are functions of the airways?

Answer 4

• conduit pipes to oxygen and carbon dioxide
• mechanical stability of airways controlled by cartilage
• smooth muscle control air flow
• protection and cleansing of air

Question 5

What are some of the structures in the airway?

Answer 5

• airway lumen
• cartilage
• ciliated cells
• goblet cells
• mucus
• blood vessels
• submucosal glands (embedded in smooth muscle so when muscle contracts, mucus is squeezed out)
• smooth muscle

Question 6

What are the different cells types in the airways?

Answer 6

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

Question 7

Give examples of lining cells

Answer 7

ciliated, intermediate, brush and basal

Question 8

Give and example of a contractile cell

Answer 8

smooth muscle cells

Question 9

Give examples of secretory cells

Answer 9

goblet (epithelial), mucous, serous (glands)

Question 10

Give examples of connective cells

Answer 10

fibroblasts, interstitial cells

Question 11

Give examples of neuroendocrine cells

Answer 11

nerves, ganglia, neuroepithelial bodies

Question 12

Give examples of vascular cells

Answer 12

endothelial, pericyte and plasma cells

Question 13

What are mucin granules?

Answer 13

They contain highly condensed form of mucin (found in mucus). The granules are found in goblet cells

Question 14

What happens to mucin when it is released out of the goblet cells?

Answer 14

It expands as it absorbs water

Question 15

What are submucosal glands?

Answer 15

They secrete mucus

Question 16

What is the structure of a submucosal gland?

Answer 16

The serous cells are peripheral to the mucus cells. The serous cells produce watery mucus that has lysozymes. These secretions go over the mucus and wash into collecting duct. The glands also secrete water, salt and enzymes.

Question 17

What is the structure of cilia?

Answer 17

They have rods within them with apical hooks.
If the cilia is cut transversely, there are 9 rods outside to 2 inside.
The rods slide over each other which uses lots of energy. There are 200 per cell.

Question 18

What is the pattern of cilia beating?

Answer 18

Metachronal rhythm - one field beats then the one behind it and etc. The one that beat first is in backstroke waiting to beat again. Allows subsquential movement. Becuase cilia movement isn’t in sync, mucus can be moved.

Question 19

How is mucus found on top of cilia?

Answer 19

Mucus is found in flakes over cilia, not a complete layer

Question 20

Which regulatory and inflammatory mediators are produced by airway epithelium?

Answer 20

• NO
• CO
• Arachidonic acid
• Chemokines
• Cytokines
• Proteases

Question 21

What is known about NOS expression in epithelium? Why is it found in these amounts?

Answer 21

There are lots of NOS in epithelium so lots of NO is produced. It could be important in controlling cilia beating as without it cilia beats much faster

Question 22

What is airway tone?

Answer 22

How relaxed or contracted their airway is - affected by inflammation

Question 23

When airways are inflamed, what happens to smooth muscle cells?

Answer 23

• Hypertrophy and proliferation of SMCs
• Increased contractile force so more secretion of mediators too (SMCs produce some secretions too) such as cytokines
• So function and phenotype change

Question 24

How do the airways react to cytokines?

Answer 24

• NOS upregulation
• COX enzymes make more prostaglandins
• chemokines recruit other inflammatory cells

Question 25

What are the features of the tracheo-bronchial circulation - where does blood return, where do the vessels come from?

Answer 25

- 1-5% of CO - Highest profusion - bronchial arteries arise from many places on aorta, intercostal arteries etc. - blood returns from tracheal circulation via systemic veins - blood returns from bronchial circulation to both sides of heart via broncial and pulmonary veins

Question 26

What are the functions of the tracheo-bronchial circulation?

Answer 26

- good gas exchange - warming and humidification of inspired air - clears inflammatory mediators and inhaled drugs - supplies airway tissue and lumen with inflammatory cells and proteinaceous plasma

Question 27

Why does plasma leak out of post capillary venules?

Answer 27

They have contractile endothelial cells. When they contract, they pull apart and a gap forms through which plasma leaks.

Question 28

What type of innervation causes endothelial cell contraction?

Answer 28

Sensory nerves with motor function supply the endothelial cells to allow contraction

Question 29

When might plasma exudation go out of control and why?

Answer 29

In inflammation or disease plasma exudation can go out of control as histamine and platelet activating factors are made that active sensory nerves

Question 30

Which things control the airway? | HINT: substances, molecules etc.

Answer 30

- nerves - inflammatory and regulatory mediators ( histamine, cytokines and arachidonic metabolites like prostaglandins) - proteinases - reactive gas species like superoxide anion and NO

Question 31

What would happen if food entered the airway?

Answer 31

``` cholinergic nerves (parasympathetic) - message to central system and cholinergic reflex causes bronchoconstriction ```

Question 32

Which 2 pathways are used to relax the airways?

Answer 32

Other animals use the parasympathetic pathway to relax but in humans adrenaline is used - causes airway relaxation. A neuronal pathway is used - produces NO which opens the airways

Question 33

Why can inflammatory cells have various different effects?

Answer 33

Inflammatory cells produce many mediators so can have various consequences

Question 34

What are some respiratory diseases affecting the airways?

Answer 34

asthma - 5% of pop COPD - 4th most common cause of death in UK, USA CF

Question 35

What is airway remodelling?

Answer 35

airway changes in structure over a long period of time

Question 36

What is asthma and why is it reversible?

Answer 36

Syndrome characterised by increased airway responsiveness to a variety of stimuli- leads to airway obstruction. Obstruction is reversible because adrenaline causes the airways to reopen. Airway inflammation leads to remodelling.

Question 37

What are the symptoms of asthma?

Answer 37

dyspnoea, wheezing and cough

Question 38

What is the histopathology of airways in a person with asthma?

Answer 38

Lumen blocked by mucus plugs with lots of eosinophils. Epithelial becomes fragile, BM thickens and blood vessels become prominent. In submucosa, eosinophil infiltration

Question 39

What happens to the airway in a person who died of asthma?

Answer 39

- epithelium becomes folded as smooth muscle contracts | - lumen is blocked by mucus plug

Question 40

What is the pathophysiological schema of asthma?

Answer 40

- PAF causes plasma exudation - ATP causes goblet cell exocytosis - epithelial fragility exposes the sensory nerves - more responsive to mediators - Leads to a central cholinergic reflex - causes SM contraction and shutting down of the airways, and mucus secretion - Hypertrophy of the smooth muscle and the glands - Increase in the number of goblet cells - chemical mediators released - Mast cells mediators cause bronchoconstriction, mucus secretion etc.