L5 Physiology of the Airway

Question 1

Why do people snore?

Answer 1

Snoring is the result of the relaxation of the uvula and soft palate.[11] These tissues can relax enough to partially block the airway, resulting in irregular airflow and vibrations. Snoring occurs in 25% of the population.

Question 2

What is sleep apnea?

Answer 2

Sleep apnea occurs in 10% of the population. In sleep apnea, patients stop breathing when they are sleeping causing them to wake up. When breathing normally the ribcage and the abdomen work together however when breathing is abnormal, they work against each other. The point at which they wake up again is an arousal.

These patients snore a lot and get sleepy during the day. They spend there entire night dozing as when they wake up, they go into stage 1 or 2 of sleep. This means they are constantly tired. Once they reach deep sleep, they stop breathing and wake up.

Question 3

What is the difference between tonic and phasic muscle?

Answer 3

Tonic muscle activity produces tone. This is permeant activity that holds the muscle in place.

Phasic activity is muscle activity that comes in phases. For example, activity that only occurs during inspiration or expiration.

Question 4

When is the control of muscles poor?

Answer 4

Sleep, under the influence of alcohol, under anaesthetics or under the influence of sedatives.

Question 5

What is the shape of ciliated epithelia at the level of the:

(i) Nose and Pharynx

Answer 5

Psuedo-stratifed columnar epithelium

Question 6

What is the shape of ciliated epithelia at the level of the:

(ii) Trachea and bronchi

Answer 6

Columnar epithelium

Question 7

What is the shape of ciliated epithelia at the level of the:

(iii) Bronchioles

Answer 7

Cuboidal epithelium.
The epithelial cells become narrower and narrower before merging with the epithelial cells. At level of the bronchioles they lose their cilia.

Question 8

What is the function of goblet cells?

Answer 8

To secrete mucin.

Question 9

When do goblet cells increase secretion?

Answer 9

When there are things that irritate the lungs present such as tobacco smoke or an infection.

Question 10

What is the structure of airway lining fluid?

Answer 10

There is a pericillary layer next to the epithelium. This is a salt water layer. The epithelium pump out chloride ions followed by sodium ions drawing out water. The cilia live within this layer.

Above the pericillary layer is a gel layer made of mucus. This is a thick, viscous layer. The purpose of this is to catch things that are inhaled.

Question 11

What is the name of the stroke cilia perform to sweep mucus out of the way?

Answer 11

Effective stroke. Every so often, the cilia will reach out into the gel layer and pull the mucus along before retiring back to the pericillary layer to perform a recovery stroke. There are millions of cilia in our airways moving mucus along at a rate of approximately 4mm/min.

Question 12

What is the purpose air airway lining fluid?

Answer 12

• Humidification of air. Air must be humidified before reaching the alveoli or it will cause the alveoli to dry out and not function. The water inter airway lining fluid will evaporate and incorporated into inhaled air, humidifying it.
• Defence. The mucus will trap pathogens and particulate matter. This will then be wept up by the Cilla and move up the airways where it can either be swallowed (and destroyed by the stomach) or coughed up.

Question 13

What is the heat and moisture exchange?

Answer 13

As you breath in, the mucosa warms and humidified the air. When you breath out, the air coming out is now warmer and humidified compared to the mucosa and so water condenses back into the mucosa. This means you don’t use that much water during breathing - you only lose 120 - 150ml in expired air. Since it evaporates on the way out, you don’t lose litres of water.

Question 14

What are the symptoms of cystic fibrosis?

Answer 14

People with CF can have a variety of symptoms, including:

• Very salty-tasting skin.
• Persistent coughing, at times with phlegm.
• Frequent lung infections including pneumonia or bronchitis.
• Wheezing or shortness of breath.
• Poor growth or weight gain in spite of a good appetite.
• Male infertility
• Diabetes
• Loss of pancreatic function
• Fatty stools

Question 15

What is the prevalence of cystic fibrosis?

Answer 15

1 in 25 have the gene for it. It is an autosomal recessive inherited disease. This leads to cystic fibrosis being in 1 in 2500 births.

Question 16

What is the cause of cystic fibrosis?

Answer 16

Cystic fibrosis is due to an abnormal CFTR Cystic fibrosis transmembrane regulator. This is a protein on epithelial cells that controls the airway lining fluid by controlling chloride secretion. The channel is not functioning and so chloride ions are not secreted into the fluid, means water is not drawn out. The secretion becomes too viscous for the cilia to move and so the individual becomes very prone to chest infections.

Question 17

At what particle size, are inhaled particles deposited on the nose and pharynx? How is this achieved?

Answer 17

Greater than 8 microns e.g. pollen.
The particle has enough inertia, so that when the air turns a corner in the airway, the particle drops out and gets trapped on the pharynx.

(Inertia is the resistance of the object to any change in its motion, including a change in direction.).

Question 18

At what particle size, are inhaled particles deposited on the large airways? How is this achieved?

Answer 18

3-9 microns. This includes fungal spores which can get into the large airways. These mode also works via inertial impaction.

Question 19

At what particle size, are inhaled particles deposited on the small airways? How is this achieved?

Answer 19

0.5-3 microns
The size of small particles makes it drop out the air and sediment at the bronchioles. Particulate matters, stone dust and asbestoses do so.

Question 20

At what particle size, are inhaled particles deposited on the alveolus? How is this achieved?

Answer 20

Particles less than 0.5 microns. These particles are able to diffuse and move via Brownian motion. This includes small (including cigarette smoking), which along with other very small particles, is usually exhaled.

Question 21

What are the non-immunological defences to pathogens in the lungs?

Answer 21

1. Physical barrier - catch on the mucous and cough it out/swallow and the enzymes in the stomach destroy it. Physical removal is how we deal with 99% of inhaled particles. The mucin stops the pathogens getting through the gel and into the cells, leading to an infection.
   
   2. Chemical inactivation - lysozymes, protease enzymes e.g. elastase, antimicrobial peptises e.g. human beta defensins (proteins produced by the epithelia that are antibiotics and kill common bacteria). The lungs produce anti-proteases as well to prevent the proteases from damaging the cells in the case they get through the mucus into the lung epithelia. These are all chemicals produced by the epithelia found in the mucous layer.
      Alveolar macrophages - The macrophages have left the body tissue looking for pathogens that may have, by chance, stuck to the alveolus. The macrophages are there to engulf them to prevent infection.

Question 22

What are the immunological defences to pathogens in the lungs?

Answer 22

Humoral:
IgA - found in the nose and large airways.
IgG - found in the small airways.
IgE - found in allergic disease

Cell-mediated response:
- Epithelial cells have can recognise pathogens in the area and so release cytokines to initiate an inflammatory response.
Macrophages can also digest pathogens. Neutrophils (infection) and eosinophils (allergy) also act as phagocytes.

Question 23

What does inhalation of nitrates lead to?

Answer 23

Inhalation of nitrates can make asthma worse and can cause airway irritation.

Question 24

What does inhalation of particulate matter lead to?

Answer 24

Inhalation of particulate matter can cause damage in the long term. It can lead to lung and systemic inflammatory responses; asthma, pneumonia, stroke, heart attack and type II diabetes.

Question 25

What is the cause of a smokers cough?

Answer 25

Cyanide is found in small amounts in tobacco. This gets to the cilia and stops the cilia working. As a result, smokers cannot push out mucus. A smokers cough is a very productive cough in the morning, this is as when they are sleeping, they are not smoking during the night. The cilia function has recovered and so when they wake up they move up all the mucus and cough it out.

Question 26

Why do most inhaled bodies enter the right main bronchus?

Answer 26

It is straighter and more continuous with the trachea than the left main bronchus.

Question 27

Why do you cough after exercising in the cold?

Answer 27

If you take a deep breath during exercise, often the air has travelled a greater distance before being humidified.
Therefore if you exercise in cold air, non-humidified air gets further down the airway, irritates the airway and makes you cough as cold air is very dry.

Question 28

Why is air that has been inhaled through the nose better humidified?

Answer 28

The air has more exposure to mucosa as it goes down if it goes down the nose and gets better humidified. This is as it takes a longer journey to get to the alveolus. In addition to this, the air becomes turbulent as it crosses over the conchae and so moves in greater contact with the airway lining fluid. By the time you get to the carina, either way, the air will be humidified.

Question 29

What is expectoration?

Answer 29

Ejecting phlegm or mucus from the throat

Question 30

On what chromosome does the gene for cystic fibrosis occur on?

Answer 30

Chromosome 7

Question 31

What is the most common mutation in cystic fibrosis?

Answer 31

Deletion of Phe 508

Question 32

What is PM2.5?

Answer 32

PM2.5(particles less than 2.5 micrometres in diameter) particles can penetrate deeply into thelung, irritate and corrode the alveolar wall, and consequently impairlungfunction. This is as deeper into the lung, the defence mechanisms are not as good.

Question 33

What are is an obstructive respiratory condition? What are the common causes?

Answer 33

Obstructive pulmonary disease is due to of the airways that air into and out of the lungs. This may be caused by:
Ø Inflammation of the lining of the airways, particularly of the smaller airways, when the lining swells and causes narrowing
Ø Mucus plugs obstructing the lumen of the airways, which occurs in acute or chronic infections when there is excessive mucus secretion
Ø Constriction of the smooth muscles in the walls of the airways, causing airway narrowing. The commonest example is asthma
Ø Loss of elasticity in the airways, usually caused by chronic infection. The elasticity of the airways is normally instrumental in keeping the airways open, so that stiffness would lead to obstruction when the airway collapses (particularly on expiration).
Common examples of obstructive pulmonary disease are asthma , COPD, chronic bronchitis and emphysema.

Question 34

What ais pulmonary diffusion capacity? What are normal values? What do these values change to in exercise?

Answer 34

Pulmonary diffusion capacity is the ability of the lungs to transfer a gas, usually oxygen (O2), or carbon dioxide (CO2), across the alveolar-capillary membrane.
Ø The diffusing capacity for both oxygen (DLO2) and carbon dioxide (DLCO2) is difficult to measure, and therefore not often used clinically.
Ø The single breath carbon monoxide (CO) diffusion test is the more usual test of pulmonary diffusion capacity.
Ø Interpretation of DLCO needs to be in the context of other clinical and physiological findings.
Ø Values for oxygen diffusion capacity at rest vary between 15 mL/min/mmHg and 35 mL/min/mmHg. The average is about 20 mL/min/mmHg.
Ø Diffusion capacity is increased in exercise to values of 65 mL/min/mmHg or more, presumably due to dilatation of the capillaries and opening up of the closed capillary bed in the lung apex.
Ø In disease, diffusion capacity is reduced.
Ø Thickening of the alveolar-capillary interface can occur in scleroderma, asbestosis, pulmonary fibrosis, pulmonary oedema and sarcoidosis.
Ø Reduction of the area of the alveolar-capillary interface may occur through emphysema or surgery.

Question 35

What are intrinsic restrictive disorders?

Answer 35

Intrinsic lung diseases is otherwise known as diseases of the lung parenchyma. The diseases cause inflammation or scarring of the lung tissue (interstitial lung disease) or result in filling of the air spaces with exudate and debris (pneumonitis). Chronic inflammation with scarring and fibrosis (interstitial fibrosis) destroys air spaces, thereby reducing lung volume. Large parts of the lung parenchyma cannot function for gaseous exchange.

Question 36

What are extrinsic restrictive disorders?

Answer 36

Extrinsic restrictive lung disease is caused by complications with tissues or structures outside of the lungs, including neurological conditions. External factors that cause an extrinsic restrictive lung disease are often associated with weakened muscles, damaged nerves, or the stiffening of the chest wall tissues.