B16 & 17 - Structure of the lungs and mechanism of breathing

What structures are found in the upper respiratory tract?

Pharynx

Nasal cavities

Vocal cords

Larynx

What is the role of the upper respiratory tract?

• Warm inhaled air (to preserve body temperature)

• Humidify air

• Filter air

What structures are found in the lower respiratory tract?

Trachea

Left and right bronchus

Left and right lung

What is a likely first point of infection for SARS-CoV-2?

Nasal ciliated and secretory cells

• Study done found high number of virions suggesting efficient viral replication

What is the role of type 1 alveolar cells?

Very thin cells

• Allow for efficient gas exchange

What is the role of type 2 alveolar cells?

Thick cells which release surfactant

• This reduces surface tension inside the alveoli, making the lungs easier to expand

What percentage of the surface of alveoli are covered by capillaries?

80-90% of the surface of alveoli

• Allows for efficient gas exchange by maintaining a gradient

What does Boyles’ Law say?

Pressure and volume have an inverse relationship

• If volume increases then pressure decreases and vice versa

How does Boyles law allow our lungs to function?

As lung volume increases, the pressure decreases below atmospheric pressure.

• This causes air to flow into the lungs

As lung volume decreases, the pressure increases above atmospheric pressure

• This causes air to flow out the lungs

What is the pleural sac?

Also known as the pleural cavity

A two-layered serous membrane which covers the lungs and attaches to the chest wall

What muscles contractions are involved in inspiration?

External intercostal muscles

Diaphragm

Scalenes

Sternocleidomastoids 

What muscle contractions are involved in expiration

Internal intercostal muscles

Abdominal muscles

Where does the thoracic cage move during inspiration?

Upwards and outwards

What causes the majority of the change in thoracic volume?

Most of the change is due to the diaphragm

• 30% of the volume change is due to muscles in the ribs

As the diaphragm contracts, thoracic volume ___________.

As the diaphragm contracts, thoracic volume increases.

What is FEV1?

Forced expiratory volume in one second (FEV1) 

• How much air a person can exhale in the first second of a forced breath 

What is MVV?

Maximum voluntary ventilation

• How much air a person can breathe in and out in 12 seconds 

What is FVC?

Forced vital capacity 

• Maximal volume of air exhaled with maximally forced effort from a maximal inspiration 

Internal intercostal muscles are not needed during resting breathing due to the elastic property of the lungs

True or False.

True.

Resting breathing is ‘passive’ and the internal intercostal muscles are not needed

What is the normal pH of the blood?

7.35-7.45

How does the body control pCO2 and blood pH?

By altering the respiratory rate to allow more or less CO2 to be removed.

What is partial pressure and how do you calculate it?

Air pressure is ~760mmHg and 21% of the air is oxygen. What is the pO2?

Partial pressure is the pressure exerted by a specific gas within a mixture of gases (like air)

Partial pressure can be calculated by using the % gas in the mixture and the pressure of the mixture.

• E.g. 760mmHg x 0.21 = 160mmHg

• pO2 = ~160mmHg

Why do you absorb less oxygen at high altitudes?

As you get higher the pressure decreases but the percentage of oxygen does not change.

• This means the partial pressure of oxygen at high altitudes will be near that of venous blood

• This means there is very little gradient to drive oxygen absorption

Where are central chemoreceptors located?

Brain stem

Where are peripheral chemoreceptors located?

Arterial chemoreceptors in carotid bodies and aortic arch

There is too much CO2 in the blood. How do chemoreceptors fix this?

Chemoreceptor senses the high pCO2 and sends signals to respiratory muscles

This allows for changes in breathing to alter conditions (e.g. faster ventilation to remove excess CO2)

Where is the rhythmic cycle generated from?

The medulla oblongata

Which neurones (inspiratory/expiratory) are found in the dorsal root ganglia?

Mainly inspiratory neurones

• Send signals to diaphragm and intercostals

Which neurones (inspiratory/expiratory) are found in the ventral root ganglia?

Contains both inspiratory and expiratory neurones

• Sends impulses to larynx, pharynx, diaphragm and external intercostals

What is the role of the Pons in respiration?

Modifies the output from the medullary centres

How do central chemoreceptors detect CO2 levels?

CO2 can cross the BBB but H+ and HCO3 cannot.

The central chemoreceptors can therefore respond to the pH of the CSF which changes when CO2 diffuses in

• CSF has little buffering capacity

What do central chemoreceptors respond to?

Changes in pCO2 (and pH)

What do Peripheral chemoreceptors respond to?

Changes in pO2

• Also detect changes in CO2 and pH

If you remove the peripheral chemoreceptors, you will stop breathing as they are key to maintaining a rhythmic breathing cycle.

True or False.

False.

They can be removed and you won’t stop breathing.

• They are not essential and are a backup system in case the central chemoreceptors fail