Anatomy of chest wall and mechanics of breathing

Question 1

What membrane lines the inside of the ribcage (superficial membrane)?

Answer 1

Parietal pleura

Question 2

What membrane lines the surface of the lungs (deeper membrane)?

Answer 2

Visceral pleura

Question 3

What respiratory structure does the parietal pleura cover?

Answer 3

Diaphragm

Question 4

Why is it important for the lungs to be stuck to the ribcage and diaphragm?

Answer 4

Lungs are effectively stuck to the ribcage and diaphragm through parietal pleura. Important because ribcage and diaphragm move to allow lungs to expand/contract.

Question 5

What is pleurisy/pleuritis?

Answer 5

Inflammation of the pleura. Lose lubrication so pleura grate against each other and make breathing hard and sore

Question 6

What is elastic recoil of the lung?

Answer 6

Rebound of the lungs inwards after having been stretched out by inhalation

Question 7

What is a pneumothorax?

Answer 7

When the sealed pleural cavity opens and air flows in causing lung collapse. Intrapleural pressure = atmospheric pressure which is bad

Question 8

Why is intrapleural pressure always negative?

Answer 8

Because the lungs and ribcage are constantly trying to pull apart

Question 9

What muscles does inspiration use?

Answer 9

External intercostals, diaphragm and accessory muscles - scalene and sternocleidomastoid

Question 10

What muscles does expiration use?

Answer 10

Expiration is passive at rest but internal intercostals and abdominal muscles used during severe respiratory load

Question 11

What happens to the diaphragm during inspiration?

Answer 11

Diaphragm contracts and descends

Question 12

What happens to the external intercostals during inspiration?

Answer 12

They contract pulling ribcage and sternum upwards; lifting ribs upwards increases anterior posterior distance of ribcage; lifting ribs upwards also moves them outwards and increases medial lateral distance; thus increasing volume of cavity

Question 13

What happens to the abdominal muscles during expiration?

Answer 13

Contract and speeds up diaphragm (relaxes and ascends) and ribcage to resting position (inwards and downwards) to decrease cavity volume

Question 14

What is Boyle’s law?

Answer 14

Pressure exerted by a gas is inversely proportional to its volume

Question 15

What is the relationship between pressure and volume in Boyle’s law?

Answer 15

When volume increases, pressure decreases and vice versa

Question 16

What direction does gas move?

Answer 16

High to low pressure

Question 17

What is intra-thoracic/alveolar pressure (PA)

Answer 17

Pressure inside the thoracic cavity (essentially inside lungs). May be -ve or +ve compared to atmospheric pressure. -ve during inspiration; +ve during expiration

Question 18

What is intrapleural pressure (Pip)?

Answer 18

Pressure inside the pleural cavity. ALWAYS -ve (in healthy lungs). Sub-atmospheric due to recoil of chest and lungs away from each other.

Question 19

What is transpulmonary pressure (PT)?

Answer 19

Difference between alveolar and intrapleural pressure. ALWAYS +ve (in healthy lungs) because PA - PIP = +ve

Question 20

What is the bulk flow of air between the atmosphere and alveoli proportional to?

Answer 20

The difference between the atmospheric and alveolar pressure

Question 21

What is the bulk flow of air between the atmosphere and alveoli inversely proportional to?

Answer 21

Airway resistance

Question 22

What is the flow called that air flows into the lungs by?

Answer 22

Bulk flow.

Question 23

What does airway resistance determine?

Answer 23

How much air flows into the lungs at any given pressure difference between atmosphere and alveoli

Question 24

What determines airway resistance?

Answer 24

Radii of the airways

Question 25

Does intrapleural pressure increase or decrease during inspiration?

Answer 25

Decrease

Question 26

How does lung expansion affect alveolar pressure?

Answer 26

It makes PA more subatmospheric, creating a pressure difference between atmosphere and alveoli, driving air flow into lungs (because PA is now lower and gas moves from high to low pressure)

Question 27

What happens to alveolar pressure during expiration?

Answer 27

Alveolar air compressed, raising alveolar pressure above atmospheric pressure and therefore driving air out the of the lungs