2. Anatomy of Chest Wall and Mechanics of Breathing

Question 1

What is meant by Boyle’s law?

Answer 1

Boyle’s Law states that the pressure exerted by a gas is inversely proportional to to its volume (P a 1/V). Note that gases (singly or in mixtures) move from areas of high pressure to areas of low pressure.

Question 2

What is Dalton’s law?

Answer 2

Dalton’s Law states that the total pressure of a gas mixture is the sum of the pressures of the individual gases.

Question 3

What is Charle’s Law?

Answer 3

Charles Law states that the volume occupied by a gas is directly related to the absolute temperature (v a T)

Question 4

What is Henry’s law?

Answer 4

Henry’s Law states that the amount of gas dissolved in a liquid is determined by the pressure of the gas and it’s solubility in the liquid.

Question 5

Where does the esophagus and the aorta pass through the thorax?

Answer 5

Between the pleural sacs

Question 6

Where does the parietal membrane fold back on itself?

Answer 6

At the lung hilux?

Question 7

What type of fluid exists in the pleural cavity?

Answer 7

Intrapleural fluid

Question 8

What is the function of pleural fluid?

Answer 8

Lubrication, two membranes can glide across each other. Fluid holds the two membranes together

Question 9

What is pleurisy?

Answer 9

Inflammation of the pleura.

Question 10

How does pressure of intrapleural cavity compare to the atmospheric pressure?

Answer 10

Subatmospheric

Question 11

What creates the outward pull of the chest?

Answer 11

Elastic recoil of the chest wall

Question 12

What pulls the lungs inward?

Answer 12

Elastic recoil of lung?

Question 13

When are inward and outward forces of the lungs equal?

Answer 13

At the end of an expiration

Question 14

How is boyle’s law applied in breathing?

Answer 14

Thoracic cavity changes in volume. increase volume = decrease pressure decrease volume = increase pressure Gases always move from high pressure to low pressure

Question 15

What brings about expiration?

Answer 15

Expiration is passive at rest, but uses internal intercostal and abdominal muscles during severe respiratory load

Question 16

What muscles are used in inspiration?

Answer 16

Sternocleidomastoids, Scalenes, External intercostals, diaphragm

Question 17

What activates the skeletal muscles?

Answer 17

Alpha motor neurones

Question 18

What direction do the internal intercostal muscles travel?

Answer 18

Opposite direction to external intercostal muscles

Question 19

What is the movement of the sternum during inspiration?

Answer 19

Moves outwards and forwards - pump handle movement

Question 20

What is the movement of the ribs during inspiration?

Answer 20

Moves outwards - bucket handle movement

Question 21

What is asthma?

Answer 21

Over-reactive constriction of bronchial smooth muscle. Increases resistance, expiration difficult.

Question 22

Why are airways open during inspiration?

Answer 22

Physical forces of inspiration holds them open

Question 23

What happens to airways during expiration?

Answer 23

Compressed by physical forces of expiration

Question 24

What happens when the pleural cavity is opened?

Answer 24

Air flows in since pleural cavity is subatmospheric Lung collapses to unstretched size

Question 25

What is Intra-thoracic (Alveolar) Pressure (PA)?

Answer 25

Pressure inside the thoracic cavity, (essentially pressure inside the lungs). May be negative or positive compared to atmospheric pressure. During rest it’s zero - since equals atmospheric pressure

Question 26

What is Intra-pleural Pressure (Pip)?

Answer 26

Pressure inside the pleural cavity, ALWAYS negative (in healthy lungs at least!)

Question 27

What is Transpulmonary pressure (PT):

Answer 27

Difference between alveolar pressure and intra-pleural pressure. ALWAYS positive (in health) because Pip is always negative. PT = Palv – Pip.

Question 28

How do these three pressures change during breathing?

Answer 28

Question 29

What factors influence bulk flow of air between the atmosphere and the alveoli?

Answer 29

The difference between atmospheric pressure and alveolar pressure Airway resistance

Question 30

What are the features or the lungs during the end of an unforced expiration?

Answer 30

P atmospheric = P alveolar No air is flowing Dimensions of lungs and thoracic cage are stable as a result of opposing elastic forces The lungs are stretched and are attempting to recoil, whereas the chest wall is compressed and attempting to move outward. This creates a subatmospheric intrapleural pressure and hence a transpulmonary pressure that opposes the forces of elastic recoil.

Question 31

What does airway resistance determine?

Answer 31

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

Question 32

What is the major determinant of airway resistance?

Answer 32

The radii of the airways