Anatomy of Chest Wall and Mechanics of Breathing

Question 1

Which gas law is breathing based on?

Answer 1

Boyle’s Law

Question 2

What does Boyle’s Law state?

Answer 2

The pressure exerted by a gas is inversely proportional to its volume

Question 3

What is the top of the lung called?

Answer 3

Apex

Question 4

What is the first lobe below the apex called in both lungs

Answer 4

Superior lobe

Question 5

What is different in the superior lobe of the left lung compared to the right

Answer 5

• Much bigger - Curved lower border

Question 6

What are the lungs and interior of the thorax covered in?

Answer 6

Pleural sac

Question 7

What is the pleural membrane made of?

Answer 7

An extremely thin layer of intrapleural fluid

Question 8

What does the visceral pleural membrane coat?

Answer 8

Outer surface of the lungs

Question 9

What does the parietal pleural membrane coat?

Answer 9

Inner surface of the ribs

Question 10

What does the interaction between the pleural membranes mean for the lungs and the ribs?

Answer 10

The lungs are effectively stuck to the ribs

Question 11

What is pleurisy?

Answer 11

Inflammation of the pleura

Question 12

Why does breathing occur?

Answer 12

Thoracic cavity changes volume

Question 13

Why do the lungs need to be “stuck” to the ribs?

Answer 13

• The lungs are trying to move in the way and would collapse
• The ribs are moving against this force to maintain the shape of the cavity

Question 14

Where do the two pleural membranes overlap?

Answer 14

The hilux of the lung

Question 15

What is the overlapping membrane known as?

Answer 15

Visceralparietal membrane

Question 16

What volume of fluid is there in the pleural cavity?

Answer 16

3ml

Question 17

What does the pleural fluid allow the membranes to do?

Answer 17

• Slide over eachother
• Stick to eachother strongly (imagine 2 microscope slides with water between them

Question 18

What symptoms, to do with the pleural membranes, can you get when you have pleurisy?

Answer 18

Pain and discomfort as they can’t slide over each other

Question 19

What is the average negative pressure of the lungs due to the interaction with the ribs?

Answer 19

-3mm Hg

Question 20

What is the name given to the force that the lungs and the ribs exert on each other due to the pleural membranes?

Answer 20

Elastic recoil

Question 21

What is pneumothorax?

Answer 21

A collapse of the lung due to loss of pleural membrane interaction

Question 22

What happens to the ribcage as the diaphragm is relaxed?

Answer 22

It rises

Question 23

What effect does the rising of the ribcage have on the thoracic cavity and what does this cause?

Answer 23

• Lowers the pressure
• Air from the atmosphere moves into the lungs

Question 24

What happens to the thoracic pressure when the air moves in?

Answer 24

• Increases above atmospheric pressure (P_ATM)

Question 25

What happens to the alveoli when air moves into them?

Answer 25

- They expand - Elastic fibres stretch

Question 26

How does air move back out of the alveoli?

Answer 26

Under elastic recoil from the elastic fibres surrounding the alveolar sacs

Question 27

What two groups of muscles can be recruited to aid in expiration during exercise?

Answer 27

- Intercostal muscles - Abdominal muscles

Question 28

How do the intercostal muscles aid in expiration?

Answer 28

- Innervating alpha motor neurone is switched off and they relax

Question 29

How do the abdominal muscles increase expiration?

Answer 29

- Contraction of them increases thoracic pressure by decreasing thoracic volume

Question 30

What shape is the diaphragm when it contracts?

Answer 30

- Flat

Question 31

What does the shape change to a flat shape of the diaphragm do to thoracic pressure?

Answer 31

- Increases volume so decreases pressure

Question 32

How does intercostal muscle contraction increase anterior posterior thoracic volume?

Answer 32

Similar to a pump handle

Question 33

How does intercostal muscle contracting increase lateral thoracic volume?

Answer 33

Similar to a bucket handle shape

Question 34

How does inspiration follow Boyle's Law?

Answer 34

Air moves in from the atmosphere from high pressure to low pressure because the volume of the container (lungs) is increased.

Question 35

How does expiration follow Boyle's Law?

Answer 35

Pressure of the thoracic cavity excedes atmospheric pressure as the volume is reduced by elastic recoil, rib cage decending and diaphragm rising

Question 36

List reasons why intrapleural pressure is always lower than alveolar pressure

Answer 36

- Alveoli have residual volume in them ALL THE TIME - Intrapleural space contains fluid - Intrapleural pressure is always negative compared to atmospheric pressure, whereas alveolar pressure is sometimes above - If intrapleural pressure equals alveolar pressure then a pneumothorax will form