Anatomy of Chest Wall and Mechanics of Breathing

Question 1

how many lobes is the right lung divided into?

Answer 1

3 (superior, middle and inferior lobe)

Question 2

how many lobes is the left lung divided into?

Answer 2

2 (superior, inferior)

Question 3

what are the lung extremities called?

Answer 3

apex and base

Question 4

what surrounds the lungs?

Answer 4

inside two pleural membranes

Question 5

what passes through the thorax?

Answer 5

the oesophagus and the aorta

Question 6

what cavity surrounds the heart?

Answer 6

the pericardial cavity

Question 7

what cavity is between the pleural membranes? what is it filled with?

Answer 7

the pleural cavity, filled with intrapleural fluid

Question 8

what is the deep pleural membrane called? what does it coat?

Answer 8

visceral pleura, coats outer surface of lungs

Question 9

what is the superficial pleural membrane called? what does it coat?

Answer 9

parietal pleura, coats inner surface of rib cage

Question 10

the 2 pleural membranes and the pleural cavity form what?

Answer 10

the pleural sac

Question 11

what is pleurisy?

Answer 11

inflammation of the pleura

Question 12

how does intrapleural pressure compare with that of the atmosphere?

Answer 12

-3mmHg at rest (subatmospheric)

Question 13

what force compensates the one applied inwards by the elasticity of the lung?

Answer 13

the elastic recoil o the chest wall going outwards

Question 14

what is a pneumothorax?

Answer 14

when air flows in the interpleural space and the pressure normalises with the atmosphere. The visceral pleura looses its adherence with the parietal pleural, the lung collapses and the rib cage expands slightly (shows importance of relationship between pleural membranes)

Question 15

what is Boyle’s law?

Answer 15

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

Question 16

why does air come in the lungs during inspiration?

Answer 16

the thoracic cavity increases its volume, the pressure decreases, air comes in the compensate (gases move from high pressure to low pressure)

Question 17

how does the thoracic cavity increase its volume?

Answer 17

external intercostals muscles, the diaphragm, sternocleistomastoids and scalenes

Question 18

how does the thoracic cavity decrease its volume?

Answer 18

expiration is passive at rest but uses internal intercostal and abdominal muscles during severe respiratory load (reducing duration of breathing cycle and allowing more breaths/min, ex: asthma)

Question 19

how do external intercostals increase cavity size?

Answer 19

by pushing ribs forward (pump handle, sternum comes away from spine) and also up (bucket handle, lateral side of rib goes up)

Question 20

what is asthma?

Answer 20

over-reactive constriction of bronchial smooth muscle, increases resistance, expiration difficult

Question 21

what is the intra-thoracic/ alveolar pressure? (Pa)

Answer 21

the pressure inside the thoracic cavity (essentially inside the lungs), may be negative (inspiration, -1mmHg) or positive (expiration, +1mmHg) as opposed to the atmospheric pressure

Question 22

what is the intra-pleural pressure? (Pip)

Answer 22

the pressure inside the pleural cavity, always negative in healthy lungs, varies between -3mmHg when resting and -6mmHg when max effort (end of inspiration, biggest volume of air moved)

Question 23

what is the transpulmonary pressure (Pt)

Answer 23

the difference between the alveolar pressure and the intra-pleural pressure, always positive in health because Pip is always negative (Pt=Pa-Pip) (and i guess negative Pa is never lower than Pip)

Question 24

what is the difference between the atmospheric and the alveolar pressure proportional to?

Answer 24

it is proportional to the difference between the atmospheric and alveolar pressures and inversely proportional to the airway resistance F=(Patm-Pa)/R

Question 25

what are the pressure differences at the end of an unforced expiration?

Answer 25

Patm=Pa, no air is flowing, dimensions of lung and thoracic cage are stable as the result of opposing elastic forces (creating a subatmospherical intrapleural pressured hence a transpulmonary pressure that opposes the recoiling forces)

Question 26

what does airway resistance determine? how does it vary?

Answer 26

it determines how much air flows into the lungs at any given pressure difference between the atmosphere and the alveoli, its major determinant is the radius of the airways