Lecture 19 – The Mechanics of Breathing I

Question 1

pRESSURE changes - during inspiration 4

Answer 1

air flows in (high to low p)
expansion
IN V, DE alveolar P
P alveoli < P atm

Question 2

pRESSURE changes - during expiration 4

Answer 2

air flows out (high to low p)
compression
DE V, IN alveolar P
P alveoli > P atm

Question 3

Role of pleural cavity in breathing 4

Answer 3

+ve/-ve pressure
Lung and chest wall seperated by serous membrane. Viseral (lines lungs) and Parietal (lines thoracic cavity).
Tissues attached to each pleura recoil in opposite directions due to their elastic properties- DE P within pleural space, occupies a greater volume but with same number of molecules.

Question 4

Role of pleural cavity in breathing - Negative pressure 3

Answer 4

Low number of molecules per volume
Collapsing force
Pulls surfaces of contained space together

Question 5

Role of pleural cavity in breathing - Positive pressure 3

Answer 5

High number of molecules per volume
Expanding force
Pushes surfaces of contained space apart

Question 6

Inspiration 7

Answer 6

FC

Question 7

Expiration 6

Answer 7

FC

Question 8

Pneumothorax 4

Answer 8

If either pleural membrane is ruptures (trauma/bleb formation/disease), the pressure gradient between pleural cavity and atm will cause air to enter the pleural space forming a pneumothorax.
Results in loss of negative pressure as IP will increase till it reaches atm pressure.
Recoil of lungs/expansion of chest wall during breathing will result in expansion of pleural cavity (at expense of lung volume which decreases).
Recoil can occur in different directions, causing lungs to collapse, atelectasis.

Question 9

Alveolar ventilation

Answer 9

Reflects volume of fres air reaching gas exchange surfaces per unit time VA = (VT - VD) x f