overview of respiration and respiratory mechanics (R1)

Question 1

internal respiration

Answer 1

• refers to intracellular mechanisms which consumes oxygen and produces carbon dioxide
• (body systems are made up of cells which need constant supply of oxygen to produce energy and function and the carbon dioxide produced by the cellular reactions must continuously be removed from our body)
• food + oxygen = energy + carbon dioxide

Question 2

external respiration

Answer 2

refers to the sequence of events that lead to the exchange of oxygen and carbon dioxide between the external environment and the cells of the body

Question 3

4 steps involved in external respiration

Answer 3

1. ventilation (mechanical process of moving gas in and out of the lungs)
2. gas exchange between alveoli and blood (the exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries)
3. gas transport in the blood (the binding and transport of oxygen and carbon dioxide in the circulating blood)
4. gas exchange at the tissue level ( the exchange of oxygen and carbon dioxide between the blood in the systematic capillaries and the body cells)

Question 4

3 body systems involved in external respiration

Answer 4

1. respiratory system
2. cardiovascular system
3. haematology system

Question 5

ventilation definition

Answer 5

the mechanical process of moving air between the atmosphere and alveolar sacs

Question 6

air flow in relation to pressure gradients

Answer 6

air flows down pressure gradient from a region of high pressure to a region of low pressure

Question 7

what happens to the thorax and lungs during inspiration

Answer 7

they expand as a result of contraction of inspiratory muscles

Question 8

relationship between intra alveolar pressure and atmospheric pressure during inspiration

Answer 8

the intra-alveolar pressure must become less than the atmospheric pressure for air to flow into the lungs during inspiration (before inspiration the intra- alveolar pressure is equivalent to the atmospheric pressure)

Question 9

boyle’s law

Answer 9

at any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas- as the volume of a gas increases the pressure exerted by the gas decreases

Question 10

what 2 forces hold the lungs to the thorax/ thoracic wall

Answer 10

1. intrapleural fluid cohesiveness (the water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. Hence the pleural membranes tend to stick together)
2. the negative intrapleural pressure (the sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and across the chest wall. So the lungs are forced to expand outwards whilst the chest is forced to squeeze inwards)

Question 11

transmural pressure gradient across lung wall

Answer 11

= intra alveolar pressure (760mmHg) minus intra pleural pressure (756mmHg)

Question 12

transmural pressure gradient across thoracic wall

Answer 12

= atmospheric pressure (760mmHg) minus intrapleural pressure (756mmHg)

Question 13

3 pressures important in ventilation

Answer 13

1. atmospheric pressure
2. intra-alveolar pressure
3. intrapleural pressure

Question 14

atmospheric pressure

Answer 14

the pressure exerted by the weight of the gas in the atmosphere on objects on the earths surface- 760mmHg at sea level)

Question 15

intra-alveolar pressure

Answer 15

the pressure within the alveoli - 760mmHg when equilibrated with atmospheric pressure

Question 16

intra-pleural pressure

Answer 16

the pressure within the pleural sac- the pressure exerted outside the lungs within the thoracic cavity (usually less than the atmospheric pressure at 756mmHg)

Question 17

inspiration

Answer 17

active process depending on muscle contraction (inspiratory muscles)

Question 18

how is the volume of thorax increased during inspiration

Answer 18

• the volume of the thorax is increased vertically by the contraction of the diaphragm flattening out its dome shape (major inspiratory muscle supplied by phrenic nerve from C3,4,5)
• the external intercostal muscle contraction lifts the ribs and moves out the sternum (bucket handle mechanism) this increases anterior-posterior dimension of thoracic cavity (and side to side dimensions)

Question 19

what effect does the increase in size of lungs during inspiration have on the intra alveolar pressure

Answer 19

causes intra alveolar pressure to fall, this is because air molecules become contained in a larger volume (boyles law)

Question 20

what happens following a decrease in intra alveolar pressure

Answer 20

air enters the lungs down its pressure gradient until the intra alveolar pressure becomes equal to the atmospheric pressure

Question 21

normal expiration

Answer 21

passive process brought about by the relaxation of inspiratory muscles, the chest wall and stretched lungs recoil to their pre-inspiratory size because of their elastic properties, the recoil of the lungs makes the intra alveolar pressure rise (because air is contained in a smaller space - boyles law), the air then leaves the lungs down its pressure gradient until the intra alveolar pressure becomes equal to the atmospheric pressure

Question 22

changes in intra alveolar and intra pleural pressures during the repiratory cycle

Answer 22

• during inspiration, intra alveolar pressure decreases below atmospheric then increases to atmospheric and intrapleural pressure decreases below 756mmHg
• during expiration, intra alveolar pressure increases above atmospheric pressure then decreases to atmospheric pressure, and intra pleural pressure increases to 765mmHg

Question 23

pneumothorax

Answer 23

air in the pleural space, abolishes transmural pressure gradient
-can either be traumatic pneumothorax (due to a puncture wound in the chest wall) or spontaneous pneumothorax (hole in lung) and both result in collapsed lung

Question 24

what causes the lungs to recoil during expiration(gives the lungs their elastic behavior)

Answer 24

• elastic connective tissue in the lungs causes the whole structure to bounce back into shape
• (even more importantly) the alveolar surface tension

Question 25

alveolar surface tension

Answer 25

attraction between water molecules at liquid air interface, which, in the alveoli this produces a force which resists the stretching of the lungs

Question 26

what would happen to the alveoli if they were lined with water alone

Answer 26

the surface tension would be too strong so the alveoli would collapse

Question 27

law of LaPlace

Answer 27

according to the law of Laplace, the smaller the alveoli(with radius, r) the higher tendency to collapse
- P = 2T divided by r( where P= inward collapsing pressure, T= surface tension, r= radius of bubble, if you regard the alveoli as spherical bubbles)

Question 28

pulmonary surfactant

Answer 28

complex mixture of lipids and proteins secreted by typeII alveoli, it lowers alveolar surface tension by interspersing between the water molecules lining the alveoli, lowers the surface tension of smaller alveoli more than that of the large alveoli, therefore prevents the alveoli from collapsing and emptying their air contents into the larger alveoli

Question 29

respiratory distress syndrome of the new born

Answer 29

developing fetal lungs are unable to synthesize surfactant until late in pregnancy therefore premature babies may not have enough pulmonary surfactant causing respiratory distress syndrome of the new born, baby has to make strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs

Question 30

alveolar interdependence

Answer 30

another factor which keeps the alveoli open, if an alveolus starts to collapse the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it

Question 31

forces that keep the alveoli open

Answer 31

• transmural pressure gradient
• pulmonary surfactant (which opposes alveolar surface tension)
• alveolar interdependence

Question 32

forces promoting alveolar collapse

Answer 32

• elasticity of stretched pulmonary connective tissue fibers
• alveolar surface tension

Question 33

changes in intra alverolar and intra pleural pressures during the respiratory cycle/cause of these changes/relationship between intra alveolar/intra pleural pressures and the transmural pressure gradient

Answer 33

• during inspiration the diaphragm and lungs contract increases the size of the lungs which causes intra alveolar pressure to fall, this is because air molecules become contained in a larger volume, a pressure gradient now exists between the atmosphere and alveoli and air flows into the lungs causing the intra alveolar pressure to rise as the air in the lungs becomes contained within a smaller space, intraalveolar pressure now exceeds atmospheric pressure in expiration and air flows out of the alveoli, decreasing the intralveolar pressure
• during inspiration the intrapleural pressure (the pressure within the pleural sac- the pressure exerted outside the lungs within the thoracic cavity) decreases as a result of rib cage expanding etc etc, however increases again during expiration due to elastic recoil (as the lungs decrease in size/recoil, the intercostals and diaphragm relax and lower the ribcage increasing the pressure exerted outwith the lungs within the thoracic cavity)
• the transmural pressure gradient across the lung wall (=intra alveolar pressure - intrapleural pressure) therefore fluctuates between inspiration and expiration due to these changes in intra alveolar/intra pleural pressure