overview of respiration and respiratory mechanics (R1) Flashcards
internal respiration
- 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
external respiration
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
4 steps involved in external respiration
- ventilation (mechanical process of moving gas in and out of the lungs)
- 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)
- gas transport in the blood (the binding and transport of oxygen and carbon dioxide in the circulating blood)
- gas exchange at the tissue level ( the exchange of oxygen and carbon dioxide between the blood in the systematic capillaries and the body cells)
3 body systems involved in external respiration
- respiratory system
- cardiovascular system
- haematology system
ventilation definition
the mechanical process of moving air between the atmosphere and alveolar sacs
air flow in relation to pressure gradients
air flows down pressure gradient from a region of high pressure to a region of low pressure
what happens to the thorax and lungs during inspiration
they expand as a result of contraction of inspiratory muscles
relationship between intra alveolar pressure and atmospheric pressure during inspiration
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)
boyle’s law
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
what 2 forces hold the lungs to the thorax/ thoracic wall
- 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)
- 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)
transmural pressure gradient across lung wall
= intra alveolar pressure (760mmHg) minus intra pleural pressure (756mmHg)
transmural pressure gradient across thoracic wall
= atmospheric pressure (760mmHg) minus intrapleural pressure (756mmHg)
3 pressures important in ventilation
- atmospheric pressure
- intra-alveolar pressure
- intrapleural pressure
atmospheric pressure
the pressure exerted by the weight of the gas in the atmosphere on objects on the earths surface- 760mmHg at sea level)
intra-alveolar pressure
the pressure within the alveoli - 760mmHg when equilibrated with atmospheric pressure
intra-pleural pressure
the pressure within the pleural sac- the pressure exerted outside the lungs within the thoracic cavity (usually less than the atmospheric pressure at 756mmHg)
inspiration
active process depending on muscle contraction (inspiratory muscles)
how is the volume of thorax increased during inspiration
- 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)
what effect does the increase in size of lungs during inspiration have on the intra alveolar pressure
causes intra alveolar pressure to fall, this is because air molecules become contained in a larger volume (boyles law)
what happens following a decrease in intra alveolar pressure
air enters the lungs down its pressure gradient until the intra alveolar pressure becomes equal to the atmospheric pressure
normal expiration
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
changes in intra alveolar and intra pleural pressures during the repiratory cycle
- 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
pneumothorax
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
what causes the lungs to recoil during expiration(gives the lungs their elastic behavior)
- elastic connective tissue in the lungs causes the whole structure to bounce back into shape
- (even more importantly) the alveolar surface tension