Ventilation Flashcards
describe airflow in the lungs
air flows from areas of high pressure to areas of low pressure
- the rate is proportional to the pressure difference where F = change in pressure/Resistance to flow)
inspiration
- change in pressure is produced by increasing lung volume (the thoracic cage expands and lung volume increases)
- this expansion is brought about by inspiratory muslces
- atmospheric pressure is then higher than alveolar pressure, causing air to move into the lungs
expiration
- volume of lungs decreases, pressure in lungs increases, forcing air out of the lungs
describe the diaphragm
- dome shaped musculotendinous sheet separating the thoracic from the abdominal cavity
- the muscular part is peripheral and tendinous part is central
- the muscle is attahced to the xiphoid process ventrally, to the inside of the lower costal cartilages and ribs by digitations laterally and to the vertebral column dorsally by crura
- innervated by the phrenic nerve
describe the intracostal muscles
external and internal muscles occupy the intercostal spaces
exterior: runs caudoventrally
interior: cranioventrally
describe how the inspiratory muscles function for inspiration
- diaphragm contracts (dome flattens and moves caudally)
- ribs are pulled cranially and outwards by contraction of the external intercostal muscles
- together these increase the volume of the thoracic cavity
describe how the inspiratory muscles function for expiration
- inspiratory muscles relax
- ribs recoil back to original position
describe the pleural cavity
the pleural cavity is the space between the visceral pleural (facing inside of body) and the parietal pleural (facing outside of body).
- fluid filled
- sub-atmospheric pressure (less than atmosphere)
- if pierced, air rushes in = pneumothorax = collapses lung
describe how the pressure within different compartments of the lungs aids respiration
alveolar pressure fluctuates between -1 mmHg (during inspiration) and 1 mmHg (during expiration)
intrapleural pressure normally negative
transpulmonary pressure: difference between alveolar pressure and intrapleural pressure
describe the sequence of events that happen during inspiration
- inspiratory muscles contract
- thoracic cavity expands
- intrapleural pressure becomes more negative
- transpulmonary pressure increases
- lungs distend
- alveolar pressure falls below atmospheric pressure
- air flows into the lungs until the alveolar pressure becomes equal to atmospheric pressure
describe the sequence of events that occur duing expiration
- relaxation of inspiratory muscles, ribs recoil back to original position
- thoracic cavity contracts
- pressure within intrapleural cavity becomes less negative
- transpulmonary pressure decreases
- lungs contract
- alveolar pressure increases above atmospheric pressure
- air flows out until alveolar pressure becomes equal to atmospheric pressure
describe how locomotion can assist ventilation
the breathing cycle of galloping animals is synchronised to the stride cycle
what 3 factors influence ventilation
- resistance to flow in the airways
- lung compliance
- alveolar surface tension
how does compliance influence ventilation
compliance is essentially how stretchy the lungs are
- depends of elasticity of the tissue and surface tension in the alveoli
- calculated by compliance=volume increase/transpu,monary pressure
- structures that contribute to compliace = coiled collagen fibres, lung elastic fibres, intercostal muscles, joints and pleura of the thoracic cage
how does resistance to flow influence ventilation
calibre of airways
- same factors as resistance to flow in blood vessels
- resistance to flow is inversely proportional to the 4th power of the tube radius (as radius of tube decreases, resistance increases)
- mouth breathing halves airway resistance
- to overcome: each bifurcation increases number of parallel branches, as lung colume increases, elastic fibres in lung pull to expand tube diameter. relaxation of smooth muscles can also increase airway diameter (tubes get smaller as you go deeping into lung, but number of tubes increases)
turbulence
- airflow pattern is turblunet (in trachea and large bronchi) and laminar (in small bronchi and bronchioles
how does alveolar surface tension influence ventilation
- surface tension occurs at the interface berween water and air
- inner surface of alveoli lined with fluid
- surface tension can restrict alveoli so they cant expand as easily
- reduced with production of surfactant (makes it easier for alveoli to expand by disrupting surface tension)
- pressure increases inside smaller alveoli (law of LaPlace => pressure inside alveolus = (2)surface tension of lining fluid/radius) therefore, to encourage equal airflow in different sized alveolus, the concentration of surfactant is higher in smaller alveoli (this prevents smaller alveoli from being disuesed)
