Mechanics of Breathing I Flashcards
What is the primary function of the respiratory system?
Ventilate gas exchange surfaces by moving air between alveoli and atmosphere via the airways
How is total ventilation calculated?
V = VT x f
Total ventilation = tidal volume x frequency of breaths per minute
Why does total ventilation not reflect the volume of air reaching respiratory surfaces and which can take part in gas exchange?
o Exchange only happens in the alveoli
o The respiratory system does not completely empty, even after maximum forced expiration
Why does the respiratory system not completely empty even at the end of a maximal forced expiration?
Some air needs to occupy the airways and a residual volume of air is left in the lungs so that alveoli don’t completely collapse
Why does the final 150ml of air of each inspiration never reach the alveoli/take part in gas exchange?
Because the resp system is a two-way pathway so air leaves and enters via the same route
What is the revised formula for VA?
o VA = (VT – VD) x f
o VD is dead space volume (the 150ml that never reaches alveoli)
Volume of air remaining in the lungs after a maximum forced expiration?
Residual Volume
Total Volume of Air an Individual is able to breathe in going from max forced inspiration to max forced expiration?
Vital Capacity
The volume of air within the lungs at the end of a maximum inspiration?
Total Lung Capacity
The additional volume of air that can be inspired at the end of a resting/quiet inspiration?
Inspiratory Reserve
The volume of air inspired/expired at rest during quiet/normal breathing pattern?
Tidal Volume
The additional volume of air that can be expired at the end of a resting/quiet expiration?
Expiratory Reserve
The volume of air within the lungs at the end of a resting/quiet expiration?
Functional Residual Capacity
what is a key factor in the behaviour of gases?
pressure, the level of force exerted by gas molecules on the surfaces of the space in which they are contained
how can pressure be conceptualised if temperature is constant?
number of gas molecules present per unit of volume
what is boyles law?
describes relationship between pressure, volume and molar quantity P α n/v
what does boyles law mean?
the pressure within a contained space can be changed by altering the volume of the space. gradient induces movement from high to low pressure areas until equal level reestablished
how is movement between air and lungs achieved?
by changing alveolar pressure
how does air move into lungs during inspiration?
alveolar pressure must fall below atmospheric
how does air move out of lungs during expiration?
alveolar pressure must rise above atmospheric
how are the pressure changes achieved in the alveoli?
by contraction/relaxation of respiratory muscles altering volume of thoracic cavity
pressure at inspiration
Palveoli < Patmosphere
pressure at expiration
Palveoli > Patmosphere
how are the lungs and chest wall separated?
by a pair of serous membranes known as pleurae
what is the visceral pleurae?
inner lining
what is the parietal pleura?
outer lining of thoracic cavity surrounding the chest, diaphragm and mediastinum
what is between the two pleura?
fluid-filled pleural cavity
why do the tissues attached to each pleura recoil in opposite direction?
due to their elastic properties, stretching the sealed pleural cavity between them
what does the recoil do to the pressure?
decreases pressure within pleural space as occupies greater volume but with same number of molecules within it
what does negative pressure do?
generates collapsing force pulling surface of contained space together. greater the force, the greater the pull
what does positive pressure do?
generates expanding force, pushing the surfaces of the space apart
what does elastic recoil of the chest wall and inspiratory resp muscle contraction do?
pulls the chest wall outwards and expands the thoracic cavity
what do elastic recoil of the lungs to?
pull visceral pleural inwards and compresses the lung volume
