Elasticity: The lung is elastic and returns passively to its pre-inspiratory volume during resting breathing. It is very easy to distend. For example, a normal breath of about 500 ml requires a distending pressure of less than 3 cm water.
Resistance: The pressure required to move gas through the airways is also very small. During normal inspiration, an air flow rate of 1 liter/sec. requires a pressure drop along the airways of less than 2 cm water.
At Right -> Scanning electron micrograph of a section of lung showing many alveoli and a small bronchiole. The pulmonary capillaries run in the walls of the alveoli. The holes in the alveolar walls are the Pores of Kohn.
|Body weight (Kg)||3.5||70|
|Surface area (m2)||0.21||1.90|
|Lung weight (g)||50||800|
|Tracheal diameter (mm)||8<||18|
|Bronchiole diameter (mm)||0.1||0.2|
|Number of Airways (x 106)||1.5||14.0|
|*Alveolar diameter (microns)||50-100||200-300|
|Alveolar surface area (m2)||4||80|
|Number of alveoli (x 106)||24||296|
|Vital capacity (ml/Kg)||33||52|
|Functional residual capacity (ml/Kg)||30||34|
|Dead space (ml/Kg)||2.2||2.2|
|Tidal volume (ml/Kg)||6||7|
|Respiratory rate at rest||40||20|
|Alveolar ventilation (ml/Kg min)||100-150||60|
|Oxygen consumption at rest (ml/Kg min)||6||3|
* Approximate and not taking into account possible variations between apex and base in vivo.
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