State and explain the changes in the lung volume, the alveolar pressure (Palv) and a irflow between the atmosphere and the lungs during passive exhalation .

Lungs are the primary organs of the respiratory system. Their key function is to extract oxygen from the atmosphere and transfer them to the blood stream and to remove the carbon dioxide in the blood, releasing them to the atmosphere.

During respiration in animals, exhalation is the passive process that involves movement of air from the lungs into the external environment. This is brought about by relaxation of the diaphragm and contraction of the lungs to push the air to the environment. Thus, the pressure increases while the volume of the lungs decrease.

Alveolar pressure is the pressure of the air inside the lung alveoli. The alveolar pressure is zero when there is no air flowing into or out of the lungs. During exhalation, the lung contracts and decreases in volume. This leads to increase in pressure inside the alveoli, creating pressure greater than the atmospheric pressure. As the atmospheric pressure is lower than the alveolar pressure, the airflow occurs out of the lungs towards the atmosphere to compensate the imbalance in pressure. Thus, air (Carbon dioxide) is pushed away from the lungs during exhalation.