AP BIOLOGY

Detailed explanation-1: -For the purpose of description the lungs are divided into zones: upper, middle and lower. Each of these zones occupies approximately one third of the height of the lungs.

Detailed explanation-2: -Zone 3 is defines as those areas of the lung where the alveolar pressure falls below that of the pulmonary venous pressure. Consequently, the blood pressure gradient determining blood flow is the traditional one between the pulmonary arterial pressure and the pulmonary venous pressure.

Detailed explanation-3: -Zone 4 can be seen at the lung bases at low lung volumes or in pulmonary edema. Pulmonary interstitial pressure (Pi) rises as lung volume decreases due to reduced radial tethering of the lung parenchyma. Pi is highest at the base of the lung due to the weight of the above lung tissue.

Detailed explanation-4: -Zone 1 is defined as that area of lung in which alveolar pressure exceeds both pulmonary arterial and venous pressures (19), and under this condition the alveolar sep-tal vessels are presumably collapsed.

Detailed explanation-5: -The left lung consists of two lobes: the left upper lobe (LUL) and the left lower lobe (LLL). The right lobe is divided by an oblique and horizontal fissure, where the horizontal fissure divides the upper and middle lobe, and the oblique fissure divides the middle and lower lobes.