MEDICAL PHYSIOLOGY

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 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-4: -Now, the lungs can be divided into three distinct zones. Zone 1 is the top of the lungs, or the apexes; zone 2 is the middle of the lungs; and zone 3 is the bottom, or bases, of the lungs.