It is more common in the apical, po

It is more common in the apical, posterior and dorsal segments of the upper lobe. It may be that when the human body is upright, the blood pressure in the posterior segment of the upper lobe tip and the dorsal segment of the lower lobe is low, the blood circulation is poor, and the macrophages are reduced, resulting in low resistance to local attack. Moreover, there is much oxygen in these parts, and the tuberculosis bacteria are aerobic bacteria. Therefore, the tuberculosis bacteria are easy to gather in these parts.