The apex of the upright human lung has a high ventilation perfusion Ratio.Therefore, the apex has a higher alveolar PO2 than the base. The other choices are incorrect because the ventilation of the apex is lower than that of the base, the pH in endcapillary blood is higher because of the reduced PCO2 at the apex, the blood flow is lower as already stated, and the alveoli are larger because of the regional differences of intrapleural pressure.