Osmotic Forces Water and Excrete and Secrete Uriniferous WasteKey Words kidney renal arteriole Bowman’s capsule filter tubule proximal convoluted tubule distal convoluted tubule collecting tubule ureter countercurrent mechanisms urine production gradients membrane filter bladder urethra drawing 16100b.800Ashley Davidoff MD TheCommonVein.net Oxygen Gradients Created by the Lungs Across the Alveolar MembraneThis diagram again shows the alveolus in teal, the arteriolar component of the capillary with red cells in blue and venular component replenished by oxygen in red. As noted above, the PO2 of the arterial blood is 40mmHg while the inspired air is 104mmHg. A pressure gradient thus exists and diffusion from the high to the low pressure occurs with a net movement of oxygen into the blood to equilibrate the pressure. Venous blood is now rich in oxygen with a PO2 of 104mmHg.42445b08bAshley Davidoff MD TheCommonVein.net