Stages of urine formation
Le Tube Proximal (TCP) (figure 3) About 2/3 of the water filtered by the glomerulus is reabsorbed as it passes through the proximal tube or nearly 120 L / d. 2/3 of the filtered Na + is also reabsorbed, which defines the iso-osmotic character of the water-sodium reabsorption in TCP. Therefore, the tubular fluid is iso-osmotic to the plasma upon arrival in the loop of Henle. The glucose is actively and fully reabsorbed at this level, provided that the blood sugar does not exceed 10 mmol per liter (beyond the filtered load exceeds the glucose reabsorption capacity by TCP, glucose transport is saturable). The bicarbonates are fully reabsorbed so coupled to Na, as their plasma concentration is less than 27 mmol per liter (saturable transport). This step conditions the balance of the acid balance achieved further downstream in the distal tube. The same is true for amino acids and other organic acids. Phosphate reabsorption occurs in TCP coupled to Na and under the hormonal c...