The loop of Henle descends and ruturns to become the distal convoluted tubule. The distal tubule empties into a collecting duct. The collecting duct descends once more through the pyramid to its tip and opens into a limb of the pelvis called a calyx. Urine is produced by a four step process as it passes through the nephron. The four steps are filtration, reabsorption, secretion, and concentration.
Filtration occurs in the glomerulus, as described above.
The filtrate contains a mixture of valuable small molecules and wastes dissolved in most of the water from the blood. The second step, reabsorption, occurs in the proximal convoluted tubule. Cells lining the tubule use active transport to recover nutrients, ions, and other desired molecules from the filtrate. Secretion occurs in the cells of the distal convoluted tubule to eliminate additional wastes not already in the filtrate. Urine is concentrated as it descends throught he collecting duct and water is drawn out by osmosis.