When blood passes through the thin capillaries of the glomerulus, there occurs ultrafiltration in the Bowman's capsule of the nephrons of the kidneys. Small molecules such as glusoce, urea, sodium chloride ions, water, amino acids pass through the capillary walls into the glomerular filtrate. However, some molecules are immediately and totally reabsorbed back to the blood in the proximal convoluted tubule such as glucose and amino acids. Water and the ions are selectively absorbed across the loop of Henle depending on their concentration in the blood. Urea is not reabsorbed and is eliminated along with excess water and ions as urine.
