High pressure pushes the blood through the glomerular walls into Bowman's capsule. In moving into Bowman's capsule to become the glomerular filtrate, the blood must pass through a basement membrane composed of carbohydrate and protein polymers including a basal lamina. The rate of filtration depends on the blood pressure. Filtration removes the formed elements as well as large proteins.

Most of the sodium and potassium and practically all of the glucose and vitamins are reabsorbed by the tubule and moved into the extracellular fluid surrounding the nephrons. . If the concentration of a particular ion is too low in the blood plasma, the tubule will selectively reabsorb less of the material. Most reabsorption occurs in the proximal convoluted tubule. Positively charged ions (Na+ and K+) are mostly actively transported with Cl- and HCO3- following by facilitated diffusion. However, in the ascending limb, Cl- is actively transported with Na+ following passively.

As the tubule descends into the medulla along the loop of Henle, water follows passively by osmosis. The filtrate passes through the urea brine bath of the medulla both in the loop of Henle and in the collecting duct. In both places, water leaves the filtrate to enter the hyperosmotic medulla, concentrating the urine

Secretion of H+ occurs in both the proximal and distal convoluted tubules, essential to pH regulation.












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