Glomerulus is red; Bowman's capsule is green.

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.

Low blood pressure or low salt in the blood causes glomerular cells to release renin, which leads to formation of angiotensin I, which after conversion to angiotensin II causes constriction of blood vessels leading to the glomeruli (reducing filtrate volume). Angiotensin II also causes aldosterone release. Aldosterone is a steroid hormone released by the adrenal cortex. Its primary function is to regulate salt reabsorption in the distal convoluted tubule (as well as the sweat glands, salivary glands, and colon).

If either the osmotic pressure of the blood plasma is too high or the plasma volume is too low, the posterior pituitary gland releases ADH (vasopressin), which increases the permeability of the collecting duct to water. Less urine is produced. Water is retained. ADH also raises blood pressure by causing vasoconstriction.