The descending loop of Henle receives isotonic fluid from the proximal convoluted tubule (PCT). The fluid is isotonic because as ions are reabsorbed by the gradient time system, water is also reabsorbed, maintaining the osmolarity of the fluid in the PCT.

It is partly responsible for the regulation of potassium, sodium, calcium and pH. It is the primary site for the kidneys' hormone based regulation of calcium (Ca).

Spironolactone opposes the actions of aldosterone and so, has the opposite effect. It is an aldosterone receptor antagonist that causes the kidneys to remove water and sodium from the body, with reduced losses of potassium.

Urine is not used in the production of detergents.

 A  high meat content can decrease urine pH (more acidic). A diet high in citrus, vegetables, or dairy can increase urine pH (more basic).

Hydronephrosis is the enlargement of one or both of the kidneys caused by obstruction of the flow of urine.

Intercalated cells come in α and β varieties and participate in acid-base homeostasis.

The anion gap may be normal or increased in a metabolic acidosis. The anion gap can be increased due to relatively low levels of cations other than sodium and potassium (e.g. calcium or magnesium).

Multicystic dysplastic kidney (MCDK) is a condition that results from the malformation of the kidney during fetal development. The kidney consists of irregular cysts of varying sizes and has no function. Multicystic dysplastic kidney is the most common type of renal cystic disease, and it is one of the most common causes of an abdominal mass in infants.

It is the metanephros, which goes on to become the adult kidney.

Insulin causes potassium entry into cells and insulin is used in the emergency treatment of severe hyperkalaemia. As insulin also causes a fall in blood glucose levels, exogenous glucose is usually given with the insulin to prevent this.

Excess parathyroid hormone raises plasma calcium levels. In primary hyper parathyroidism, there is a primary increase in parathyroid hormone and so a rise in plasma calcium.

Prostaglandins are powerful vasodilators and there is a normal tonic level of vasodilation in the renal blood vessels, which is caused by the prostaglandins.

The basic problem is usually loss of water, treatment is usually with careful replacement of this loss. As with hyponatremia, it is important not to replace the loss too quickly. This is because the cells make compensatory changes during hyperosmolar conditions and a sudden change can be dangerous as the cells do not have time to readjust back to normal. The best way to prevent this is to keep checking the plasma sodium to ensure that it is not changing too quickly.

The 3Na⁺/2K⁺ ATPase pumps sodium out of cells and potassium into cells to maintain this situation.