Question

The specific gravity of urine varies throughout the day, and from day to day. Why would the specific gravity vary? Give 3 examples as to why and how they vary?

Answer 1

Answer:

Normal specific gravity of urine is 1.000 to 1.030. The kidney excretes waste in the form of urine and solutes in the urine determine the specific gravity of urine. The kidneys are a part of the compensatory mechanism of the body that regulates the pH of blood by reabsorption of sodium and tubular secretion of hydrogen and ammonium ions.

To maintain a constant ideal pH of the blood, the body has several compensatory mechanisms in the blood, the lungs and the kidneys. The kidneys maintain normal pH balance by reabsorption of sodium and the tubular secretion of hydrogen and ammonium ions. So, according to the changes in the pH of blood the concentration of solutes in the urine also changes.

For example, during dehydration the kidney will try to compensate by reducing the amount of water in the urine and so the specific gravity will be increased. Same goes for conditions of diarrhea, excessive sweating and renal artery stenosis. During excessive intake of fluids as seen in conditions like psychogenic polydipsia, the amount of water in the urine is increased, thereby decreasing the specific gravity of urine. During proteinuria, excess amounts of proteins are seen in the urine and this increases the specific gravity, Same thing happens during renal failure and diabetes.