Tubular fluid

Tubular fluid is a fluid that passes through the tubules of the kidney. It is initially identical to the blood plasma that enters the kidney, but as it passes through the tubules, its composition is altered by the absorption and secretion of various substances. The final product is urine, which is excreted from the body.

Composition

The composition of tubular fluid changes as it passes through the different parts of the nephron, the functional unit of the kidney. Initially, it is identical to the blood plasma, but it becomes more concentrated as water and various solutes are reabsorbed back into the bloodstream. The composition of the final urine is determined by the balance between these processes of reabsorption and secretion.

Function

The main function of the tubular fluid is to carry waste products and excess substances from the blood to be excreted in the urine. This process is crucial for maintaining the body's homeostasis, or stable internal environment. The kidneys also use the tubular fluid to regulate the body's balance of electrolytes, such as sodium, potassium, and calcium, and to control the pH of the blood by excreting hydrogen ions and reabsorbing bicarbonate ions.

Pathology

Abnormalities in the composition or volume of the tubular fluid can lead to various kidney diseases. For example, if the tubules are unable to reabsorb enough water, it can result in polyuria, or excessive urination, and dehydration. On the other hand, if the tubules reabsorb too much water, it can lead to oliguria, or reduced urination, and fluid overload. Other conditions, such as kidney stones, can occur if certain substances in the tubular fluid become too concentrated and form crystals.

See also

• Nephron
• Kidney function
• Renal physiology