The Kidneys and Homeostasis

How do the kidneys help maintain homeostasis?

The kidneys play an important role in maintaining homeostasis. Besides removing wastes, the kidneys also maintain blood pH and regulate the water content of the blood. The kidneys respond directly to the composition of the blood. They are also influenced by the endocrine system. Disruption of proper kidney function can lead to serious health problems.

Control of Kidney Function To a large extent, the activity of the kidneys is controlled by the composition of the blood itself. For example, if you eat salty food, the kidneys will respond to the excess salt in your blood by returning less salt to your blood during reabsorption. If the blood is too acidic, then the kidneys excrete more hydrogen ions in the urine. If your blood glucose levels rise past a certain point, the kidneys will even excrete glucose into the urine. This is one of the danger signals of diabetes, a disease caused by the body's inability to control the concentration of glucose in the blood.

Glands release hormones that also influence kidney function. For example, if you have not consumed enough fluids or if you have sweat excessively, your pituitary gland releases antidiuretic hormone (ADH) into your blood. This hormone causes the kidneys to reabsorb more water and to excrete less water in the urine. If the blood contains excess water, ADH secretion stops and more water is excreted.

Did you know that the color of your urine is an indicator of how hydrated you are? A pale yellow color indicates that you are well hydrated because your kidneys are releasing a good amount of water. A darker color indicates that the water level in your blood is low, causing your kidneys to conserve water.

Urine Testing Medical professionals can learn a lot about a person's health from a simple urine sample. The presence of protein or glucose in urine can be indicators of diseases such as dangerously high blood pressure or diabetes. Although many filtered substances are reabsorbed into the blood, drugs generally remain in the filtrate and are eliminated in urine. This is why the effects of many drugs wear off over time and why urine tests are often used to detect the use of illegal drugs.

In Your Notebook Explain in your own words why urine can reveal a lot about a person's health.

Kidney Disorders The kidneys are the master chemists of the blood supply. If anything goes wrong with the kidneys, serious medical problems will likely follow. Three of these problems are kidney stones, kidney damage, and kidney failure.

▸ Kidney Stones Sometimes substances such as calcium, magnesium, or uric acid salts in the urine crystallize and form kidney stones. When kidney stones block a ureter, they cause great pain. Kidney stones are often treated using ultrasound waves. The sound waves pulverize the stones into smaller fragments, which are eliminated with the urine.

Table of Contents