Sodium & Water Balance in the Body

Sodium functions as an electrolyte in the human body. It plays a role in normal blood pressure, regulation of blood volume, nutrient absorption, nutrient transport and maintenance of the cell membrane potential. The human body tightly controls amounts of these substances to prevent complications and promote normal function in the tissues and organs.

A man is holding a water bottle. Credit: Comstock Images/Stockbyte/Getty Images

Significance

The amount of sodium in the blood has a close relationship to the amount of water in the body. MedlinePlus reports that blood sodium level depends on the amount of sodium and water you consume and the amount you excrete in your urine. Some sodium also leaves the body in sweat and fecal matter. Too little water and sodium levels increase. Too much water and sodium levels decrease. Both conditions cause complications.

Anatomy & Physiology

The brain and urinary system work to regulate the amounts of sodium and water in the body. The hypothalamus, a gland in the brain, controls thirst. It also secretes a hormone that alerts the kidneys to conserve more water instead of excreting it in the urine. The kidneys respond to changes in blood volume by secreting a hormone that produces enzymes known as angiotensin I and angiotensin II. These enzymes play a role in thirst, blood pressure and water retention.

Hormones & Enzymes

Aldosterone and antidiuretic hormone help control sodium and water balance in the body. Aldosterone, secreted by the kidneys, increases the reabsorption of water and sodium. Antidiuretic hormone reduces the amount of water excreted in the urine. This results in the conservation of body water and decreased urine production. The enzyme renin responds to low blood volume or decreased sodium levels. It also affects the release of aldosterone by the kidneys.

Problems

Dehydration occurs when fluid loss exceeds the amount of fluid you consume. Causes of dehydration include high fever, excessive vomiting and diarrhea, excessive sweating, burns and increased urination, according to MayoClinic.com.

Hyponatremia, also known as low sodium levels, occurs in cases of vomiting, sweating, congestive heart failure, diarrhea, burns, cirrhosis of the liver, kidney disease and secretion of excess antidiuretic hormone. Hypernatremia occurs when the amount of sodium in the blood increases. Normal sodium levels range from 137 to 145 mEq/L, as reported by UT Southwestern Medical Center. Treatment for these conditions restores sodium levels to normal to prevent serious complications such as seizures, coma and death.

Lifestyle Factors

Drinking enough water prevents dehydration and abnormal sodium levels. East Carolina University reports that men ages 19 to 50 need 11 cups of water per day, while women in the same age group only need 8 cups of water per day. The amount of sodium you consume in your diet also affects sodium and water balance. If you have high sodium levels, your doctor may advise you to avoid high-sodium foods. Examples of high-sodium foods include canned soups, canned vegetables, frozen meals, processed luncheon meats, potato chips and salted nuts.

Intense physical activity increases sweating and allows sodium and water to escape from the body. To prevent dehydration and hyponatremia caused by excessive exercise, replace lost fluids with water or sports drink.

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