Which of the following occurs when blood volume and pressure become too high?

The body obtains sodium through food and drink and loses it primarily in sweat and urine. Healthy kidneys maintain a consistent level of sodium in the body by adjusting the amount excreted in the urine. When sodium consumption and loss are not in balance, the total amount of sodium in the body is affected. The amount (concentration) of sodium in the blood may be

The total amount of sodium in the body affects the amount of fluid in blood (blood volume) and around cells. The body continually monitors blood volume and sodium concentration. When either becomes too high, sensors in the heart, blood vessels, and kidneys detect the increases and stimulate the kidneys to increase sodium excretion, thus returning blood volume to normal.

When blood volume or sodium concentration becomes too low, the sensors trigger mechanisms to increase blood volume. These mechanisms include the following:

• The pituitary gland secretes vasopressin (sometimes called antidiuretic hormone). Vasopressin causes the kidneys to conserve water.

As people age, the body is less able to maintain fluid and sodium balance for several reasons:

• Decreased thirst: As people age, they sense thirst less quickly or less intensely and thus may not drink fluids when needed.

• Changes in the kidneys: Aging kidneys may become less able to reclaim water and electrolytes from the urine (concentrate urine), and, as a result, more water may be excreted in urine.

• Less fluid in the body: In older people, the body contains less fluid. Only 45% of body weight is fluid in older people, compared with 60% in younger people. This change means that a slight loss of fluid and sodium, as can result from a fever or from not eating and drinking enough (sometimes for only a day or two), can have more serious consequences in older people.

The above situations can result in losing fluid or not consuming enough fluid and thus can cause a high sodium level in blood (hypernatremia Hypernatremia (High Level of Sodium in the Blood) In hypernatremia, the level of sodium in blood is too high. Hypernatremia involves dehydration, which can have many causes, including not drinking enough fluids, diarrhea, kidney dysfunction... read more ) and/or dehydration Dehydration Dehydration is a deficiency of water in the body. Vomiting, diarrhea, excessive sweating, burns, kidney failure, and use of diuretics may cause dehydration. People feel thirsty, and as dehydration... read more . Because these situations are more common among older people, hypernatremia is also more common among them. Hypernatremia is poorly tolerated by older people and can result in confusion, coma, and death if severe.

A low sodium level in blood (hyponatremia Hyponatremia (Low Level of Sodium in the Blood) In hyponatremia, the level of sodium in blood is too low. A low sodium level has many causes, including consumption of too many fluids, kidney failure, heart failure, cirrhosis, and use of diuretics... read more ) is more common among older people. Hyponatremia usually results when the body retains too much fluid, as occurs in heart failure or liver disease. Hyponatremia also occurs in older people who take certain types of diuretics (thiazide diuretics such as hydrochlorothiazide), particularly if the kidneys are not functioning normally. Diuretics, which are sometimes called water pills, are drugs that help the body eliminate excess fluid. Using liquid nutritional supplements or receiving intravenous fluids that are low in sodium while in the hospital also may cause hyponatremia in older people.

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