9 water. copyright © 2007 thomson delmar learning, a division of thomson learning inc. all rights...

9

Water

Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.9-2

Objectives

Describe the functions of water in the body.

Explain fluid balance and its maintenance. Name the causes and consequences of

water depletion. Give some causes and consequences of

positive fluid balance. Describe the acid-base balance in the

human body.


Facts

Humans can live about 30–45 days without food.

Humans can live only 10–14 days without water.

Water is present in all body cells. Water is 50%–60% of the body weight of

normal adults. The percentage is highest in newborns; it

decreases with age.(continues)


Facts

Two basic compartments1. Intracellular fluid (ICF): within cells; 65% of

total body fluid2. Extracellular fluid (ECF): outside cells; 35%

of total body fluid Found in intravascular fluid (in blood stream)

interstitial fluid (between cells) and glandular secretions.

(continued)


Functions

Major component of blood plasma Solvent for nutrients and waste products Necessary for hydrolysis of nutrients Essential for metabolism Lubricant in joints and digestion Cools the body through perspiration Provides some mineral elements


Sources

Drinking water is the best source. Other beverages are second-best source. Other sources include fruits, vegetables,

soups, milk, and gelatin desserts. Energy metabolism produces water.


Estimated Daily Fluid Intake for an Adult

Ingested liquids: 1,500 mL Water in foods: 700 mL Water from oxidation: 200 mL Total: 2,400 mL


Fluid and Electrolyte Balance

Electrolytes are measured in milliequivalents (mEq/L).

Sensible (noticeable) water loss is water lost through urine.

Insensible (unnoticeable) water loss is in feces, perspiration, and respiration.

Waste products of metabolism excreted in the form of urine (500 mL of water each day).

(continues)



Solute: substance dissolved in a solution Osmosis: water flows from the side with

the lesser amount of solute to the side with the greater solute concentration

Sodium, chloride, and potassium maintain the balance between intracellular and extracellular fluids.

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Potassium is the principal electrolyte in intracellular fluid.

Sodium is the principal electrolyte in extracellular fluid.

Osmolality measures particles in a solution.

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When electrolytes in extracellular fluid are increased, ICF moves to the ECF to equalize the concentration of electrolytes on both sides of the membrane. This reduces the amount of water in the cells.

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The hypothalamus stimulates the pituitary gland to excrete ADH (antidiuretic hormone).

ADH causes kidneys to reabsorb water. Thirst causes a healthy person to drink

fluids.

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When sodium in ECF is reduced, water flows from ECF into cells, causing cellular edema.

Adrenal glands secrete aldosterone, which triggers kidneys to increase the amount of sodium reabsorbed.

When sodium is replaced in the ECF, excess water moves back to the ECF and edema is relieved.

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Amount of water use varies, depending on age, size, activity, environmental temperature, and physical condition.

Average adult requirement is 1 mL for every calorie of food consumed.

(continued)


• How many glasses of fluid would be required for an adult eating 1,800 kcal/day?

Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.

9-15


• 1 mL × 1,800 cal = 1,800 cc• 1,800 cc 240 oz = 7.5 glasses of water• It is recommended that adults drink eight 8-ounce

glasses of fluid a day.• Youth, fever, diarrhea, unusual perspiration, and

hyperthyroidism increase the requirement.


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Dehydration

Occurs when amount of water in the body is inadequate

Caused by inadequate intake or abnormal loss

Loss can occur from severe diarrhea, vomiting, hemorrhage, burns, diabetes mellitus, excessive perspiration, excessive urination, or the use of certain medications, such as diuretics.

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Dehydration

Symptoms include low blood pressure, thirst, dry skin, fever, and mental disorientation.

As water is lost, electrolytes are also lost. Treatment involves replacement of

electrolytes and fluids.

(continues)

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Dehydration

10% loss of body water can cause serious problems.

Blood volume and nutrient absorption are reduced, and kidney function is upset.

20% loss can cause circulatory failure and death.

Infants are at high risk for dehydration when fever, vomiting, and diarrhea occur.

Treatment may involve IV fluids.(continues)

(continued)


Dehydration

Thirst sensation lags behind the body’s need for water, especially in the elderly, children, athletes, and the ill.

Feeling thirsty is not a reliable indicator of when the body needs water.

Fluids should be drunk throughout the day to prevent dehydration.

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Dehydration

Failure to replace water lost through perspiration could lead to one of the four stages of heat illness:

1. Heat fatigue2. Heat cramp3. Heat exhaustion4. Heat stroke

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Signs of Dehydration

Health history reveals inadequate intake of fluids

Decrease in urine output Weight loss Eyes appear sunken Tongue has increased furrows and

fissures

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Signs of Dehydration

Oral mucous membranes are dry Decreased skin turgor Changes in neurological status

(continued)


Excess Water Accumulation

Positive water balance–more water taken in than excreted; edema results

May be caused by hypothyroidism, congestive heart failure, hypoproteinemia, some infections, some cancers, and some renal conditions

Fluids and sodium may be restricted.


Acid-Base Balance

Regulation of hydrogen ions Acid gives off hydrogen ions. Base picks up hydrogen ions. Acidic substances have pH 1 to 7. Alkaline substances have pH 7 to 14. A pH of 7 is considered neutral.

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Acid-Base Balance

Blood plasma has pH of 7.35 to 7.45. Intracellular fluid has pH of 6.8. Kidneys maintain acid-base balance. What a person eats affects the acidity of

the urine, not of the body.

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Buffer Systems

Regulate hydrogen ion content in body fluids

Mixture of a weak acid and a strong base Normal buffer system ratio of base to acid

is 20:1 Carbonic acid and sodium bicarbonate

form the body’s main buffer system.

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Buffer Systems

Carbonic acid moves easily to buffer a strong alkali, and sodium bicarbonate moves easily to buffer a strong acid.

Amounts are easily adjusted by the lungs and kidneys to suit the body’s needs.

End products of metabolism are carbon dioxide and water, and together they can form carbonic acid.

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Buffer Systems

The medulla oblongata in the brain causes the breathing rate to increase if the amount of carbon dioxide is more concentrated than it should be. This increases the rate at which the body rids itself of carbon dioxide.

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Buffer Systems

Excess sodium bicarbonate is excreted via the kidneys.

The kidneys can excrete urine from pH 4.5 to pH 8.

The pH of average urine is 6.

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Acidosis and Alkalosis

Renal failure, uncontrolled diabetes mellitus, starvation, or severe diarrhea can cause acidosis.

Alkalosis can occur when the body has suffered a loss of hydrochloric acid from severe vomiting or has ingested too much alkali, such as too many antacid tablets.


• A client is unhappy with her low-sodium, fluid-restricted diet. How can the health care professional best help the client?


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• Discuss realistic ways of planning menus for her and with her.

• Base menus on good nutrition, and on the client’s normal habits and desires.

• Review former diet with the client.• Point out high-salt and high-liquid foods and

present alternative foods in a positive manner.


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Conclusion

Water is a component of all tissues. Solvent for nutrients and body wastes Provides transport for both Essential for hydrolysis, lubrication, and

maintenance of normal temperature Best sources are water, beverages, fruits,

vegetables, soups, and water-based desserts

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Conclusion

Dehydration can result from lack of water. Positive water balance is an excess

accumulation of water in the body. Acid-base balance is the regulation of

hydrogen ions in the body. Healthy people have intricate

maintenance systems for fluid, electrolytes, and acid-base balance.

(continued)

9 water. copyright © 2007 thomson delmar learning, a division of thomson learning inc. all rights...

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