Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Chapter 9 Water.

Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.

Chapter 9

Water


Objectives

• Describe functions of water in body

• Explain fluid balance and its maintenance

• Name causes and consequences of water depletion

• Give some causes and consequences of positive fluid balance

• Describe acid-base balance in human body


Facts

• Humans can live approximately 30 to 45 days without food but only 10 to 14 days without water

• Present in all body cells

• 50 to 60 percent of body weight of normal adults– Percentage highest in newborns and decreases with age

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Facts

• Two basic compartments:– Intracellular fluid (ICF)

• Within cells

• 65 percent of total body fluid

– Extracellular fluid (ECF)• Outside cells

• 35 percent of total body fluid

• Found in intravascular fluid (in bloodstream), interstitial fluid (between cells), and glandular secretions


Functions

• Major component of blood plasma

• Solvent and transport for nutrients and waste products

• Essential component for hydrolysis and metabolism

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Functions

• Lubricant in joints and digestion

• Body coolant through perspiration

• Shock absorber


Sources

• Best:– Drinking water

• Second-best:– Other beverages

• Other:– 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 measured in milliequivalents (mEq/L)

• Water losses must be replaced in volume and electrolyte content

• Sensible water loss– Noticeable

– Water lost through urine

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• Insensible water loss– Unnoticeable

– Water lost through feces, perspiration, and respiration

• Solute– Substance dissolved in solution

• Osmosis– Water flows from side with lesser amount of solute to side

with greater solute concentration

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• Potassium, sodium, and chloride maintain balance between ICFs and ECFs

• Potassium– Principal electrolyte in ICF

• Sodium– Principal electrolyte in ECF

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• Osmolality– Measures particles in solution

• When electrolytes in ECF increase, ICF moves to ECF to equalize concentration of electrolytes on both sides of membrane– Reduces amount of water in cells

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• Hypothalamus stimulates pituitary gland to excrete antidiuretic hormone (ADH)

• ADH causes kidneys to reabsorb water

• Thirst causes healthy person to drink fluids

• When sodium in ECF reduced, water flows from ECF into cells– Causes cellular edema

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• Adrenal glands secrete aldosterone– Triggers kidneys to increase amount of sodium reabsorbed

• When sodium replaced in ECF, excess water moves back to ECF– Relieves edema

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• Amount of water use varies– Depends on age, size, activity, environmental temperature,

and physical condition

• Average adult requirement:– 1 milliliter (mL) for every calorie of food consumed


Stop and Share

• Consider the following question:– How many glasses of fluid would be required for an adult

eating 1,800 kilocalories per day?

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Stop and Share

• 1 mL × 1,800 calories = 1,800 cubic centimeters (cc)

• 1,800 cc 240 ounces (oz) = 7.5 glasses of water

• Recommended for adults to drink eight 8-oz glasses of fluid per day

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Stop and Share

• Increased requirements during youth, fever, diarrhea, unusual perspiration, and hyperthyroidism


Dehydration

• Occurs when amount of water in body inadequate

• Caused by inadequate intake or abnormal loss– Loss can occur from severe diarrhea, vomiting,

hemorrhage, burns, diabetes mellitus, excessive perspiration, excessive urination, or use of certain medications (e.g., diuretics)

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Dehydration

• Symptoms:– Low blood pressure, thirst, dry skin, fever, and mental

disorientation

• As water lost, electrolytes also lost

• Treatment:– Replacement of electrolytes and fluids

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Dehydration

• 10 percent loss of body water can cause serious problems

• 20 percent loss of body water can cause circulatory failure and death

• Blood volume and nutrient absorption reduced

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Dehydration

• Kidney function upset

• Infants at high risk for dehydration during fever, vomiting, and diarrhea

• Treatment may involve intravenous (IV) fluids

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Dehydration

• Thirst sensation lags behind body’s need for water– Especially in elderly, children, athletes, and ill

– Feeling thirsty not reliable indicator of when body needs water

• Prevention:– Drink fluids throughout day

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Dehydration

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

1. Heat fatigue

2. Heat cramp

3. Heat exhaustion

4. Heat stroke


Signs of Dehydration

• Health history reveals inadequate intake of fluids

• Decrease in urine output

• Weight loss

• Sunken eyes

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Signs of Dehydration

• Increased furrows and fissures on tongue

• Dry oral mucous membranes

• Decreased skin turgor

• Changes in neurological status


Excess Water Accumulation

• Positive water balance– More water taken in than excreted

• Results in edema

• 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 of 1 to 7

• Alkaline substances have pH of 7 to 14

• pH of 7 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 person eats affects acidity of urine– Not of body


Buffer Systems

• Regulate hydrogen ion content in body fluids

• Mixture of weak acid and strong base

• Normal buffer system ratio of base to acid:– 20:1

• Carbonic acid and sodium bicarbonate form body’s main buffer system

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Buffer Systems

• Carbonic acid moves easily to buffer strong alkali

• Sodium bicarbonate moves easily to buffer strong acid

• Amounts easily adjusted by lungs and kidneys to suit body’s needs

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Buffer Systems

• End products of metabolism:– Carbon dioxide and water

• Together, can form carbonic acid

• Medulla oblongata in brain causes breathing rate to increase if amount of carbon dioxide more concentrated than should be– Increases rate at which body rids itself of carbon dioxide

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Buffer Systems

• Excess sodium bicarbonate excreted via kidneys

• Kidneys can excrete urine from pH of 4.5 to 8

• pH of average urine:– 6


Acidosis and Alkalosis

• Acidosis can be caused by renal failure, uncontrolled diabetes mellitus, starvation, or severe diarrhea

• Alkalosis can occur when body has suffered loss of hydrochloric acid from severe vomiting or has ingested too much alkali (e.g., too many antacid tablets)


Stop and Share

• Consider the following scenario:– A client is unhappy with her low-sodium, fluid-restricted

diet. How can you best help her?

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Stop and Share

• Discuss realistic ways of planning menus– Base menus on good nutrition and her normal habits and

desires

• Review her former diet with her– Point out high-salt and high-liquid foods

– Present alternative foods in positive manner


Conclusion

• Water– Component of all tissues

– Solvent for nutrients and body wastes• Provides transport for both

• Essential for the following:– Hydrolysis

– Lubrication

– Maintenance of normal temperature

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Conclusion

• Best sources:– Water, beverages, fruits, vegetables, soups, and water-

based desserts

• Dehydration can result from lack of water

• Positive water balance– Excess accumulation of water in body

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Conclusion

• Acid-base balance– Regulation of hydrogen ions in body

• Healthy people have intricate maintenance systems for fluid, electrolytes, and acid-base balance

Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Chapter 9 Water.

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