Download Fundamentals of Nutrition

Chapter 9
Water
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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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Functions
• Major component of blood plasma
• Solvent and transport for nutrients and waste
products
• Essential component for hydrolysis and
metabolism
(continues)
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Functions
• Lubricant in joints and digestion
• Body coolant through perspiration
• Shock absorber
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Sources
• Best:
– Drinking water
• Second-best:
– Other beverages
• Other:
– Fruits, vegetables, soups, milk, and gelatin desserts
• Energy metabolism produces water
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Fluid and Electrolyte Balance
• 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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Fluid and Electrolyte Balance
• Potassium, sodium, and chloride maintain
balance between ICFs and ECFs
• Potassium
– Principal electrolyte in ICF
• Sodium
– Principal electrolyte in ECF
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Fluid and Electrolyte Balance
• 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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Fluid and Electrolyte Balance
• 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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Fluid and Electrolyte Balance
• 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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Fluid and Electrolyte Balance
• 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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Stop and Share
• Consider the following question:
– How many glasses of fluid would be required for an adult
eating 1,800 kilocalories per day?
(continues)
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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
(continues)
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Stop and Share
• Increased requirements during youth, fever,
diarrhea, unusual perspiration, and
hyperthyroidism
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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)
(continues)
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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
(continues)
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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
(continues)
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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
(continues)
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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
(continues)
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Dehydration
• Failure to replace water lost through
perspiration could lead to one of four stages of
heat illness:
1.
2.
3.
4.
Heat fatigue
Heat cramp
Heat exhaustion
Heat stroke
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Signs of Dehydration
• Health history reveals inadequate intake of
fluids
• Decrease in urine output
• Weight loss
• Sunken eyes
(continues)
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Signs of Dehydration
•
•
•
•
Increased furrows and fissures on tongue
Dry oral mucous membranes
Decreased skin turgor
Changes in neurological status
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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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
(continues)
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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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
(continues)
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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
(continues)
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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
(continues)
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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
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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)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Stop and Share
• Consider the following scenario:
– A client is unhappy with her low-sodium, fluid-restricted
diet. How can you best help her?
(continues)
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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
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Conclusion
• Best sources:
– Water, beverages, fruits, vegetables, soups, and waterbased desserts
• Dehydration can result from lack of water
• Positive water balance
– Excess accumulation of water in body
(continues)
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
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.