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Chapter 19
Water, Electrolyte, Water, Electrolyte, and Acid-Base and Acid-Base
BalanceBalance
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Fluid compartmentsFluid compartments
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Fluid movementFluid movement
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What determines the amount and direction of fluid that flows between body compartments?
A.The volume of fluid in one of the compartmentsB.The concentration of solutesC.The pH of the fluidD.The concentration of hydrogen ions in the fluid
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Correct answer: B
Rationale:None of the other factors influences fluid shifts between body compartments.
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Regulation of intake & Regulation of intake & outputoutput
Water loss varies in amount. To maintain balance, the body uses
mechanisms to adjust intake and output.
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Mechanisms to Mechanisms to ↑↑ intake intake1. Physical changes stimulate thirst
center in hypothalamus.2. Salivation decreases, causing dry
mouth and thirst.3. Water consumption occurs.
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Mechanisms to Mechanisms to ↓↓ output output1. Physical changes stimulate the
hypothalamus.2. This stimulates the posterior pituitary
to secrete antidiuretic hormone (ADH).3. ADH prompts the kidneys to reabsorb
water and produce less urine.4. Fluid loss slows until water is ingested.
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Antidiuretic hormone (ADH) is released in response to:
A.a rise in blood pressure.B.an increase in fluid volume.C.a decrease in both serum sodium and osmolarity.D.an increase in both serum sodium and osmolarity.
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Correct answer: D
Rationale:ADH is secreted in the volume of total body water declines, which leads to a drop in blood pressure and an increase in serum sodim and osmolarity.
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Disorders of water balanceDisorders of water balanceCan result from abnormality in:Fluid volumeFluid concentrationDistribution of fluid between compartments
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Fluid deficiencyFluid deficiency Volume depletionVolume depletion: results from blood
loss or loss of both water and sodium DehydrationDehydration: results when the body
eliminates more water than sodium
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DehydrationDehydration
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Fluid excessFluid excess Kidneys usually compensate by
producing more urine. Specific type includes water
intoxication.
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Fluid accumulationFluid accumulation Involves the accumulation of fluid
between compartments EdemaEdema: Fluid accumulation in
interstitial spaces, causing tissue swelling
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Which condition results when the body eliminates more water than sodium?
A.EdemaB.DehydrationC.Water intoxicationD.Volume depletion
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Correct answer: B
Rationale:Edema is the accumulation of fluid in interstitial spaces. Water intoxication is the consumption of more water than sodium. Volume depletion is the loss of both sodium and water.
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Electrolyte balanceElectrolyte balance Crucial for proper body functioning Major cationsMajor cations: Na+, K+ Ca+, H+
Major anionsMajor anions: Cl−, HCO3−, Pi
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SodiumSodium Main electrolyte in extracellular fluid Determines volume of total body
water Influences how body water is
distributed Plays a key role in depolarization
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Sodium regulationSodium regulation
Serum osmolarity ↓ Aldosterone prompts renal tubules to
reabsorb Na+
Antidiuretic hormone (ADH) suppressed → kidneys secrete water
Serum Na+ levels increase
↓↓Serum NaSerum Na++
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Sodium regulationSodium regulation
Serum osmolarity ↑ Aldosterone prompts renal tubules to
reabsorb Na+. Antidiuretic hormone (ADH) causes
kidneys to reabsorb water. ADH stimulates thirst. Serum Na+ levels decline.
↑ ↑ SSerum Naerum Na++
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Sodium imbalancesSodium imbalancesHypernatremia
Plasma concentration greater than 146 mEq/L
Indicates fluid deficit Usually self-corrects
by triggering thirst
Hyponatremia
Plasma concentration less than 139 mEq/L
Results from excess body water
Usually corrected by excretion of excess water
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Potassium imbalancesPotassium imbalancesHyperkalemiaHyperkalemia
Plasma concentration above 5.0 mEq/L
May occur suddenly or gradually
Makes nerve and muscle cells irritable
HypokalemiaHypokalemia Plasma concentration
less than 3.5 mEq/L May result from
diuretics, vomiting, or chronic diarrhea
Makes cells less excitable
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Calcium imbalancesCalcium imbalancesHypercalcemiaHypercalcemia
Plasma concentration greater than 5.8 mEq/L
May result from hyperparathyroidism, hypothyroidism, alkalosis
Inhibits depolarization
HypocalcemiaHypocalcemia Plasma concentration
less than 4.5 mEq/L May result from
hypoparathyroidism, hyperthyroidism, acidosis, diarrhea
Increases excitation of nerves and muscles
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What is the main cation of extracellular fluid?
A.PotassiumB.SodiumC.ChlorideD.Calcium
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Correct answer: B
Rationale: Potassium is the main cation in intracellular fluid. Chloride is the most abundant extracellular anion and is linked to sodium. Calcium exists mostly outside the cell but is not the chief extracellular cation.
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Acid-base balanceAcid-base balance Influences homeostasis Slight deviations can be fatal pH of blood ranges from 7.35 to 7.45
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Chemical buffersChemical buffers Includes bicarbonate, phosphate, and
protein buffer systems Use weak base to bind H+ ions and
weak acid to release them
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Physiological buffersPhysiological buffers Includes respiratory and urinary
systems. Lungs expel CO2 to lower pH. Kidneys expel H+ ions to lower pH.
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Respiratory control of pHRespiratory control of pH Central chemoreceptors in the brainstem detect
a decline in pH from an accumulation of CO2. They signal the respiratory centers to increase
the rate and depth of breathing. The lungs blow off CO2. Less CO2 is available to combine with water to
form carbonic acid; the concentration of H+ ions decreases and pH rises.
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Renal control of pHRenal control of pH Expels H+ ions and reabsorbs
bicarbonate Is the most powerful buffer system Is also the slowest to respond
<View animation “Renal control of pH”
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When the body’s pH rises above normal, which reaction would occur first?
A.Respiratory rate would increaseB.Kidneys would excrete hydrogen ionsC.Hydrogen would bind with bicarbonateD.Hydrogen would bind with carbonic acid
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Correct answer: C
Rationale: Although both an increase in respiratory rate and the excretion of hydrogen ions from the kidneys would help lower pH, neither would be the first response. Hydrogen does not bind with carbonic acid.
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Acid-base imbalancesAcid-base imbalances Respiratory imbalances Respiratory imbalances result from
an excess or deficiency of COCO22 Metabolic imbalances Metabolic imbalances result from an
excess or deficiency of bicarbonatebicarbonate
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CAUSES OF ACID GAIN(Acidosis)
CAUSES OF ACID LOSS(Alkalosis)
RESPIRATORY Retention of CO2 (hypoventilation—such as from emphysema or pneumonia—as well as apnea)
Loss of CO2 (hyperventilation)
METABOLIC Increased production of acids (such as ketone bodies in diabetes mellitus or lactic acid in anaerobic metabolism)
Consumption of acidic drugs (such as aspirin)
Inability of the kidneys to excrete H+ ions
Loss of bicarbonate (such as chronic diarrhea)
Loss of gastric juices (such as through vomiting or suctioning)
Excessive ingestion of bicarbonates (such as antacids)
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Compensation for acid-base Compensation for acid-base imbalancesimbalances
Respiratory system responds to metabolic disturbances by adjusting ventilation.
Renal system responds by adjusting the rate of H+ ion excretion.
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Which electrolyte disturbance would result from acidosis?
A.HypernatremiaB.HyponatremiaC.HyperkalemiaD.Hypokalemia
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Correct answer: C
Rationale: Acidosis does not affect the concentration of sodium in the blood. Hypokalemia would result from alkalosis, caused as potassium moves into the cell to balance the movement of hydrogen ions out of the cell.