chapter19 - fluid, electrolyte, acid-base balance

Copyright © 2012 F.A. Davis Company

Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach

Chapter 19

Water, Electrolyte, Water, Electrolyte, and Acid-Base and Acid-Base

BalanceBalance



Fluid compartmentsFluid compartments



Fluid movementFluid movement



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



Correct answer: B

Rationale:None of the other factors influences fluid shifts between body compartments.



Regulation of intake & Regulation of intake & outputoutput

Water loss varies in amount. To maintain balance, the body uses

mechanisms to adjust intake and output.



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.



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.



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.



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.



Disorders of water balanceDisorders of water balanceCan result from abnormality in:Fluid volumeFluid concentrationDistribution of fluid between compartments



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



DehydrationDehydration



Fluid excessFluid excess Kidneys usually compensate by

producing more urine. Specific type includes water

intoxication.



Fluid accumulationFluid accumulation Involves the accumulation of fluid

between compartments EdemaEdema: Fluid accumulation in

interstitial spaces, causing tissue swelling



Which condition results when the body eliminates more water than sodium?

A.EdemaB.DehydrationC.Water intoxicationD.Volume depletion



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.



Electrolyte balanceElectrolyte balance Crucial for proper body functioning Major cationsMajor cations: Na+, K+ Ca+, H+

Major anionsMajor anions: Cl−, HCO3−, Pi



SodiumSodium Main electrolyte in extracellular fluid Determines volume of total body

water Influences how body water is

distributed Plays a key role in depolarization



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++



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++



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



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



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



What is the main cation of extracellular fluid?

A.PotassiumB.SodiumC.ChlorideD.Calcium



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.



Acid-base balanceAcid-base balance Influences homeostasis Slight deviations can be fatal pH of blood ranges from 7.35 to 7.45



Chemical buffersChemical buffers Includes bicarbonate, phosphate, and

protein buffer systems Use weak base to bind H+ ions and

weak acid to release them



Physiological buffersPhysiological buffers Includes respiratory and urinary

systems. Lungs expel CO2 to lower pH. Kidneys expel H+ ions to lower pH.



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.



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”

http://resources.fadavis.com/thompson/Renal%20Control%20of%20pH.mp4



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



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.



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



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)



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.



Which electrolyte disturbance would result from acidosis?

A.HypernatremiaB.HyponatremiaC.HyperkalemiaD.Hypokalemia



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.

chapter19 - fluid, electrolyte, acid-base balance

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