chapt21 electrolyte balance

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Chapter 21

Lecture

PowerPoint

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Hole’s Human Anatomy

and PhysiologyTwelfth Edition

Shier �� Butler �� Lewis

Chapter

21

Water, Electrolyte, and

Acid-Base Balance


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21.1: Introduction

• The term balance suggests a state of equilibrium

• For water and electrolytes that means equal amounts enter

and leave the body

• Mechanisms that replace lost water and electrolytes and

excrete excesses maintain this balance

• This results in stability of the body at all times

• Keep in mind water and electrolyte balance are

interdependent

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21.2: Distribution of Body Fluids

• Body fluids are not uniformly distributed

• They occupy compartments of different volumes that

contain varying compositions

• Water and electrolyte movement between these

compartments is regulated to stabilize their distribution and

the composition of body fluids

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Fluid Compartments

• Of the 40 liters of water in the

body of an average adult, about

two-thirds is intracellular fluid and

one-third is extracellular fluid

• An average adult female is about

52% water by weight, and an

average male about 63% water by

weight

Extracellular

fluid

(37%)

Intracellular

fluid

(63%)

40

38

36

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

Liters


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Total body water

Interstitial fluid

Plasma

Lymph

Transcellular fluid

Extracellular fluid

(37%)

Membranes of

body cells

Intracellular fluid

(63%)


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Body Fluid Composition

• Extracellular fluids are generally

similar in composition including

high concentrations of sodium,

calcium, chloride and bicarbonate

ions

• Intracellular fluids have high

concentrations of potassium,

magnesium, phosphate, and sulfate

ions

Ion concentration (m Eq/L)

20

30

50

60

70

80

90

100

110

120

130

140

Relative concentrations and ratios of ions in extracellular and intracellular fluids

150

40

10

0

14:1Ratio

(Extracellular: intracellular)

Na+

1:28

K+

5:1

Ca+2

1:19

Mg+2

26:1

Cl−−−−

3:1

HCO3−−−−

1:19

PO4−−−−3

1:2

SO4−−−−2

Extracellular fluid

Intracellular fluid


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Movement of Fluid

Between Compartments

• Two major factors regulate the movement of water and

electrolytes from one fluid compartment to another

• Hydrostatic pressure

• Osmotic pressure

Interstitial fluid

Capillary wall

Transcellular

fluid

Lymph

Plasma

Serous

membrane

Intracellular

fluidCell

membrane

Lymph

vessel

Fluid leaves plasma

at arteriolar end of

capillaries because

outward force of

hydrostatic pressure

predominates

Fluid returns to

plasma at venular

ends of capillaries

because inward force

of colloid osmotic

pressure predominates

Hydrostatic pressure

within interstitial

spaces forces fluid

into lymph capillaries

Interstitial fluid is

in equilibrium with

transcellular and

intracellular fluids


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21.3: Water Balance

• Water balance exists when water intake equals water output

• Homeostasis requires control of both water intake and water

output

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Water Intake

• The volume of water gained each day varies among

individuals averaging about 2,500 milliliters daily for an

adult:

• 60% from drinking

• 30% from moist foods

• 10% as a bi-product of

oxidative metabolism of

nutrients called water of

metabolismWater in

beverages

(1,500 mL or 60%)

Average daily intake of waterWater lost in sweat

(150 mL or 6%)

Total output

(2,500 mL)

Average daily output of water

(a) (b)

Total intake

(2,500 mL)

Water in

moist food

(750 mL or 30%)

Water of

metobolism

(250 mL or 10%)

Water lost in feces

(150 mL or 6%)

Water lost through

skin and lungs

(700 mL or 28%)

Water lost in urine

(1,500 mL or 60%)


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Regulation of Water Intake

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Water Output

• Water normally enters the body only through the mouth, but

it can be lost by a variety of routes including:

• Urine (60% loss)

• Feces (6% loss)

• Sweat (sensible perspiration) (6% loss)

• Evaporation from the skin (insensible perspiration)

• The lungs during breathing

(Evaporation from the skin and the lungs is a 28% loss)

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Regulation of Water Output

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21.4: Electrolyte Balance

• An electrolyte balance exists when the quantities of

electrolytes the body gains equals those lost

Urine

Electrolyte intake

Fluids

Feces

Electrolyte output

Foods

Perspiration

Metabolic

reactions


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Electrolyte Intake

• The electrolytes of greatest importance to cellular functions

release sodium, potassium, calcium, magnesium, chloride,

sulfate, phosphate, bicarbonate, and hydrogen ions

• These ions are primarily obtained from foods, but some are

from water and other beverages

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Regulation of Electrolyte Intake

• Ordinarily, a person obtains sufficient electrolytes by

responding to hunger and thirst

• A severe electrolyte deficiency may cause salt craving

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Electrolyte Output

• The body loses some electrolytes by perspiring typically on

warmer days and during strenuous exercise

• Some are lost in the feces

• The greatest output is as a result of kidney function and urine

output

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Regulation of Electrolyte Output

• The concentrations of positively charged ions, such as

sodium (Na+), potassium (K+) and calcium (Ca+2) are of

particular importance

• These ions are vital for nerve impulse conduction, muscle

fiber contraction, and maintenance of cell membrane

permeability

Aldosterone is secreted

Adrenal cortex is signaled

Potassium ion

concentration increases

Renal tubules

increase reabsorption of

sodium ions and increase

secretion of potassium ions

Sodium ions are

conserved and potassium

ions are excreted

Calcium ion

concentration decreases

Calcium ion concentration

returns toward normal

Normal phosphate

concentration is maintained

Addition of phosphate

to bloodstream

Renal tubules conserve

calcium and increase

secretion of phosphate

Parathyroid glands

are stimulated

Parathyroid hormone

is secreted

Intestinal absorption

of calcium increases

Activity of bone-resorbing

osteoclasts increases

Increased phosphate

excretion in urine


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21.1 Clinical Application

Water Balance Disorders

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21.2 Clinical Application

Sodium and Potassium Imbalances

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21.5: Acid-Base Balance

• Electrolytes that ionize in water and release hydrogen ions

are acids

• Substances that combine with hydrogen ions are bases

• Acid-base balance entails regulation of the hydrogen ion

concentrations of body fluids

• This is important because slight changes in hydrogen ion

concentrations can alter the rates of enzyme-controlled

metabolic reactions, shift the distribution of other ions, or

modify hormone actions

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Sources of Hydrogen Ions

Aerobic

respiration

of glucose

Anaerobic

respiration

of glucose

Incomplete

oxidation of

fatty acids

Oxidation of

sulfur-containing

amino acids

Hydrolysis of

phosphoproteins

and nucleic acids

Carbonic

acid

Lactic

acid

Acidic ketone

bodies

Sulfuric

acid

Phosphoric

acid

H+

Internal environment


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Strengths of Acids and Bases

• Acids:

• Strong acids ionize more completely and release more H+

• Weak acids ionize less completely and release fewer H+

• Bases:

• Strong bases ionize more completely and release more OH-

• Weak bases ionize less completely and release fewer OH-

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Regulation of Hydrogen Ion

Concentration

• Either an acid shift or an alkaline (basic) shift in the body

fluids could threaten the internal environment

• Normal metabolic reactions generally produce more acid

than base

• The reactions include cellular metabolism of glucose, fatty

acids, and amino acids

• Maintenance of acid-base balance usually eliminates acids

in one of three ways:

• Acid-base buffer systems

• Respiratory excretion of carbon dioxide

• Renal excretion of hydrogen ions

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Acid-Base Buffer Systems

• Bicarbonate buffer system

• The bicarbonate ion converts a strong acid to a weak acid

• Carbonic acid converts a strong base to a weak base

H+ + HCO3- � H2CO3 � H+ + HCO3

-

• Phosphate buffer system

• The monohydrogen phosphate ion converts a strong acid to a weak acid

• The dihydrogen phosphate ion converts a strong base to a weak base

H+ + HPO4-2 � H2PO4

- � H+ + HPO4-2

• Protein buffer system

• NH3+ group releases a hydrogen ion in the presence of excess base

• COO- group accepts a hydrogen ion in the presence of excess acid

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Respiratory Secretion of Carbon Dioxide

• The respiratory center in the

brainstem helps regulate

hydrogen ion concentrations in

the body fluids by controlling

the rate and depth of breathing

• If body cells increase their

production of CO2…

More CO2 is eliminated through lungs

Rate and depth of breathing increase

Respiratory center is stimulated

Cells increase production of CO2

CO2 reacts with H2O to produce H2CO3

H2CO3 releases H+


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Renal Excretion of Hydrogen Ions

• Nephrons help regulate the

hydrogen ion concentration

of body fluids by excreting

hydrogen ions in the urine

High intake of proteins

Increased concentration

of H+ in urine

Increased secretion

of H+ into fluid of

renal tubules

Increased concentration

of H+ in body fluids

Increased metabolism

of amino acids

Increased formation

of sulfuric acid and

phosphoric acid

Concentration of H+

in body fluids returns

toward normal


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Time Course of Hydrogen Ion Regulation

• Various regulators of

hydrogen ion

concentration operate at

different rates

• Acid-base (chemical)

buffers function rapidly

• Respiratory and renal

(physiological buffers)

mechanisms function

more slowly

Phosphate

buffer system

Protein

buffer system

First line of defense

against pH shift

Second line of

defense against

pH shift

Chemical

buffer system

Physiological

buffers

Bicarbonate

buffer system

Respiratory

mechanism

(CO2 excretion)

Renal

mechanism

(H+ excretion)


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21.6: Acid-Base Imbalances

• Chemical and physiological buffer systems ordinarily

maintain the hydrogen ion concentration of body fluids within

very narrow pH ranges

• Abnormal conditions may disturb the acid-base balance

7.35

Survival range

Normal pH range

pH scale

7.45 8.07.06.8 7.8

Acidosis Alkalosis


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Acidosis

• Acidosis results from the

accumulation of acids or loss of

bases, both of which cause

abnormal increases in the

hydrogen ion concentrations of

body fluids

• Alkalosis results from a loss of

acids or an accumulation of

bases accompanied by a decrease

in hydrogen ion concentrations

pH rises

pH drops

Increased concentration of H+

pH scale

7.4

Acidosis

Alkalosis

Decreased concentration of H+

Accumulation

of acids

Loss of

bases

Loss of

acids

Accumulation

of bases


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Acidosis

• Two major types of acidosis are respiratory acidosis and

metabolic acidosis

Accumulation of CO2

Respiratory

acidosis

Decreased rate

and depth of

breathing

Obstruction of

air passages

Decreased

gas exchange Accumulation of nonrespiratory acids

Metabolic acidosis

Excessive loss of bases

Kidney failure

to excrete acids

Excessive production of acidic

ketones as in diabetes mellitus

Prolonged diarrhea

with loss of alkaline

intestinal secretions

Prolonged vomiting

with loss of intestinal

secretions



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Alkalosis

• Respiratory alkalosis develops as a result of hyperventilation

• Metabolic alkalosis results from a great loss of hydrogen ions

or from a gain in bases, both accompanied by a rise in the pH

of blood

Excessive loss of CO2

Hyperventilation

Decrease in concentration of H2CO3

Decrease in concentration of H+

Respiratory alkalosis

• Anxiety

• Fever

• Poisoning

• High altitude

Loss of acids

Net increase in alkaline substances

Metabolic alkalosis

Gastric

drainage

Vomiting with loss

of gastric secretions


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Important Points in Chapter 21:

Outcomes to be Assessed

21.1: Introduction

� Explain the balance concept.

� Explain the importance of water and electrolyte balance.

21.2: Distribution of Body Fluids

� Describe how body fluids are distributed in compartments.

� Explain how fluid composition varies among compartments and how

fluids move from one compartment to another.

21.3: Water Balance

� List the routes by which water enters and leaves the body.

� Explain the regulation of water input and water output.

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21.4: Electrolyte Balance

� List the routes by which electrolytes enter and leave the body.

� Explain the regulation of the input and the output of electrolytes.

21.5: Acid-Base Balance

� Explain acid-base balance.

� Identify how pH number describes the acidity and alkalinity of a body

fluid.

� List the major sources of hydrogen ions in the body.

� Distinguish between strong acids and weak acids.

� Explain how chemical buffer systems, the respiratory system, and the

kidneys keep the pH of body fluids relatively constant.

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21.6: Acid-Base Imbalances

� Describe the causes and consequences of increase or decrease in body

fluid pH.

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Quiz 21

Complete Quiz 21 now!

Read Chapter 22.

chapt21 electrolyte balance

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