chapt21 electrolyte balance
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 21
Lecture
PowerPoint
2
Hole’s Human Anatomy
and PhysiologyTwelfth Edition
Shier ���� Butler ���� Lewis
Chapter
21
Water, Electrolyte, and
Acid-Base Balance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
3
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
4
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
5
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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7
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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8
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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9
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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11
Regulation of Water Intake
12
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
14
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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15
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
16
Regulation of Electrolyte Intake
• Ordinarily, a person obtains sufficient electrolytes by
responding to hunger and thirst
• A severe electrolyte deficiency may cause salt craving
17
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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19
21.1 Clinical Application
Water Balance Disorders
20
21.2 Clinical Application
Sodium and Potassium Imbalances
21
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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23
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-
24
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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27
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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28
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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29
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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30
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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31
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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32
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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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
33
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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34
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.
35
Important Points in Chapter 21:
Outcomes to be Assessed
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.
36
Important Points in Chapter 21:
Outcomes to be Assessed
21.6: Acid-Base Imbalances
� Describe the causes and consequences of increase or decrease in body
fluid pH.
37
Quiz 21
Complete Quiz 21 now!
Read Chapter 22.
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