Download Acid-Base Balance

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Hole’s Essentials of Human
Anatomy & Physiology
David Shier
Jackie Butler
Ricki Lewis
Power Points prepared by Melanie Waite-Altringer
Biology Faculty Member of
Anoka-Ramsey Community College
APR Enhanced
Lecture Outlines
Chapter 18
Water, Electrolyte, and
Acid-Base Balance
2
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Introduction
A.
B.
To be in balance, the quantities of fluids and
electrolytes (molecules that release ions in
water) leaving the body should be equal to the
amounts taken in.
Anything that alters the concentrations of
electrolytes will also alter the concentration of
water, and vice versa.
3
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Distribution of Body Fluids
A.
B.
Fluids occur in compartments in the body, and
movement of water and electrolytes between
compartments is regulated.
Fluid Compartments
1.
The average adult female is 52% water
by weight, while a male is 63% water,
the difference due to the female’s
additional adipose tissue.
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2.
3.
The intracellular fluid compartment
includes all the water and electrolytes
within cells.
The extracellular fluid compartment
includes all water and electrolytes
outside of cells (interstitial fluid,
plasma, and lymph).
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4.
Transcellular fluid includes the
cerebrospinal fluid of the central
nervous system, fluids within the
eyeball, synovial fluid of the joints,
serous fluid within body cavities, and
exocrine gland secretions.
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Fig18.01
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Total body water
Interstitial fluid
Plasma
Membranes of
body cells
Intracellular fluid
(63%)
Lymph
Extracellular
fluid (37%)
Transcellular
fluid
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C.
Body Fluid Composition
1.
Extracellular fluids have high
concentrations of sodium, chloride, and
bicarbonate ions, and lesser amounts of
potassium, calcium, magnesium,
phosphate, and sulfate ions.
2.
Intracellular fluid has high
concentrations of potassium, phosphate,
and magnesium ions, and lesser
amounts of sodium, chloride, and
bicarbonate ions.
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D.
Movement of Fluid between Compartments
1.
Hydrostatic pressure and osmotic
pressure regulate the movement of
water and electrolytes from one
compartment to another.
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2.
Although the composition of body
fluids varies from one compartment to
another, the total solute concentrations
and water amounts are normally equal.
3.
A net gain or loss of water will cause
shifts affecting both the intracellular
and extracellular fluids due to osmosis.
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Fig18.03
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Capillary wall
Plasma
Interstitial fluid
Fluid returns to
plasma at venular
ends of capillaries
because inward force
of colloid osmotic
Lymph
pressure predominates
vessel
Lymph
Transcellular
fluid
Serous
membrane
Fluid leaves plasma
at arteriolar end of
capillaries because
outward force of
hydrostatic pressure
predominates
Intracellular
fluid
Cell
membrane
Hydrostatic pressure
within interstitial
spaces forces fluid
into lymph capillaries
Interstitial fluid is
in equilibrium with
transcellular and
intracellular fluids
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Water Balance
A.
B.
Water balance exists when water intake equals
water output.
Water Intake
1.
The volume of water gained each day
varies from one individual to the next.
2.
About 60% of daily water is gained
from drinking, another 30% comes from
moist foods, and 10% from the water of
metabolism.
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3.
Regulation of Water Intake
a.
The thirst center in the
hypothalamus is the primary
regulator of water intake.
b.
The thirst mechanism derives from
the osmotic pressure of extracellular
fluids and a thirst center in the
hypothalamus.
c.
Once water is taken in, the resulting
distention of the stomach will
inhibit the thirst mechanism.
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D.
Water Output
1.
Water is lost in urine, feces,
perspiration, evaporation from skin
(insensible perspiration), and from the
lungs during breathing.
2.
The route of water loss depends on
temperature, relative humidity, and
physical exercise.
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3.
Regulation of Water Output
a.
The distal convoluted tubules of
the nephrons and collecting ducts
regulate water output.
b.
Antidiuretic hormone from the
posterior pituitary causes a
reduction in the amount of water
lost in the urine.
c.
When drinking adequate water,
the ADH mechanism is inhibited,
and more water is expelled in
urine.
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Fig18.04
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Average daily intake of water
Average daily intake of water
Water of
metabolism
(250 mL or 10%)
Water lost in sweat
(150 mL or 6%)
Water lost in feces
(150 mL or 6%)
Water in
moist food
(750 mL or 30%)
Water lost through
skin and lungs
(700 mL or 28%)
Total intake
(2,500 mL)
Total output
(2,500 mL)
Water in
beverages
(1,500 mL or 60%)
(a)
Water lost in urine
(1,500 mL or 60%)
(b)
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Electrolyte Balance
A.
B.
An electrolyte balance exists when the
quantities of electrolytes gained equals the
amount lost.
Electrolyte Intake
1.
The electrolytes of greatest importance
to cellular metabolism are sodium,
potassium, calcium, magnesium,
chloride, sulfate, phosphate,
bicarbonate, and hydrogen ions.
2.
Electrolytes may be obtained from food
or drink or produced as a by-product of
metabolism.
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3.
Regulation of Electrolyte Intake
a.
A person ordinarily obtains
sufficient electrolytes from foods
eaten.
b.
A salt craving may indicate an
electrolyte deficiency.
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C.
Electrolyte Output
1.
Losses of electrolytes occur through
sweating, in the feces, and in urine.
2.
Regulation of Electrolyte Output
a.
The concentrations of sodium,
potassium, and calcium, are very
important.
b.
Sodium ions account for 90% of
the positively charged ions in
extracellular fluids; the action of
aldosterone on the kidneys
regulates sodium reabsorption.
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c.
d.
Aldosterone also regulates
potassium ions; potassium ions
are excreted when sodium ions
are conserved.
Calcium concentration is
regulated by parathyroid
hormone, which increases the
concentrations of calcium and
phosphate ions in extracellular
fluids and by calcitonin which
does basically the reverse.
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e.
Generally, the regulatory
mechanisms that control
positively charged ions (cations)
secondarily control the
concentrations of negatively
charged ions (anions).
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Acid-Base Balance
A.
Electrolytes that ionize in water and release
hydrogen ions are acids; those that combine
with hydrogen ions are bases.
B.
Maintenance of homeostasis depends on the
control of acids and bases in body fluids.
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C.
Sources of Hydrogen Ions
1.
Most hydrogen ions originate as byproducts of metabolic processes,
including: the aerobic and anaerobic
respiration of glucose, incomplete
oxidation of fatty acids, oxidation of
amino acids containing sulfur, and the
breakdown of phosphoproteins and
nucleic acids.
23
Fig18.06
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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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D.
Strengths of Acids and Bases
1.
Acids that ionize more completely are
strong acids; those that ionize less
completely are weak acids.
2.
Bases release hydroxyl and other ions,
which can combine with hydrogen ions,
thereby lowering their concentration.
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E.
Regulation of Hydrogen Ion Concentration
1.
Acid-base buffer systems, the
respiratory center in the brain stem, and
the kidneys regulate pH of body fluids.
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2.
Acid-Base Buffer Systems
a.
The chemical components of a
buffer system can combine with a
strong acid and convert it to a
weaker one.
b.
The chemical buffer systems in
body fluids include the
bicarbonate buffer system, the
phosphate buffer system, and the
protein buffer system.
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3.
Respiratory Excretion of Carbon Dioxide
a.
The respiratory center in the brain
stem helps to regulate hydrogen
ion concentration by controlling
the rate and depth of breathing.
b.
During exercise, the carbon dioxide,
and thus the carbonic acid, levels in
the blood increase.
c.
In response, the respiratory center
increases the rate and depth of
breathing, so the lungs excrete
more carbon dioxide.
28
Fig18.07
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Cells increase production of CO2
CO2 reacts with H2O to produce H2CO3
H2CO3 releases H+
Respiratory center is stimulated
Rate and depth of breathing increase
More CO2 is eliminated through lungs
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4.
Renal Excretion of Hydrogen Ions
a.
5.
Nephrons secrete excess hydrogen
ions in the urine.
Time Course of Hydrogen Ion Regulation
a.
Chemical buffers are considered
the body’s first line of defense
against shifts in pH; physiological
buffer systems (respiratory and renal
mechanisms) function more slowly
and constitute secondary defenses.
30
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Acid-Base Imbalances
A.
Chemical and physiological buffer systems
usually keep body fluids within very narrow
pH ranges but abnormal conditions may
prevent this.
1.
A pH below 7.35 produces acidosis
while a pH above 7.45 is called
alkalosis.
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B.
Acidosis
1.
Two major types of acidosis are
respiratory and metabolic acidosis.
a.
Respiratory acidosis results from
an increase of carbonic acid
caused by respiratory center
injury, air passage obstructions, or
disease processes that decrease gas
exchange.
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b.
c.
Metabolic acidosis is due to
either an accumulation of acids or
a loss of bases, and has many
causes including kidney disease,
vomiting, diarrhea, and diabetes
mellitus.
Increasing respiratory rate or the
amount of hydrogen ions released
by the kidney can help
compensate for acidosis.
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Fig18.12
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Kidney failure
to excrete acids
Excessive production of acidic
ketones as in diabetes mellitus
Accumulation of nonrespiratory acids
Metabolic acidosis
Excessive loss of bases
Prolonged diarrhea
with loss of alkaline
intestinal secretions
Prolonged vomiting
with loss of intestinal
secretions
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C.
Alkalosis
1.
Alkalosis also has respiratory and
metabolic causes.
a.
Respiratory alkalosis results from
hyperventilation causing an
excessive loss of carbon dioxide.
b.
Metabolic alkalosis is caused by
a great loss of hydrogen ions or
from a gain in bases perhaps
from vomiting or use of drugs.
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Fig18.13
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• Anxiety
• Fever
• Poisoning
• High altitude
Hyperventilation
Excessive loss of CO2
Decrease in concentration of H2CO3
Decrease in concentration of H+
Respiratory alkalosis
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