Anatomy and Physiology, Sixth Edition
Rod R. Seeley
Idaho State University
Trent D. Stephens
Idaho State University
Philip Tate
Phoenix College
Chapter 27
Lecture Outline*
*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
27-1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 27
Water, Electrolytes, and
Acid-Base Balance
27-2
Body Fluids
• Intracellular
– All fluids inside cells of body
– About 40% of total body weight
• Extracellular
– All fluids outside cells
– About 20% of total body weight
– Subcompartments
• Interstitial fluid and plasma; lymph, CSF, synovial
fluid
27-3
Body Fluid Compartments
27-4
Water Content Regulation
• Content regulated so total
volume of water in body
remains constant
• Kidneys primary regulator
of water excretion
• Regulation processes
–
–
–
–
–
Osmosis
Osmolality
Baroreceptors
Learned behavior
???
• Sources of water
– Ingestion
– Cellular metabolism
• Routes of water loss
– Urine
– Evaporation
• Perspiration
• Respiratory passages
– Feces
27-5
Extracellular Fluid Osmolality
• Osmolality
– Adding or removing
water from a solution
changes this
• Decreased osmolality
– Inhibits thirst and ADH
secretion
• Increased osmolality
– Triggers thirst and
ADH secretion
27-6
Hormonal Regulation of
Blood Osmolality
27-7
Regulation of ECF Volume
• Mechanisms
– Neural
– Renin-angiotensinaldosterone
– Atrial natriuretic
hormone (ANH)
– Antidiuretic hormone
(ADH)
• Increased ECF results in
–
–
–
–
Decreased aldosterone secretion
Increased ANH secretion
Decreased ADH secretion
Decreased sympathetic
stimulation
• Decreased ECF results in
–
–
–
–
Increased aldosterone secretion
Decreased ANH secretion
Increased ADH secretion
Increased sympathetic stimulation
27-8
Hormonal Regulation of
Blood Volume
27-9
Hormonal Regulation of
Blood Volume
27-10
Regulation of ECF Volume
27-11
Regulation of ICF and ECF
27-12
Regulation of Electrolytes in ECF
• Electrolytes
– Molecules or ions with an
electrical charge
• Water ingestion adds
electrolytes to body
• Kidneys, liver, skin, lungs
remove from body
– Concentration changes only
when growing, gaining or
losing weight
• Na+ Ions
– Dominant ECF cations
– Responsible for 90-95% of
osmotic pressure
• Regulation of Na+ ions
– Kidneys major route of
excretion
– Small quantities lost in
sweat
• Terms
– Hypernatremia:
• high sodium
– Hyponatremia
• low sodium
27-13
Mechanisms Regulating Blood Sodium
27-14
Mechanisms Regulating Blood Sodium
27-15
Abnormal Plasma Levels of
Sodium Ions
27-16
Regulation of Chloride,
Potassium, Magnesium Ions
• Chloride ions
– Predominant anions in
ECF
• Magnesium ions
– Capacity of kidney to
reabsorb is limited
– Excess lost in urine
– Decreased extracellular
magnesium results in
greater degree of
reabsorption
• Potassium ions
– Maintained in narrow
range
– Affect resting
membrane potentials
– Aldosterone increases
amount secreted
• Terms
– Hyperkalemia
– Hypokalemia
27-17
Potassium Ion Regulation in ECF
27-18
Abnormal Concentration of Potassium
Ions
27-19
Abnormal Plasma Levels of
Magnesium Ions
27-20
Regulation of Blood Magnesium
27-21
Regulation of Calcium Ions
• Regulated within
narrow range
– Elevated extracellular
levels prevent
membrane
depolarization
– Decreased levels lead
to spontaneous action
potential generation
• Terms
– Hypocalcemia
– Hypercalcemia
• PTH increases Ca2+
extracellular levels
and decreases
extracellular
phosphate levels
• Vitamin D stimulates
Ca2+ uptake in
intestines
• Calcitonin decreases
extracellular Ca2+
levels
27-22
Regulation of Calcium Ions
27-23
Regulation of Phosphate Ions
• Under normal conditions, reabsorption of phosphate occurs
at maximum rate in the nephron
• An increase in plasma phosphate increases amount of
phosphate in nephron beyond that which can be
reabsorbed; excess is lost in urine
27-24
Regulation of Blood Phosphate
27-25
Acids and Bases
and Buffers
• Acids
– Release H+ into
solution
• Bases
– Remove H+ from
solution
• Acids and bases
– Grouped as strong or
weak
• Buffers: Resist changes in
pH
– When H+ added, buffer
removes
– When H+ removed, buffer
replaces
• Types of buffer systems
– Carbonic acid/bicarbonate
– Protein
– Phosphate
27-26
Regulation of Acid-Base Balance
27-27
Regulation of Acid-Base Balance
27-28
Buffer Systems
27-29
Respiratory Regulation of
Acid-Base Balance
• Respiratory regulation of pH is achieved
through carbonic acid/bicarbonate buffer
system
– As carbon dioxide levels increase, pH decreases
– As carbon dioxide levels decrease, pH increases
– Carbon dioxide levels and pH affect respiratory
centers
• Hypoventilation increases blood carbon dioxide levels
• Hyperventilation decreases blood carbon dioxide levels
27-30
Respiratory Regulation of
Acid-Base Balance
27-31
Renal Regulation of Acid-Base
Balance
• Secretion of H+ into filtrate and reabsorption of
HCO3- into ECF cause extracellular pH to
increase
• HCO3- in filtrate reabsorbed
• Rate of H+ secretion increases as body fluid pH
decreases or as aldosterone levels increase
• Secretion of H+ inhibited when urine pH falls
below 4.5
27-32
Kidney Regulation of
Acid-Base Balance
27-33
Hydrogen Ion Buffering
27-34
Acidosis and Alkalosis
• Acidosis: pH body fluids below 7.35
– Respiratory: Caused by inadequate ventilation
– Metabolic: Results from all conditions other
than respiratory that decrease pH
• Alkalosis: pH body fluids above 7.45
– Respiratory: Caused by hyperventilation
– Metabolic: Results from all conditions other
than respiratory that increase pH
• Compensatory mechanisms
27-35
Acidosis and Alkalosis
27-36