Download Chapter 21

BIO 139- Human Anatomy &
Physiology II
SPRING 2013
1
Chapter 21- Water,
Electrolyte, and Acid-Base
Balance
MARY CAT FLATH, PH.D.
Copyright 2013 Dr. Mary Cat Flath
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
2
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
Inorganic Substances
3
 Oxygen
 Carbon Dioxide
 Water
 Salts
 Acids
 Bases
Copyright 2013 Dr. Mary Cat Flath
Inorganic Substances:
OXYGEN and Carbon Dioxide
4
 OXYGEN

Is required for cellular respiration
Animal
cells use oxygen to release
energy from nutrients
By-product is carbon dioxide
Copyright 2013 Dr. Mary Cat Flath
Inorganic Substances: WATER
5
 Water is a polar molecule that demonstrates hydrogen bonding and






therefore it possesses very unique characteristics.
a.
Water is an excellent solvent
b.
Water participates in many chemical reactions
• Dehydration (synthesis) is when water is removed from
adjacent atoms (of molecules) to form a bond between them.
• Hydrolysis (degradation) is when water is used to break
bonds between molecules.
c.
Water is an excellent temperature buffer.
d.
Water provides an excellent cooling mechanism
e.
Water serves as a lubricant
f.
Water is the most abundant component in cells (about 5270%).
Copyright 2013 Dr. Mary Cat Flath
Inorganic Molecules: Acids, Bases, Salts
6
 Acids, Bases, and Salts
 When dissolved in water, these release cations and
anions.


These ions are referred to as electrolytes (charged particles)
Electrolytes must be maintained within a very narrow range in our blood
and tissues (i.e. homeostasis);
Needed for muscle contraction, nerve impulses, bone
growth, et cetera;
 Examples include Na+, K+, Cl-, Ca+, PO4-; HCO3-, etc.

Copyright 2013 Dr. Mary Cat Flath
Acids
7
Acids dissociate (ionize) in water to form:
 a. a hydrogen cation, H+, and
 b. an anion.
 c. Example = HCl (hydrochloric acid).
• H2O

 HCl → H+ + Cl-
Copyright 2013 Dr. Mary Cat Flath
Bases
8
 Bases dissociate (ionize) in water to form:



a
b.
c.
a hydroxyl anion, OH-, and
a cation.
Example = NaOH (sodium hydroxide).

H2O


 NaOH → Na+ + OH

Copyright 2013 Dr. Mary Cat Flath
Salts
9
 Salts dissociate (ionize) into ions when
dissolved in water.

an anion is formed and

a cation is formed.

Example = NaCl in water.
H2O

↓
 NaCl → Na+ + Cl
Copyright 2013 Dr. Mary Cat Flath
Acid and Base Concentration
10
 The relative concentrations of hydrogen ions and hydroxyl
ions determine the pH in our blood, fluids, and tissues.
 pH in body = [H+] + [OH-] .
 pH = -log[H+];
 pH Scale ranges from 0 to 14.
 0 ---------------------------7---------------------------14
 acidic
[H+] > [OH-]
Copyright 2013 Dr. Mary Cat Flath
neutral
[H+] = [OH-]
basic
[H+] < [OH-]
Fig. 2.10
pH Scale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Relative
amounts
of H+ (red)
and OH–
(blue)
Acidic
H+
pH 0
Acidic
2.0
gastric
juice
1
3.0
apple
juice
4.2
tomato
juice
6.6
cow’s
milk
5.3
cabbage
Copyright 2013 Dr. Mary Cat Flath
6
8.0
egg
white
7.0
distilled
water
6.0
corn
2
3
4
5
+
H concentration increases
8.4
7.4
sodium
human bicarbonate
blood
7
Neutral
11
8
OH–
10.5
milk of
magnesia
9
10
11
concentration increases
11.5
household
ammonia
Basic
OH–
12
13
14
Basic (alkaline)
Physiologic pH
12
 Physiologic pH = 7.4 (7.35-7.45)
 a.
 b.
pH < 7.35 = acidosis; lethal below 7.0;
pH > 7.45 = alkalosis; lethal above 7.8.
 c. Buffering Systems prevent abrupt pH changes
keeping pH near 7.4
Copyright 2013 Dr. Mary Cat Flath
Buffering Systems
13
 Definition:





Buffers prevent abrupt change in pH.
usually weak acids;
function by donating H+ when needed and by accepting H+ when
in excess;
very important in biological systems!
Example = the carbonic acid (H2CO3) buffering system.
H2CO3

HCO3+
H+
carbonic acid
 (H+ donor)

bicarbonate ion
(H+ acceptor)
 when pH is rising equation goes to the right
 when pH is falling equation goes to the left
Copyright 2013 Dr. Mary Cat Flath
hydrogen ion
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
14
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
Introduction
15
• Homeostasis has been a unifying theme in BIO 137 and BIO
139.
• The ability of an organism to maintain a relatively stable
internal environment.
• Water and electrolytes are included in this delicate balance
or state of equilibrium.
• Water and electrolyte input must equal their output.
• Keep in mind water and electrolyte balance are
interdependent
Copyright 2013 Dr. Mary Cat Flath
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
16
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
Distribution of Body Fluids
17
 Water Content of the Body
 Infants = 73% of body weight
 Males = 63% of body weight
 Females = 52% of body weight
 Total amount of water is affected by age, body mass,
and body fat.
Copyright 2013 Dr. Mary Cat Flath
Distribution of Body Fluids
18
 Fluid Compartments in the Body
 Two main fluid compartments
 INTRACELLULAR COMPARTMENT
Fluid inside cells
 63% of body weight


EXTRACELLULAR COMPARTMENT
Includes blood plasma, interstitial fluid, and lymph
 37% of body weight

Copyright 2013 Dr. Mary Cat Flath
Fluid Compartments
19
•
An average adult female is about 52% water by weight,
and an average male about 63% water by weight
There are about 40 liters of water (with its dissolved
electrolytes) in the body, distributed into two major
compartments:
• Intracellular fluid – 63% - fluid inside cells
• Extracellular fluid – 37% - fluid outside cells
• Interstitial fluid
• Blood plasma
• Lymph
• Transcellular fluid – separated from other
extracellular fluids by epithelial layers
• Cerebrospinal fluid
• Aqueous and vitreous humors
• Synovial fluid
• Serous fluid
Copyright 2013 Dr. Mary Cat Flath
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40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
Extracellular
fluid
(37%)
Liters
•
Intracellular
fluid
(63%)
20
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Total body water
Interstitial fluid
Plasma
Membranes of
body cells
Intracellular fluid
(63%)
Lymph
Transcellular fluid
Extracellular fluid
(37%)
Copyright 2013 Dr. Mary Cat Flath
Distribution of Body Fluids
21
Electrolyte Concentration
The overall concentration of electrolytes is the same
in the two fluid compartments.
However, there are different concentrations of
specific ions in the different compartments.
Copyright 2013 Dr. Mary Cat Flath
Distribution of Body Fluids
22
BODY FLUID COMPOSITION
BODY FLUID
EXTRACELLULAR
FLUID: Blood
plasma, interstitial
fluid, and lymph
INTRACELLULAR
FLUID
HIGH
CONCENTRATION
Na+, Cl-, Ca++, HCO3-,
(plasma – high
proteins)
K+, PO4-, Mg++, SO4Negatively charged
proteins (A-)
LOW
CONCENTRATION
K+, Mg++, PO4-, SO4-
Na+, Cl-, HCO3-
Copyright 2013 Dr. Mary Cat Flath
Body Fluid Composition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Relative concentrations and ratios of ions in extracellular and intracellular fluids
150
140
Extracellular fluid
130
Intracellular fluid
120
110
Ion concentration (m Eq/L)
• Extracellular fluid composition:
• high concentrations of sodium,
calcium, chloride and
bicarbonate ions
• Low concentrations of
potassium, magnesium,
phosphate and sulfate
• Blood plasma, interstitial fluid
and lymph
• Intracellular fluid composition
• high concentrations of
potassium, magnesium,
phosphate, sulfate, and
proteins.
• Low concentration of sodium,
chloride, and bicarbonate ions
100
90
80
70
60
50
40
30
20
10
0
Na+
Ratio 14:1
K+
Ca+2
Mg+2
Cl-
1:28
5:1
1:19
26:1
(Extracellular: intracellular)
Copyright 2013 Dr. Mary Cat Flath
HCO3- PO4-3 SO4-2
3:1
1:19
23
1:2
Distribution of Body Fluids
• Movement of Fluid Between Compartments
• Two major factors regulate the movement of water and electrolytes
from one fluid compartment to another
• Hydrostatic pressure
Fluid leaves plasma
at arteriolar end of
• Osmotic pressure
Capillary wall
capillaries because
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outward force of
hydrostatic pressure
predominates
Plasma
Interstitial fluid
Transcellular
fluid
Serous
membrane
Copyright 2013 Dr. Mary Cat Flath
Fluid returns to
plasma at venular
ends of capillaries
because inward force
Lymph of colloid osmotic
vessel pressure predominates
Hydrostatic pressure
Lymph within interstitial
spaces forces fluid
into lymph capillaries
Intracellular
fluid
Cell
membrane
Interstitial fluid is
in equilibrium with
transcellular and
24
intracellular fluids
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
25
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
Water Intake
26
• 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
Average daily intake of water
Average daily output of water
• 10% as a bi-product of
Water lost in sweat
(150 mL or 6%)
Water of
Water lost in feces
oxidative metabolism of
metobolism
(150 mL or 6%)
(250 mL or 10%)
Water
in
Water lost through
nutrients called water of
moist food
skin and lungs
(750 mL or 30%)
(700 mL or 28%)
metabolism
Total intake
Total output
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(2,500 mL)
(2,500 mL)
Water in
beverages
(1,500 mL or 60%)
(a)
Copyright 2013 Dr. Mary Cat Flath
Water lost in urine
(1,500 mL or 60%)
(b)
Regulation of Water Intake
27
The primary regulator of water intake is thirst.
Copyright 2013 Dr. Mary Cat Flath
Water Output
28
• 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 Lungs is a 28% loss)
Copyright 2013 Dr. Mary Cat Flath
ADH regulates water reabsorption in
the nephron (DCT and CD)
29
Triggers for ADH release include:
Stimulation of posterior pituitary
Prolonged fever
Excessive sweating, vomiting, or diarrhea
concentrates blood plasma
Severe blood loss
Traumatic burns
Increased plasma osmolality
Copyright 2013 Dr. Mary Cat Flath
Regulation of Water Output
30
The osmoreceptor-ADH mechanism in the hypothalamus regulates
the concentration of urine produced in the kidney..
Copyright 2013 Dr. Mary Cat Flath
See Clinical Application 21.1
31
Water Balance Disorders:
Dehydration
Water Intoxication
Edema
Copyright 2013 Dr. Mary Cat Flath
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
32
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
Electrolyte Balance
33
• An electrolyte balance exists when the quantities of electrolytes
the body gains equals those lost
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Foods
Fluids
Metabolic
reactions
Electrolyte intake
Electrolyte output
Perspiration
Copyright 2013 Dr. Mary Cat Flath
Feces
Urine
Electrolyte Intake
34
• The electrolytes of greatest importance to cellular functions are
• 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, and some are by-products of
metabolism
Copyright 2013 Dr. Mary Cat Flath
Regulation of Electrolyte Intake
35
• Ordinarily, a person obtains sufficient electrolytes by
responding to hunger and thirst
• A severe electrolyte deficiency may cause salt craving (rare)
Copyright 2013 Dr. Mary Cat Flath
Electrolyte Output
36
• The body loses some electrolytes by perspiring (more 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
Copyright 2013 Dr. Mary Cat Flath
Regulation of Electrolyte Output
37
 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
 Sodium ions account for nearly 90% of the positively charged ions in
extracellular fluids.
 Regulation of Na+: Aldosterone causes reabsorption of Na+
in DCT
 Regulation of K+: Aldosterone causes secretion/excretion of
K+ in DCT.
 Regulation of Ca++: Calcitonin decreases blood Ca++ and
PTH increases blood Ca++
Copyright 2013 Dr. Mary Cat Flath
Regulation of Electrolyte Output
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Potassium ion
concentration increases
Calcium ion
Concentration decreases
Parathyroid glands
are stimulated
Adrenal cortex is signaled
Parathyroid hormone
is secreted
Aldosterone is secreted
Renal tubules conserve
calcium and increase
secretion of phosphate
Intestinal absorption
of calcium increases
Activity of bone-resorbing
osteoclasts increases
Renal tubules
increase reabsorption of
sodium ions and increase
secretion of potassium ions
Increased phosphate
excretion in urine
Addition of phosphate
to bloodstream
Sodium ions are
conserved and potassium
ions are excreted
Copyright 2013 Dr. Mary Cat Flath
Calcium ion concentration
returns toward normal
Normal phosphate
concentration is maintained
38
Sodium and Potassium Imbalances
39
Hyponatremia (low blood sodium) caused by prolonged sweating, diarrhea,
vomiting, renal disease, Addison’s disease, or excessive water intake can result
in osmosis of water into cells – water intoxication.
Hypernatremia (high blood sodium) caused by water loss (diabetes
insipidus –ADH deficiency, osmotic diuresis- Diabetes Mellitus, increased
perspiration, high fever or heat stroke) or sodium gain (hyperaldosteronism)
can result in CNS disturbances – confusion, stupor, coma.
Hypokalemia (low blood potassium) caused by diuretics, renal disease, or
alkalosis can result in muscle weakness or paralysis, respiratory difficulty, and
atrial and ventricular arrhythmias.
Hyperkalemia (high blood potassium) caused by renal disease, drugs,
Addisons’s disease, or acidosis can result in paralysis of skeletal muscle and
cardiac arrest.
Copyright 2013 Dr. Mary Cat Flath
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
40
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
Acid-Base Balance
41
• pH is an indirect measure of the H+ ion concentration
• Our body maintains a slightly alkaline pH of 7.35-7.45.
• Metabolic and respiratory processes work together to keep
H+ levels in this normal range.
Copyright 2013 Dr. Mary Cat Flath
Normal Metabolism produces Acids/
Hydrogen Ions
42
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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
Acids MUST be neutralized.
Copyright 2013 Dr. Mary Cat Flath
Regulation of Hydrogen Ion
Concentration
43
• pH greater than 7.45 = alkalosis
• pH less than 7.35 = acidosis
• Acid-base balance is maintained (usually by elimination of
acids) in one of three ways:
• Chemical Buffer Systems – work immediately
• Respiratory excretion of carbon dioxide – works in minutes
to hours
• Renal excretion of hydrogen ions – works in hours to 2-3
days and has longer maintenance
Copyright 2013 Dr. Mary Cat Flath
Chemical Buffer Systems
44
Chemical buffer systems are in all body fluids and are based on chemicals that
combine with excess acids or bases. These act immediately.
• Bicarbonate buffer system
• H2CO3 ↔ H + + HCO3• When pH is rising: →
• When pH is falling: ←
• Phosphate buffer system
• H2PO4-  H+ + HPO4-2
• When pH is rising: →
• When pH is falling: ←
• Protein buffer system
• Involve plasma proteins (i.e. albumin) and certain proteins in cells
(hemoglobin in red blood cells).
Copyright 2013 Dr. Mary Cat Flath
Respiratory Buffer System
45
Bicarbonate Buffering System is the main buffer in ECF
CA
CO2 + H2O ↔ H2CO3 ↔ H + + HCO3Changes in CO2 concentration lead directly to changes in
H+ and pH.
CO2 concentration and H+ concentration are directly
proportional
H+ concentration and pH are inversely proportional
Copyright 2013 Dr. Mary Cat Flath
Respiratory Buffer System
46
Decreased ventilation leads to a increased CO2 in the body
pushing the reaction to the right.
Increased ventilation leads to a decreased CO2in the body
pushing the reaction to the left.
This system works within minutes to hours, but it is only
temporary.
Copyright 2013 Dr. Mary Cat Flath
Respiratory Excretion of Carbon
Dioxide: Physiologic Buffer System
• The respiratory center in the
brainstem helps regulate
hydrogen ion concentrations in
the body fluids by controlling
the rate and depth of breathing
(Pontine/pneumotaxic area in
pons)
• If body cells increase their
production of CO2…
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright 2013 Dr. Mary Cat Flath
47
More CO2 is eliminated through lungs
Renal Regulation of Acid-Base Balance
48
The kidneys can secrete and reabsorb HCO3and H+ ions to regulate pH.
The kidneys respond within hours to days.
Copyright 2013 Dr. Mary Cat Flath
Renal Excretion of Hydrogen Ions
49
• Nephrons help regulate the hydrogen ion concentration of
body fluids by excreting hydrogen ions in the urine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
High intake of proteins
Increased metabolism
of amino acids
Increased concentration
of H+ in urine
Increased secretion
of H+ into fluid of
renal tubules
Increased formation
of sulfuric acid and
phosphoric acid
Copyright 2013 Dr. Mary Cat Flath
Concentration of H+
in body fluids returns
toward normal
Increased concentration
of H+ in body fluids
Time Course of pH 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 = minutes to several
days to begin to resist pH
changes.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bicarbonate
buffer system
First line of defense
against pH shift
Chemical
buffer system
Phosphate
buffer system
Protein
buffer system
Second line of
defense against
pH shift
Respiratory
mechanism
(CO2 excretion)
Physiological
buffers
Renal
mechanism
(H+ excretion)
Copyright 2013 Dr. Mary Cat Flath
50
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
51
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath
21.6: Acid-Base Imbalances
52
• Chemical and physiological buffer systems ordinarily
maintain the hydrogen ion concentration of body fluids
within very narrow pH range of 7.35-7.45.
• Abnormal conditions may disturb the acid-base balance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Alkalosis
Acidosis
pH scale
6.8
7.0
7.35 7.45
7.8
8.0
Normal pH range
Copyright 2013 Dr. Mary Cat Flath
Survival range
52
Abnormalities in Acid-Base Balance
• 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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Accumulation
of acids
Loss of
bases
Increased concentration of H+
Acidosis
pH drops
pH scale
7.4
Alkalosis
pH rises
Decreased concentration of H+
Copyright 2013 Dr. Mary Cat Flath
Loss of
acids
Accumulation
of bases
53
Abnormalities in Acid-Base Balance
54
Health problems may lead to imbalances in acid-base
concentrations and fluid and electrolyte balance
Diabetes Mellitus
COPD
Kidney Disease
Vomiting
Diarrhea
Hormonal Imbalances
Copyright 2013 Dr. Mary Cat Flath
Abnormalities in Acid-Base Balance
55
RESPIRATORY IMBALANCES affect carbonic acid
concentrations = CARBON DIOXIDE – CO2
METABOLIC IMBALANCES affect
BICARBONATE ION CONCENTRATIONS – HCO3-
Copyright 2013 Dr. Mary Cat Flath
Abnormalities in Acid-Base Balance
56
During Abnormalities in Acid-Base Balance
THE RESPIRATORY AND
URINARY SYSTEMS ACT
TO COMPENSATE
Copyright 2013 Dr. Mary Cat Flath
Abnormalities in Acid-Base Balance
57
In the kidneys,
this involves the secretion and reabsorption of what ions???
If H+ is secreted,
then HCO3- is reabsorbed.
If HCO3- is secreted,
then H+ is reabsorbed.
Loss of 1 HCO3- is the same as gain of 1 H+ and vice versa
Copyright 2013 Dr. Mary Cat Flath
Abnormalities in Acid-Base Balance
58
Respiratory Acidosis
(↑H+ = ↓pH)
Respiratory Alkalosis
(↓H+ = ↑pH)
(increased H2CO3 )=↑CO2
(decreased H2CO3) = ↓CO2
Metabolic Acidosis
(↑H+ = ↓pH)
Metabolic Alkalosis
(↓H+ = ↑pH)
↓HCO3- (or increase in other
↑HCO3- (or loss of acids)
acids)
Copyright 2013 Dr. Mary Cat Flath
Respiratory Acidosis (pH< 7.35)
59
Increased H2CO3 leads to ↑CO2 causing ↑ H+ = ↓pH
Causes:
Hypoventilation
Caused by lung disease (asthma, CF, COPD),
anesthesia, drug overdose, atelectasis
Stimulates Respiratory Centers (including Dorsal Respiratory
Group) which leads to
increased ventilation and expiration of excess CO2
Compensation: Kidneys reabsorption of HCO3- and
kidneys secretion/excretion of excess H+
Copyright 2013 Dr. Mary Cat Flath
Respiratory Alkalosis (pH > 7.45)
60
↓ H2CO3 leads to ↓CO2 = ↑pH
Causes:
Hyperventilation possibly caused by anxiety, pulmonary
embolism, fear, or mechanical ventilation
causes respiratory center to decrease ventilation
Compensation:
Kidneys secretion/excretion of HCO3- OR
kidneys reabsorption of H+
Copyright 2013 Dr. Mary Cat Flath
Renal Control of Acid-Base Balance
61
Kidneys are only organ that can rid body of acids
(not just H+) generated by cellular metabolism.
HCO3- is key indicator of metabolic acidosis or
metabolic alkalosis.
Copyright 2013 Dr. Mary Cat Flath
Metabolic Acidosis (pH< 7.35)
62
Decreased pH and decreased HCO3Causes:
Diabetes Mellitus, severe diarrhea, renal failure, shock,
Accumulation of non-respiratory acids or excessive loss
of HCO3Ingestion of excessive alcohol
Starvation
Compensation:
kidneys secretion/excretion of H+ AND
reabsorption of HCO3- AND
increased CO2 release by lungs
Copyright 2013 Dr. Mary Cat Flath
Metabolic Alkalosis (pH > 7.45)
63
Increased pH and increased HCO3Causes:
Severe vomiting, diuretics, excessive base intake
Compensation:
kidneys secretion of HCO3- and
decreased respiration
Copyright 2013 Dr. Mary Cat Flath
Maintaining Metabolic Acid-Base Balance in Kidney
64
Reabsorption of HCO3- (by nephron)
OR
Secretion/excretion of HCO3- (by nephron)
Copyright 2013 Dr. Mary Cat Flath
Acidosis
• Two major types of acidosis are respiratory acidosis and
metabolic acidosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Kidney failure
to excrete acids
Excessive production of acidic
ketones as in diabetes mellitus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Decreased rate
and depth of
breathing
Obstruction of
air passages
Decreased
gas exchange
Accumulation of nonrespiratory acids
Metabolic acidosis
Accumulation of CO2
Excessive loss of bases
Respiratory
acidosis
Copyright 2013 Dr. Mary Cat Flath
Prolonged diarrhea
with loss of alkaline
intestinal secretions
Prolonged vomiting
with loss of intestinal
secretions
65
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
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• Anxiety
• Fever
• Poisoning
• High altitude
Gastric
drainage
Vomiting with loss
of gastric secretions
Hyperventilation
Loss of acids
Excessive loss of CO2
Decrease in concentration of H2CO3
Net increase in alkaline substances
Decrease in concentration of H+
Copyright 2013 Dr.
Mary Catalkalosis
Flath
Respiratory
Metabolic alkalosis
66
Abnormalities in Acid-Base Balance
Respiratory Acidosis
↓pH and↑CO2
Causes: Hypoventilation (lung
disease, anesthesia, drug
overdose, atelectasis)
Respiratory Centers (Dorsal)
↑ ventilation and expiration of
excess CO2
Respiratory Alkalosis
↑pH and↓CO2
67
Causes: Hyperventilation
(anxiety, PE, fear, poisoning, high
altitudes, mechanical ventilation)
Respiratory Centers ↓ventilation
Metabolic Acidosis
Metabolic Alkalosis
↓pH and ↓HCO3-
↑pH and ↑HCO3-
Causes: diabetes mellitus,
severe diarrhea, renal failure,
shock
Kidneys reabsorb HCO3- and
secrete H+ and respiration rate
is increased
Copyright 2013 Dr. Mary Cat Flath
Causes: Severe vomiting,
diuretics, excessive base intake
Kidneys secrete HCO3- and
reabsorb H+ and respiration rate
is decreased
Abnormalities in Acid-Base Balance
Respiratory Acidosis
Metabolic Acidosis
Copyright 2013 Dr. Mary Cat Flath
Respiratory Alkalosis
↑
68
Metabolic Alkalosis
Abnormalities in Acid-Base Balance
Respiratory Acidosis
↓pH and↑CO2
Causes: Hypoventilation (lung
disease, anesthesia, drug
overdose, atelectasis)
Respiratory Centers (Dorsal)
↑ ventilation and expiration of
excess CO2
Respiratory Alkalosis
↑pH and↓CO2
69
Causes: Hyperventilation
(anxiety, PE, fear, poisoning, high
altitudes, mechanical ventilation)
Respiratory Centers ↓ventilation
Metabolic Acidosis
Metabolic Alkalosis
↓pH and ↓HCO3-
↑pH and ↑HCO3-
Causes: diabetes mellitus,
severe diarrhea, renal failure,
shock
Kidneys reabsorb HCO3- and
secrete H+ and respiration rate
is increased
Copyright 2013 Dr. Mary Cat Flath
Causes: Severe vomiting,
diuretics, excessive base intake
Kidneys secrete HCO3- and
reabsorb H+ and respiration rate
is decreased
Chapter 21- Water, Electrolyte, and
Acid-Base Balance
70
 Review of Inorganic Substances from
Chap 2
 Introduction
 Distribution of Body Fluids
 Water Balance
 Electrolyte Balance
 Acid-Base Balance
 Acid-Base Imbalances
Copyright 2013 Dr. Mary Cat Flath