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NURS1004 Week 7 Lecture
Fluid, Electrolyte Balance
Lecture is in three parts.
Prepared by Didy Button
© 2012 Pearson Education, Inc.
An Introduction to the Chemical Level of
Organization
• Chemistry
• Is the science of change
• The structure of atoms
• The basic chemical building blocks
• How atoms combine to form increasingly complex
structures
© 2012 Pearson Education, Inc.
2-1 Atoms and Atomic Structure
• Matter
• Is made up of atoms
• Atoms join together to form chemicals with different
characteristics
• Chemical characteristics determine physiology at the
molecular and cellular levels
© 2012 Pearson Education, Inc.
2-1 Atoms and Atomic Structure
• Subatomic Particles
• Proton
• Positive charge, 1 mass unit
• Neutron
• Neutral, 1 mass unit
• Electron
• Negative charge, low mass
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2-1 Atoms and Atomic Structure
• Atomic Structure
• Atomic number
• Number of protons
• Nucleus
• Contains protons and neutrons
• Electron cloud
• Contains electrons
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Figure 2-1 The Structure of Hydrogen Atoms
Electron shell
Hydrogen-1
mass number: 1
A typical hydrogen
nucleus contains a
proton and no neutrons.
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Hydrogen-2,
deuterium
Hydrogen-3,
tritium
mass number: 2
mass number: 3
A deuterium (2H)
nucleus contains a
proton and a neutron.
A tritium (3H) nucleus
contains a pair of
neutrons in addition
to the proton.
Table 2-1 Principal Elements in the Human Body
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Table 2-1 Principal Elements in the Human Body
© 2012 Pearson Education, Inc.
2-1 Atoms and Atomic Structure
• Elements and Isotopes
• Elements are determined by the atomic number of an
atom
• Remember atomic number = number of protons
• Elements are the most basic chemicals
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2-1 Atoms and Atomic Structure
• Elements and Isotopes
• Isotopes are the specific version of an element based
on its mass number
• Mass number = number of protons plus the number of
neutrons
• Only neutrons are different because the number of
protons determines the element
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2-1 Atoms and Atomic Structure
• Atomic Weights
• Exact mass of all particles
• Measured in moles
• Average of the mass numbers of the isotopes
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2-1 Atoms and Atomic Structure
• Electrons and Energy Levels
• Electrons in the electron cloud determine the reactivity of an
atom
• The electron cloud contains shells, or energy levels that hold a
maximum number of electrons
• Lower shells fill first
• Outermost shell is the valence shell, and it determines
bonding
• The number of electrons per shell corresponds to the number
of atoms in that row of the periodic table
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Figure 2-2 The Arrangement of Electrons into Energy Levels
The first energy level
can hold a maximum of
two electrons.
Hydrogen, H
Atomic number: 1
Mass number: 1
1 electron
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Helium, He
Atomic number: 2
Mass number: 4
(2 protons + 2 neutrons)
2 electrons
Figure 2-2 The Arrangement of Electrons into Energy Levels
The second and third
energy levels can
each contain up to 8
electrons.
Lithium, Li
Atomic number: 3
Mass number: 6
(3 protons + 3 neutrons)
3 electrons
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Neon, Ne
Atomic number: 10
Mass number: 20
(10 protons + 10 neutrons)
10 electrons
2-2 Molecules and Compounds
•
Chemical Bonds
•
Involve the sharing, gaining, and losing of electrons in the
valence shell
•
Three major types of chemical bonds
1. Ionic bonds
•
Attraction between cations (electron donor) and anions
(electron acceptor)
2. Covalent bonds
•
Strong electron bonds involving shared electrons
3. Hydrogen bonds
•
Weak polar bonds based on partial electrical attractions
© 2012 Pearson Education, Inc.
2-2 Molecules and Compounds
• Chemical Bonds
• Form molecules and/or compounds
• Molecules
• Two or more atoms joined by strong bonds
• Compounds
• Two or more atoms OF DIFFERENT ELEMENTS
joined by strong or weak bonds
• Compounds are all molecules, but not all molecules are
compounds
• H2 = molecule only
© 2012 Pearson Education, Inc.
H2O = molecule and compound
2-2 Molecules and Compounds
• Ionic Bonds
• One atom—the electron donor—loses one or more
electrons and becomes a cation, with a positive
charge
• Another atom—the electron acceptor—gains those
same electrons and becomes an anion, with a
negative charge
• Attraction between the opposite charges then draws
the two ions together
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Figure 2-3a The Formation of Ionic Bonds
Attraction between
opposite charges
Formation of ions
Sodium atom
Formation of an
ionic compound
Sodium ion (Na+)
Sodium chloride (NaCl)
Chlorine atom
Chloride ion (Cl−)
1 A sodium (Na) atom loses an
electron, which is accepted by a chlorine (Cl) atom. 2 Because the
sodium (Na+) and chloride (Cl−) ions have opposite charges, they are
attracted to one another. 3 The association of sodium and chloride
ions forms the ionic compound sodium chloride.
Formation of an ionic bond.
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Figure 2-3b The Formation of Ionic Bonds
Chloride ions
(Cl−)
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Sodium ions
(Na+)
Sodium chloride
crystal. Large
numbers of sodium and
chloride ions form a
crystal of sodium
chloride (table salt).
2-2 Molecules and Compounds
• Covalent Bonds
• Involve the sharing of pairs of electrons between
atoms
• One electron is donated by each atom to make the pair
of electrons
• Sharing one pair of electrons is a single covalent
bond
• Sharing two pairs of electrons is a double covalent
bond
• Sharing three pairs of electrons is a triple covalent
bond
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Figure 2-4 Covalent Bonds in Four Common Molecules
Molecule
Electron Shell Model and
Structural Formula
Hydrogen
(H2)
H−H
Oxygen
(O2)
O=O
Carbon
dioxide
(CO2)
Nitric
oxide
(NO)
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O=C=O
N=O
2-2 Molecules and Compounds
• Covalent Bonds
• Nonpolar covalent bonds
• Involve equal sharing of electrons because atoms
involved in the bond have equal pull for the electrons
• Polar covalent bonds
• Involve the unequal sharing of electrons because one
of the atoms involved in the bond has a
disproportionately strong pull on the electrons
• Form polar molecules — like water
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Figure 2-5 Polar Covalent Bonds and the Structure of Water
Hydrogen
atom
Hydrogen
atom
Oxygen atom
δ+
Hydrogen
atom
Oxygen
atom
2δ−
© 2012 Pearson Education, Inc.
δ+
2-2 Molecules and Compounds
• Hydrogen Bonds
• Bonds between adjacent molecules, not atoms
• Involve slightly positive and slightly negative portions
of polar molecules being attracted to one another
• Hydrogen bonds between H2O molecules cause
surface tension
© 2012 Pearson Education, Inc.
Figure 2-6 Hydrogen Bonds between Water Molecules
δ+
δ+
2δ−
2δ−
δ+
δ+
2δ−
δ+
δ+
δ+
2δ−
δ+
2δ−
δ+
δ+
δ+
2δ−
KEY
Hydrogen
Oxygen
Hydrogen bond
© 2012 Pearson Education, Inc.
2δ−
2-2 Molecules and Compounds
• Molecular Weights
• The molecular weight of a molecule is the sum of
the atomic weights of its component atoms
• H = approximately 1
• O = approximately 16
• H2 = approximately 2
• H2O = approximately 18
© 2012 Pearson Education, Inc.
2-2 Molecules and Compounds
• States of Matter
• Solid
• Constant volume and shape
• Liquid
• Constant volume but changes shape
• Gas
• Changes volume and shape
END of Part I ( there are 3 Parts this week)
© 2012 Pearson Education, Inc.
NURS1004 Week 7 Lecture
Fluid, Electrolyte Balance
Part II.
Prepared by Didy Button
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• Fluid in the Body
• Water accounts for roughly:
• 60% of male body weight
• 50% of female body weight
• Mostly in intracellular fluid
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2-6 Properties of Water
• Water
• Accounts for up to two-thirds of your total body weight
• A solution is a uniform mixture of two or more
substances
• It consists of a solvent, or medium, in which atoms,
ions, or molecules of another substance, called a
solute, are individually dispersed
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2-6 Properties of Water
• Solubility
• Water’s ability to dissolve a solute in a solvent to
make a solution
• Reactivity
• Most body chemistry occurs in water
• High Heat Capacity
• Water’s ability to absorb and retain heat
• Lubrication
• To moisten and reduce friction
© 2012 Pearson Education, Inc.
2-6 Properties of Water
• The Properties of Aqueous Solutions
• Ions and polar compounds undergo ionization, or
dissociation in water
• Polar water molecules form hydration spheres around
ions and small polar molecules to keep them in
solution
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Figure 2-9 The Activities of Water Molecules in Aqueous Solutions
Hydration
spheres
Negative
pole
H
Cl−
Positive
pole
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Na+
Glucose
molecule
Figure 2-9a The Activities of Water Molecules in Aqueous Solutions
Negative
pole
H
Positive
pole
Water molecule. In a
water molecule, oxygen
forms polar covalent
bonds with two
hydrogen atoms.
Because both hydrogen
atoms are at one end of
the molecule, it has an
uneven distribution of
charges, creating
positive and negative
poles.
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Figure 2-9b The Activities of Water Molecules in Aqueous Solutions
Hydration
spheres
Cl−
Na+
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Sodium chloride in
solution. Ionic compounds,
such as sodium chloride,
dissociate in water as the
polar water molecules break
the ionic bonds in the large
crystal structure. Each ion in
solution is surrounded by
water molecules, creating
hydration spheres.
Figure 2-9c The Activities of Water Molecules in Aqueous Solutions
Glucose
molecule
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Glucose in solution.
Hydration spheres also
form around an organic
molecule containing
polar covalent bonds. If
the molecule binds
water strongly, as does
glucose, it will be
carried into solution—in
other words, it will
dissolve. Note that the
molecule does not
dissociate, as occurs
for ionic compounds.
Table 2-2 Important Electrolytes that Dissociate in Body Fluids
© 2012 Pearson Education, Inc.
2-6 Properties of Water
• The Properties of Aqueous Solutions
• Electrolytes and body fluids
• Electrolytes are inorganic ions that conduct electricity
in solution
• Electrolyte imbalance seriously disturbs vital body
functions
© 2012 Pearson Education, Inc.
2-6 Properties of Water
• The Properties of Aqueous Solutions
• Hydrophilic and hydrophobic compounds
• Hydrophilic
• hydro- = water, philos = loving
• Interacts with water
• Includes ions and polar molecules
• Hydrophobic
• phobos = fear
• Does NOT interact with water
• Includes nonpolar molecules, fats, and oils
© 2012 Pearson Education, Inc.
2-6 Properties of Water
• Colloids and Suspensions
• Colloid
• A solution of very large organic molecules
• For example, blood plasma
• Suspension
• A solution in which particles settle (sediment)
• For example, whole blood
• Concentration
• The amount of solute in a solvent (mol/L, mg/mL)
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Roles for water in the body:
1. Temperature control (perspiration).
2. Transport of nutrients & wastes (blood,
interstitial fluid, urine, lymph, CSF).
3. Hydrolysis of food components in the gut
during digestion, eg:
C12H22O11 + H2O  C6H12O6 + C6H12O6
sucrose + water  glucose + fructose
4. Maintain blood volume (& therefore BP)
© 2012 Pearson Education, Inc.
Water intakes and losses
Intake:
• Food consumed provides ~ 48% of our water
• Liquids drunk provide ~ 40%
• Produced by metabolism ~ 12%
(catabolism of glucose, fatty acids & building
proteins from amino acids)
Losses:
• 43% in urine, 7% in faeces,
• 33% evaporated from skin
• 17% evaporated from lungs
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• Fluid in the Body
• Water accounts for roughly:
• 60% of male body weight
• 50% of female body weight
• Mostly in intracellular fluid
© 2012 Pearson Education, Inc.
An Introduction to Fluid, Electrolyte, and Acid–
Base Balance
• Water
• Is 99% of fluid outside cells (extracellular fluid)
• Is an essential ingredient of cytosol (intracellular fluid)
• All cellular operations rely on water
• As a diffusion medium for gases, nutrients, and waste
products
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27-1 Fluid, Electrolyte, and Acid–Base Balance
• The Body
• Must maintain normal volume and composition of:
• Extracellular fluid (ECF)
• Intracellular fluid (ICF)
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Fluid compartments in the body
Intra cellular fluid (ICF)
Extra cellular fluid (ECF)
The concentrations of solutes in the fluid within
cells (ICF) is very different to the fluid that is
outside cells (ECF)
Electrolyte
ICF (mmol/L)
ECF (mmol/L)
K
160
4
Na
10
140
SO
40
5
Cl
4
100
Protein
1.5
0.5
© 2012 Pearson Education, Inc.
Figure 27-3 Fluid Gains and Losses
Water absorbed across
digestive epithelium
(2000 mL)
Water vapor lost
in respiration and
evaporation from
moist surfaces
(1150 mL)
ICF
Metabolic
water
(300 mL)
ECF
Water lost in
faeces (150 mL)
Water secreted
by sweat glands
(variable)
Plasma membranes
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Water lost in urine
(1000 mL)
27-1 Fluid, Electrolyte, and Acid–Base Balance
Compartments % of body water
ECF
• Vascular 7 %
• Interstitial 18% ECF
• Connective tissue fluid 10 %
ICF
• Intra-cellular fluid (ICF) 63 %
• Trans-cellular 2%
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• Major Subdivisions of ECF
• Interstitial fluid of peripheral tissues
• Plasma of circulating blood
• Minor Subdivisions of ECF
• Lymph, perilymph, and endolymph
• Cerebrospinal fluid (CSF)
• Synovial fluid
• Serous fluids (pleural, pericardial, and peritoneal)
• Aqueous humor
© 2012 Pearson Education, Inc.
27-1 Fluid, Electrolyte, and Acid–Base Balance
•
Fluid Balance
• Is a daily balance between:
• Amount of water gained
• Amount of water lost to environment
• Involves regulating content and distribution of body
water in ECF and ICF
• The Digestive System
• Is the primary source of water gains
• Plus a small amount from metabolic activity
• The Urinary System
• Is the primary route of water loss
© 2012 Pearson Education, Inc.
27-1 Fluid, Electrolyte, and Acid–Base Balance
•
Electrolyte Balance
• Electrolytes are ionic substances (Na+, K+, Ca2+,
Mg2+, Cl-, HCO3 -) or substances which form ions
when they dissolve.
• Electrolytes are ions released through dissociation of
inorganic compounds
• Can conduct electrical current in solution
• Electrolyte balance
• When the gains and losses of all electrolytes are equal
• Primarily involves balancing rates of absorption across
digestive tract with rates of loss at kidneys and sweat
glands
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27-2 Fluid Compartments
• Exchange among Subdivisions of ECF
• Occurs primarily across endothelial lining of
capillaries
• From interstitial spaces to plasma
• Through lymphatic vessels that drain into the venous
system
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Figure 27-1a The Composition of the Human Body
SOLID COMPONENTS
(31.5 kg; 69.3 lbs)
Kg
Proteins
Lipids
Minerals
Carbohydrates Miscellaneous
The body composition (by weight, averaged for both
sexes) and major body fluid compartments of a 70-kg
individual.
© 2012 Pearson Education, Inc.
Figure 27-1a The Composition of the Human Body
WATER (38.5 kg; 84.7 lbs)
Other
Plasma
Liters
Interstitial
fluid
Intracellular fluid
Extracellular fluid
The body composition (by weight, averaged
for both sexes) and major body fluid
compartments of a 70-kg individual.
© 2012 Pearson Education, Inc.
Figure 27-1b The Composition of the Human Body
WATER 60%
ICF
ECF
Intracellular
fluid 33%
Interstitial
fluid 21.5%
Plasma 4.5%
Solids 40%
(organic and inorganic materials)
Other
body
fluids
(≤1%)
SOLIDS 40%
Adult males
A comparison of the body compositions of adult
males and females, ages 18–40 years.
© 2012 Pearson Education, Inc.
Figure 27-1b The Composition of the Human Body
WATER 50%
ECF
ICF
Intracellular
fluid 27%
Interstitial
fluid 18%
Plasma 4.5%
Solids 50%
(organic and inorganic materials)
Other
body
fluids
(≤1%)
SOLIDS 50%
Adult females
© 2012 Pearson Education, Inc.
A comparison of the body compositions of adult
males and females, ages 18–40 years.
27-2 Fluid Compartments
• Membrane Functions
• Plasma membranes are selectively permeable
• Ions enter or leave via specific membrane
channels
• Carrier mechanisms move specific ions in or out of
cell
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27-2 Fluid Compartments
• The Osmotic Concentration of ICF and ECF
• Is identical
• Osmosis eliminates minor differences in
concentration
• Because plasma membranes are permeable to water
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• Basic Concepts in the Regulation of Fluids and
Electrolytes
1. All homeostatic mechanisms that monitor and adjust
body fluid composition respond to changes in the
ECF, not in the ICF
2. No receptors directly monitor fluid or electrolyte
balance
3. Cells cannot move water molecules by active
transport
4. The body’s water or electrolyte content will rise if
dietary gains exceed environmental losses, and will
fall if losses exceed gains
END of Part II
© 2012 Pearson Education, Inc.
NURS1004 Week 7 Lecture part III
Prepared by
Didy Button
Berman et al. 2012 Kozier & Erb’s
Fundamentals of Nursing
2nd Australian ed. p 1624.
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• An Overview of the Primary Regulatory
Hormones
• Affecting fluid and electrolyte balance
1. Antidiuretic hormone
2. Aldosterone
3. Natriuretic peptides
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• Antidiuretic Hormone (ADH)
• Stimulates water conservation at kidneys
• Reducing urinary water loss
• Concentrating urine
• Stimulates thirst center
• Promoting fluid intake
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• ADH Production
• Osmoreceptors in hypothalamus
• Monitor osmotic concentration of ECF
• Change in osmotic concentration
• Alters osmoreceptor activity
• Osmoreceptor neurons secrete ADH
© 2012 Pearson Education, Inc.
27-2 Fluid Compartments
• ADH Release
• Axons of neurons in anterior hypothalamus
• Release ADH near fenestrated capillaries
• In neurohypophysis (posterior lobe of pituitary gland)
• Rate of release varies with osmotic concentration
• Higher osmotic concentration increases ADH release
© 2012 Pearson Education, Inc.
27-3 Fluid Movement
• Movement of Water and Electrolytes
• When the body loses water:
• Plasma volume decreases
• Electrolyte concentrations rise
• When the body loses electrolytes:
• Water is lost by osmosis
• Regulatory mechanisms are different
© 2012 Pearson Education, Inc.
Figure 27-3 Fluid Gains and Losses
Water absorbed across
digestive epithelium
(2000 mL)
Water vapor lost
in respiration and
evaporation from
moist surfaces
(1150 mL)
ICF
Metabolic
water
(300 mL)
ECF
Water lost in
feces (150 mL)
Water secreted
by sweat glands
(variable)
Plasma membranes
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Water lost in urine
(1000 mL)
Table 27-1 Water Balance
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27-3 Fluid Movement
• Allocation of Water Losses
• Dehydration (Water Depletion)
• Develops when water loss is greater than gain
• If water is lost, but electrolytes retained:
• ECF osmotic concentration rises
• Water moves from ICF to ECF
• Net change in ECF is small
© 2012 Pearson Education, Inc.
27-3 Fluid Movement
• Severe Water Loss
• Causes:
• Excessive perspiration
• Inadequate water consumption
• Repeated vomiting
• Diarrhea
• Homeostatic responses
• Physiologic mechanisms (ADH and renin secretion)
• Behavioral changes (increasing fluid intake)
© 2012 Pearson Education, Inc.
Figure 27-4 Fluid Shifts between the ICF and ECF
Intracellular
fluid (ICF)
Extracellular
fluid (ECF)
The ECF and
ICF are in
balance, with
the two
solutions
isotonic.
Decreased ECF volume Water loss from
ECF reduces
volume and
makes this
solution
hypertonic with
respect to the ICF.
Decreased ICF volume
© 2012 Pearson Education, Inc.
Increased
ECF volume
An osmotic water
shift from the ICF
into the ECF
restores osmotic
equilibrium but
reduces the ICF
volume.
27-4 Electrolyte Balance
• Electrolyte Balance
• Requires rates of gain and loss of each electrolyte in
the body to be equal
• Electrolyte concentration directly affects water balance
• Concentrations of individual electrolytes affect cell
functions
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Sodium
• Is the dominant cation in ECF
• Sodium salts provide 90% of ECF osmotic
concentration
• Sodium chloride (NaCl)
• Sodium bicarbonate (NaHCO3)
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Normal Sodium Concentrations
• In ECF
• About 140 mEq/L
• In ICF
• Is 10 mEq/L or less
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Potassium
• Is the dominant cation in ICF
• Normal potassium concentrations
• In ICF
• About 160 mEq/L
• In ECF
• 3.5–5.5 mEq/L
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Rules of Electrolyte Balance
1. Most common problems with electrolyte balance are
caused by imbalance between gains and losses of
sodium ions
2. Problems with potassium balance are less common,
but more dangerous than sodium imbalance
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Sodium Balance
• Total amount of sodium in ECF represents a
balance between two factors
1. Sodium ion uptake across digestive epithelium
2. Sodium ion excretion in urine and perspiration
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Large Changes in ECF Volume
• Are corrected by homeostatic mechanisms that
regulate blood volume and pressure
• If ECF volume rises, blood volume goes up
• If ECF volume drops, blood volume goes down
© 2012 Pearson Education, Inc.
Figure 27-5 The Homeostatic Regulation of Normal Sodium Ion Concentrations in Body Fluids
ADH Secretion Increases
Recall of Fluids
The secretion of ADH
restricts water loss and
stimulates thirst, promoting
additional water
consumption.
Because the ECF
osmolarity increases,
water shifts out of
the ICF, increasing
ECF volume and
lowering Na+
concentrations.
Osmoreceptors
in hypothalamus
stimulated
HOMEOSTASIS
RESTORED
HOMEOSTASIS
DISTURBED
Decreased Na+
levels in ECF
Na+
Increased
levels in ECF
HOMEOSTASIS
Normal Na+
concentration
in ECF
© 2012 Pearson Education, Inc.
Start
Figure 27-5 The Homeostatic Regulation of Normal Sodium Ion Concentrations in Body Fluids
HOMEOSTASIS
HOMEOSTASIS
DISTURBED
Normal Na+
concentration
in ECF
Start
HOMEOSTASIS
RESTORED
Decreased Na+
levels in ECF
Osmoreceptors
in hypothalamus
inhibited
Increased Na+
levels in ECF
Water loss reduces
ECF volume,
concentrates ions
ADH Secretion Decreases
As soon as the osmotic
concentration of the ECF
drops by 2 percent or more,
ADH secretion decreases, so
thirst is suppressed and
water losses at the kidneys
increase.
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Homeostatic Mechanisms
• A rise in blood volume elevates blood pressure
• A drop in blood volume lowers blood pressure
• Monitor ECF volume indirectly by monitoring blood
pressure
• Baroreceptors at carotid sinus, aortic sinus, and right
atrium
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Hyponatremia
• Body water content rises (overhydration)
• ECF Na+ concentration <136 mEq/L
• Hypernatremia
• Body water content declines (dehydration)
• ECF Na+ concentration >145 mEq/L
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
•
•
Potassium Balance
•
98% of potassium in the human body is in ICF
•
Cells expend energy to recover potassium ions
diffused from cytoplasm into ECF
Processes of Potassium Balance
1. Rate of gain across digestive epithelium
2. Rate of loss into urine
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Potassium Loss in Urine
• Is regulated by activities of ion pumps
• Along distal portions of nephron and collecting system
• Na+ from tubular fluid is exchanged for K+ in peritubular
fluid
• Are limited to amount gained by absorption across
digestive epithelium (about 50–150 mEq or 1.9–5.8
g/day)
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Factors in Tubular Secretion of K+
1. Changes in K+ concentration of ECF
2. Changes in pH
3. Aldosterone levels
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Changes in Concentration of K + in ECF
• Higher ECF concentration increases rate of
secretion
• Changes in pH
• Low ECF pH lowers peritubular fluid pH
• H+ rather than K+ is exchanged for Na+ in tubular
fluid
• Rate of potassium secretion declines
© 2012 Pearson Education, Inc.
27-4 Electrolyte Balance
• Aldosterone Levels
• Affect K+ loss in urine
• Ion pumps reabsorb Na+ from filtrate in exchange
for K+ from peritubular fluid
• High K+ plasma concentrations stimulate
aldosterone
© 2012 Pearson Education, Inc.
27-7 Age and Fluid, Electrolyte Balance
• Aging and Fluid Balance
• Body water content, ages 40–60
• Males 55%
• Females 47%
• After age 60
• Males 50%
• Females 45%
© 2012 Pearson Education, Inc.
27-7 Age and Fluid, Electrolyte Balance
• Aging and Fluid Balance
• Decreased body water content reduces dilution of
waste products, toxins, and drugs
• Reduction in glomerular filtration rate and number of
functional nephrons
• Reduces pH regulation by renal compensation
• Ability to concentrate urine declines
• More water is lost in urine
• Insensible perspiration increases as skin becomes
thinner
© 2012 Pearson Education, Inc.
27-7 Age and Fluid, Electrolyte Balance
• Aging and Fluid Balance
• Maintaining fluid balance requires higher daily water
intake
• Reduction in ADH and aldosterone sensitivity
• Reduces body water conservation when losses exceed
gains
• Muscle mass and skeletal mass decrease
• Cause net loss in body mineral content
Last Slide.
© 2012 Pearson Education, Inc.