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ADVANCED PHYSIOLOGYADVANCED PHYSIOLOGY
FLUID & FLUID & ELECTROLYTESELECTROLYTES
Part 1Part 1
Instructor Terry WisethInstructor Terry Wiseth
NORTHLAND COLLEGENORTHLAND COLLEGE
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FLUID ELECTROLYTE FLUID ELECTROLYTE HOMEOSTASISHOMEOSTASIS
In a healthy individual fluid volume and electrolyte concentrations are maintained within strict homeostatic limits through the interaction of several organ systems
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FLUID ELECTROLYTE FLUID ELECTROLYTE HOMEOSTASISHOMEOSTASIS
Total body water (TBW) can be divided by cell membranes into two main compartments:1) Extracellular fluid (ECF)1) Extracellular fluid (ECF)
fluid outside cells1/3 of total body water
2) Intracellular fluid (ICF)2) Intracellular fluid (ICF)fluid inside cells2/3 of total body water
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FLUID ELECTROLYTE FLUID ELECTROLYTE HOMEOSTASISHOMEOSTASISThe ECFECF is further divided into:
1) Blood plasma (80%)1) Blood plasma (80%)2) Interstitial fluid (20%)2) Interstitial fluid (20%)
These two ECF compartments are separated by a capillary membrane
Interstitial fluid
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FLUID COMPARTMENTSFLUID COMPARTMENTS
Effectively there are three compartments
1) Intracellular1) Intracellular2) Interstitial2) Interstitial3) Plasma3) Plasma
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FLUID COMPARTMENTSFLUID COMPARTMENTS
CYTOPLASMCYTOPLASM
INTERSTITIALINTERSTITIALFLUIDFLUID
PLASMAPLASMA(Intracellular)(Intracellular)
(Extracellular)(Extracellular)
CapillaryCapillary
CellCell
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ELECTROLYTESELECTROLYTESDissolved ions in the:
Cell, interstitial fluid, bloodPotassium (K)Sodium (Na)Calcium (Ca)Magnesium (Mg)Chlorine (Cl)Bicarbonate (H2CO3) Proteins (Pr)
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ELECTROLYTESELECTROLYTESThere are three key concepts in
consideration of fluid and electrolyte management:1) Cell Membrane Permeability1) Cell Membrane Permeability2) Osmolarity2) Osmolarity3) Electroneutrality3) Electroneutrality
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CELL MEMBRANE CELL MEMBRANE PERMEABILITYPERMEABILITY
Refers to the ability of a cell membrane to allow certain substances to pass freely
Other substances like charged ions (NaNa++) cannot cross the membrane and are trapped on one side of it
H2O
Na+
Na+
H2O
Na+
Na+
Na+
H2O
H2O
H2O
H2O
H2O
H2O
Na+
Na+
Na+
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CELL MEMBRANE CELL MEMBRANE PERMEABILITYPERMEABILITY
In other words“No Trespassing”Cell membranes allow some things to
pass and blocks passage of others
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OSMOLARITYOSMOLARITYOsmolarityOsmolarity is a property of
particles in solutionIf a substance
can dissociate insolution, it willcontribute to theosmolarity of thesolution
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OSMOLARITYOSMOLARITYIn other wordsIn other words
“Water, water every where but not a drop to drink”
If you are thirsty, you cannot drink salt water
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ELECTRONEUTRALITYELECTRONEUTRALITYThe principle of ElectroneutralityElectroneutrality
means that the overall number of positive and negative charges balances
For instance, in conditions like renal tubular acidosis where HCO3
- is lost, chloride is retained
Cl-
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ELECTRONEUTRALITYELECTRONEUTRALITYIn other words
“Cells do not make good batteries”
Positive and negative charges inside and outside the cell must be equal
+-+-+-+-
+-+-+-+-
-
+
Click to show a charged battery
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ELECTROLYTESELECTROLYTESWhen the body is in “fluid
balance” it means that the various body compartments (cells, tissues, organs) contain the required amount of fluids to carry out normal bodily functions
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ELECTROLYTESELECTROLYTESFluid balance and electrolyte
balance are inseparableIn a healthy individual, the
volume of fluid in each compartment remains stable
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ELECTROLYTESELECTROLYTESLoss of electrolytes can have
serious consequences for the body
In severe dehydration, the loss of electrolytes can result in circulatory problems such as tachycardia (rapid heart beat) and problems with the nervous systemsuch as loss ofconsciousnessand shock
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ELECTROLYTESELECTROLYTESElectrolytes serve three
general functions to maintain:1) Normal metabolism1) Normal metabolism2) Proper fluid movement 2) Proper fluid movement
between compartmentsbetween compartments3) The acid-base balance3) The acid-base balance
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ELECTROLYTE COMPOSITION OF ELECTROLYTE COMPOSITION OF PLASMA AND INTERSTITIAL PLASMA AND INTERSTITIAL
FLUIDFLUID
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ELECTROLYTESELECTROLYTES
0 50 100 150 200
Na+
K+
Ca++
Mg++
Cl-
HCO3-
Protein
INTERSTITIALFLUIDPLASMA
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IONS AND MOLECULESIONS AND MOLECULES
IonsIons are charged atoms
ex: Na+, Cl-, Mg++
MoleculesMolecules are formed when two or more atoms or ions are combined
ex: H2O, C6H12O6, NaCl
Na+ Cl-
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MOVEMENT OF BODY MOVEMENT OF BODY FLUIDSFLUIDSFluid moves between the
compartments of the body through various mechanisms
Substances leave and enter capillaries via three mechanisms:1) Vesicular transport1) Vesicular transport2) Diffusion2) Diffusion3) Bulk flow3) Bulk flow
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VESICULAR TRANSPORT AND VESICULAR TRANSPORT AND DIFFUSIONDIFFUSION
Vesicular transport and diffusion are associated with the movement of solutessolutes (electrolytes)(electrolytes)
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BULK FLOWBULK FLOWBulk flow is the most important
process for the maintenance of relative volumesvolumes (fluids) (fluids) of blood and interstitial fluidBulk flow involves the
movement of both solvent (fluids) and solute into the interstitial space
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MOVEMENT OF IONS AND MOVEMENT OF IONS AND MOLECULESMOLECULES
Ions and molecules pass through membranes by:Simple DiffusionPassage through channelsFacilitated DiffusionActive Transport (Na-K pum
p)
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FLUID COMPARTMENTSFLUID COMPARTMENTSDescribes the distribution of water
in the bodyFluid compartments are separated
by semipermeable membranessemipermeable membranesCapillary wall separates the plasma and the interstitial fluid
Cell membrane separates the cytoplasm and interstitial fluid
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FLUID COMPARTMENTSFLUID COMPARTMENTS
CAPILLARY WALLCAPILLARY WALL
CELL MEMBRANECELL MEMBRANEINTERSTITIALINTERSTITIAL
FLUIDFLUID
PLASMAPLASMA
CYTOPLASMCYTOPLASM
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FLUID SHIFTSFLUID SHIFTS
Accumulations of fluids in a tissue or in a body cavity is called third space third space compartmentcompartmentEx: liver diseaseliver disease may lead to
significant accumulations of fluid in the peritoneal cavityRepresents a fluid loss as it is trapped
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FACTORS CONTROLLING FACTORS CONTROLLING EXCHANGES OF FLUIDSEXCHANGES OF FLUIDS
1) Diffusion1) Diffusion
2) Filtration2) Filtration
a) Hydrostatic Pressure a) Hydrostatic Pressure
b) Osmotic (Oncotic) b) Osmotic (Oncotic) PressurePressure
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DIFFUSIONDIFFUSIONWater, small molecules and
ionsMovement of molecules from
areas of higher concentration to areas of lower concentration
Click to View Animation
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FILTRATIONFILTRATIONNet flow of water is due to overall
effect of pressure on both sides of a membrane
Fluid is filtered out of capillaries in response to changes in:
1) Hydrostatic Pressures1) Hydrostatic Pressures2) Oncotic (Osmotic) Pressures2) Oncotic (Osmotic) Pressures
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HYDROSTATIC PRESSURE HYDROSTATIC PRESSURE (HP)(HP)
Fluid pressureEx: blood pressure in the capillariesEx: blood pressure in the capillaries
H2O H2O H2O H2OH2OH2OH2OH2O
H2O H2O
H2O H2O
8
4
6
6
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HYDROSTATIC PRESSURE HYDROSTATIC PRESSURE (HP)(HP)
Fluid pressureEx: blood pressure in the capillariesEx: pressure exerted by interstitial Ex: pressure exerted by interstitial
fluidfluid
H2OH2O
H2O
H2OH2O
H2O
H2OH2O
H2O H2O
H2O H2O
8
4
6
6
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HYDROSTATIC PRESSURE IN PLASMAHYDROSTATIC PRESSURE IN PLASMABlood Pressure at ArterialArterial end
of capillaries is 30 mm Hg30 mm HgBlood Pressure at VenousVenous end
of capillaries is 10 mm Hg10 mm HgDifference in pressure forces
fluid out of plasma to the interstitial fluid
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HYDROSTATIC PRESSURE IN HYDROSTATIC PRESSURE IN PLASMAPLASMA
Art
eri
ole
sid
e
Ven
ule
sid
e
H2O H2O H2O H2O
H2O H2O H2O H2O
Osmotic Pressure
Hydrostatic Pressure
Osmotic Pressure
Net Pressure on Fluids
NetPressur
eon
Fluids
Click to View
Osmotic Pressure
Click to View
Hydrostatic Pressure
Click toView Net
Pressure
on Fluids
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HYDROSTATIC PRESSURE INHYDROSTATIC PRESSURE ININTERSTITIAL FLUIDINTERSTITIAL FLUIDThe lymphatic system drains
interstitial fluid creating a negative interstitial pressure
Hydrostatic pressure in interstitial space is -- 6 mm Hg 6 mm HgSupplies a pulling force (suction)
drawing fluid out of the capillaries
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OSMOTIC (ONCOTIC) OSMOTIC (ONCOTIC) PRESSUREPRESSURE
Drawing force resulting from the pressure created by presence of protein dissolved in the:CytoplasmPlasmaInterstitial fluid
Pressure which develops when there is net movement of water across a membrane (osmosis)(osmosis)
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OSMOTIC (ONCOTIC) OSMOTIC (ONCOTIC) PRESSUREPRESSURE
Pressure created is directly proportional to solute concentrationThus osmotic pressure is
dependent on the concentration of urea, glucose, amino acids, electrolytes and proteins
Oncotic pressureOncotic pressure definespressures which are the resultof protein concentration differences
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OSMOTIC (ONCOTIC) OSMOTIC (ONCOTIC) PRESSUREPRESSURE
Solute
Solvent
HIGHOSMOTIC PRESSUR
E
LOWOSMOTIC PRESSUR
E
Semi-permeable membrane
Click to View Change
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ONCOTIC PRESSURE IN ONCOTIC PRESSURE IN PLASMAPLASMA
Oncontic pressure at the arterial end of capillaries is 28 mm Hg28 mm Hg
Oncotic pressure of interstitial fluid is5 mm Hg5 mm HgDue to a higher protein
concentration in plasma (albumin)
Capillary
Pr- Pr-Pr- Pr- Pr-
Pr-Pr-
Pr-
Pr-
Pr-
Pr-
Pr-
Pr-
Pr-
Pr-Pr-
Pr- Pr-
Pr-Pr- Pr-
H2O H2O
H2O H2O
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ONCOTIC PRESSUREONCOTIC PRESSURE
Capillary
H2O H2O
PROTEIN (OP)
INTERSTITIAL FLUIDPROTEIN (OP)
Opposing oncotic pressure (OP) inside and Opposing oncotic pressure (OP) inside and outside of a capillary. A higher protein outside of a capillary. A higher protein concentration in plasma as compared to concentration in plasma as compared to interstitial fluid, thus it has a greater interstitial fluid, thus it has a greater oncotic pressureoncotic pressure
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CAPILLARY-INTERSTITIAL CAPILLARY-INTERSTITIAL FLUID EXCHANGESFLUID EXCHANGES
Hydrostatic and osmotic (oncotic) pressures create opposing inward and outward forces on the capillary
CapillaryHydrostatic Pressures
Osmotic Pressures
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OUTWARD FORCESOUTWARD FORCES
Arterial end of capillary exerts hydrostatic pressure (30 mm (30 mm Hg)Hg)
Capillary 30 Hydrostatic Pressures
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OUTWARD FORCESOUTWARD FORCESInterstitial fluid oncotic pressure
(5 mm Hg)(5 mm Hg)Negative interstitial fluid pressure
(-6 mm Hg)(-6 mm Hg)Total outward pressure 41 mm Hg41 mm Hg
Capillary30
Hydrostatic
Pressures
Osmotic Pressure
s
5
6 Interstitial Fluid (Pull)
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INWARD FORCESINWARD FORCESPlasma oncotic pressure (28 mm (28 mm
Hg)Hg)
Capillary
28Osmotic
Pressures
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INWARD FORCESINWARD FORCESNet outward filtration of 13 mm Hg13 mm Hg
results in plasma fluid loss41 mm Hg - 28 mm Hg = 13 mm 13 mm
HgHg
Capillary
28Osmotic Pressure
s
30Hydrostat
ic Pressures
Osmotic Pressure
s
5
6 Interstitial Fluid (Pull)
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Opposing forces that influence fluid shifts across the capillary wall. The net effect is outflow of fluid (41 - 28) with a net pressure of 13
Arterial endof capillary
30 mm Hg (HP) 28 mm Hg (OP)
Interstitial fluid
- 6 mm Hg(HP)
5 mm Hg(OP)
Total pressureTotal pressuredrawing fluid outdrawing fluid out
Inward Inward drawingdrawing
forceforce
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ABNORMAL CAPILLARY ABNORMAL CAPILLARY DYNAMICSDYNAMICS
Loss of protein and fluid from plasma to interstitial fluid is provided a return to the circulatory system by way of the lymphatic system
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ABNORMAL CAPILLARY ABNORMAL CAPILLARY DYNAMICSDYNAMICS
Increased capillary fluid loss occurs when there is:1) Increased Capillary 1) Increased Capillary
Hydrostatic PressureHydrostatic Pressure2) Increased Interstitial Fluid 2) Increased Interstitial Fluid
Oncotic PressureOncotic Pressure3) Decreased Plasma Oncotic 3) Decreased Plasma Oncotic
PressurePressureAccumulations of fluid in
interstitial spaces is called edemaedema
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CONDITIONS FOR EDEMACONDITIONS FOR EDEMA
CapillaryCapillaryIncreasedIncreasedHPHP
- HP OP
OPOP
Interstitial fluidInterstitial fluid
Increased capillary Hydrostatic Pressure
(HP)
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CONDITIONS FOR EDEMACONDITIONS FOR EDEMA
CapillaryCapillaryHPHP
- HP- HP OPOP
DecreasedDecreasedOPOP
Interstitial fluidInterstitial fluid
Decreased plasma OncoticDecreased plasma OncoticPressure (loss of protein)Pressure (loss of protein)
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CONDITIONS FOR EDEMACONDITIONS FOR EDEMA
CapillaryCapillaryHPHP
- HP- HP IncreasedIncreasedOPOP
OPOP
Interstitial fluidInterstitial fluid
Increased Oncotic PressureIncreased Oncotic Pressurein interstitial fluidin interstitial fluid
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EDEMAEDEMAVarious liver diseases that
result in decreased protein synthesis lead to edema
Noxious gases, inflammation (pneumonia), or respiratory burns may cause increased permeability of pulmonary capillaries with loss of proteins and fluid
Cause of pulmonary edema in these cases may be a combination of factors
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CAUSES FOR EDEMACAUSES FOR EDEMAI) MalnutritionII) Capillary wall damageIII) Obstructed lymph flowIV) Fluid accumulation in the lungsV) Left ventricle heart failureVI) Congestive heart failureVII) GlomerulonephritisVIII) Nephrotic syndromeIX) Large doses of blood or salt
sol.
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I) MALNUTRITIONI) MALNUTRITIONDecreased or cessation of food
intake leads to decreased synthesis of protein by the liver
Resulting in markedlowering of plasma proteinDecreased oncotic
pressure causes a lowered tendency to draw waterinto the capillaries
Thus fluids accumulate outside the capillaries
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MALNUTRITIONMALNUTRITION
CapillaryCapillary
NormalNormal
ProteinProtein DecreasedDecreasedProteinProtein
MalnutritionMalnutrition
HH22OO HH22OODecreased ProteinDecreased Protein
In malnutrition, there is a decreased synthesis of protein by the liver, resulting in a lowered protein level in plasma. A decrease in oncotic pressure causes a diminished tendency to draw water into capillaries. The net result is edema
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KWASHIORKOR AND KWASHIORKOR AND MARASMUSMARASMUS
Reduced osmolarity from lack of protein in the diet results in a fluid shift, as more water moves out of the capillaries into the interstitial spaces like the peritoneal cavity
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II) CAPILLARY WALL II) CAPILLARY WALL DAMAGEDAMAGEDamage which increases capillary
permeability to proteinsEx: exposure to certain
chemicalsVenomsBacterial toxinsInflammatory response
Protein loss leads to decrease in capillary oncotic pressure
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CAPILLARY WALL DAMAGECAPILLARY WALL DAMAGE
CapillaryCapillary
NormalNormal
HH22OO HH22OO
Venom or ToxinsVenom or Toxins(Increased Proteins)(Increased Proteins)
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Excess fluids and proteins in interstitial fluid are collected and returned to plasma by lymphatic vessels
Tumor or surgical removal of lymph nodes can obstruct flow which leads to edema
III) OBSTRUCTED LYMPH III) OBSTRUCTED LYMPH FLOWFLOW
mammogram
abdominal surgery
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PULMONARY EDEMAPULMONARY EDEMAPulmonary capillaries are more
permeable to proteins than capillaries in other parts of the bodyThus lungs are more
susceptible to edema
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Tendency toward increased oncotic pressure (water drawing force)
Interstitial fluid space is limited in lung tissue
Thus excessive fluid in the interstitial fluid space leaks readily into the alveoli interfering with gas exchange
PULMONARY EDEMAPULMONARY EDEMA
RBC
Alveoli
Interstitium
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ALVEOLAR EDEMAALVEOLAR EDEMA
In this section of lung the alveolar walls are congested (arrow A)(arrow A) and the alveolar spaces are filled with pink fluid (arrow B)(arrow B). A few alveolar macrophages (arrow C)(arrow C) are present but there is no significant inflammation
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PULMONARY EDEMAPULMONARY EDEMAFactors which protect the lungs
from fluid accumulations:1) A high rate of lymph flow 1) A high rate of lymph flow
away from the lungsaway from the lungs2) Pulmonary capillary 2) Pulmonary capillary
pressure that is lower than pressure that is lower than systemic capillary pressuresystemic capillary pressure
Great deal of congestion is present as well as fluid in the
alveoli
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PULMONARY EDEMAPULMONARY EDEMA
Principles of water balance in the lungs are the same as in peripheral tissues
Any condition that causes increased capillary hydrostatic pressure, decreased capillary oncotic pressure, or increased capillary permeability may lead to pulmonary edema
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V) LEFT VENTRICLE HEART V) LEFT VENTRICLE HEART FAILUREFAILURE
Pulmonary edema is characteristic of various forms of heart failure
If the left ventricle of the heart fails as a pump:1) Pulmonary circulation is
slowed and there is a buildup of blood in the pulmonary vessels
2) Blood pressure increases
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HYDROSTATIC EDEMAHYDROSTATIC EDEMA
This radiograph demonstrates pulmonary arteriesthat are much larger than their accompanying bronchi (A). In addition the bronchial walls are thickened. The patient was treated with diureticsand the subsequent scan (right) shows normal appearing bronchi (B) in which the bronchialwalls are thin and the pulmonary artery and bronchus are the same size
pulmonaryartery
pulmonaryartery
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VI) CONGESTIVE HEART VI) CONGESTIVE HEART FAILUREFAILURE
The heartfails as apump
Increased pulmonary venous and capillary pressure because of increased blood volume (increased hydrostatic pressure)
coronary bypass
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VII) VII) GLOMERULONEPHRITISGLOMERULONEPHRITIS
Inflammatory kidney diseaseEdema is caused by fluid
retentionThus there is increased
capillary hydrostatic pressure
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VIII) NEPHROTIC VIII) NEPHROTIC SYNDROMESYNDROMEUrinary protein loss and decreased
plasma proteinGeneralized edema as the result of
lowered plasma oncotic pressure
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Pulmonary edema is the result of increased blood volume
Thus increased hydrostatic pressure
Individuals with heart or kidney disease are especially susceptible
IX) ADMINISTRATION OF LARGE IX) ADMINISTRATION OF LARGE AMOUNTS OF BLOOD OR SALT AMOUNTS OF BLOOD OR SALT
SOLUTIONSSOLUTIONS
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INTERSTITIAL FLUID-INTERSTITIAL FLUID-CELLULAR DYNAMICSCELLULAR DYNAMICS
Water movement between cells and the interstitial fluids
Electrolyte composition is a major factor in this exchangeOsmotic pressure is the
drawing force
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ELECTROLYTE ELECTROLYTE CONCENTRATIONSCONCENTRATIONS
Meq/liter
Interstitial Fluid
Muscle Cells
Na+ 145.5 12 K+ 4.8 150 Ca++ 2.8 0.0000001 Mg++ 1.0 7 Cl - 116.6 3 HCO3
- 27.4 10
PO4- - - 2.3 116
Protein - 8.0 40
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PRINCIPLE ELECTROLYTE PRINCIPLE ELECTROLYTE IN IN INTERSTITIAL FLUIDINTERSTITIAL FLUID
Meq/liter InterstitialFluid
MuscleCells
Na+ 145.5 12K+ 4.8 150Ca++ 2.8 0.0000001Mg++ 1.0 7Cl - 116.6 3HCO3
- 27.4 10PO4
- - - 2.3 116Protein - 8.0 40
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MAIN MAIN INTRACELLULARINTRACELLULAR IONSIONS
Meq/liter InterstitialFluid
MuscleCells
Na+ 145.5 12K+ 4.8 150Ca++ 2.8 0.0000001Mg++ 1.0 7Cl - 116.6 3HCO3
- 27.4 10PO4
- - - 2.3 116Protein - 8.0 40
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FLUID IMBALANCEFLUID IMBALANCE
Fluid imbalance may occur and result in either: Cellular dehydrationCellular dehydration Cellular hydrationCellular hydration
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CELL DEHYDRATION IN CELL DEHYDRATION IN DIABETESDIABETES
H2OH2OH2OH2OH2OH2OH2OH2OH2O
glucose
Ex: diabetes Glucose concentrations increase
in extracellular fluidsIncreased conc. gradients outside
the cells draw water out of the cells by creating an osmotic pull
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CELL HYDRATIONCELL HYDRATIONNaNa++ ions predominate in
extracellular fluidThus NaNa++ plays a major role in
determining osmotic pressureLow NaNa++ in extracellular fluid
creates an intracellular osmotic pull on HH2200
Decreased soluteconcentration
Decreased osmoticpressure
Hydration of
cells
Na+ loss Click to View
Animation
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CELL HYDRATIONCELL HYDRATIONLow sodium levels can be
caused by diuretics, vomiting or low Na+ intake
If low sodium levels are combined with excess water intakeCell hydration is
exaggerated
Excess water intake
Low sodiumlevels
+ =Cell hydration
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EFFECTS OF IMBALANCE EFFECTS OF IMBALANCE ON COMPARTMENTSON COMPARTMENTS
Intravascular (plasma) compartment is the most likely to be affected by volume changes first
Interstitial and intracellular compartments are less likely to be affected and thus represent fluid reservoirsfluid reservoirs
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SUDDEN LOSS OR GAINS SUDDEN LOSS OR GAINS OF FLUIDSOF FLUIDS
Sudden loss or gain of fluids affect only intravascular compartmentsex: hemorrhage
Both compartments sharelosses or gains equally ifthey occur over a period of hours
Significant shifts of fluids between compartments require several hours
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LOSS OF HYPOTONIC LOSS OF HYPOTONIC FLUIDFLUIDLoss of hypotonic fluidhypotonic fluid (solute(solute
concentration less than that ofconcentration less than that of plasma)plasma) has a concentrating effect on extracellular fluidThis results in an increase of
osmotic pressureWater is drawn out of cells
in response to increasedextracellular osmoticpressure
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FLUID BALANCE FLUID BALANCE DISORDERSDISORDERSTotal volume of water in the
body is 60% of body weightIntracellular fluidIntracellular fluid === 67% === 67%PlasmaPlasma =========== 8% =========== 8%Interstitial fluidInterstitial fluid ===== 25% ===== 25%
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REGULATION OF FLUID REGULATION OF FLUID INTAKEINTAKEThirst is a
powerful regulator of fluid consumption
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REGULATION OF FLUID REGULATION OF FLUID INTAKEINTAKEThirst center in the hypothalamushypothalamus
is stimulated by:1) Cellular dehydration1) Cellular dehydration2)2) Decreased salivary productionDecreased salivary production3) Increased blood osmotic 3) Increased blood osmotic
pressurepressure4) Decreased blood volume4) Decreased blood volume
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THIRSTTHIRST1) 1) Cellular dehydrationCellular dehydrationInadequate intake of waterIncrease in extracellular solute concentration
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THIRSTTHIRST2)2) Decreased salivary productionDecreased salivary production
Dry sensation of the mucosa of the mouth and pharynx
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THIRSTTHIRST3)3) Increased blood osmotic Increased blood osmotic
pressurepressureStimulates osmoreceptors in the hypothalamus which in turn stimulate the thirst centerof the hypothalamus
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THIRSTTHIRST4)4) Decreased blood volume Decreased blood volume
(decreased blood pressure)(decreased blood pressure)Stimulates the release of reninrenin by the kidney
Renin promotes synthesis of angiotensin IIangiotensin II whichaffects the thirstcenter of thehypothalamus
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STIMULATION OF THIRST BY DEHYDRATIONSTIMULATION OF THIRST BY DEHYDRATIONdehydration
decreased flowof saliva
increased bloodosmotic pressure
decreasedblood volume
dry mouthand pharynx
stimulates osmoreceptorsin hypothalamus
decreased blood pressure
increased renin releaseby juxta-glomerular
cells of kidney
increasedangiotensin II
production
stimulates thirst centerin hypothalamus
increases thirst
increases fluid intake
increases body water to normallevel and relieves dehydration
1
2
3
4
5
6
7
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REGULATION OF FLUID REGULATION OF FLUID LOSSLOSSFluid loss can be adjusted by:
1) Antidiuretic hormone (ADH)Vasopressin
2) Atrial natriuretic peptide (ANP)
3) Aldosterone
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REGULATION OF FLUID REGULATION OF FLUID OUTPUTOUTPUT
ADHADH and aldosterone slow fluid lossesANPANP causes diuresis
(increased urine production)
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DEHYDRATIONDEHYDRATIONIf the body is dehydrated:
- Blood pressure falls- Glomerular filtration decreases
Water is thus conserved
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EXCESSIVE FLUID IN EXCESSIVE FLUID IN BLOODBLOODExcessive fluid in the blood causes:
- Increased blood pressure- Increased glomerular filtration
Thus increased fluid output
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Click to View
Animation
EXCESSIVE FLUID
RETENTION
OTHER FACTORS CAUSING EXCESSIVE OTHER FACTORS CAUSING EXCESSIVE FLUID RETENTIONFLUID RETENTION
EXTENSIVE SKINDESTRUCTION
HEAVY PERSPIRATION
HYPERTENSION
HYPERVENTILATION
VOMITING
DIARRHEA
FEVER
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EFFECTS OF FLUID EFFECTS OF FLUID EXCESSEXCESSFluid excess initially affects the
extracellular compartmentsIncreased fluid volume can
result in cerebral, pulmonary or generalized edema
Usually the result of inadequateinadequate renal outputrenal output rather than fluid intake
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EFFECTS OF FLUID EFFECTS OF FLUID EXCESSEXCESSIf the retained water is hypotonichypotonic as
compared to plasma the effect is to dilute the extracellular fluidThis causes a decrease in
osmolalityosmolalityWhen interstitial fluid is dilute as
compared to intracellular fluid, water is drawn into the cells by osmotic pull
Results in increased cellularvolume and changes in cellfunction occurMost apparent in CNS tissue
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INTRAVENOUS INFUSIONINTRAVENOUS INFUSIONIf the total body water is
increased by IV infusion of an isotonic solutionisotonic solution the result will be:Increased extracellular volume With little or no effect on
cellular volumeNet result is no change in solute
concentrations in plasma, interstitial fluids and intracellular fluid and no effect on cells
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INTRAVENOUS INFUSIONINTRAVENOUS INFUSIONInfusion of a hypertonic hypertonic
solutionsolution results in:Diffusion of both solute and
water into the interstitial fluid occurs
This concentration of solutes in interstitial fluid is higher than normalCreates an osmotic drawing force
Pulls water out of the cell
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SUMMARY OF SUMMARY OF OVERHYDRATION OR WATER OVERHYDRATION OR WATER
INTOXICATIONINTOXICATION1) If the fluid is hypotonichypotonic2) If the fluid retained is isotonic isotonic
to plasma3) If the excess fluid is hypertonichypertonic
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HYPOTONICHYPOTONIC1) If the fluid is hypotonichypotonic
Increase in extracellular volumeA dilutional effectSubsequent cellular dehydration
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ISOTONICISOTONIC
2) If the fluid retained is isotonic isotonic to plasmaExpansion of the
extracellular compartmentNo effect on cells
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HYPERTONICHYPERTONIC
3) If the excess fluid is hypertonichypertonicIncreased extracellular volumeCellular dehydration
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CAUSES FOR CAUSES FOR OVERHYDRATIONOVERHYDRATION
1) Psychiatric disorder of compulsive water drinking (psychogenic psychogenic polydipsiapolydipsia) 10 -15 liters/day
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CAUSES FOR CAUSES FOR OVERHYDRATIONOVERHYDRATION
2) Forced water ingestion as a form of punishment (child child abuseabuse)
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CAUSES FOR CAUSES FOR OVERHYDRATIONOVERHYDRATION
3) Inappropriate ADH secretionADH also called VasopressinVasopressinPromotes water retention
(reabsorption) by increasing permeability of the collecting ducts in the kidney
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CAUSES FOR CAUSES FOR OVERHYDRATIONOVERHYDRATION
ADH is also a powerful vasoconstrictor of arteriolesHead trauma, lung cancers, pneumonia, CNS diseases, encephalitis
Some types of tumors secrete substances with ADH-like activity
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DEHYDRATIONDEHYDRATIONEffects of a fluid deficit depend
on:VolumeRate of lossAmount of electrolytes lost
with water
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HYPOTONIC LOSSHYPOTONIC LOSSSimple dehydration is sometimes
called hypotonic losshypotonic lossEffects of hypotonic fluid loss
(water loss exceeds solute loss) has a concentrating effectResults in increased
osmolality andhypernatremia(increased NaNa++
concentration)
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HYPOTONIC LOSSHYPOTONIC LOSSWater is drawn out of cells into
the extracellular compartmentCell volume depletion
stimulates the release of ADHADH (antidiuretic hormone) and aldosteronealdosteroneADH mediates renal water
retentionAldosterone favors
NaNa++ and water retention
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SUMMARY OF HYPOTONIC SUMMARY OF HYPOTONIC DEHYDRATIONDEHYDRATION
Immediate effect of water loss is hypernatremiahypernatremia
Physiological responses to correct the imbalance:Movement of cellular water to
extracellular compartmentsHormonal responses that
increase extracellular volume
H2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
OH2
O
120
CAUSES FOR CAUSES FOR DEHYDRATIONDEHYDRATION
1) 1) Excessive sweatingExcessive sweating
2) 2) Insensible fluid lossInsensible fluid loss
3) 3) DiuresisDiuresis
4) 4) Diabetes insipidusDiabetes insipidus
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CAUSES FOR CAUSES FOR DEHYDRATIONDEHYDRATION1) 1) Excessive sweatingExcessive sweating
Sweat is hypotonicMay result in hypernatremia
with losses of electrolytes
122
CAUSES FOR CAUSES FOR DEHYDRATIONDEHYDRATION
2) 2) Insensible fluid lossInsensible fluid lossFrom the skin or lungs
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CAUSES FOR DEHYDRATIONCAUSES FOR DEHYDRATION3) DiuresisDiuresis
Solute cleared from the blood by the kidney and not reabsorbed remains in the glomerular filtrate
This high solute concentration creates an osmotic pull that draws water in that directionResults in increasedurine output andwater loss
124
DIURESISDIURESISMannitolMannitol (polysaccharide) is
sometimes used in cerebral edemaNon-reabsorbable solute and creates an osmoticpull on waterpromoting water loss
125
CAUSES FOR CAUSES FOR DEHYDRATIONDEHYDRATION4) Diabetes insipidusDiabetes insipidus
Deficiency of ADHExcessive urination and thirst
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ELDERLYELDERLY
Older individuals havea decreased renalcapacity to save water
Significant if: Fluid intake is limited
(decreased diet) Insensible fluid loss is
increased (fever)
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ELDERLYELDERLYElderly are also susceptible to
water intoxicationIncreased ADH secretion
(stress of surgery, pneumonia, meningitis)
Reduction in renal blood flowDecreased urine volume and water retention
Heart failure, liverdisease, drug induced hypotension
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INFANTSINFANTSInfants have a greater
surface area compared to weightIncreased insensible fluid loss
Infants have less renal concentrating ability than an adult
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MOVEMENT OF BODY MOVEMENT OF BODY FLUIDSFLUIDSPressures acting to move
substances out of the capillary include:Blood Hydrostatic Pressure Blood Hydrostatic Pressure
(BHP)(BHP)Interstitial Fluid Osmotic Interstitial Fluid Osmotic
Pressure (IFOP)Pressure (IFOP)
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MOVEMENT OF BODY MOVEMENT OF BODY FLUIDSFLUIDSBlood colloid osmotic pressure
(BCOP) and interstitial fluid hydrostatic pressure act to push substances into the capillary
At the arterial end of the capillary the sum of the outward moving pressures is dominant and substances move into the interstitial fluid (filtration)
At the venous end the inward pressure is dominant and the substances move into the capillary (reabsorption)
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MOVEMENT OF BODY MOVEMENT OF BODY FLUIDSFLUIDSThe exchange of interstitial and
intracellular fluid is controlled mainly by the presence of the electrolytes sodium and potassium
Potassium is the chief intracellular cation and sodium the chief extracellular cation
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MOVEMENT OF BODY MOVEMENT OF BODY FLUIDSFLUIDSBecause the osmotic pressure of
the interstitial space and the ICF are generally equal water typically does not enter or leave the cell
A change in the concentration of either electrolyte will cause water to move into or out of the cell via osmosis
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