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The Cellular Environment: Fluids The Cellular Environment: Fluids and Electrolytes, Acids and Basesand Electrolytes, Acids and Bases
Alterations in Water Movement: Alterations in Water Movement: EdemaEdema
Accumulation of fluid within the interstitial Accumulation of fluid within the interstitial spacesspaces
CausesCauses Increase in capillary hydrostatic pressureIncrease in capillary hydrostatic pressure Losses or diminished production of plasma albuminLosses or diminished production of plasma albumin Increases in capillary permeabilityIncreases in capillary permeability Lymph obstruction (lymphedema)Lymph obstruction (lymphedema)
HypernatremiaHypernatremia Serum sodium >147 mEq/LSerum sodium >147 mEq/L Related to sodium gain or water lossRelated to sodium gain or water loss Water movement from the ICF to the ECFWater movement from the ICF to the ECF
Water deficitWater deficit DehydrationDehydration Pure water deficitsPure water deficits Renal free water clearanceRenal free water clearance ManifestationsManifestations
• Tachycardia, weak pulse, and postural hypotensionTachycardia, weak pulse, and postural hypotension
• Elevated hematocrit and serum sodium levelsElevated hematocrit and serum sodium levels
HyperchloremiaHyperchloremia Occurs with hypernatremia or a bicarbonate deficit Occurs with hypernatremia or a bicarbonate deficit Usually secondary to pathophysiologic processesUsually secondary to pathophysiologic processes Managed by treating underlying disordersManaged by treating underlying disorders
Decreased osmolalityDecreased osmolality Hyponatremia or free water excessHyponatremia or free water excess Hyponatremia decreases the ECF osmotic Hyponatremia decreases the ECF osmotic
pressure, and water moves into the cell pressure, and water moves into the cell Water movement causes symptoms related to Water movement causes symptoms related to
Hypotonic AlterationsHypotonic Alterations Water excessWater excess
Compulsive water drinkingCompulsive water drinking Decreased urine formationDecreased urine formation Syndrome of inappropriate ADH (SIADH)Syndrome of inappropriate ADH (SIADH)
• ADH secretion in the absence of hypovolemia or ADH secretion in the absence of hypovolemia or hyperosmolalityhyperosmolality
• Hyponatremia with hypervolemiaHyponatremia with hypervolemia
Manifestations: cerebral edema, muscle twitching, Manifestations: cerebral edema, muscle twitching, headache, and weight gainheadache, and weight gain
PotassiumPotassium Major intracellular cationMajor intracellular cation Concentration maintained by the NaConcentration maintained by the Na++,K,K++ pump pump Regulates intracellular electrical neutrality in Regulates intracellular electrical neutrality in
relation to Narelation to Na++ and H and H++
Essential for transmission and conduction of Essential for transmission and conduction of nerve impulses, normal cardiac rhythms, and nerve impulses, normal cardiac rhythms, and skeletal and smooth muscle contractionskeletal and smooth muscle contraction
Potassium LevelsPotassium Levels Changes in pH affect KChanges in pH affect K++ balance balance
Hydrogen ions accumulate in the ICF during states Hydrogen ions accumulate in the ICF during states of acidosis. Kof acidosis. K++ shifts out to maintain a balance of shifts out to maintain a balance of cations across the membrane.cations across the membrane.
Aldosterone, insulin, and catecholamines Aldosterone, insulin, and catecholamines influence serum potassium levelsinfluence serum potassium levels
HypokalemiaHypokalemia Potassium level <3.5 mEq/LPotassium level <3.5 mEq/L Potassium balance described by changes in Potassium balance described by changes in
HyperkalemiaHyperkalemia Potassium level >5.5 mEq/LPotassium level >5.5 mEq/L Hyperkalemia is rare due to efficient renal Hyperkalemia is rare due to efficient renal
excretionexcretion Caused by increased intake, shift of KCaused by increased intake, shift of K++ from from
ICF, decreased renal excretion, insulin ICF, decreased renal excretion, insulin deficiency, or cell traumadeficiency, or cell trauma
Like calcium, most phosphate (85%) is also located Like calcium, most phosphate (85%) is also located in the bonein the bone
Necessary for high-energy bonds located in Necessary for high-energy bonds located in creatine phosphate and ATP and acts as an anion creatine phosphate and ATP and acts as an anion bufferbuffer
Calcium and phosphate concentrations are rigidly Calcium and phosphate concentrations are rigidly controlledcontrolled CaCa++++ x HPO x HPO44
– –– – = K = K+ + (constant)(constant)
If concentration of one increases, that of the other If concentration of one increases, that of the other decreasesdecreases
MagnesiumMagnesium Intracellular cationIntracellular cation Plasma concentration is 1.8 to 2.4 mEq/LPlasma concentration is 1.8 to 2.4 mEq/L Acts as a co-factor in protein and nucleic acid Acts as a co-factor in protein and nucleic acid
synthesis reactionssynthesis reactions Required for ATPase activityRequired for ATPase activity Decreases acetylcholine release at the Decreases acetylcholine release at the
Negative logarithm of the HNegative logarithm of the H++ concentration concentration
Each number represents a factor of 10. If a Each number represents a factor of 10. If a solution moves from a pH of 7 to a pH of 6, the solution moves from a pH of 7 to a pH of 6, the HH+ + ions have increased 10-fold. ions have increased 10-fold.
pHpH Inverse logarithm of the HInverse logarithm of the H++ concentration concentration HH++ high in number, pH is low (acidic) high in number, pH is low (acidic) HH++ low in number, pH is high (alkaline) low in number, pH is high (alkaline) Ranges from 0 to 14Ranges from 0 to 14 Each number represents a factor of 10. Each number represents a factor of 10.
If a solution moves from a pH of 6 to a pH of 5, the If a solution moves from a pH of 6 to a pH of 5, the HH++ has increased 10 times has increased 10 times
pHpH Acids are formed as end products of protein, Acids are formed as end products of protein,
carbohydrate, and fat metabolismcarbohydrate, and fat metabolism To maintain the body’s normal pH (7.35-7.45) To maintain the body’s normal pH (7.35-7.45)
the Hthe H++ must be neutralized or excreted must be neutralized or excreted Bones, lungs, and kidneys are major organs Bones, lungs, and kidneys are major organs
involved in regulation of acid-base balanceinvolved in regulation of acid-base balance
Buffering SystemsBuffering Systems A buffer is a chemical that can bind excessive A buffer is a chemical that can bind excessive
HH++ or OH or OH–– without a significant change in pH without a significant change in pH A buffering pair consists of a weak acid and A buffering pair consists of a weak acid and
its conjugate base its conjugate base The most important plasma buffering systems The most important plasma buffering systems
are the carbonic acid–bicarbonate system are the carbonic acid–bicarbonate system and hemoglobinand hemoglobin
Carbonic Acid–Bicarbonate PairCarbonic Acid–Bicarbonate Pair Operates in the lung and the kidneyOperates in the lung and the kidney The greater the partial pressure of carbon The greater the partial pressure of carbon
dioxide, the more carbonic acid is formeddioxide, the more carbonic acid is formed At a pH of 7.4, the ratio of bicarbonate to carbonic At a pH of 7.4, the ratio of bicarbonate to carbonic
acid is 20:1acid is 20:1 Bicarbonate and carbonic acid can increase or Bicarbonate and carbonic acid can increase or
decrease, but the ratio must be maintaineddecrease, but the ratio must be maintained
Carbonic Acid–Bicarbonate PairCarbonic Acid–Bicarbonate Pair If amount of bicarbonate decreases, the pH If amount of bicarbonate decreases, the pH
decreases, causing a state of acidosisdecreases, causing a state of acidosis The pH can be returned to normal if the The pH can be returned to normal if the
amount of carbonic acid also decreasesamount of carbonic acid also decreases This type of pH adjustment is called compensationThis type of pH adjustment is called compensation
The respiratory system compensates by increasing or The respiratory system compensates by increasing or decreasing ventilationdecreasing ventilation
The renal system compensates by producing acidic The renal system compensates by producing acidic or alkaline urineor alkaline urine
Four categories of acid-base imbalances Four categories of acid-base imbalances Respiratory acidosis—elevation of pRespiratory acidosis—elevation of pCOCO2 2 due to due to
ventilation depressionventilation depression Respiratory alkalosis—depression of pRespiratory alkalosis—depression of pCOCO22 due to due to
alveolar hyperventilationalveolar hyperventilation Metabolic acidosis—depression of HCOMetabolic acidosis—depression of HCO33
–– or an or an
increase in noncarbonic acidsincrease in noncarbonic acids Metabolic alkalosis—elevation of HCOMetabolic alkalosis—elevation of HCO33
–– usually due to usually due to
an excessive loss of metabolic acidsan excessive loss of metabolic acids
Alters bicarbonate and HAlters bicarbonate and H++ levels in response to levels in response to acidosis or alkalosisacidosis or alkalosis• Much slower responseMuch slower response
CompensationCompensation When adjustments are made to bicarbonate When adjustments are made to bicarbonate
and carbonic acid in order to maintain the and carbonic acid in order to maintain the 20:1 ratio 20:1 ratio and and therefore maintain normal pHtherefore maintain normal pH The actual values for bicarbonate to carbonic acid The actual values for bicarbonate to carbonic acid
ratio are ratio are not normal but the normal ratio is not normal but the normal ratio is achievedachieved
Correction occurs when the values for BOTH Correction occurs when the values for BOTH components of the buffer pair (carbonic acid and components of the buffer pair (carbonic acid and bicarbonate) have also returned to bicarbonate) have also returned to normalnormal levels levels
Anion GapAnion Gap Used cautiously to distinguish different types Used cautiously to distinguish different types
of metabolic acidosisof metabolic acidosis By rule, the concentration of anions (–) By rule, the concentration of anions (–)
should equal the concentration of cations (+). should equal the concentration of cations (+). Not all normal anions are routinely measured. Not all normal anions are routinely measured.
Normal anion gap = Normal anion gap = Na Na++ + K + K++ = Cl = Cl–– + HCO + HCO33
As these abnormal anions accumulate, the As these abnormal anions accumulate, the measured anions have to decrease to measured anions have to decrease to maintain electroneutralitymaintain electroneutrality