Water, Electrolyte, and Acid-Base Balance

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Body water & Electrolytes

Body water contains dissolved mineral salts or electrolytes that dissociate in solution, yielding
Cations: + charged Ions
Anion: - charged Ions
Body fluids: electrically neutral
Sum of Cations balanced by sum of Anions
In disease, Ion concentrations may vary but the electrical neutrality is always maintained

Intracellular & Extracellular I

Disturbances of body water are associated with corresponding change in electrolytes
If electrolyte concentration changes, there is a corresponding change in body water and vice versa
Body Consists of 70% water
Intracellular water (inside cells)
Extracellular water (within interstitial tissues surrounding cells, blood plasma, and lymph)
Rule of thirds
2/3 of body weight is H2O
2/3 H2O is within cells
1/3 of H2O is extracellular in tissues surrounding cells

Intracellular & Extracellular II

Adult female: water content is 10% lower than adult male due to higher body fat than water
Fluids and electrolytes diffuse freely between the intravascular and interstitial fluids
Because capillaries are impermeable to protei, the interstitial fluid contains very little protein

Intracellular & Extracellular
Cell Memebrane:

separetes intracellular fluid from interstitial fluid by a cell membrane
Freely permeable to water
Impermeable to Na+ and K+

Intracellular & Extracellular Chief intracellular Ions & Chief extracellular Ions

Chief intracellular Ions
K+ (potassium)
PO4 2 (phosphate)
Chief extracellular Ions
Na+ (sodium)
Cl- (Cloride)
Differences in concentration of ions on different sides of the cell membrane result from metabolic activity of the cell

Intracellular & Extracellular Amount of
K+ & Na+

Amount of sodium in the body determines the volume of extracellular fluid as the chief extracellular cation
Amount of potassium in the body determines the volume of intracellular fluids as the chief intracellular cation

Intracellular & Extracellular
Electrolyte disturbances

primary concern is the concentration of various ions and the interrelation of positively and negatively charged ions with one another than the actual number

Intracellular & Extracellular Fluid
Equivalent weight

Units of concentration of electrolytes
Expressed in units that define ability to combine with other ions
Molecular weight of substance in grams divided by valence

Regulation of Body Fluid & Electrolyte Concentration

Amount of H2O & electrolytes in body: represents the balance between amounts ingested in food and fluids and amounts excreted via urine, GI tract, perspiration, and as H2O vapor excreted by lungs

Regulation of Body Fluid & Electrolyte Concentration Disturbances of H2O balance

Dehydration is the most common
Inadequate intake: diarrhea or vomiting
Excess H2O loss: comatose or debilitated patients
Overhydration is less common
Excessive fluid intake when renal function is impaired: renal disease, excessive intake of fluids, excessive administration of IV fluids

Regulation of Body Fluid & Electrolyte Concentration Disturbances of Electrolye balance

Conditions that produce H2O also disturb electrolyte composition
Most result from depletion of body electolytes

Regulation of Body Fluid & Electrolyte Concentration Depletion of electrolytes

Vomiting or diarrhea: sodium and patassium depletion
excessive use of diuretics
excessive diuresis in diabetic acidosis
Renal tubular disease

Regulation of Body Fluid & Electrolyte Concentration Diuretic promote excretion of salt and H2O

by the kidneys while impairing reabsorption of these substances
patients with heart failure, liver cirrhosis, kidney disease

Regulation of Body Fluid & Electrolyte Concentration Uncrontrolled Diabetes

excessive loss of H2O in urine from the diuretic effect of glucose

Regulation of Body Fluid & Electrolyte Concentration Renal tubular disease

regenerating renal tubules unable to conserve elctrolytes and water

Acid Base Balance

Body produces large amounts of acid from normal metabolic processes, such as breakdown of proteins and glucose or oxidation of fat
Body fluids remain slightly alkaline
pH is maintained within a anrrow range:7.38 to 7.42
Regulatory mechanisms maintain pH
Neutralize and eliminate the acids as soon as they are produced to maintain normal pH

Acid Base Balance

Blood buffers: resist pH change
Lungs: control carbonic acid (H2CO3) concentration
Kidneys: control bicarbonate concentration

Blood Buffer System

Minimize change in hydrogen ion by converting stron acids and bases into weaker ones chemically
weak acid and its salts
weak base and its salts

Blood Buffer System
Respiratory control of carbonic acid

carbonic acid (H2CO3) : dissolved as CO2 in plasma
Hyperventilation: lowers CO2 and H2CO3 in plasma
Decreased or inadequate ventilation: raises CO2 and H2CO3 in plasma

Blood Buffer System
Renal control of bicarbonate concentration

kidneys selectively reabsorb filtered bicarbonate
kidneys can manufacture bicarbonate to replace amounts lost in buffering acids from metabolic process

Blood Buffer System
In any buffer system

pH depends on ration of bicarbonate to H2CO3
normal ration: 20 parts Na bicarbonate: 1 part H2CO3

Disturbances in Acid Base Balance

Blood pH shifts to acidic side
from an excess of H2CO3
from a reduced amount of bicarbanate

Disturbances in Acid Base Balance

Blood pH shifts to basic side
from a decrease in H2CO3
from an excess of bicarbonate

Classification of Acid Base Balance
Disturbances Metabolic

disturbance lies in bicarbonate member of the buffer pair

Classification of Acid Base Balance
Disturbances Respiratory

disturbance lies in carbonic acid member of the buffer pair

Classification of Acid Base Balance
Disturbances Metabolic Acidosis

increased endogenous acid generated
amount of acid generated exceeds body's buffering capacity
excess acid is neutralized by bicarbonate
Bicarbonate in plasma falls from being consumed in neutralizing excess acid
Uremia, ketosis, lactic acidosis
Compensation:by hyperventilation to lower PCO2 and increased bicarbonate production in kidneys

Classification of Acid Base Balance
Disturbances Metabolic alkalosis

increased plasma bicarbonate
from loss of gastric juice, chloride depletion, excess corticosteroids, excess antacids
with coexisting potassium deficiency
Compensation:inefficient, requires simultaneous correction of patassium deficiency

Classification of Acid Base Balance
Disturbances Respiratory acidosis

increased H2CO3 concentration
inefficient excretion of CO2 by lungs
leads to retention of CO2 and rise in H2CO3
compensation:increased bicarbonate production in kidney

Classification of Acid Base Balance
Disturbances Respiratory alkalosis

Reduced H2CO3 concentration
Hyperventilation lowers PCO2 and H2CO3 levels falls
Relative excess of bicarbonate
Compensation:excretion of bicarbonate by kidneys

Diagnostic evaluation of Acid Base Balance

Clinical evaluation is determined of concentration of bicarbonate in plasma as an index of patients overall status
Laboratory studies
Blood pH

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