Fluid, Electrolyte, and AcidBase Balance

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Fluid, Electrolyte, and Acid-Base Balance
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Body Fluids

• Body fluids make up 55-60 of total body weight
  in an adult they can make up to 75 of the body
  weight of an infant
• These fluids are solutions, mixtures of solutes
  (solids, ions and electrolytes) within a solvent
  (water)
• The concentration of body fluids varies depending
  on conditions within the body

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Body Fluids (continued)

• About 2/3 of body fluid is the fluid within
  cells, called intracellular fluid
• 1/3 of body fluid is the fluid outside cells,
  called extracellular fluid
• About 80 of extracellular fluid is interstitial
  fluid, fluid that fills the spaces between the
  cells of a tissue 20 is blood plasma

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Body Fluids (continued)

• Selectively permeable membranes separate body
  fluids (ex. the plasma membrane)
• Water moves into and out of cells by osmosis
• The concentration of solutes in the body fluids
  determines which direction osmosis occurs

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Fluid Intake and Output

• The percentage of water that makes up body weight
  decreases with age
• The main source of this fluid is that which is
  ingested by the mouth (ex. Food and drink)
• Generally, fluid intake should balance fluid
  output (by sweating, urination, etc.)

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Electrolytes

• Body fluids contain many dissolved substances
  such as electrolytes and nonelectrolytes
• Electrolytes are compounds that have at least one
  ionic bond, which is a chemical bond formed
  between ions, or charged atoms
• Cations are positively charged ions anions are
  negatively charged ions

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Electrolytes (continued)

• Charged atoms have gained or lost electrons,
  negatively charged subatomic particles
• Electrolytes are capable of conducting an
  electric current
• They dissociate into ions when dissolved in a
  fluid such as water
• Examples of electrolytes include mostly inorganic
  compounds (which do not contain the element
  carbon) such as acids, bases, and salts

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Nonelectrolytes

• Nonelectrolytes are compounds formed with
  covalent bonds, chemical bonds formed between
  atoms that share electron pairs
• Nonelectrolytes do not dissociate in water to
  form ions and do not conduct an electric current
• Examples include most organic compounds (which do
  contain carbon) such as glucose and urea

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Functions of Electrolytes

• Many electrolytes are essential minerals
• They are more numerous than nonelectrolytes, so
  they tend to control osmosis
• Electrolytes help maintain the acid-base balance
  needed for normal cell activity
• They carry an electrical current, so they are
  important in nerve impulse conduction, muscle
  contraction, and secretion of some hormones and
  neurotransmitters

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Important Ions of the Body

• The number of ions in a volume of fluid
  (concentration) is indicated in milliequivalents
  per liter (mEq/liter)
• The most important ions include
• Sodium (Na)
• Potassium (K)
• Calcium (Ca2)
• Magnesium (Mg2)
• Chloride (Cl-)
• Phosphate (HPO42-)

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Sodium (Na)

• Sodium is the most abundant extracellular ion
  it makes up about 90 of extracellular cations
• It is found in greater amounts outside cells due
  to the sodium-potassium pump and its active
  transport of Na out of cells and K into cells
• Na is needed for nerve impulse conduction and
  muscle contraction
• It creates osmotic pressure in extracellular
  fluid, causing water to follow it

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Sodium (Na) (continued)

• Na is also involved in buffer systems, which
  prevent drastic pH changes in body fluids
• It can be lost from the body through
  perspiration, vomiting, diarrhea, diuretic use,
  and burns
• Most individuals exceed the bodys normal daily
  requirements of sodium ions
• The kidneys excrete excess Na and conserve it
  when levels are low
• Hypernatremia occurs when Na levels are high in
  the blood hyponatremia occurs when levels are
  low in the blood

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Potassium (K)

• Potassium is the most abundant intracellular
  cation
• It is also needed for nerve impulse conduction
  and muscle contraction
• Abnormal levels of K in the blood can cause
  problems with cardiac functioning
• Hyperkalemia occurs when K levels are high in
  the blood it can cause death from heart
  fibrillation, involuntary cardiac muscle
  contractions
• Hypokalemia occurs when levels are low in the
  blood it can result from vomiting, diarrhea,
  diuretic use, and/or kidney disease

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Calcium (Ca2)

• Calcium is the most abundant ion in the body
• It is mainly an extracellular electrolyte found
  in the skeleton and teeth as a mineral salt
  (combined with phosphate HPO42-) 98 is found
  is this form
• The blood contains a small amount of Ca2, and
  some is also found in muscle cells and the fluid
  outside them

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Calcium (Ca2) (continued)

• Ca2 is a structural component of bones and teeth
• It is also involved in blood clotting, muscle
  contraction, and the release of neurotransmitters
• Hypercalcemia occurs when Ca2 levels in the
  blood are high hypocalcemia occurs when Ca2
  levels in the blood are low
• As phosphate levels go up, calcium levels go down

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Magnesium (Mg2)

• Magnesium is mainly an intracellular electrolyte
• Most is in bone (50) or the fluid inside cells
  (45)
• Mg2 activates the enzymes needed to metabolize
  carbohydrates and proteins
• It is also involved in the structure of DNA, RNA,
  and ribosomes

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Magnesium (Mg2) (continued)

• Mg2 triggers the sodium-potassium pump, is
  involved in nervous system and muscular activity,
  and in myocardial functioning
• Hypermagnesemia occurs when levels of Mg2 in the
  blood are high
• Hypomagnesemia occurs when levels of Mg2 in the
  blood are low

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Chloride (Cl-)

• Cl- is the main extracelluar anion of the body
• It is important in the determination of which
  direction water moves by osmosis
• It is also found in combination with hydrogen to
  form hydrochloric acid (HCl) in the gastric
  glands of the stomach
• Hyperchloremia occurs when there are high levels
  of Cl- in the blood Hypochloremia occurs when
  there are low levels in the blood

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Phosphate (HPO42-)

• HPO42- is mainly an intracellular electrolyte
• About 85 of the phosphate in an adult is in the
  bones and teeth as calcium phosphate salts
• The remainder is combined with lipids
  (phospholipids) to form cellular membranes and is
  found in DNA, RNA, and ATP

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Phosphate (HPO42-) (continued)

• It is also involved in buffer systems of the body
• Hyperphosphatemia occurs then there are high
  levels of HPO42- in the blood
• Hypophosphatemia occurs when there are low levels
  of HPO42- in the blood

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Acid-Base Balance

• The acid-base balance in body fluids depends on
  the hydrogen ion (H) concentration
• Solutions with more H than OH- are acids and
  have a pH of less than 7
• Solutions with more OH- than H are bases
  (alkaline) and have a pH of more than 7

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Acid-Base Balance (continued)

• The pH of extracellular fluid, including the
  blood, is normally between 7.35 and 7.45
• Various metabolic activities in the body produce
  H ions, so the body tends to produce more acids
  than bases
• To deal with pH changes, the body has buffers,
  which are chemical substances that resist changes
  in pH they make strong acids and bases weaker

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Acid-Base Balance (continued)

• The respiratory system and the urinary system
  also help in keeping the pH of fluids in the body
  at about 7.4
• A decrease in CO2 raises the pH and makes body
  fluids more alkaline
• An increase in CO2 in the body fluids (as a
  result of cellular respiration) makes the pH
  lower and body fluids more acidic

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Acid-Base Balance (continued)

• The CO2 in blood reacts with water to form
  carbonic acid
• CO2 H2O ? H2CO3 ? H HCO3-

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Acid-Base Balance (continued)

• Changes in the rate and depth of breathing can,
  therefore, change the pH of body fluids
• An increase in breathing rate and depth
  (hyperventilation) raises pH since CO2 is exhaled
• A decrease in breathing rate and depth
  (hypoventilation) lowers pH since CO2 accumulates

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Acid-Base Balance (continued)

• The pH of body fluids can affect breathing rate
• If the blood becomes more acidic, the breathing
  rate increases to get rid of CO2
• If the blood becomes more alkaline, the breathing
  rate decreases

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Acid-Base Balance (continued)

• The kidneys carry out tubular secretion, which
  involves adding materials to the filtrate during
  urine formation
• As the blood becomes more acidic, the kidneys
  excrete more H to raise the pH of the blood (the
  pH of urine is about 6, on average)
• Less H is excreted if the blood pH needs to be
  lowered this does not happen often, though,
  because bodily processes tend to make body fluids
  acidic

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Acid-Base Imbalances

• If the pH of the blood decreases below 7.35,
  acidosis occurs acidosis causes CNS depression
  an individual can go into a coma and even die
• If the pH of the blood increases above 7.45,
  alkalosis occurs alkalosis causes CNS
  excitation an individual can experience
  nervousness, muscle spasms, convulsions, and even
  death
• Compensation is a physiological response to an
  acid-base imbalance that attempts to normalize
  blood pH