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2012-05-07 21:55:29
water electrolyte acid base balace

water, electrolyte & acid-base balance
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  1. describe the major fluid compartments:
    • 65% intracellular fluid (ICF)
    • 35% extracellular fluid (ECF), subdivided into
    • 25% tissue (interstitial) fluid
    • 10% blood plasma

    • Humans: 55% water, 40L
    • fluid compartments: areas separeated by selectively permeable membranes
    • water moves by osmosis
  2. indentify the sources of water gain and loss:
    • gain (intake)
    • metabolic water: a by product of dehydration synthesis rxns and aerobic respiration, 200 mL
    • food: 700mL/day
    • drink: 1,600mL/day

    • loss (output)
    • feces: 200/mL/day
    • expired air: insensible water loss: output thru breath unaware, 300mL/day
    • cutaneous transpiraton: insensible water loss, unaware, water diffuses thru the epidermis and evaporates, 400mL/day
    • sweat: sensible water loss, awear, wetness on skin, 100 mL/day
    • urine: sensible water loss, awear, 1,500 mL/day

    obligatory water loss: output that is relatively unavoidable

    400ml/day is minimum urine output need for waste elimination
  3. describe the mechanisms regulating water intake:
    dehydration: reduces blood volume and pressure, and raises blood osmolarity

    • increased blood osmolarity
    • stimulates hypothalamic osmoreceptors
    • reduces salvation
    • dry mouth
    • sense of thirst
    • ingestion of water

    • reduced blood pressure
    • renin
    • angiotensin II
    • stimulates hypothalamic osmorecptors
    • reduces salvation
    • dry mouth
    • sense of thirst
    • ingestion of water

    • ingestion of water
    • cools and moistens mouth
    • rehydrates blood - long term inhibition of thirst
    • distends stomach and intestines - short term inhibition of thirst
  4. describe the mechanisms regulating water output:
    primary regulation: changes in urine volumes, reflects vascular hydration status

    • Na+/water regulation
    • separate, but linked
    • as salt is reabsorbed or excreted, proportionate amounts of water accompany it

    • dehydration
    • blood volumes declines, blood osmolarity rises
    • increased osmolarity stimulates osmoreceptors, to hypothal to release ADH
    • stimulates distal convoluted tubule and collecting ducts
    • increases water reabsorption
    • reduces urine volume
    • increases ratio of Na+:H2o in urine (slows decline in blood volume and rise in osmolarity) , *forms a negative feedback loop
  5. define and provide examples of fluid deficiency:
    • fluid deficiency: output exceeds intake over a long enough period of time
    • volume depletion (hypovolemia): proprotionate amounts of water and sodium are lost without replacement
    • total body water declines but osmolarity remains normal
    • examples: hemorrage, sever burns, chronic vomiting, diarrhea

    • dehydration (negative water balance):
    • body eliminates significantly more water than sodium
    • all fluid compartments lose water
    • increased osmolarity
    • net cells shrink, water moves out of the cell, become dysfunctional
    • example: lack of fluid intake
  6. define and provide examples of fluid excess:
    • volume excess
    • both sodium and water are retained
    • normal osmolarity
    • can cause edema
    • example: aldosterone hypersecretion

    • hypotonic hydration
    • water intoxication, postivie water balance
    • more water than Na+ is retained or ingested
    • osomolarity is reduces, hypotonic
    • cells swell
    • examples: ADH hypersecretion, and drinking too much water
  7. Identify that happens to the total body water and osmolarity for volume depletion (hypovolemia):
    • total body water: decreased
    • osmolarity: normal (isotonic)
  8. Identify that happens to the total body water and osmolarity for dehydration (negtaive water balance):
    • total body water: decreased
    • osmolarity: increased (hypertonic)
  9. Identify that happens to the total body water and osmolarity for volume excess:
    • total body water: increased
    • osmolarity: normal (isotonic)
  10. Identify that happens to the total body water and osmolarity for hypotonic hydration (positive water balance, water intoxication):
    • total body water: increased
    • osmolarity: decreased (hypotonic)
  11. identify the reasons electrolyes are physiologicall important:
    • chemically reactive, particpate in metabolism
    • determine electrical potential across cell membranes
    • affect osmolarity, and bodys water content and distribution
  12. describe, in general, the electrolyte composition of the blood plasma and intracellular fluid:
    • blood plasma
    • Na+ 145
    • K+ 4
    • Cl- 103
    • Ca2+ 5
    • inorganic phosphates 4
    • osmolarity: 300 mOsm/L
    • more Na+ and Cl-

    • intracellular fluid
    • Na+ 12
    • K+150
    • Cl- 4
    • Ca2+ <1
    • inorganic phosphates 75
    • osmolarity: 300 mOsm/L
    • more K+ and inorganic phosphates
  13. identify the fxn of sodium and define hypernatremia and hyponatremia:
    • principal cation of the ECF, 90-95% of its osmolarity
    • most significant in determining total body water and the distribution of water among fluid compartments
    • adults need .05g/day
    • excess is excreted by kidneys

    • hypernatremia
    • plasma sodium concentration in excess of 145mEq/L
    • causes water rentention, hypertension, and edema

    • hyponatremia
    • plasma concentration less than 130 mEq/L
    • easily corrected
  14. describe how aldosterone regulates Na+ and K+ balance:
    • water follows Na+
    • urine contains less NaCl and more potassium and has a lower pH
    • strongly influcences sodium reabsorption, little effect on plasma sodium concentration

    • only way to change Na+ concentration is by ADH
    • modifies water excretion independent of sodium

    in the case of hypernatremia - increase amount of water reabsorbed, normal Na+

    in the case of hyponaterma - decrease water reabsorption, normal Na+
  15. describe how parathryoid hormone regulates Ca2+ and phosphate balance:
    • Ca2+
    • low Ca2+ inside cell - regulated by PTH
    • PTH effects:
    • bone deposition and reabsorption
    • intestinal absorption
    • urinary excretion

    • PO4
    • high PO4 inside cell - regulated by:
    • increased Ca2+ reabsorption in DCT
    • increased PO4 excretion (PTH)
    • PO4 imbalance is not problematic - plenty in diet
  16. define hypercalcemia and hypocalcemia:

    • increased plamsa Ca2+
    • reduces sodium perbeability of plamsa membranes and inhibits depolarization of the never and muslce cells
    • causes: muscluar weakness, depressed reflexes, cardiac arrhythemia

    • hypocalcemia
    • decreased plasma Ca2++
    • increases sodium premeability of plasam membranes, over exciteable nervouse/muscluar systems
    • causes: tetany
  17. describe the imporatance of maintainig the pH of body fluids:
    • essential for protein fxn
    • metabolism
    • fxn of enzymes
  18. describe acids, bases, and buffers:
    • acids
    • chemcials that release H+
    • strong: HCl = H+ (+) Cl-
    • weak: H2CO3 = H+ (+) HCO3-

    • bases
    • chemicals that accept H+
    • strong: OH- (+) H+ = H2O
    • weak: HCO3-

    • buffers
    • stablilze pH
    • remove or add H+ to solutions
    • coverts strong acid or base to a weak one
    • H2CO3 <--> H+ (+) HCO3-
  19. define buffer systems and list the major buffer systems of the intracellular and extracellular fluids:
    buffer systems: composed of weak acids and weak bases

    • ECF
    • bicarbonate buffer system: solution of carbonic acid and bicarbonate ions
    • CO2 + H2O <--> H2CO3 <--> HCO3- (+) H+

    • ICF
    • phosphate buffer systems: a solution of HPO4(2)- and H2PO4-
    • H2PO4- <---> HPO4(2)- + H+
    • important in renal tubules and ICF
    • protein buffer systems: some amino acids have carboxyl (-COOH) groups which release H+, others have an amino (-NH2) group, which binds to H+ when pH falls
    • 3/4 of chemical buffering in body fluids
    • HgB and plasma proteins
  20. identify the sources of hydrogen ion gain and loss:
    • H+ gain
    • increased CO2 (hypoventilation)
    • decreased HCO3- metabolism (diarrhea, urine)

    • H+ loss
    • increased CO2 (hyperventilation)
    • decreased H+ metabolis, due to high protein in diet, excess H+, urine acidic (vomit, urine)
  21. describe the role of buffer systems, the respiratory system, and the urinary system in maintaining acid-base balance:
    stabalize pH

    • buffers
    • 1st mechanism
    • fast, msec - sec.
    • least buffering capacity

    • respiratory
    • 2nd in terms of speed
    • sec. - min.
    • via CO2 levels
    • middle level buffering capacity

    • urianry (renal)
    • 3rd in speed
    • slow
    • hours- days
    • via HCO3-/H+ levels
    • most buffering capacity
  22. describe the mechanisms by which the kidneys control blood pH:
    • when pH is balanced
    • HCO3- filtered, but cant be directly reabsorbed
    • filtered HCO3- recylced into new HCO3-
    • all filtered HCO3- recovered, no net gain or loss
    • H2O + CO2 > H2CO3 > HCO3- (goes into interstitial fluid), H+ goes into tubular fluid, combinds with HCO3- > H2CO3, then dissoicates into H2O and CO2, water is excreted and CO2 goes back into the tubular cells and begins rxn again
    • normal pH: all filtered HCO3- is recovered

    • excess H+
    • typcial: when all HCO3- is gone from tubular fluid, secreteds H+ combinds with HPO4(2)- * phosphate buffer*
    • H2O + CO2 > H2CO3 > H+ into tubular fluid, combindes with HPO4(2)- > H2PO4-, excreted, gets rid of extra H+
    • HCO3- is recovered in interstitial fluid
    • interstitial fluid impacts: HCO3- recovered, net HCO3- gain, net H+ loss, neurtralize acid
    • excess H+ is greater w/ amino acid catabolism, H+ secreted + excreted as NH4+
    • glutamine: breaks down into HCO3- recovered in interstitial fluid, NH4+ (antiports with Na+)

    • acidosis
    • pH < 7.35
    • all filtered HCO3- is recovered and extra H+ is secreted
    • excreted: binds to phosphates, as NH4+

    • alkalosis
    • pH > 7.45
    • not all filtered HCO3- is recovered, so HCO3- is excreted
  23. define acidosis:
    • a pH below 7.35
    • increased acidity
    • increased H+
    • decreased pH
  24. define alkalosis:
    • a pH above 7.45
    • increased alkalinity
    • decreased H+
    • increased pH
  25. distinguish beteween respiratory and metabolic acid-base imbalances:
    • respiratory
    • pH changes by respiratory system
    • renal system compensates (change in CO2)
    • if possible, respiratory system helps correct

    • metabolic
    • pH cnages not caused by changes in CO2
    • respiration system compenstates, if possible
    • renal system helps correct
  26. describe the problem, cause, repriratory compenstation, and renal compensation for respiratory acidosis:
    • problem: increased CO2, increased H+
    • cause: hypoventilation, emphysema
    • respiratory comp: increased ventilation, decrease CO2
    • renal comp: increased H+ excretion
  27. describe the problem, cause, repriratory compenstation, and renal compensation for respiratory alkalosis:
    • problem: decreased CO2, decreased H+
    • cause: hyperventilation, high altitude
    • respiratory comp: decreased ventilation, increase CO2
    • renal comp: increased HCO3-
  28. describe the problem, cause, repriratory compenstation, and renal compensation for metabolic acidosis:
    • problem: increased H+ or decreased HCO3-
    • cause: excercise, diabetes, chronic diarrhea
    • respiratory comp: increased ventilation, decreased CO2
    • renal comp: increased H+ excretion
  29. describe the problem, cause, repriratory compenstation, and renal compensation for metabolic alkalosis:
    • problem: decreased H+, or increased HCO3-
    • causes: vomiting
    • respiratory comp: decreased ventilation, increased CO2
    • renal comp: increased HCO3-
  30. define hyperkalemia:
    • K+ > 5.5 mEq/L
    • less concentration difference between the ICF and ECF, so outward diffusion is reduced (increased K+ in ECF)
    • more K+ remains inside the cell
    • plasma membrane has a less negative resting potenitial, closer to the threshold at which it will set off action potenial (more depolarized)
    • cells more excitable
  31. define hypokalemia:
    • K+ < 3.5 mEq/L
    • ECF K+ concentration falls
    • more K+ mves from the ICF to the ECF
    • cells become hyperpolarized
    • never/muscle cells less excitable
    • reflected in: muscle weakness, decreased muscle tone, irregular electrical activity
  32. the most abundant cation in the extracelluar fluid (ECF) is:

    A. Cl-
    B. phosphate (Pi)
    C. Na+
    D. K+
    E. Ca2+
    C. Na+
    (this multiple choice question has been scrambled)
  33. all of the following inhibit the sense of thirst EXCEPT:

    A. cooling the skin
    B. moistening the mouth
    C. stretching the stomach and intestines
    D. rehydrating the blood
    A. cooling the skin
    (this multiple choice question has been scrambled)
  34. in hypovolemia, total body water _______ and osmolarity ______.

    A. decreases; remains normal
    B. decreases; decreases
    C. decreases; decreases
    D. increases; remains normal
    A. decreases; remains normal
    (this multiple choice question has been scrambled)
  35. the largest body water compartment is the:

    A. interstitial fluid
    B. blood plasma
    C. intracellular fluid
    D. extracellular fluid
    C. intracellulary fluid
    (this multiple choice question has been scrambled)
  36. Approximately 28% of the typical water intake comes from ___________, whereas __________ constitutes about 12% of water output. [Refer to Figure 24.2]

    food, expired air
    cutaneous transpiration, urine
    metabolic water, feces
    drink, sweat
    drink, urine
    food, expired air
  37. Regarding fluid imbalance, ____________ is characterized by elevated body water and ____________ osmolarity.

    dehydration, reduced
    volume depletion, elevated
    volume excess, elevated
    volume depletion, reduced
    hypotonic hydration, reduced
    hypotonic hydration, reduced
  38. ____________ occurs when proportionate amounts of water and sodium are lost without replacement.

    metabolic acidosis
  39. Dehydration can lead to an increase in [Na+] in the blood. Place the following events in the correct sequence for countering this physiological problem.

    aquaporins inserted into the collecting duct
    osmoreceptors stimulated
    blood osmolarity decreases
    elevated blood osmolarity
    release of ADH
    increased water reabsorption
    • elevated blood osmolarity
    • osmoreceptors stimulated
    • released of ADH
    • aquaporins inserted into the collecting ducts
    • increased water reabsroption
    • blood osmolarity decreases
  40. A deficiency of potassium in the blood is called:

  41. Which of the following electrolytes is the most abundant in intracellular fluid?

  42. The best chemical buffers are a combination of:

    a strong acid and a weak base
    a strong base and a weak acid
    a weak acid and a weak base
    a strong acid and a strong base
    a weak acid and a weak base
  43. Which of the following buffer systems is most important in the renal tubules and ICF?

    shamwow buffer system
    phosphate buffer system
    protein buffer system
    bicarbonate buffer system
    phosphate buffer system
  44. Which of the following is the first line of defense (i.e. is the first to respond) against changes in pH?

    respiratory system
  45. Increased excretion of ammonium chloride (NH4Cl) in the urine most likely indicates:

  46. Overuse of antacids or chronic vomiting can result in which of the following?

    respiratory acidosis
    metabolic acidosis
    respiratory alkalosis
    metabolic alkalosis
    metabolic alkalosis