chapter 47 quiz 2 electrolytes and acid base physiology
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Questions and Answers

What is the main determinant of extracellular fluid (ECF) volume?

  • Chloride (Cl-)
  • Magnesium (Mg2+)
  • Potassium (K+)
  • Sodium (Na+) (correct)

    • What accounts for nearly all the osmotically active solute in plasma and interstitial fluid?

  • Potassium (K+)
  • Calcium (Ca2+)
  • Sodium (Na+) (correct)
  • Chloride (Cl-)

    • What is the approximate total body content of Na+ in mmol?

  • 4000 mmol (correct)
  • 2000 mmol
  • 3000 mmol
  • 5000 mmol

    • How much of the total body Na+ content is intracellular?

    <p>10%</p> Signup and view all the answers

    Where is Na+ mainly reabsorbed in the nephron?

    <p>Proximal convoluted tubule</p> Signup and view all the answers

    Which hormone influences active Na+ absorption in the small intestine and colon?

    <p>Aldosterone</p> Signup and view all the answers

    What is the primary action of PTH when ionized Ca2+ levels decrease?

    <p>Stimulates osteoclast bone resorption to release Ca2+ into the ECF</p> Signup and view all the answers

    What is the final step in the manufacture of active vitamin D (calcitriol)?

    <p>Renal hydroxylation of 25-hydroxy-calciferol to 1,25-dihydroxycalciferol under the influence of PTH</p> Signup and view all the answers

    What is the primary effect of hyperphosphatemia on calcium homeostasis?

    <p>Inhibits the renal hydroxylation of vitamin D to 1,25-dihydroxycalciferol</p> Signup and view all the answers

    What percentage of circulating calcium is in the biologically active ionized form?

    <p>50%</p> Signup and view all the answers

    What is one of the mechanisms that may lead to hyperkalemia in organic acidemia?

    <p>Activation of H+/K+ exchange</p> Signup and view all the answers

    What is the primary cellular action of magnesium (Mg2+) that highlights its diverse clinical applications?

    <p>Modulation of ion channel activity</p> Signup and view all the answers

    Which cell type in the collecting ducts is responsible for the regulation of potassium (K+) secretion under the influence of aldosterone?

    <p>Intercalated cells</p> Signup and view all the answers

    How do principal cells influence potassium (K+) secretion in the collecting ducts?

    <p>Maintaining low intracellular Na+ concentrations</p> Signup and view all the answers

    What is the approximate percentage of total body magnesium found in the extracellular fluid (ECF)?

    <p>1%</p> Signup and view all the answers

    What is the main reason for hypokalemia associated with diuretics that increase distal tubular Na+ content?

    <p>Increased K+ efflux into the tubule</p> Signup and view all the answers

    How does acidemia affect the degree of albumin-protein binding of calcium?

    <p>Acidemia decreases protein binding and increases the ionized calcium fraction</p> Signup and view all the answers

    How do intercalated cells respond in low potassium (K+) settings?

    <p>Increased K+ reabsorption at the expense of acid loss</p> Signup and view all the answers

    What is the primary role of magnesium (Mg2+) in energy metabolism?

    <p>Mg2+ is required for ATP phosphorylation reactions, interacting with the outer two PO43− groups of ATP</p> Signup and view all the answers

    Which hormone is essential for maintaining serum calcium concentrations between 4.5 and 5 mEq/L?

    <p>Parathyroid hormone (PTH)</p> Signup and view all the answers

    What is the role of Ca2+ in coagulation processes?

    <p>Linking coagulation factors to platelets</p> Signup and view all the answers

    How is cytoplasmic free Ca2+ kept low in cells?

    <p>By pumping Ca2+ into the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the dominant intracellular cation in the body?

    <p>Potassium</p> Signup and view all the answers

    What is the primary mechanism involved in excretion of total body excess Na+ mentioned in the text?

    <p>Pressure natriuresis</p> Signup and view all the answers

    How does low potassium intake combined with chronic action of digitalis-like factor contribute to hypertension?

    <p>By inhibiting vascular smooth muscle cell Na+/K+ ATPases</p> Signup and view all the answers

    What is the primary role of K+ in excitable tissues according to the text?

    <p>Modulating resting membrane potential</p> Signup and view all the answers

    Which process involves shifts in K+ between extracellular fluid (ECF) and intracellular fluid (ICF)?

    <p>Acute K+ distribution</p> Signup and view all the answers

    How does insulin influence intracellular levels of Na+ and K+?

    <p>Stimulates Na+/H+ antiporter, leading to intracellular Na+ increase and K+ uptake</p> Signup and view all the answers

    How do catecholamines influence K+ handling in muscles?

    <p>Stimulate Na+/K+ ATPase activity, leading to increases in intracellular K+</p> Signup and view all the answers

    What is the primary function of cell membrane Na+/K+ ATPase according to the text?

    <p>To maintain gradients of ions in cells</p> Signup and view all the answers

    What is the primary role of Mg2+ in maintaining normal transmembrane electrochemical gradients?

    <p>Mg2+ supports the activity of ion-pumping ATPases to stabilize cell membranes and organelles.</p> Signup and view all the answers

    How does Mg2+ antagonize the effects of Ca2+ physiologically (physiologic competitive antagonism of Ca2+)?

    <p>Mg2+ inhibits L-type Ca2+ channels and modifies membrane potential to prevent Ca2+ influx.</p> Signup and view all the answers

    How does Mg2+ antagonize NMDA receptors in the central nervous system?

    <p>Mg2+ reduces Ca2+ entry by specific ion channels, thereby inhibiting a diverse array of excitable tissue cellular actions.</p> Signup and view all the answers

    What is the primary mechanism of Mg2+ absorption ?

    <p>absorbed from the GI tract by a saturable transport system and passive diffusion</p> Signup and view all the answers

    What is the main determinant of total body Mg2+ levels?

    <p>plasma Mg2+ concentration</p> Signup and view all the answers

    How do catecholamines and glucagon affect the intracellular-extracellular balance of magnesium distribution?

    <p>Catecholamines, acting by both - and -adrenoreceptors, and glucagon lead to extrusion of magnesium from intracellular stores.</p> Signup and view all the answers

    What is the primary function of phosphate in energy metabolism?

    <p>ATP synthesis</p> Signup and view all the answers

    Which molecule is formed with the help of phosphate?

    <p>2,3-diphosphoglycerate (2,3-DPG)</p> Signup and view all the answers

    Where is the majority of total body phosphorus stored?

    <p>In bone</p> Signup and view all the answers

    How is GI uptake of phosphate primarily achieved?

    <p>By paracellular diffusion</p> Signup and view all the answers

    Which form of inorganic phosphate predominates in the plasma at normal pH?

    <p>$HPO_{4}^{2-}$ (divalent)</p> Signup and view all the answers

    What happens to postprandial increases in serum phosphate levels according to the text?

    <p>They are rapidly dealt with by increased renal excretion</p> Signup and view all the answers

    What is the primary regulator of phosphate (PO43-) absorption in the intestine and kidneys?

    <p>Calcitriol (1,25-dihydroxycalciferol)</p> Signup and view all the answers

    What is the primary role of chloride (Cl-) in the body?

    <p>All of the above</p> Signup and view all the answers

    How is chloride (Cl-) primarily excreted from the body?

    <p>Through renal excretion, primarily in the proximal tubule</p> Signup and view all the answers

    Which cells in the distal nephron are responsible for regulated control of chloride (Cl-) excretion?

    <p>Intercalated cells</p> Signup and view all the answers

    What is the primary action of parathyroid hormone (PTH) on phosphate (PO43-) handling?

    <p>Reduces renal PO43- reabsorption</p> Signup and view all the answers

    What is the primary mechanism by which gastrointestinal (GI) secretions are formed?

    <p>Cellular chloride secretion followed by paracellular sodium and water movement</p> Signup and view all the answers

    what is the normal sodium concentration gradient between the intracellular and extracellular compartments

    <p>1:15</p> Signup and view all the answers

    sodium concentration gradient between the intracellular and extracellular compartments is maintained by: ATPases and is vital for

    <p>ATPases</p> Signup and view all the answers

    maintaining SODIUM concentration gradient is vital for the function of:

    <p>excitable tissues, including action potentials and membrane potential, and for handling of renal solute</p> Signup and view all the answers

    daily Na+ intake is

    <p>2 to 3 mEq/kg/day at birth</p> Signup and view all the answers

    which route is the predominant for Na loss

    <p>renal</p> Signup and view all the answers

    what is the correct matching for systems involved in the control of circulating volume

    <p>atrial volume sensing: ANP release</p> Signup and view all the answers

    what is the correct matching for systems involved in the control of circulating volume

    <p>atrial volume sensing = ANP release empty = empty hypothalamic osmoreceptor = ADH release juxtaglomerular apparatus = RAA activation</p> Signup and view all the answers

    Daily requirements of K?

    <p>Term infants require 2 to 3 mEq/kg/day</p> Signup and view all the answers

    daily K+ intake is a similar magnitude to ?

    <p>entire ECF K+ content</p> Signup and view all the answers

    Transmembrane potentials particularly depend on K+ permeability. how Transmembrane potentials achieved ?

    <p>achieved when K efflux is equal to K influx</p> Signup and view all the answers

    what is the function of skeletal muscle in the presence of hypokalemia

    <p>expression of Na+/K+ ATPase is reduced</p> Signup and view all the answers

    Other factors that may influence ECF to ICF K+ balance ?

    <p>aldosterone</p> Signup and view all the answers

    In addition to mechanisms involving aldosterone in a feedback loop, it is likely that feed-forward mechanisms also exist, what is the main function of feed-forward mechanisms.

    <p>rapidly modulate renal K+</p> Signup and view all the answers

    where its found the calcium major storage

    <p>bones</p> Signup and view all the answers

    calcium play important role in?

    <p>muscular contraction</p> Signup and view all the answers

    Increases in cytoplasmic Ca2+ concentration is

    <p>key mediator of cell death pathways</p> Signup and view all the answers

    the kidney covert 25-hydroxy-calciferol to 1,25-dihydroxycalciferol (calcitriol) under the influence of PTH. wha is the main action of the active vit D(calcitriol) ?

    <p>stimulates osteoclastic bone resorption and absorption of Ca2+ from the GI tract.</p> Signup and view all the answers

    which other electrolytes can affect Ca2+ homeostasis ?

    <p>magnesium</p> Signup and view all the answers

    you are in the OR and the surgeon ask if you can take a blood sample to check the calcium level ? what is the best way to take the sample?

    <p>take blood sample without tourniquet</p> Signup and view all the answers

    what is the primary intracellular anion

    <p>magnesium</p> Signup and view all the answers

    why the Free ionized Mg2+ levels within the cytoplasm and ECF are low ?

    <p>because most of magnesium is sequestered within organelles</p> Signup and view all the answers

    Within the plasma, where is the majority of Mg2+ is found

    <p>majority is in the biologically active ionized form</p> Signup and view all the answers

    magnesium Excretion is via?

    <p>GI tract and kidneys</p> Signup and view all the answers

    75% of magnesium is freely filtered at the glomerulus, what is the primary tubule for reabsorption.

    <p>thick ascending loop of Henle</p> Signup and view all the answers

    what is the effect of adrenergic stimulation on magnesium?

    <p>decreases in serum Mg2+ concentrations</p> Signup and view all the answers

    of total body magnesium, majority found in?

    <p>bone</p> Signup and view all the answers

    another important function of phosphate in body

    <p>buffer system</p> Signup and view all the answers

    which type of phosphate normally found in plasma?

    <p>inorganic phosphates</p> Signup and view all the answers

    which type of phosphate normally found intracellular ?

    <p>organic phosphates</p> Signup and view all the answers

    typical daily intake of phosphate is

    <p>1 g</p> Signup and view all the answers

    what is the main mechanism of GI uptake

    <p>paracellular diffusion</p> Signup and view all the answers

    Plasma inorganic PO43− is freely filtered at the glomerulus, at which tubule occur the majority of reabsorption

    <p>proximal tubule</p> Signup and view all the answers

    what is the main effect of vitamin D on phosphate absorption

    <p>increases GI and renal absorption</p> Signup and view all the answers

    what is the main effect of PTH on phosphate absorption

    <p>reduces renal reabsorption.</p> Signup and view all the answers

    chloride is the second most abundant electrolyte in the extracellular compartment, therefore responsible for?

    <p>third of plasma osmolality and two thirds of plasma negative charge.</p> Signup and view all the answers

    Most Cl− intake is derived from dietary NaCl, and the GI tract absorbs and secretes large amounts of Cl− in the form of?

    <p>gastric hydrochloric acid</p> Signup and view all the answers

    how is the GI secretions formed?

    <p>paracellular movement of Na+ into the lumen, with water moving down its osmotic gradient</p> Signup and view all the answers

    What is the normal range for anion gap in the plasma?

    <p>4 to 11 mEq/L</p> Signup and view all the answers

    In cases of excess organic acids, what leads to an increase in the anion gap?

    <p>Reduction in HCO3− concentration</p> Signup and view all the answers

    Which model places changes in plasma HCO3− at the core of plasma acid-base balance?

    <p>Anion gap model</p> Signup and view all the answers

    Which ions are represented by 'unmeasured' anions in the anion gap model

    <p>PO43−, sulfate, and anionic proteins</p> Signup and view all the answers

    In the presence of excess Cl− administration, what happens to the anion gap even if HCO3− falls?

    <p>It remains normal</p> Signup and view all the answers

    According to the Stewart model, which of the following is NOT an independent variable that determines plasma pH?

    <p>Bicarbonate (HCO3-)</p> Signup and view all the answers

    What is the normal range for the apparent Strong Ion Difference (SID) in plasma?

    <p>35-45 mEq/L</p> Signup and view all the answers

    How does a reduction in the Strong Ion Difference (SID) affect plasma pH according to the Stewart model?

    <p>It leads to a fall in plasma pH.</p> Signup and view all the answers

    What is the primary advantage of the Stewart model of acid-base balance compared to the traditional approach?

    <p>It is better at explaining acid-base disturbances caused by fluid administration.</p> Signup and view all the answers

    intravascular fluid therapy may affect acid-base by?

    <p>A + B</p> Signup and view all the answers

    What did a meta-analysis of studies comparing saline with balanced perioperative fluid regimes confirm?

    <p>Clearance of biochemical abnormalities within the first or second postoperative day in saline groups</p> Signup and view all the answers

    What was associated with significant hyperkalemia in a trial involving patients undergoing renal transplants?

    <p>Extracellular acidosis due to saline administration</p> Signup and view all the answers

    In the emergency department and intensive care settings, which group of patients showed the greatest effect from receiving saline compared to balanced crystalloid?

    <p>Medical patients with sepsis</p> Signup and view all the answers

    What is the primary cause of hyperchloremic acidosis during high-volume saline infusion?

    <p>The high concentration of chloride ions in saline reduces the strong ion difference (SID)</p> Signup and view all the answers

    How does lactated Ringer's solution differ from normal saline in terms of its effect on acid-base balance?

    <p>The lactate in Lactated Ringer's solution is metabolized, providing an effective SID that counteracts acidosis</p> Signup and view all the answers

    Which of the following is a potential deleterious effect of saline-induced hyperchloremic acidosis?

    <p>Coagulopathy</p> Signup and view all the answers

    According to the Stewart model, what is the primary determinant of plasma pH?

    <p>The strong ion difference (SID)</p> Signup and view all the answers

    Which of the following solutions has an effective strong ion difference (SID) closest to that of plasma?

    <p>Lactated Ringer's solution</p> Signup and view all the answers

    What is the primary mechanism by which saline infusion causes a reduction in plasma bicarbonate concentration?

    <p>Dilution of bicarbonate ions</p> Signup and view all the answers

    IV NaHCO3 to treat metabolic acidosis should be

    <p>reserved for the emergency treatment such as severe hyperkalemia and arrhythmias associated with tricyclic antidepressant overdose.</p> Signup and view all the answers

    What negative effect does IV HCO3− administration bring due to its significant Na+ content?

    <p>Hyperosmolar hypernatremia</p> Signup and view all the answers

    What is the major challenge posed by the conversion of HCO3− to CO2 when administered in excess?

    <p>Intracellular acidosis</p> Signup and view all the answers

    What role does acidosis play during strenuous exercise according to the text?

    <p>It helps in O2 offloading to tissues</p> Signup and view all the answers

    What is the primary reason for HCO3− administration being disputed in critically ill patients?

    <p>It may contribute to hypernatremia</p> Signup and view all the answers

    What is one of the potential negative effects of administering IV NaHCO3 to treat metabolic acidosis?

    <p>Conversion of HCO3- to CO2, leading to a physiologic challenge for patients with ventilatory impairment</p> Signup and view all the answers

    What is one potential reason why the clinical benefit of HCO3- administration may not be apparent in many situations?

    <p>Both a and b</p> Signup and view all the answers

    What is one of the negative effects of IV HCO3- administration mentioned in the text?

    <p>Significant sodium content and osmotic load, leading to potential hyperosmolar hypernatremia and volume overload</p> Signup and view all the answers

    What is the main challenge posed by the conversion of administered HCO3- to CO2 according to the text?

    <p>Excess CO2 production that must be exhaled, which may present a significant physiologic challenge for patients with ventilatory impairment</p> Signup and view all the answers

    when the treatment with bicarbonate should be stoped?

    <p>ph above 7.2</p> Signup and view all the answers

    In situations in which HCO3− administration is required, the total dose required to correct the base deficit can be calculated using

    <p>weight and base deficit</p> Signup and view all the answers

    treatment with HCO3− due to metabolic acidosis can lead in certain situations to “overshoot” toward metabolic alkalosis. when dose this can occur ?

    <p>renal disease with impaired HCO3− distribution</p> Signup and view all the answers

    HCO3− total dose required to correct the base deficit can be calculated using the equation: Dose (mEq) =0.3 × weight(kg) × base deficit(mEq/L).

    <p>half of the total calculated dose should be given</p> Signup and view all the answers

    Study Notes

    Acid-Base Balance

    • Stewart's model proposes that plasma pH is dependent on three independent variables:
      • pCO2 (plasma CO2 tension)
      • Atot (total plasma concentration of nonvolatile buffers)
      • SID (strong ion difference)
    • SID is the difference between the total charge of plasma-strong cations (Na+, K+, Mg2+, Ca2+) and strong anions (Cl-, lactate, sulfate, and others)
    • Normal plasma SID is approximately 42 mEq/L, and reductions in SID lead to a fall in plasma pH

    Henderson-Hasselbach Equation

    • Represents the HCO3- buffer system
    • Plasma HCO3- concentration is an independent determinant of plasma pH

    Anion Gap

    • Defined as the difference between the most abundant measured cation and anion concentrations in the plasma ([Na+] + [K+]) - ([Cl-] + [HCO3-])
    • Normal anion gap is 4 to 11 mEq/L
    • In the presence of excess organic acids, the accumulation of unmeasured anions is accompanied by a reduction in HCO3- to buffer the excess H+ ions, leading to an increase in the anion gap

    Hyperchloremic Acidosis

    • Caused by the administration of fluid with Cl- concentration higher than that of plasma
    • Leads to a metabolic acidosis due to the Cl- content
    • Can be explained by the Henderson-Hasselbach model (dilution of bicarbonate and a resultant base deficit) or the Stewart model (reduction of apparent SID and therefore reduction of plasma pH)

    Bicarbonate Administration

    • Should be reserved for the emergency treatment of select conditions, such as severe hyperkalemia and arrhythmias associated with tricyclic antidepressant overdose

    • Has negative effects, including:

      • Carbon dioxide production
      • Osmotic load and hyperosmolar hypernatremia
      • ECF expansion and volume overload### Sodium Physiology

    • Serum Na+ concentrations are maintained within a tight range (138-142 mEq/L) despite variations in water intake.

    • The excretion of total body excess Na+ relies on inefficient passive mechanisms, particularly the pressure-volume effect.

    • Long-term ingestion of excess salt combined with low potassium ingestion contributes to hypertension.

    Potassium Physiology

    • K+ is the dominant intracellular cation in the body, with a total body content of approximately 4000 mmol, 98% of which is intracellular.
    • The ratio of ICF to ECF K+ balance is vital in maintaining cellular resting membrane potential.
    • Daily requirements reflect age and growth, with more K+ required at higher metabolic rates.
    • Transmembrane potentials depend on K+ permeability, with K+ egress occurring through ion channels down its concentration gradient.

    Acute K+ Distribution

    • Acute K+ distribution involves shifts in K+ between the ECF and ICF, performed by ion transport systems under the influence of insulin, catecholamines, and ECF pH.
    • The cell membrane Na+/K+ ATPase exports three Na+ for every two K+ imported and is the means by which the gradients of these ions are maintained.

    Magnesium Physiology

    • Mg2+ helps maintain normal transmembrane electrochemical gradients, effectively stabilizing cell membranes and organelles.
    • Mg2+ also antagonizes Ca2+ and N-methyl-d-aspartate (NMDA) receptors within the central nervous system.
    • Mg2+ is absorbed from the GI tract by a saturable transport system and passive diffusion, with excretion via the GI tract and kidneys.

    Phosphate Physiology

    • PO43− is the most abundant intracellular anion and helps form biologic molecules such as ATP, DNA, and RNA, membrane phospholipids, and hydroxyapatite in bone.
    • PO43− is required for energy metabolism, cellular signaling, cellular replication, and protein synthesis.
    • Normal plasma inorganic phosphates are maintained at 3 to 5 mg/dL, with most intracellular PO43− being organic.

    Chloride Physiology

    • Chloride (Cl−) has a key role in maintaining plasma osmolality, preserving electrical neutrality, and acid-base status.
    • Normal plasma values are 97 to 107 mEq/L, with Cl− responsible for nearly a third of plasma osmolality and two thirds of plasma negative charge.
    • Most Cl− intake is derived from dietary NaCl, and the GI tract absorbs and secretes large amounts of Cl−.

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    Learn about the role of sodium (Na+) as the dominant extracellular cation and its significance in regulating extracellular fluid volume. Explore the concentration gradient between intracellular and extracellular compartments.

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