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?

10% Signup and view all the answers

Where is Na+ mainly reabsorbed in the nephron?

Proximal convoluted tubule Signup and view all the answers

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

Aldosterone Signup and view all the answers

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

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

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

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

What is the primary effect of hyperphosphatemia on calcium homeostasis?

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

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

50% Signup and view all the answers

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

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

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

Modulation of ion channel activity 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?

Intercalated cells Signup and view all the answers

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

Maintaining low intracellular Na+ concentrations Signup and view all the answers

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

1% Signup and view all the answers

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

Increased K+ efflux into the tubule Signup and view all the answers

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

Acidemia decreases protein binding and increases the ionized calcium fraction Signup and view all the answers

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

Increased K+ reabsorption at the expense of acid loss Signup and view all the answers

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

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

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

Parathyroid hormone (PTH) Signup and view all the answers

What is the role of Ca2+ in coagulation processes?

Linking coagulation factors to platelets Signup and view all the answers

How is cytoplasmic free Ca2+ kept low in cells?

By pumping Ca2+ into the sarcoplasmic reticulum Signup and view all the answers

What is the dominant intracellular cation in the body?

Potassium Signup and view all the answers

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

Pressure natriuresis Signup and view all the answers

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

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

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

Modulating resting membrane potential Signup and view all the answers

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

Acute K+ distribution Signup and view all the answers

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

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

How do catecholamines influence K+ handling in muscles?

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

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

To maintain gradients of ions in cells Signup and view all the answers

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

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

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

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

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

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

What is the primary mechanism of Mg2+ absorption ?

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

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

plasma Mg2+ concentration Signup and view all the answers

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

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

What is the primary function of phosphate in energy metabolism?

ATP synthesis Signup and view all the answers

Which molecule is formed with the help of phosphate?

2,3-diphosphoglycerate (2,3-DPG) Signup and view all the answers

Where is the majority of total body phosphorus stored?

In bone Signup and view all the answers

How is GI uptake of phosphate primarily achieved?

By paracellular diffusion Signup and view all the answers

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

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

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

They are rapidly dealt with by increased renal excretion Signup and view all the answers

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

Calcitriol (1,25-dihydroxycalciferol) Signup and view all the answers

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

All of the above Signup and view all the answers

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

Through renal excretion, primarily in the proximal tubule Signup and view all the answers

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

Intercalated cells Signup and view all the answers

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

Reduces renal PO43- reabsorption Signup and view all the answers

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

Cellular chloride secretion followed by paracellular sodium and water movement Signup and view all the answers

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

1:15 Signup and view all the answers

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

ATPases Signup and view all the answers

maintaining SODIUM concentration gradient is vital for the function of:

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

daily Na+ intake is

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

which route is the predominant for Na loss

renal Signup and view all the answers

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

atrial volume sensing: ANP release Signup and view all the answers

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

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

Daily requirements of K?

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

daily K+ intake is a similar magnitude to ?

entire ECF K+ content Signup and view all the answers

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

achieved when K efflux is equal to K influx Signup and view all the answers

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

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

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

aldosterone 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.

rapidly modulate renal K+ Signup and view all the answers

where its found the calcium major storage

bones Signup and view all the answers

calcium play important role in?

muscular contraction Signup and view all the answers

Increases in cytoplasmic Ca2+ concentration is

key mediator of cell death pathways 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) ?

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

which other electrolytes can affect Ca2+ homeostasis ?

magnesium 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?

take blood sample without tourniquet Signup and view all the answers

what is the primary intracellular anion

magnesium Signup and view all the answers

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

because most of magnesium is sequestered within organelles Signup and view all the answers

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

majority is in the biologically active ionized form Signup and view all the answers

magnesium Excretion is via?

GI tract and kidneys Signup and view all the answers

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

thick ascending loop of Henle Signup and view all the answers

what is the effect of adrenergic stimulation on magnesium?

decreases in serum Mg2+ concentrations Signup and view all the answers

of total body magnesium, majority found in?

bone Signup and view all the answers

another important function of phosphate in body

buffer system Signup and view all the answers

which type of phosphate normally found in plasma?

inorganic phosphates Signup and view all the answers

which type of phosphate normally found intracellular ?

organic phosphates Signup and view all the answers

typical daily intake of phosphate is

1 g Signup and view all the answers

what is the main mechanism of GI uptake

paracellular diffusion Signup and view all the answers

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

proximal tubule Signup and view all the answers

what is the main effect of vitamin D on phosphate absorption

increases GI and renal absorption Signup and view all the answers

what is the main effect of PTH on phosphate absorption

reduces renal reabsorption. Signup and view all the answers

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

third of plasma osmolality and two thirds of plasma negative charge. 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?

gastric hydrochloric acid Signup and view all the answers

how is the GI secretions formed?

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

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

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

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

Reduction in HCO3− concentration Signup and view all the answers

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

Anion gap model Signup and view all the answers

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

PO43−, sulfate, and anionic proteins Signup and view all the answers

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

It remains normal Signup and view all the answers

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

Bicarbonate (HCO3-) Signup and view all the answers

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

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

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

It leads to a fall in plasma pH. Signup and view all the answers

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

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

intravascular fluid therapy may affect acid-base by?

A + B Signup and view all the answers

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

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

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

Extracellular acidosis due to saline administration 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?

Medical patients with sepsis Signup and view all the answers

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

The high concentration of chloride ions in saline reduces the strong ion difference (SID) 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?

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

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

Coagulopathy Signup and view all the answers

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

The strong ion difference (SID) Signup and view all the answers

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

Lactated Ringer's solution Signup and view all the answers

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

Dilution of bicarbonate ions Signup and view all the answers

IV NaHCO3 to treat metabolic acidosis should be

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

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

Hyperosmolar hypernatremia Signup and view all the answers

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

Intracellular acidosis Signup and view all the answers

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

It helps in O2 offloading to tissues Signup and view all the answers

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

It may contribute to hypernatremia Signup and view all the answers

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

Conversion of HCO3- to CO2, leading to a physiologic challenge for patients with ventilatory impairment 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?

Both a and b Signup and view all the answers

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

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

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

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

when the treatment with bicarbonate should be stoped?

ph above 7.2 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

weight and base deficit 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 ?

renal disease with impaired HCO3− distribution 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).

half of the total calculated dose should be given 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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Description

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.