11 Renal regulation of ions & Regulation of Acid-Base Balance

Flashcards covering renal regulation of electrolytes (Sodium, Potassium, Calcium, Magnesium, Phosphate) and the regulation of Acid-Base balance, including ABG interpretation and compensatory mechanisms.

What is the function of the Countercurrent multiplier (Loop of Henle)?

It establishes a gradient of osmolarity from the cortex ($300\,mOsm/L$) to the papilla ($1200\,mOsm/L$) aided by Urea recycling.

What is the role of the Countercurrent exchanger (Vasa recta)?

It maintains the corticopapillary osmotic gradient established by the Countercurrent multiplier.

How does the Collecting duct act as an osmotic equilibrating device?

Depending on plasma levels of ADH, it allows collecting duct urine to equilibrate with the hyperosmotic medullary gradient.

What is the normal plasma concentration of Sodium ($Na^+$)?

$$142\,mEq/L$$

What is the normal plasma concentration of Potassium ($K^+$)?

$$4\,mEq/L$$

What are the characteristics of Hyponatremia?

It is defined as a [serum sodium] < $135\,mEq/L$, with dilutional hyponatremia being the most common form.

• common electrolyte disorder

• excess water retention

What are the clinical signs and symptoms of Hyponatremia?

Nausea, malaise, stupor, coma, and seizures.

How is Hypernatremia defined and what is its most common cause?

It is a rise in serum sodium concentration greater than $145\,mEq/L$, most commonly resulting from free water loss.

What are the clinical symptoms of Hypernatremia?

Irritability, stupor, and coma.

What is the reference range for serum potassium in adults?

$$3.5-5.1\,mEq/L$$

Which factors influence the shift of potassium into cells?

Increased ECF pH (alkalosis), insulin, and epinephrine.

What factors cause potassium to shift out of cells into the ECF?

Decreased ECF pH (acidosis), digitalis, $O_2$ lack (ATP depletion), hyperosmolality, hemolysis, infection, ischemia, and trauma.

What are the primary routes of potassium output from the body?

Urinary excretion ($90\,mEq/day$) and feces ($10\,mEq/day$).

What is the diagnostic threshold for Hypokalemia?

A serum K⁺ level < $3.5\,mEq/L$ ($3.5\,mmol/L$).

Severe hypokalemia may induce which two dangerous conditions?

Dangerous arrhythmias and rhabdomyolysis.

What diagnostic tool can distinguish renal from nonrenal loss of potassium?

Transtubular potassium concentration gradient (TTKG).

What are common renal causes of potassium loss?

• Increased aldosterone or cortisol

• diuretics (thiazides, loop diuretics)

• metabolic alkalosis

What are the ECG changes associated with Hypokalemia?

Slightly prolonged PR interval, ST depression, shallow T waves, and prominent U waves.

What is the diagnostic threshold for Hyperkalemia?

A serum potassium level greater than $5.0\,mEq/L$ ($5.0\,mmol/L$).

Which drugs are known to potentially cause Hyperkalemia?

ACE inhibitors, ARBs, potassium-sparing diuretics (spironolactone, triamterene, amiloride), NSAIDs, trimethoprim, cyclosporine, and heparin.

What are the classic ECG changes associated with Hyperkalemia?

Peaked T waves, widened QRS, prolonged PR interval, and flat or absent P waves.

What represents the physiologically active form of calcium necessary for muscle contraction and nerve function?

Ionized calcium.

What is the normal range for total plasma calcium?

$8.5-10.5\,mg/dL$ ($2.1\,2.6\,mmol/L$).

What is the normal range for ionized calcium?

$4.6-5.3\,mg/dL$ ($1.15-1.32\,mmol/L$).

Which three substances control the balance of calcium in the body?

Parathyroid hormone (PTH), Calcitonin, and Vitamin D.

How much calcium do the kidneys filter daily and how much is reabsorbed in the proximal convoluted tubule?

The kidneys filter about $10,800\,mg/d$ and reabsorb about $60\%$ in the proximal convoluted tubule.

What percentage of the filtered load of calcium is typically excreted?

About $0.5\%$ to $2\%$ (approximately $50-200\,mg\,Ca^{2+}/d$).

What should be checked to diagnose Hypocalcemia?

Decreased serum PTH, vitamin D, or magnesium levels.

What are the physical signs associated with Hypocalcemia deficit?

Tetany, Chvostek sign (facial twitching), and Trousseau sign (carpal spasm).

What are the most common causes of Hypercalcemia?

Primary hyperparathyroidism and malignancy-associated hypercalcemia.

What are the symptoms described by the mnemonic for Hypercalcemia?

Stones (renal), bones (pain), groans (abdominal pain), thrones (increased urinary frequency), and psychiatric overtones (anxiety, altered mental status).

What is the primary anion in the Intracellular Fluid (ICF)?

Phosphate

What is the normal phosphate range for adults?

$2.8$ to $4.5\,mg/dL$

What are the causes of Hyperphosphatemia?

Acute or chronic renal failure, chemotherapy, and excessive ingestion of phosphate or vitamin D.

What are common causes of Hypophosphatemia?

Malnourishment/malabsorption, alcohol withdrawal, and use of phosphate-binding antacids.

Where is the majority ($50\%$ to $60\%$) of the body's magnesium contained?

In the bone.

What is the normal magnesium level for adults?

$1.3$ to $2.1\,mEq/L$ ($1.8$ to $2.6\,mg/dL$).

What are the common causes of Hypermagnesemia ($>2.5\,mEq/L$)?

Renal failure, oliguria, dehydration, Addison's disease, and use of magnesium-containing antacids or enemas.

What are the clinical signs of Hypermagnesemia?

Loss of deep tendon reflexes (DTRs), lethargy, bradycardia, hypotension, and respiratory/cardiac arrest.

What ECG changes are observed in Hypermagnesemia?

Tall T wave, widened QRS, flattened P wave, and increased PR interval.

What are the causes of Hypomagnesemia ($<1.0\,mEq/L$)?

Malabsorption (Kwashiorkor), chronic alcoholism, chronic renal diseases, and prolonged nasogastric suction.

What are the clinical signs of Hypomagnesemia deficit?

Hyperactive DTRs and CNS changes.

What is the normal range for blood pH?

$$7.35-7.45$$

At what pH levels does death typically occur?

Below $6.8$ or above $8.0$

How is Acidosis (acidemia) defined in terms of pH?

A pH below $7.35$

How is Alkalosis (alkalemia) defined in terms of pH?

A pH above $7.45$

Which equation represents the carbonic acid equilibrium in the blood?

$$CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$$

What are the three primary systems that regulate hydrogen ion concentration?

1. Buffers system, 2. Respiratory Regulation, 3. Renal Regulation.

What is the 'first line of defense' against pH changes and how quickly do they react?

Chemical buffer systems (Bicarbonate, Phosphate, Protein); they react within seconds.

What is the most important extracellular fluid (ECF) buffer?

Bicarbonate Buffer System ($NaHCO_3/H_2CO_2$).

What is the normal ratio of bicarbonate to carbonic acid in the blood?

Approximately $20:1$

Where is the Phosphate buffer system most powerful and concentrated?

Intracellularly and within the kidney tubules.

Which blood protein acts as a significant buffer due to its acidic and basic groups?

Albumin

Which buffer in Red Blood Cells (RBCs) plays an important role in respiratory regulation of pH?

Hemoglobin buffer

What is considered the 'second line of defense' in acid-base balance?

The respiratory mechanism (Exhalation of carbon dioxide).

How do the lungs respond to a decrease in pH?

The respiratory center stimulates deeper and faster breathing to exhale more $CO_2$, thereby decreasing blood acidity.

Where are the chemoreceptors located that control the rate of respiration?

In the respiratory center of the brain (medulla oblongata and pons).

What is the 'most effective' but slow regulator of pH?

The renal mechanism.

By what three main processes do kidneys regulate acid-base balance?

Excretion of $H^+$ ions, reabsorption of bicarbonate ($HCO_3^-$), and excretion of ammonium ions ($NH_4^+$).

What is the normal pH of urine and why is it usually acidic?

The normal pH is $6.0$ because the kidneys eliminate $H^+$ ions generated by normal metabolism.

What defines Metabolic Acidosis/Alkalosis?

They are caused by an imbalance in acid or base production or excretion by the kidneys.

What defines Respiratory Acidosis/Alkalosis?

They are caused by changes in carbon dioxide exhalation due to lung or breathing disorders.

What are the potential causes of Respiratory Acidosis?

Lung diseases (COPD, asthma), airway obstruction, drugs (anesthetics, sedatives, narcotics), and neuromuscular diseases.

What are the common causes of Metabolic Acidosis?

Diabetic Ketoacidosis (DKA), Lactic acidosis, chronic renal failure, diarrhea, and ingestion of methanol or aspirin.

What are the causes of Respiratory Alkalosis?

Hyperventilation, anxiety, fever, sepsis, and mechanical overventilation.

What are the causes of Metabolic Alkalosis?

Loss of $H^+$ ions via GI tract (vomiting, gastric suctioning), diuretic use (Frusemide), and excessive $NaHCO_3$ use.

In Respiratory Acidosis, what are the characteristic levels of $pH$, $PCO_2$, and $HCO_3^-$?

$pH$ is decreased ($\downarrow$), $PCO_2$ is increased ($\uparrow$), and $HCO_3^-$ is increased ($\uparrow$) as a compensatory response.

What is the compensatory response for Metabolic Acidosis?

Hyperventilation (immediate).

What is the compensatory response for Respiratory Acidosis?

Increased renal $HCO_3^-$ reabsorption (delayed).

What is the Henderson-Hasselbalch equation provided in the text?

$$pH = 6.1 + \log\frac{[HCO_3^-]}{0.03 \times PCO_2}$$

What formula is used to predict respiratory compensation for simple metabolic acidosis?

Winters formula: $PCO_2 = 1.5 [HCO_3^-] + 8 \pm 2$

What is the formula for the Anion Gap?

Anion gap $= Na^+ - (Cl^- + HCO_3^-)$

What does 'MUDPILES' stand for in high anion gap metabolic acidosis?

Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates.

What does 'HARDASS' stand for in normal anion gap metabolic acidosis?

Hyperchloremia, Addison disease, Renal tubular acidosis, Diarrhea, Acetazolamide, Spironolactone, Saline infusion.

What is the normal range for $P_{a}CO_2$ in an Arterial Blood Gas (ABG) analysis?

$$35-45\,mmHg$$

What is the normal range for bicarbonate ($HCO_3^-$) in an ABG?

$$22-26\,mEq/L$$

What is the normal range for $P_{a}O_2$?

$$80-100\,mmHg$$

What is the normal $O_2$ saturation ($SaO_2$) range?

$$95-100\%$$

In ABG interpretation, if the primary cause is respiratory, how does $CO_2$ relate to $pH$?

The $CO_2$ level moves in the opposite direction of the $pH$ level.

In ABG interpretation, if the primary cause is metabolic, how does $HCO_3^-$ relate to $pH$?

The $HCO_3^-$ level moves in the same direction as the $pH$ level.

What defines a Mixed Acid-Base Disorder?

The presence of more than one primary acid-base disturbance at the same time.

What indicates that compensation is in progress according to Step 5 of ABG interpretation?

Either $CO_2$ or $HCO_3^-$ moves in the opposite direction of the $pH$.

How does the respiratory system compensate for primary metabolic alkalosis?

By slow and shallow breathing to 'retain' $CO_2$.

How does the renal system compensate for primary respiratory acidosis?

By excreting more $H^+$ in urine and retaining more $HCO_3^-$.

What is the difference between partial and complete compensation?

Partial: $pH$ remains abnormal. Complete: $pH$ returns to the normal range.

Calculate the state: $pH=7.18$, $PaCO_2=68\uparrow$, $HCO_3^-=29\uparrow$.

Partly compensated respiratory acidosis.

Calculate the state: $pH=7.56$, $CO_2=50\uparrow$, $HCO_3^-=38\uparrow$.

Partly compensated metabolic alkalosis.

How does high $CO_2$ impact the blood $pH$?

It lowers the $pH$ value (acidosis).

What is the normal Base Excess range?

$$\pm 2$$

Which cation is predominantly located in the Intracellular Fluid ($159\,mEq/kg\,H_2O$)?

Potassium ($K^+$).

What is the main extracellular cation?

Sodium ($Na^+$).

What is a major clinical sign of Magnesium deficit ($<1.0\,mEq/L$) involving deep tendon reflexes?

Hyperactive DTRs.

What condition is associated with a 'U wave' on an ECG?

Hypokalemia.

What is the effect of Alkalosis on potassium distribution?

It causes a shift of potassium into the cells.

What is the relationship between serum sodium and irritability/coma?

High serum sodium concentration (Hypernatremia) causes irritability, stupor, and coma.