Renal Pathophysiology Chapter 7

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Questions and Answers

What is the primary cause of the patient's hypokalemia in this case?

Impaired renal potassium excretion

Excessive fluid retention

Increased dietary potassium intake

Increased urinary potassium loss (correct)

What factor is most likely contributing to the patient's recent onset of hypertension?

Hyperkalemia affecting renal function

Increased sodium retention due to low potassium levels (correct)

High total CO2 levels causing metabolic alkalosis

Decreased blood volume from muscle weakness

Which of the following syndromes is associated with hypokalemia and hypertension?

Liddle Syndrome

Bartter syndrome

Gitelman syndrome

Syndrome of apparent mineralocorticoid excess (correct)

What physiological mechanism can lead to urinary potassium wasting?

Increased sodium delivery to the distal nephron Signup and view all the answers

Which primary electrolyte imbalance is most consistent with the laboratory findings of this patient?

Hypokalemia with metabolic alkalosis Signup and view all the answers

What primarily regulates potassium balance in the body?

Na-K-ATPase pump Signup and view all the answers

Which of the following conditions can lead to hyperkalemia?

Hypoaldosteronism Signup and view all the answers

What is the expected effect of hypokalemia on membrane potential?

Membrane potential becomes more electronegative Signup and view all the answers

Which process is responsible for most potassium reabsorption in the nephron?

Proximal tubule Signup and view all the answers

How does metabolic acidosis affect potassium levels in the body?

Increases plasma potassium concentration Signup and view all the answers

What is the role of beta-adrenergic blockade on plasma potassium levels?

It decreases K+ secretion Signup and view all the answers

Which of the following is NOT a function of potassium in the body?

Hemoglobin synthesis Signup and view all the answers

What happens to sodium channels during hyperkalemia?

Decreased sodium influx Signup and view all the answers

Intense physical exercise can contribute to which of the following?

Release of potassium from muscle cells Signup and view all the answers

Which factor does NOT contribute to hyperkalemia in chronic renal failure?

Increased insulin production Signup and view all the answers

Study Notes

Objectives of Study

Understand factors regulating potassium balance, focusing on transcellular distribution and urinary excretion.
Recognize major causes of hyperkalemia, with emphasis on impaired urinary potassium excretion.
Learn physiologic principles for therapies aimed at reversing hyperkalemia.
Identify factors and mechanisms leading to lowered plasma potassium and urinary potassium wasting.
Describe clinical implications of conditions such as Syndrome of apparent mineralocorticoid excess and various syndromes affecting potassium handling.

Case Presentation

Patient: 49-year-old woman with moderate, recent-onset hypertension and mild muscle weakness.
Lab results:
- Plasma sodium (Na): 140 mEq/L
- Plasma potassium (K): 3.1 mEq/L
- Plasma chloride (Cl): 98 mEq/L
- Total CO2: 32 mEq/L
- Urine sodium: 80 mEq/L
- Urine potassium: 60 mEq/L

Physiologic Effects of Potassium

Total body potassium (K) approximately 3,000-4,000 mEq, with 98% intracellularly stored.
Na-K-ATPase pump functions with a 3:2 ion transport ratio, influencing intracellular and extracellular potassium concentrations.
Changes in K+ levels influence membrane potential, affecting Na-channel function.
Abnormal potassium levels can cause muscle weakness and cardiac arrhythmias, largely dependent on the magnitude and rate of change.

Regulation of Potassium Balance

Average extracellular volume is between 12-14 L; healthy plasma potassium levels range from 4-5 mEq/L.
Daily potassium intake is 40-100 mEq; hyperkalemia avoided by increased cellular uptake via the Na-K-ATPase pump and enhanced renal excretion within 6-8 hours.

Urinary Potassium Excretion

Glomerular filtration rate (GFR) is about 180 L/day, with a plasma potassium around 4.5 mEq leading to a filtered load of approximately 810 mEq.
Significant passive reabsorption occurs in the proximal tubule and thick ascending loop of Henle.
Secretion happens in principal cells of collecting ducts, where increased intracellular potassium alters luminal membrane potential.

Hyperkalemia

Hyperkalemia can arise from decreased cell entry, increased cell release, or reduced urinary excretion.
Distinct mechanisms involved in acute versus chronic hyperkalemia, including changes in Na-K-ATPase activity.
Impaired urinary potassium excretion primarily due to hypoaldosteronism and decreased distal urinary flow, often linked to heart failure or advanced renal failure.

Hyperkalemia and Metabolic Acidosis

Metabolic acidosis triggers an increase in hydrogen ions (H+), pushing potassium out of cells, leading to a rise of approximately 0.6 mEq/L of K per 0.1 pH unit decrease.
Conditions such as chronic renal failure exacerbate hyperkalemia during metabolic acidosis.

Etiologies of Hyperkalemia

Insulin deficiency: Leads to increased plasma potassium, particularly in uncontrolled diabetes where hyperosmolality impacts osmotic balance.
Beta Adrenergic Blockade: Reduces potassium entry into cells.
Muscle Breakdown: Intense exercise and trauma can cause liberation of intracellular potassium, further increasing serum levels.

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Description

This quiz focuses on the regulation of potassium balance, emphasizing transcellular distribution and urinary excretion. Designed for students of renal pathophysiology, it aims to deepen understanding of the factors influencing potassium homeostasis in the body.