Renal Physiology

Structure

• Components:

  • Proximal Convoluted Tubule (PCT)

  • Distal Convoluted Tubule (DCT)

  • Collecting Duct

  • Nephron Loop

  • Vasa Recta

3. Urine Formation Steps

A. Blood Flow and Filtration

• Glomerular Filtration:

  • Renal corpuscle creates a plasma-like filtrate from blood.

  • Movement and filtration steps involved include:

    1. Flow through the renal corpuscle.

    2. Removal of blood cells and plasma proteins while allowing water and small solutes.

B. Tubular Reabsorption

• Process:

  • Ions and nutrients filtered at the glomerulus are reabsorbed by renal tubules.

• Mechanisms:

  • Cation exchange and chloride ion transport for sodium ions.

  • Establishment of an osmotic gradient along the nephron.

C. Water Reabsorption

• Proximal Convoluted Tubules and Collecting Ducts:

  • Water reabsorption occurs via aquaporins, moving toward sodium concentration in blood.

  • Key for maintaining plasma volume and water balance.

4. Tubular Secretion

• Function:

  • Maintains acid-base balance through urine acidification.

• Mechanism:

  • Specialized transport systems eliminate weak acids/bases from blood, adding them to filtrate.

5. Renal Dysfunction Effects

• Consequences of Reduced Function:

  • Decreased urine flow (oliguria or anuria).

  • Accumulation of toxic products and ions.

  • Possible outcomes: uremia, edema, hypertension.

6. Clinical Indications for Diuretic Use

A. Types of Diuretics

• Classes:

  • Osmotic agents

  • Carbonic anhydrase inhibitors

  • Thiazide and thiazide-like compounds

  • Organic acids

  • Potassium-sparing diuretics

  • ADH antagonists

B. Mechanism of Action

• Diuretics function by inhibiting water and sodium reabsorption in the kidneys, producing diuresis.

7. Specific Diuretic Classes

A. Osmotic Diuretics

• Indications:

  • Anuria, oliguria, acute renal failure, drug toxicity, cerebral edema, glaucoma.

• Mechanism:

  • Administered IV, attract fluid from tissues, and prevent water reabsorption.

• Adverse effects: Nausea, dizziness, headache, strain on cardiac function.

B. Carbonic Anhydrase Inhibitors

• Indications:

  • CHF, glaucoma, epilepsy, acute mountain sickness.

• Mechanism:

  • Inhibits carbonic anhydrase, affecting sodium and potassium secretion.

• Adverse effects: Drowsiness, gastrointestinal distress, hyperuricemia, and metabolic acidosis.

C. Thiazide and Thiazide-like Diuretics

• Indications:

  • Edema, hypertension, heart failure.

• Mechanism:

  • Inhibit sodium transport, increase chloride and potassium excretion.

  • Can cause hypochloremic alkalosis and hypokalemia.

• Adverse effects: Orthostatic hypotension, hypokalemia, hyperuricemia.

D. Organic Acid (Loop) Diuretics

• Indications:

  • Edema, thiazide-resistance, CHF, liver cirrhosis.

• Mechanism:

  • Inhibit sodium/chloride transport, resulting in significant losses.

• Adverse effects: Nausea, hypotension, hypokalemia, ototoxicity.

E. Potassium-Sparing Diuretics

• Indications:

  • Treats edema, hypertension, prevents hypokalemia.

• Mechanism:

  • Inhibit potassium secretion, resulting in mild diuresis.

• Adverse effects: Nausea, hyperkalemia, gynecomastia.

8. Antidiuretic Hormone (ADH)

• Function:

  • Regulates water balance by controlling urine water loss.

• Antagonists:

  • The vaptans interfere with ADH receptors to enhance water elimination.

9. Preferred Treatment Approaches

• Conditions and Treatments:

  • ADH Antagonists: Hyponatremia.

  • Carbonic Anhydrase Inhibitors: Glaucoma, alkalosis, altitude sickness.

  • Loop Diuretics: CHF, hypertension, acute renal failure.

  • Thiazides: Hypertension, mild heart failure.

  • Potassium-Sparing Diuretics: Post-myocardial infarction.

10. Adverse Effects

• Common Effects:

  • Electrolyte imbalances, orthostatic hypotension, dehydration, overdose concerns.

11. Drug Interactions and Incompatibilities

• Concerns with Diuretics:

  • Can potentiate digoxin toxicity.

  • Should not be combined with lithium.

  • Some diuretics are incompatible with specific infusions.