Lecture on Renal Physiology for USMLE Preparation

Introduction

• Presenter: Newly graduated pediatric resident and soon-to-be pediatric intensive care fellow.
• Passion: Teaching and changing medical education.
• Focus: Integrative learning for USMLE Step 1 and Step 2.
• Objectives: Active recall and application of knowledge.
• Community Engagement: Participants from various countries and regions.

Ground Rules

• Mute audio during the presentation.
• Questions should be submitted via the chat box for review at the end.
• Stay engaged and active throughout the lecture.

Inspirational Quote

• "True success is achieved by stretching oneself, learning to feel comfortable when you are uncomfortable."

Key Topics Covered

Functional Organization of the Kidney

• Basic Functional Unit: Nephron.
• Types of Nephrons:
  • Juxtamedullary (long loops into medulla)
  • Cortical (majority)
• Susceptibility to Ischemic Injury:
  • Medulla and proximal convoluted tubule are most vulnerable.

Renal Perfusion

• Renal Blood Flow: 20-25% of cardiac output.
• Heart Failure Effects: Decreased cardiac output affects renal perfusion.

Glomerular Physiology

• Key Processes:
  • Filtration, reabsorption, secretion, and excretion.
• Filtration Fraction: GFR/RPF, normal is 20%.
• Effects of Drugs:
  • NSAIDs reduce prostaglandins, affecting afferent arteriole and GFR.
  • ACE inhibitors affect efferent arteriolar tone.

Measurement of Renal Function

• GFR: Measured by inulin, practically by creatinine clearance.
  • Creatinine clearance overestimates GFR by 10%.
• Renal Plasma Flow: Measured by PAH clearance, underestimates by 10%.

Trip Through the Nephron

Proximal Convoluted Tubule

• Sodium Reabsorption: Coupled with glucose, amino acids, etc.
  • Secondary Active Transport.
  • Fancoli Syndrome: Failure to reabsorb substances.
• Sympathetic Nervous System: Enhances sodium reabsorption.
• SGLT2 Inhibitors: Treat diabetes by promoting glucose excretion.

Loop of Henle

• Descending Limb: Permeable to water.
• Ascending Limb: Permeable to solutes, sodium-potassium-chloride transporter.
  • Inhibited by loop diuretics like furosemide.

Distal Convoluted Tubule

• Sodium-Chloride Symporter: Inhibited by thiazide diuretics.
• Parathyroid Hormone: Increases calcium reabsorption.

Collecting Duct

• Principal Cells: Affected by aldosterone and ADH.
  • Aldosterone: Increases ENaC channels.
  • ADH: Increases aquaporins.
• Intercalated Cells: Handle acid-base balance.

Conclusion

• Encouragement: Positive action combined with positive thinking leads to success.
• Upcoming Webinar: Review of top missed concepts from question banks.
• Community Engagement: Encouragement to stay active in learning and connect on social media.

Resources & Further Reading

• First Aid, UWorld, Pathoma, BRS, Kaplan for USMLE preparation.

Note: The notes provide a structured overview of the key concepts covered in the lecture on renal physiology, highlighting the functional and clinical aspects crucial for USMLE preparation.