Overview of Renal Physiology Concepts

Sep 25, 2024

Renal Physiology Overview

Introduction

  • Brief overview of the renal playlist videos
  • Topics covered: Proximal Convoluted Tubule, Glomerular Filtration, Loop of Henle, Distal Convoluted Tubule, Collecting Duct

Glomerulus

  • Afferent arterioles supply material to the glomerulus (capillary bed for filtration)
  • Pressures involved in filtration:
    • Glomerular Hydrostatic Pressure: Exerted by systemic blood pressure
    • Osmotic Pressure: Due to blood proteins pulling water into the bloodstream
    • Capsular Hydrostatic Pressure: Due to filtrate back pressure
    • Capsular Osmotic Pressure: Should be zero; no proteins filtered
  • Net Filtration Pressure: Approx. 10 mmHg
  • Glomerular Filtration Rate (GFR): Approx. 125 mL/min, directly proportional to net filtration pressure

Nephron Structure

  • A nephron consists of:
    • Glomerular capillaries + Bowman's capsule
    • Proximal Convoluted Tubule
    • Loop of Henle
    • Distal Convoluted Tubule
  • Approx. 1.2 million nephrons per kidney (2.4 million total in humans)

Proximal Convoluted Tubule (PCT)

  • Role: Major site for reabsorption
  • Substances Reabsorbed:
    • Sodium: ~65%
    • Water: Follows sodium (~65%)
    • Potassium: ~60%
    • Chloride: ~50-60%
    • Calcium: ~60%
    • Bicarbonate: ~85-90%
    • Urea: ~50%
    • Glucose & Amino Acids: 100% reabsorbed under normal conditions
  • Tubular Reabsorption: Movement from kidney tubules to blood
  • Mechanisms include sodium-glucose and sodium-amino acid co-transport.

Loop of Henle

  • Osmolality gradient:
    • Descending limb: ~300 to 1200 mOsm/kg as you go deeper into medulla
    • Ascending limb: pumps sodium, potassium, and chloride; reabsorbs about 25% sodium
  • Countercurrent multiplier mechanism: Water reabsorbs as it follows sodium and other solutes

Distal Convoluted Tubule (DCT)

  • Early DCT:
    • Sodium and chloride reabsorption via symporters
    • Depends on ATP for sodium-potassium pumps
  • Late DCT:
    • Hormonal regulation (aldosterone)
    • Increases sodium reabsorption and potassium excretion
  • Parathyroid Hormone (PTH): Regulates calcium reabsorption; inhibits phosphate reabsorption

Collecting Duct

  • Antidiuretic Hormone (ADH): Increases water reabsorption by inserting aquaporins
  • Intercalated Cells:
    • A Cells: Function in acidosis; secrete H+ and reabsorb bicarbonate
    • B Cells: Function in alkalosis; excrete bicarbonate and reabsorb Cl-
  • Urea Recycling: Contributes to medullary interstitial gradient; allows for more water reabsorption

Conclusion

  • Recap of key concepts from renal physiology videos
  • Encourage engagement (like, comment, subscribe)