Understanding Nephron Structure and Function

Oct 3, 2024

Nephron Function and Structure

Overview of the Kidney

  • Function: Filtering and osmoregulation occur in the nephrons.
  • Location: Nephrons are located in the medulla of the kidney.
  • Quantity: Approximately 1 million nephrons per kidney.

Structure of the Nephron

  • Components:
    • Afferent arteriole
    • Glomerulus (network of capillaries)
    • Renal capsule (Bowman's capsule)
    • Proximal convoluted tubule (PCT)
    • Loop of Henle
    • Distal convoluted tubule (DCT)
    • Collecting ducts

Function of Nephron

  • Primary Function: Urine formation through blood filtration to remove waste.
  • Components of Urine: Excess water, dissolved salts/ions, urea, and small substances like hormones or excess vitamins.
  • Exclusions: Proteins, blood cells (too large to filter out), glucose (reabsorbed actively).

Stages of Filtration and Reabsorption

Ultrafiltration

  • Location: Glomerulus
  • Mechanism: High pressure in glomerulus forces small molecules and water into the renal capsule.
  • Outcome: Formation of glomerular filtrate; large proteins and blood cells remain in the blood.

Selective Reabsorption (PCT)

  • Primary Focus: Reabsorption of 85% of the filtrate.
  • Key Adaptations:
    • Microvilli increase surface area.
    • Numerous mitochondria for energy in active transport.
  • Mechanism:
    • Sodium ions actively transported out of PCT cells into blood, creating a gradient.
    • Sodium ions diffuse back into PCT cells through co-transporter proteins, alongside glucose.
    • Glucose diffuses into the blood, ensuring all initially filtered glucose is reabsorbed.

Loop of Henle

  • Structure:
    • Ascending Limb: Thick walls, impermeable to water; sodium ions actively transported out.
    • Descending Limb: Thin walls, permeable to water.
  • Function: Maintains sodium ion gradient, enabling water reabsorption by osmosis into the blood.

Distal Convoluted Tubule & Collecting Duct

  • Process:
    • Filtrate becomes dilute by the DCT because of sodium ions transported out previously.
    • Additional water reabsorbed by osmosis in DCT and collecting duct.
    • Remaining filtrate forms urine.

Application: Length of Loop of Henle

  • Desert Animals: Longer Loop of Henle to reabsorb more water, essential in a low-water environment.
  • Mechanism: Longer loop provides larger surface area for sodium ion transport, enhancing water reabsorption, leading to concentrated urine.

Summary

  • Nephron Components: Renal capsule, PCT, Loop of Henle, DCT, Collecting ducts.
  • Processes:
    • Glomerular filtrate creation in renal capsule.
    • Glucose and water reabsorption in PCT.
    • Sodium ion gradient maintenance in Loop of Henle for water reabsorption.
    • Further reabsorption in DCT and collecting ducts.
  • Next Steps: Watch upcoming video on osmoregulation for understanding feedback mechanisms in kidney function.
  • Practice: Engage with practice questions to test knowledge.
  • Subscribe: Stay updated with more educational content.