Lecture Notes: Nephron Structure and Function

Overview of Nephrons

• A nephron consists of two main parts:
  • Renal Corpuscle: Site of filtration.
  • Renal Tubule: Involved in tubular reabsorption and secretion.
• Renal Tubule Components:
  • Proximal Convoluted Tubule (PCT)
  • Loop of Henle (Nephron Loop)
  • Distal Convoluted Tubule (DCT)

Nephron Types

• Cortical Nephrons:
  • Make up 80-85% of nephrons.
  • Mostly located in the cortex with a small part of the Loop of Henle in the medulla.
• Juxtamedullary Nephrons:
  • Comprise 15-20% of nephrons.
  • Feature a long Loop of Henle that extends deep into the medulla.

Blood Supply to Nephrons

• Afferent Arteriole: Brings blood to the renal corpuscle.
• Efferent Arteriole: Carries blood away post-filtration.
• Peritubular Capillaries: Surround tubules; site of reabsorption and secretion.
• Vasa Recta: Associated with the Loop of Henle.

Renal Corpuscle Details

• Includes:
  • Glomerulus: Knot of capillaries.
  • Bowman’s Capsule: Encompasses the glomerulus.
• Layers:
  • Visceral Layer: Contains podocytes.
  • Parietal Layer: Simple squamous epithelium.
  • Capsular Space: Between layers for fluid flow.

Tubular Epithelium

• Proximal Convoluted Tubule: Simple cuboidal epithelium with microvilli.
• Loop of Henle:
  • Descending limb: Simple squamous epithelium.
  • Ascending limb: Simple cuboidal to columnar epithelium.
• Distal Convoluted Tubule/Collecting Ducts: Simple cuboidal epithelium.

Juxtaglomerular Apparatus (JGA)

• Consists of:
  • Juxtaglomerular Cells: In the afferent arteriole, involved in blood pressure regulation.
  • Macula Densa: In the DCT, regulates filtration rate.

Nephron Cell Types

• Podocytes: Part of the filtration barrier.
• Principal Cells: Contain receptors for ADH and aldosterone, involved in water and sodium balance.
• Intercalated Cells: Maintain blood pH.
• Mesangial Cells: Regulate glomerular filtration rate (discussed further in future lectures).

Nephron Count and Function

• Nephron number is constant from birth, only size increases.
• Kidney function does not significantly decline until 25% of normal function remains.
• Removal of a kidney leads to enlargement of the remaining kidney to maintain function.

Lecture Goals

1. Draw and label nephron parts.
2. Describe cortical and juxtamedullary nephrons.
3. Explain the Juxtaglomerular Apparatus (JGA).
4. Detail cell types: podocytes, macula densa, juxtaglomerular, principal, intercalated, and mesangial cells.