Lecture Notes: The Nephron and Its Functions

Overview of the Nephron

• Nephron Function: The nephron is the functional unit of the kidney responsible for filtering blood and forming urine.
• Key Structures:
  • Glomerulus: Receives blood from the afferent arteriole (going towards).
  • Bowman's Capsule: Collects the filtered fluid.
  • Efferent Arteriole: Carries blood away from the glomerulus.

Fluid Filtration and Desert Adaptation Example

• Fluid Filtration: Large volumes of fluid are filtered out and collected in Bowman's capsule.
• Desert Rodent Adaptation: Some animals have extremely efficient kidneys that can concentrate urine into solid crystals.

Components of the Nephron

1. Proximal Convoluted Tubule (PCT)

• Location: Close to the glomerulus.
• Function:
  • Reabsorbs ions (e.g., sodium, chloride) and nutrients (e.g., amino acids, glucose).
  • Reabsorbs approximately 65% of nutrients.
  • Water follows sodium reabsorption.

2. Loop of Henle

• Structure: Descending and ascending limbs.
  • Descending Limb: Reabsorbs water, impermeable to ions.
  • Ascending Limb: Reabsorbs ions (e.g., sodium, chloride, potassium), impermeable to water.
• Process:
  • Countercurrent Multiplication: Active ion transport in the ascending limb creates a salty medulla, facilitating passive water absorption in the descending limb.
  • Involves energy use in the ascending limb and passive water absorption in the descending limb.
  • Interstitium: Space around the nephron aiding in nutrient and water movement.

3. Distal Convoluted Tubule (DCT)

• Location: Further from the glomerulus than the PCT.
• Function: Reabsorbs additional ions (e.g., sodium, chloride).
• Juxtaglomerular Apparatus: Located where the DCT contacts the glomerulus, involved in blood pressure regulation.

4. Collecting Duct

• Role: Collects leftover fluid from multiple DCTs.
• Reabsorbs:
  • Water and some urea to maintain medullary osmolarity.
  • Urea recycling helps in water reabsorption.

Blood Supply and Reabsorption

• Efferent Arteriole Path: Branches into peritubular capillaries that reabsorb nutrients from the interstitium back into the bloodstream.
• Blood Flow:
  • Nutrients reabsorbed into the bloodstream go through peritubular capillaries.
  • Blood returns to the body via the renal vein.

Urine Formation

• Final Steps:
  • Collecting duct sends remaining contents to renal calyces.
  • Processed contents become urine to be excreted.

These notes provide a comprehensive overview of nephron structure and function, crucial for understanding kidney physiology.