Lecture on Nephron Function in the Kidney

Overview of Nephron

• Functional unit of filtration in the kidney.
• Key components:
  • Bowman's Capsule: Surrounds blood vessels, site of initial filtration.
  • Collecting Duct: Transports urine to the calyx and ureter.
• Nephrons reside in renal pyramids, including the renal medulla and cortex.

Blood Supply and Filtration Process

• Renal artery: Delivers blood to nephron.
• Glomerulus: Coiled blood vessels inside the Bowman's capsule.
  • Blood pressure increases, forcing fluid into Bowman's capsule (filtration).
  • 20% of blood plasma exits and becomes filtrate.

Filtration and Reabsorption

• Filtrate: Fluid from blood plasma in Bowman's capsule.
• Filtration of ~180 liters of plasma daily.
  • Main processes: Filtration and Reabsorption to conserve body's fluid.

Pathway of Filtrate

1. Proximal Convoluted Tubule: Reabsorbs two-thirds of water and essential nutrients back into circulation.
2. Nephron Loop (Loop of Henle):
   • Descending Limb: Water diffuses out into medulla due to high salt concentration (osmosis).
   • Ascending Limb: Impermeable to water; sodium and chloride actively transported out, creating salty medulla.
3. Distal Convoluted Tubule: Water reabsorption regulated by ADH, can become permeable to water based on body's needs.
4. Collecting Duct: Final concentration of urine; branches from multiple nephrons, water reabsorption dependent on ADH presence.

Hormonal Regulation

• ADH (Anti-Diuretic Hormone): Released by pituitary gland.
  • Increases water reabsorption in distal convoluted tubule and collecting duct.
  • Presence or absence regulates urine concentration.

Summary of Nephron Function

• Filtration:
  • Blood enters glomerulus, 20% plasma filters into Bowman's Capsule.
• Reabsorption:
  • Occurs primarily in proximal convoluted tubule, nephron loop, and distal convoluted tubule.
  • Water reabsorption regulated by medulla's saltiness and ADH.
• Urine Formation:
  • Excess fluid exits collecting duct, travels to ureter and bladder for expulsion.

Conclusion

• The nephron efficiently filters blood plasma, reabsorbs useful components, and regulates urine concentration through hormonal signals like ADH.
• Final video of the anatomy and physiology course for the year!