Nephron Structure and Function

Overview

• Nephrons are the functional units of filtration in the kidney.
• Located in renal pyramids, including the renal medulla and part of the renal cortex.
• Consist of structures such as the capsule, a loop, and a collecting duct.

Kidney and Nephron Anatomy

• Nephrons are millions in number and surrounded by blood vessels.
• Blood vessels bring blood into the kidneys, visible in kidney models and diagrams.
• Key parts of the nephron include:
  • Bowman’s Capsule: Surrounds blood vessels for initial filtration.
  • Glomerulus: Coiled artery where blood enters and filtration begins.
  • Proximal Convoluted Tubule: Located next to the Bowman’s Capsule.
  • Loop of Henle (Nephron Loop): Dips into medulla and return to cortex.
  • Distal Convoluted Tubule: Farther from Bowman’s Capsule.
  • Collecting Duct: Collects urine from multiple nephrons to ureter.

Filtration in the Nephron

• Blood from renal artery enters glomerulus.
• High pressure forces plasma into Bowman’s Capsule, forming "filtrate".
• 20% of blood plasma becomes filtrate.

Processes in Nephron

• Reabsorption: Recovers vital substances back into the bloodstream.
  • Occurs mainly in proximal tubule.
  • 2/3 of water and many nutrients reabsorbed.

Loop of Henle

• Descending Limb:
  • Water diffuses out due to surrounding high salt concentration (osmosis).
• Ascending Limb:
  • Impermeable to water.
  • Active transport of sodium and chloride ions out, creating salty medulla.

Regulation of Water Reabsorption

• Distal Convoluted Tubule & Collecting Duct:
  • Water reabsorption depends on body's hydration status.
  • Regulated by Anti-Diuretic Hormone (ADH).
• ADH:
  • Released by pituitary gland.
  • Increases permeability of distal tubule and collecting duct to water.
  • More ADH leads to less urine (conservation of water).
  • Less ADH leads to more urine (excretion of excess water).

Summary of Filtration and Reabsorption

• Blood enters via renal artery to the glomerulus.
• Filtration in Bowman’s Capsule forms filtrate.
• Reabsorption occurs throughout nephron; loop of Henle critical for osmosis.
• ADH regulates water reabsorption in distal tubule and collecting duct.
• Waste and excess water expelled through ureter to bladder.

Conclusion

• Filtration and reabsorption are complex processes involving multiple ions and hormones.
• ADH plays a key role in regulating urine production based on body hydration needs.
• Finished anatomy and physiology series, signaling a wrap for the summer.