Nephron: Functional Unit of the Kidney

Jul 26, 2024

Nephron: Functional Unit of the Kidney

Overview of the Kidney and Nephrons

  • Nephrons are the functional units of filtration in the kidney.
  • Millions of nephrons in the kidney are located in the renal pyramids, including the renal cortex and medulla.
  • Blood vessels surround the nephron tubules.

Kidney Anatomy

  • Renal Cortex: Top half of the kidney.
  • Renal Medulla: Bottom half of the kidney.
  • Major Components of Nephron: Glomerulus, Bowman’s Capsule, Proximal Convoluted Tubule, Nephron Loop, Distal Convoluted Tubule, Collecting Duct.

Functional Process of the Nephron

Bowman’s Capsule and Glomerulus

  • Renal artery: Brings blood to the nephron.
  • Glomerulus: Coiled section of the artery inside the Bowman’s capsule.
  • Filtration: Blood plasma (about 20%) exits the glomerulus and enters Bowman’s capsule to become filtrate.

Filtrate through the Nephron

  1. Proximal Convoluted Tubule (PCT):
    • Close to Bowman’s capsule.
    • Two-thirds of the water and essential nutrients are reabsorbed back into the bloodstream.
  2. Nephron Loop (Loop of Henle):
    • Descends into the medulla (salty area).
    • Descending Limb: Water diffuses out due to osmosis.
    • Ascending Limb: Impermeable to water; Sodium and chloride actively transported out to maintain medullary saltiness.
  3. Distal Convoluted Tubule (DCT):
    • Further regulation of water reabsorption.
    • Water reabsorption regulated by Anti-Diuretic Hormone (ADH).
  4. Collecting Duct:
    • Multiple nephrons connected to each collecting duct.
    • Final site for filtrate before entering the ureter.
    • Water permeability regulated by ADH.

Role of ADH

  • ADH (Anti-Diuretic Hormone):
    • Released by the pituitary gland.
    • Increased ADH: Increases permeability of DCT and collecting duct to water, leading to more reabsorption and less urine.
    • Decreased ADH: Decreases permeability, leading to more water in urine and thus, increased urine output.

Summary

  • Blood Filtration: Blood enters glomerulus → Filtration occurs, filtrate enters Bowman’s capsule.
  • Reabsorption: Essential water and nutrients reabsorbed in PCT and nephron loop.
  • Osmosis in Nephron Loop: Water leaves descending limb, osmosis driven by medullary saltiness created by ascending limb.
  • Final Reabsorption: Regulated by ADH in DCT and collecting duct.
  • Urine Formation: Water not reabsorbed becomes urine, exits through collecting duct, ureter, and then the bladder.

Quick Recap: Blood filtration > PCT (reabsorption) > Descending nephron loop (osmosis) > Ascending nephron loop (active transport of NaCl) > DCT > Collecting duct (ADH regulation) > Urine formation.