Lecture on Kidney Function and Nephron Anatomy

Overview of Kidney and Nephron Function

• Kidneys are critical organs with nephrons as their functional units.
• Nephrons are involved in urine formation through four steps:
  • Filtration
  • Reabsorption
  • Secretion
  • Excretion
• Focus on Reabsorption and Secretion in the nephron.

Key Terminology

• Reabsorption: Movement from nephron back into circulation.
• Secretion: Movement from circulation back into the nephron.

Nephron Anatomy Recap

• Afferent arteriole: Brings plasma to nephron head.
• Glomerulus: Network of vessels at nephron head.
• Efferent arteriole: Exits nephron head, forming vasorector.
• Vasorector: Capillaries aiding reabsorption and secretion.

Nephron Structure

• Bowman's Capsule: Nephron head.
• Proximal Convoluted Tubules
• Loop of Henle
• Distal Convoluted Tubules
• Collecting Duct

Reabsorption in Nephron Segments

• Proximal Convoluted Tubule:
  • Reabsorbs sodium, chloride, potassium, glucose, amino acids, urea, bicarbonate, and water.
  • Secretes creatinine, drugs, hydrogen ions.
• Loop of Henle:
  • Descending limb: Water reabsorption.
  • Ascending limb: Sodium, chloride, and potassium reabsorption.
• Distal Convoluted Tubules:
  • Reabsorbs sodium, chloride, potassium, calcium, magnesium, bicarbonate.
  • Secretion of hydrogen ions and potassium.
• Collecting Duct:
  • Reabsorbs sodium, chloride, urea, and water.

Detailed Reabsorption and Secretion Mechanisms

• Proximal Convoluted Tubule Details:
  • Sodium-glucose/amino acid symporter
  • Sodium-potassium ATPase pump
  • Carbonic anhydrase reaction for acid-base balance
  • Majority of calcium reabsorption.
• Ascending Loop of Henle:
  • Trisymporter for potassium, chloride, sodium.
  • Sodium-potassium ATPase repetition.

Distal Convoluted Tubule and Collecting Duct

• Distal Convoluted Tubule:
  • Sodium-chloride symporter.
  • Paracellular reabsorption of magnesium and calcium.
• Collecting Duct:
  • Sodium and hydrogen ion exchange for acid-base regulation.
  • Aldosterone regulation for sodium and potassium balance.
  • Aquaporins regulated by antidiuretic hormone (ADH) for water reabsorption.

Hormonal Control

• Aldosterone: Increases sodium reabsorption and potassium secretion in response to low blood pressure.
• Antidiuretic Hormone (ADH/Vasopressin): Regulates aquaporins in collecting duct to retain water, concentrating urine.

Urine Composition

• Primarily water, nitrogenous waste, metabolites.
• May contain low numbers of red and white blood cells, high numbers indicate possible infection.