Filtration Process in the Kidneys

Overview

• Filtration in the kidneys involves three main filters.
• Filtration is size-dependent, primarily filtering based on the size of substances.

First Filter: Fenestrated Capillary

• Acts like a fishing net filtering out larger elements.
• Blocks:
  • Formed elements: Red blood cells, white blood cells, and platelets.
• Allows:
  • Smaller substances like ions and water to pass.

Second Filter: Basement Membrane

• Located outside the capillary.
• Blocks:
  • Large proteins.
• Allows:
  • Medium-sized and some small proteins to pass.

Third Filter: Podocytes

• Made of epithelial cells with extensions called filtration slits.
• Blocks:
  • Medium and some small proteins.

Filtrate Components

• Includes:
  • Water, ions, wastes (urea, uric acid, creatinine), glucose, amino acids, certain drugs.
• Excludes:
  • Large proteins and formed elements.

Waste Breakdown and Functions

• Urea:
  • Produced in the liver from amino acids.
  • Ammonia is converted to urea (non-toxic).
• Uric Acid:
  • Breakdown of nucleic acids.
  • Can cause gout if accumulated (precipitates in cooler areas of the body).
• Creatinine:
  • Breakdown product of creatine, used in ATP storage and energy.

Gout and Uric Acid Crystals

• High uric acid can crystallize, particularly in colder extremities like toes.
• Crystals lodge in joints, causing gout.
• Treatment includes hydration and certain medications.

Kidney Function and Disease

• Filtration issues lead to proteinuria (protein in urine).
• Initial signs of kidney disease include microalbuminuria.
• Advanced kidney disease requires dialysis or transplant.
• Diabetes and Filtration:
  • High glucose in urine due to transport maximum limits.