Kidney Function and Structure

Introduction

• The kidneys filter the blood.
• Dirty blood enters; clean blood exits.
• Waste products exit as urine.

Structure of the Kidney

• Cortex: Outermost part
• Medulla: Middle part
• Pelvis: Inner part
• Renal Artery: Supplies blood to the kidney
• Renal Vein: Blood vessel that leaves the kidney
• Ureter: Tube exiting the kidney, connects to the bladder

Nephrons

• Tiny structures inside the kidneys (~1 million per kidney)
• Responsible for filtering blood

Nephron Structure

Glomerulus

• Capillary network with high-pressure filtering
• Blood enters through a wide vessel, exits via a narrow vessel

Bowman's Capsule (Renal Capsule)

• Surrounds the glomerulus
• High pressure forces material from glomerulus into Bowman's capsule

Filtration Process

• Ultrafiltration: Small molecules like urea move into Bowman's capsule
• Larger molecules (e.g., red blood cells, proteins) cannot pass

Tubular Reabsorption

• Selective Reabsorption: Useful materials (glucose, salts, water) move back into the blood via active transport
• Glucose is fully reabsorbed; excess salts and water are left
• Urea and waste materials remain in the nephron

Parts of the Nephron

• Proximal Convoluted Tubule: First tube segment
• Distal Convoluted Tubule: Tube segment after the loop
• Loop of Henle: Middle tube section
  • Descending Limb: Material moves down
  • Ascending Limb: Material moves up
• Collecting Duct: Final section before ureter

Kidney Function Summary

• Dirty blood gets separated into filtrate and useful blood components
• Filtrate contains waste and useful materials
• Selective reabsorption recovers useful materials
• Clean blood (complete with necessary components) exits through the renal vein
• Waste materials (urea, excess salts, and water) form urine

Common Exam Question

• Diagram labeling: Recognize glomerulus and tubule
• Describe functions:
  • X (Glomerulus): Ultrafiltration - small molecules move into renal capsule under high pressure
  • Y (Tubule): Selective reabsorption of useful molecules (e.g., glucose) into the blood capillary
• Key point: Always specify the direction and process of movement (ultrafiltration vs. selective reabsorption)