Lecture Notes: The Kidney and Nephron Function

Overview of the Kidney

• Purpose: Primarily responsible for excreting waste and maintaining water and electrolytes balance.
• Functions:
  • Waste excretion
  • Water and electrolyte balance
  • Hormone production (not covered in detail)
• Location: Two kidneys located near the back, on either side of the spine.

Structure of the Kidney

• Parts:
  • Renal Cortex: Outer part of the kidney.
  • Renal Medulla: Middle section of the kidney; important for filtration and waste excretion.

The Nephron: Functional Unit of the Kidney

• Function: Filtration of blood to excrete waste and maintain water balance.
• Structure:
  • Starts in the cortex, dips into the medulla, and returns to the cortex.
  • Contains approximately 1 million nephrons per kidney.

Blood Flow and Filtration

• Afferent Arteriole: Brings blood to the nephron.
• Glomerulus: A network of capillaries where blood filtration begins.
  • Filters out fluid and small molecules into the Bowman's space.
• Efferent Arteriole: Carries remaining blood away from the glomerulus.

Bowman's Capsule

• Surrounds the glomerulus and collects filtrate.
• Filtrate includes micromolecules like sodium, glucose, and amino acids.

Proximal Tubule

• Role: Reabsorption of vital nutrients from filtrate back to blood.
• Process:
  • Active transport of sodium, glucose, and amino acids.
  • Water reabsorption begins.

Loop of Henle

• Function: Major site for water reabsorption and salt balance.
• Structure:
  • Descending Limb: Permeable to water, reabsorbs it into the salty medulla.
  • Ascending Limb: Impermeable to water; actively pumps out salts.

Distal Convoluted Tubule

• Function: Further reabsorption of calcium, sodium, and additional water.

Collecting Duct

• Role: Final concentration of urine.
• Function:
  • Passes through the medulla, allowing further water reabsorption regulated by hormones.
  • Collects processed filtrate from multiple nephrons.

Final Pathway

• Filtrate becomes urine, passes through ureters to the urinary bladder.

Key Points

• The kidney's ability to regulate water and salt is crucial.
• The nephron structure is highly specialized for efficient filtration and reabsorption.
• Understanding the nephron's parts gives insight into kidney function.