Lecture on the Urinary System

Introduction

• Recent discussions focused on metabolism of food.
• Metabolism results in toxic waste needing cleanup.
• Liver directs dead cells and chemicals to be excreted by digestive and urinary systems.
• Urinary system's key role: filter toxic leftovers like nitrogenous waste from protein metabolism.

Function of Kidneys

• Main role is filtering blood, regulating water volume, ion concentrations, and pH levels.
• Kidneys filter nitrogenous waste, creating urine.
• Blood filtration process:
  • Remove everything from blood to determine what to keep or to excrete.
  • Analogous to cleaning out a fridge by removing everything first.

Anatomy of the Urinary System

• Kidneys: Bean-shaped, located retroperitoneally near the spine.
• Kidney Structure:
  • Three layers: cortex (outer), medulla (middle, cone-shaped tissue), renal pelvis (innermost).
  • Kidneys filter 120-140 liters of blood daily.
  • Blood enters through renal arteries, which branch into capillaries.

Nephrons: Functional Units

• About a million nephrons per kidney.
• Nephrons consist of:
  • Renal corpuscle (in cortex) and renal tubule (between cortex and medulla).
  • Glomerular Capsule & Glomerulus: Capillaries allow fluid and waste products to pass but block larger molecules.
  • Filtrate: Fluid that passes into capsule sent to renal tubule.

Tubular Structure & Function

• Proximal Convoluted Tubule (PCT): Reabsorbs sodium ions, uses ATP from mitochondria.
• Loop of Henle: Drives water reabsorption by creating salt gradient in medulla.
• Distal Convoluted Tubule (DCT): Filtrate becomes urine, urea plays a role in salt gradient.
• Collecting Duct: Final reabsorption of water and urea recycling.

Urea Recycling

• Urea leaves urine in medulla, enhances reabsorption of water in loop of Henle.
• Active transport removes extra waste in final tubular secretion.

Conclusion

• Kidneys filter metabolic waste, regulate water and salt in blood.
• Nephrons perform filtration, reabsorption, and secretion.
• Future lessons will cover regulation of absorption and excretion.

Additional Information

• Credits for the episode's production, support from Patreon.

References

• Lecture filmed in the Dr. Cheryl C. Kinney Crash Course Studio.
• Written by Kathleen Yale, edited by Blake de Pastino, consulted by Dr. Brandon Jackson.
• Directed and edited by Nicole Sweeney; sound design by Michael Aranda.
• Graphics team is Thought Cafe.