Lecture: Urinary System and Kidney Function

Introduction to Metabolism and Waste Management

• Metabolism of food leads to chemical waste.
• Liver and lungs help manage waste but can't remove it.
• Urinary system, especially kidneys, filters and removes toxic leftovers from blood.

Functions of the Urinary System

• Regulates water volume, ion concentrations, and pH levels.
• Influences red blood cell production and blood pressure.
• Filters nitrogenous waste, primarily urea, from the blood.

Kidney Anatomy and Function

• Kidneys are dark red, fist-sized, bean-shaped, retroperitoneal organs.
• Each kidney has three layers:
  • Cortex: Outer layer.
  • Medulla: Cone-shaped tissue that secretes urine into tubules.
  • Renal Pelvis: Funnel-shaped tube moving urine to ureter.
• Kidneys filter 120-140 liters of blood daily.

Nephrons: The Functional Units of Kidneys

• Each kidney contains about a million nephrons.
• Nephrons perform blood processing in three steps:
  1. Filtration
  2. Reabsorption
  3. Secretion
• Each nephron consists of:
  • Renal Corpuscle: Contains glomerulus for filtration.
  • Renal Tubule: Includes proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT).

Filtration Process

• Blood enters glomerulus; filtrate includes fluid, waste, ions, glucose, amino acids.
• Larger molecules like blood cells and proteins remain in the blood.

Reabsorption and Tubule Function

• Proximal Convoluted Tubule (PCT): Active transport pulls sodium ions, reabsorbs nutrients.
• Loop of Henle: Creates salt concentration gradient, facilitates water reabsorption.
• Distal Convoluted Tubule (DCT) & Collecting Duct: Final reabsorption stages, urine formation.

Urea Recycling and Tubular Secretion

• Urea Recycling: Urea helps maintain salt gradient, re-enters loop of Henle.
• Tubular Secretion: Selective removal of waste from blood, such as hydrogen, potassium.

Conclusion

• Kidneys are complex systems that filter blood, maintain balance, and produce urine.
• Next topic: Regulation of absorption and excretion, effects of dysregulation.