Lecture Notes: Introduction to the Excretory System

Overview

• Focus on the often overlooked excretory system.
• Key Points:
  • Maintain osmotic balance (water and solutes regulation).
  • Get rid of metabolic waste (carbon dioxide and nitrogenous waste).

Organs in the Excretory System

• Skin: Excretes water and substances.
• Liver: Detoxification; produces urea. Excretes bile (breakdown of red blood cells) and urochrone (breakdown of heme)
• Lungs: Excrete carbon dioxide.
• Kidneys: Major focus of the lecture.
• Intestines: Excrete ions and calcium through feces.

Kidneys and the Urinary System

• Structures:
  • Two kidneys (lower back).
  • Bladder (holds urine).
  • Ureters (drain urine from kidneys to bladder).
  • Urethra (excretes urine outside the body).
• Function: Filter blood and produce urine.

Nephron: Functional Unit of the Kidney

• Each kidney contains around a million nephrons.
• Processes waste from blood to create urine.
• Key Structures:
  • Glomerulus: Capillary network.
  • Bowman's capsule: Surrounds the glomerulus.
• Filtrate: The fluid containing water, glucose, amino acids, salts, ions, medications, vitamins, and urea.

Processes in the Nephron

1. Proximal Tubule:

   • Reabsorption: NaCl, water, glucose, amino acids, and bicarbonate.
   • Secretion: H+ ions, ammonium ions.
   • Role in pH regulation.

2. Loop of Henle:

   • Descending limb:
     • High presence of aquaporins allows water reabsorption.
     • NaCl remains in the filtrate.
   • Ascending limb:
     • NaCl exits through diffusion and active transport.

3. Distal Convoluted Tubule:

   • Secretion: H+, ammonium, potassium.
   • Reabsorption: NaCl, water, bicarbonate.
   • Role in pH regulation.

4. Collecting Duct:

   • Final urine formation.
   • Reabsorption: NaCl, water (regulated by hormones), some urea.
   • Urine concentration varies with hydration levels.

Hormonal and Osmotic Regulation

• Hormonal control influences water reabsorption.
• Diuretics: Medications that increase water in filtrate, used for conditions like high blood pressure.

Kidney Function and Treatment

• Compromised Kidney Function:
  • Dialysis (hemodialysis or peritoneal) used when transplant isn't possible.
• Nephrology as a field focuses on kidney function.

Conclusion

• The excretory system, particularly the kidneys, plays a crucial role in maintaining homeostasis by regulating waste excretion and osmotic balance.
• Encouragement to explore further into nephrology careers and kidney-related studies.