Lecture on the Excretory System

Introduction

• Many people are familiar with systems like the circulatory, nervous, digestive, and muscular systems.
• Focus on the excretory system, specifically the kidneys and nephron.

Obstacles for Survival

1. Osmotic Balance
   • Manage water and solutes in the body.
2. Metabolic Wastes
   • Need to get rid of metabolic wastes (e.g., carbon dioxide, nitrogenous wastes).

Organs in the Excretory System

• Skin: Excretes water and substances.
• Liver: Involved in detoxification and produces urea.
• Lungs: Excretes carbon dioxide.

Urinary System

• Kidneys: Filter blood and produce urine.
• Bladder: Holds urine.
• Ureters (2): Drain urine from kidneys to the bladder.
• Urethra: Tube for urine to exit the body.

Kidney Function

• Nephron: Functional unit of the kidney.
  • Each kidney has around a million nephrons.
  • Processes waste products from blood to create urine.

Nephron Structure and Function

1. Glomerulus and Bowman's Capsule

   • Blood pressure forces fluid into Bowman's Capsule (filtrate).
   • Filtrate includes water, glucose, amino acids, salts, ions, medications, vitamins, and urea.

2. Proximal Tubule

   • Reabsorbed: NaCl, water, glucose, amino acids, K+, HCO3-.
   • Secreted: H+ ions, NH4+
   • Important for reabsorption and pH regulation.

3. Loop of Henle

   • Descending Limb: Water reabsorbed, filtrate becomes more concentrated.
   • Ascending Limb: NaCl diffuses out (thin segment), pumped out (thick segment), filtrate becomes dilute.

4. Distal Convoluted Tubule

   • Reabsorbed: NaCl, water, bicarbonate
   • Secreted: H+, NH4+, K+
   • Plays a role in pH regulation.

5. Collecting Duct

   • Controlled reabsorption of water and NaCl.
   • Filtrate becomes more concentrated (hormonal control).
   • Urea reabsorbed by diffusion.
   • Produces final urine output.

Additional Considerations

• Diuretics: Increase urine water content, used for high blood pressure, heart failure, etc.
• Dialysis: For compromised kidney function (hemodialysis or peritoneal dialysis).
• Nephrologists: Specialize in kidney function.

Conclusion

• Emphasize the complexity of the excretory system.
• Encourage curiosity and exploration of kidney-related careers.