Excretory System Lecture Notes

Introduction

• Commonly well-known body systems:
  • Circulatory (heart)
  • Nervous (brain)
  • Digestive
  • Muscular
• One often overlooked: Excretory System
  • Focus of lecture: Kidneys and Nephron

Key Survival Challenges

1. Maintain osmotic balance
   • Manage water and solutes
2. Eliminate metabolic wastes
   • Carbon dioxide, nitrogenous wastes (e.g., from protein breakdown)
   • Excretory system addresses these issues

Organs and Structures in Excretory System

• Skin: Excretes water and substances
• Liver: Detoxification, produces urea
• Lungs: Excrete carbon dioxide
• Urinary System (focus):
  • Kidneys (2): Filter blood, produce urine
  • Bladder (1): Holds urine
  • Ureters (2): Drain urine from kidneys to bladder
  • Urethra (1): Excretes urine from body

Kidneys and Nephron Function

1. Kidneys produce urine by filtering blood
2. Nephron: Functional unit of kidney
   • Each kidney has ~1 million nephrons
   • Process waste to create urine

Nephron Structure and Function

1. Glomerulus:
   • Special mass of capillaries
   • Surrounded by Bowman’s Capsule
   • Blood pressure forces fluid into Bowman’s capsule (filtrate)
2. Filtrate Components:
   • Water, glucose, amino acids, salts, H+ ions, bicarbonate, medications, vitamins, urea
3. Proximal Tubule:
   • NaCl, water, glucose, amino acids, K+, bicarbonate reabsorbed
   • H+ ions, ammonium ions secreted
   • Role in pH regulation
4. Loop of Henle:
   • Descending Limb: Water reabsorbed via aquaporins
     • High solute concentration in filtrate
   • Ascending Limb: NaCl reabsorbed (diffuse in thin segment, pumped in thick segment)
     • Filtrate becomes dilute
5. Distal Convoluted Tubule:
   • Secretes: H+, ammonium, K+
   • Reabsorbs: NaCl, water, bicarbonate
   • Further pH regulation
6. Collecting Duct:
   • Final urine formation
   • NaCl, water reabsorbed (hormonally controlled)
   • Urea reabsorbed by diffusion

Excretion Pathway

1. Nephron -> Ureters -> Bladder
2. Urine stored in bladder -> Urethra -> Excretion

Complexity and Hormonal Influences

• Nephron controls substance reabsorption and secretion
• Hormones influence osmotic balance
• Medications can alter osmotic values (e.g., diuretics)

Kidney Function Treatments

• Dialysis: For severely compromised kidney function
  • Hemodialysis, Peritoneal dialysis
• Careers: Nephrologist specializes in kidney function

Conclusion

• Excretory system is intricate and vital
• Importance of understanding its function and impact on overall health

Remember: Stay curious!