Homeostasis and the Excretory System

Introduction to Homeostasis

• Homeostasis: Regulation of a stable internal environment.
• All organs contribute to maintaining homeostasis.
• Excretory system: Key player in maintaining water and substance levels (osmoregulation).

Excretory System Overview

• Components: Kidneys, ureters, bladder, and urethra.
• Function: Remove unnecessary byproducts from the body.

Osmoregulation in Animals

• Different animals have varied excretion methods due to evolutionary adaptations.
• Ammonia byproduct from protein metabolism is toxic.
  • Mammals/amphibians/sharks: Convert ammonia to urea (low toxicity).
  • Birds/insects/desert-adapted animals: Convert to uric acid (paste form for water conservation).

Human Excretory System

Kidneys

• Major role in filtering blood and maintaining balance.
• Process: Filter large amount of fluid, reabsorb 99%, excrete 1% as urine.
• Daily filtration: Approximately 180 liters of fluid; 1.5 liters excreted as urine.

Nephrons

• Structure: Composed of filtering units called nephrons (1 million per kidney).
• Filtration process:
  • Blood enters through renal arteries, reaches glomerulus (capillary tangle).
  • Filtrate forced into Bowman's capsule.
  • Filtrate components: Water, urea, small ions/molecules.

Tubules in the Nephron

• Proximal Convoluted Tubule: Reabsorbs organic solutes and some ions/water.
• Loop of Henle: Key functions include:
  • Water extraction in descending limb.
  • Salt pumping in ascending limb.
  • Creates hypertonic medulla, aiding further water reabsorption.
• Distal Convoluted Tubule: Fine-tunes ion balances via pumps and hormones.

Urine Formation

• Collecting ducts channel remaining filtrate to medulla.
• Hormones regulate water reabsorption, determining urine concentration.
  • Alcohol affects anti-diuretic hormone, leading to dehydration.
• Urine travels through ureters to the bladder, then expelled via urethra.

Comparative Analysis

• Kangaroo rats: Extremely concentrated urine, long Loop of Henle.
• Beavers: Short Loop of Henle, less water reabsorption due to aquatic habitat.

Conclusion

• The excretory system's intricate processes ensure water balance and waste removal.
• Adaptations vary by species and environmental needs.

Additional Resources

• Further learning: Crash Course Biology on YouTube.
• Engage with questions via comments or social media.