Excretory Products and Their Elimination

Introduction

• Today's topic: Excretion and elimination of metabolic waste.
• Importance of understanding different excretory structures and processes in various organisms.

Key Concepts of Excretion

• Excretion Definition: Removal of metabolic waste from the body.
• Metabolic waste produced by cellular processes must be eliminated.
• Major organ involved: Kidney (part of a larger system).

Topics Covered

1. Excretion in different organisms.
2. Human excretory system.

What is Excretion?

• Excretion: Removal of metabolic waste (not confusion with "ejection").
• Waste includes substances like urea, ammonia, and uric acid.
• Waste enters the bloodstream, filtered by the kidneys, and excreted as urine.

Types of Excretory Products

• Urea: Main excretory product in humans; less toxic than ammonia.
• Ammonia: Highly toxic; requires significant water for elimination (ammonotelism).
• Uric Acid: Least toxic, requires negligible water for excretion.

Excretion in Organisms

• Ammonotelic Organisms: Eliminate ammonia; common in aquatic animals (e.g., bony fish, tadpoles).
• Ureotelic Organisms: Produce urea as a waste product; common in mammals.
• Uricotelic Organisms: Excrete uric acid; found in birds and reptiles.

Urea Cycle

• Deamination: Removal of amino groups from amino acids, resulting in ammonium ions.
• Ammonium ions converted to urea in the liver via the Krebs-Henseleit cycle.
• Urea travels to the kidneys for excretion.

Osmoregulation

• Osmoregulation: Maintenance of water and ionic balance in the body.
• Kidneys play a crucial role in both excretion and osmoregulation.

Human Excretory System

Components

• Kidneys: Pair of organs responsible for filtering blood and producing urine.
• Ureters: Tubes that carry urine from kidneys to the urinary bladder.
• Urinary Bladder: Stores urine until excretion.
• Urethra: The duct through which urine is discharged.

Kidney Structure

• Positioned between T12 and L3 vertebrae, protected by 11th and 12th floating ribs.
• Covered by three layers:
  • Renal fascia (outermost): Connects kidney to abdominal wall.
  • Adipose tissue (middle): Provides protection.
  • Renal capsule (innermost): Gives shape and protection.
• Cortex: Outer region; Medulla: Inner region with medullary pyramids.

Nephron

• Functional unit of the kidney; millions present in each kidney.

Ureter and Urinary Bladder

• Ureter: 22-30 cm long; lined with transitional epithelium for stretching.
• Urinary Bladder: Pear-shaped; contains three muscular layers (smooth muscle).
• Sphincters:
  • Internal sphincter: Involuntary control.
  • External sphincter: Voluntary control.

Urethra

• Short in females (4 cm), long in males (20 cm); carries urine and sperm in males.

Conclusion

• Understanding excretion is crucial for biology.
• Review and study notes for better grasp on the concepts discussed.