Bihar Board - Class 11 biology - Chapter 19: Excretory Products and Their Elimination Handwritten Notes

Excretion is the biological process by which an organism eliminates metabolic waste products to maintain homeostasis. This chapter focuses on the human excretory system, the formation of urine, and mechanisms for the removal of nitrogenous wastes.

Key Points

1. Modes of Excretion in Animals

   • Ammonotelism: Excretion of ammonia (e.g., fish, amphibians).
   • Ureotelism: Excretion of urea (e.g., humans, mammals).
   • Uricotelism: Excretion of uric acid (e.g., birds, reptiles).

2. Human Excretory System

   • Kidneys: Primary organs of excretion, involved in urine formation.
   • Ureters: Tubes that carry urine from the kidneys to the urinary bladder.
   • Urinary Bladder: Temporarily stores urine before elimination.
   • Urethra: Carries urine out of the body during micturition.

3. Structure of the Kidney

   • Cortex and Medulla: Outer and inner regions of the kidney.
   • Nephron: The functional unit of the kidney, responsible for filtering blood and forming urine.
     • Bowman’s Capsule: Encases the glomerulus and filters blood.
     • Proximal Convoluted Tubule (PCT): Reabsorbs nutrients, ions, and water.
     • Loop of Henle: Maintains osmolarity gradient for water reabsorption.
     • Distal Convoluted Tubule (DCT): Secretes ions and fine-tunes reabsorption.
     • Collecting Duct: Final adjustment of urine concentration.

4. Urine Formation

   • Filtration: Blood is filtered in the glomerulus, producing filtrate.
   • Reabsorption: Essential substances (e.g., glucose, water, ions) are reabsorbed into the blood.
   • Secretion: Wastes like hydrogen and potassium ions are secreted into the tubule.
   • Concentration of Urine: Hormones like ADH regulate water reabsorption in the collecting ducts, concentrating the urine.

5. Regulation of Kidney Function

   • Antidiuretic Hormone (ADH): Controls water reabsorption based on hydration levels.
   • Renin-Angiotensin Mechanism: Regulates blood pressure and kidney filtration rate.
   • Aldosterone: Promotes sodium reabsorption and water retention.
   • Atrial Natriuretic Factor (ANF): Reduces sodium reabsorption, lowering blood pressure.

6. Excretory Structures in Other Organisms

   • Flame Cells: Found in flatworms for excretion.
   • Malpighian Tubules: Excretory structures in insects.
   • Green Glands: Excretory organs in crustaceans.

7. Disorders of the Excretory System

   • Kidney Stones: Hard deposits of minerals in the kidneys causing pain and obstruction.
   • Uremia: Accumulation of urea in the blood due to kidney failure.
   • Glomerulonephritis: Inflammation of the glomeruli, affecting filtration.
   • Dialysis: Artificial blood filtration used in cases of kidney failure.

Conclusion

Excretion is a crucial process for maintaining the internal environment of the body. The human excretory system, especially the kidneys, plays a pivotal role in waste elimination and homeostasis. Understanding the excretory processes and associated disorders highlights the importance of kidney health and proper waste management in the body.

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