Excretory Products and Their Elimination: Class 11 Biology Notes

Excretory Products and Their Elimination: Class 11 Biology Notes

Introduction

Excretion is the biological process by which metabolic waste products are removed from the body. Proper elimination of wastes like urea, carbon dioxide, and excess salts is essential to maintain homeostasis. This post covers the excretory products, organs of excretion, nephron structure, urine formation, and disorders related to the excretory system.

1. Excretory Products

Human excretion removes various metabolic wastes:

  • Nitrogenous Wastes:
    • Urea: Produced in the liver from ammonia. Main excretory product in humans.
    • Uric Acid: Excreted in small amounts; formed from purine metabolism.
    • Creatinine: Derived from creatine in muscles.
  • Carbon Dioxide: Excreted through lungs as a result of respiration.
  • Excess Water and Salts: Eliminated through kidneys, sweat glands, and skin.

2. Organs of Excretion

  • Kidneys: Primary excretory organs; filter blood to produce urine.
  • Ureters: Transport urine from kidneys to urinary bladder.
  • Urinary Bladder: Stores urine temporarily.
  • Urethra: Expels urine from the body.
  • Lungs: Remove carbon dioxide and water vapor.
  • Skin: Excretes sweat containing water, salts, and small amounts of urea.

3. Structure of Kidney

  • Bean-shaped, located retroperitoneally.
  • Cortex: Outer layer containing renal corpuscles.
  • Medulla: Inner region containing loops of Henle and collecting ducts.
  • Nephron: Functional unit of the kidney (~1 million per kidney).

Nephron Structure:

  • Bowman’s Capsule: Surrounds glomerulus; site of filtration.
  • Proximal Convoluted Tubule (PCT): Reabsorbs nutrients, salts, and water.
  • Loop of Henle: Concentrates urine by reabsorbing water and salts.
  • Distal Convoluted Tubule (DCT): Fine-tunes salt and pH balance.
  • Collecting Duct: Collects urine from multiple nephrons; final water reabsorption occurs here.

4. Process of Urine Formation

  1. Glomerular Filtration: Blood pressure forces plasma, waste, and small molecules into Bowman’s capsule.
  2. Tubular Reabsorption: Useful substances like glucose, amino acids, and water are reabsorbed into the blood.
  3. Tubular Secretion: Additional wastes, hydrogen ions, and drugs are secreted into tubules.
  4. Excretion: Final urine passes through ureters → urinary bladder → urethra.

5. Regulation of Excretion

  • Antidiuretic Hormone (ADH): Increases water reabsorption in the collecting duct.
  • Aldosterone: Promotes sodium reabsorption in the DCT.
  • Renin-Angiotensin System: Helps regulate blood pressure and kidney function.

6. Disorders of Excretory System

  • Kidney Stones (Nephrolithiasis): Hard deposits of salts in kidneys.
  • Urinary Tract Infection (UTI): Infection in ureters, bladder, or urethra.
  • Chronic Kidney Disease (CKD): Gradual loss of kidney function.
  • Hemodialysis: Artificial blood filtration when kidneys fail.

MCQs for Exam Preparation

  1. The functional unit of the kidney is:
    • A) Nephron
    • B) Bowman’s capsule
    • C) Glomerulus
    • D) Loop of Henle
    • Answer: A) Nephron
  2. Which hormone increases water reabsorption in the kidney?
    • A) Insulin
    • B) ADH
    • C) Thyroxine
    • D) Aldosterone
    • Answer: B) ADH
  3. Urea is formed in the liver from:
    • A) Glucose
    • B) Ammonia
    • C) Fatty acids
    • D) Creatinine
    • Answer: B) Ammonia
  4. The structure where glomerular filtration occurs is:
    • A) Proximal tubule
    • B) Loop of Henle
    • C) Bowman’s capsule
    • D) Collecting duct
    • Answer: C) Bowman’s capsule
  5. Which of the following is NOT excreted by the kidneys?
    • A) Urea
    • B) Excess salts
    • C) Glucose
    • D) Water
    • Answer: C) Glucose
  6. Which organ removes carbon dioxide from the body?
    • A) Kidney
    • B) Lungs
    • C) Liver
    • D) Skin
    • Answer: B) Lungs
  7. Urine formation involves all the following except:
    • A) Filtration
    • B) Reabsorption
    • C) Photosynthesis
    • D) Secretion
    • Answer: C) Photosynthesis
  8. Where does the final concentration of urine take place?
    • A) Proximal convoluted tubule
    • B) Loop of Henle
    • C) Distal convoluted tubule
    • D) Collecting duct
    • Answer: D) Collecting duct
  9. Excess water and salts are removed from the body mainly by:
    • A) Heart
    • B) Kidneys and skin
    • C) Lungs only
    • D) Liver
    • Answer: B) Kidneys and skin
  10. Kidney stones are mainly composed of:
    • A) Urea
    • B) Calcium salts
    • C) Proteins
    • D) Water
    • Answer: B) Calcium salts