NEET Challenge on Excretory System

Aug 1, 2024

NEET 50 Days Challenge - Excretory Products and Their Elimination

Introduction

  • Warm welcome to students for the NEET 50 Days Challenge.
  • Objective: Complete the syllabus before the NEET exam in May.
  • Chapter focus: Excretory products and their elimination.

Session Overview

  • Topics to discuss:
    • Human excretory system
    • Mechanism of urine formation
    • Function of tubules

Excretion Basics

  • Definition of excretion: Removal of nitrogenous waste from the body.
  • Types of nitrogenous waste:
    • Ammonia: Highly toxic, requires large amounts of water for excretion (ammonotelic organisms: bony fishes, aquatic amphibians).
    • Urea: Less toxic, requires less water for excretion (ureotelic organisms: mammals, terrestrial amphibians).
    • Uric Acid: Least toxic, requires minimal water (excreted by birds, reptiles, and insects).

Excretory Organs

  • Skin: Excretes waste through sweat and sebaceous glands.
  • Lungs: Eliminate carbon dioxide (200 ml/min).
  • Liver: Eliminates waste like bile, bilirubin, cholesterol, etc.
  • Saliva: Helps in the elimination of small amounts of nitrogenous waste.
  • Kidneys: Main organ for the elimination of substances, studied in detail.

Human Excretory System

  • Kidneys are located retroperitoneally.
  • Positioned between the 11th and 12th rib.
  • Each kidney has a length of 10-12 cm, width of 5-7 cm, and weight around 150-170 grams.

Kidney Anatomy

  • Renal Capsule: Protects the kidney.
  • Cortex and Medulla: The outer (cortex) and inner (medulla) regions of the kidney.
  • Nephrons: Functional units of the kidney (over 2 lakh per kidney).
  • Medullary Pyramids and Renal Columns: Structures in the medulla with nephron openings.

Types of Nephrons

  • Cortical Nephrons: Majority, shorter loops of Henle.
  • Juxtaglomerular Nephrons: Fewer in number, longer loops of Henle, play a role in concentrating urine.

Mechanism of Urine Formation

  1. Glomerular Filtration: Blood filtered in the glomerulus.
  2. Reabsorption: Substances absorbed back into the blood from the nephron tubules.
  3. Secretion: Waste products secreted into the nephron from the blood.

Glomerular Filtration Details

  • Normal filtration rate: 125 ml/min from 650 ml plasma.
  • Net Filtration Pressure: 10 mm Hg (55 mm Hg - 30 mm Hg - 15 mm Hg).

Reabsorption

  • Occurs mainly in the Proximal Convoluted Tubule (PCT), Loop of Henle, and Distal Convoluted Tubule (DCT).
  • Substances include glucose, amino acids, NaCl, water, HCO3, K+, etc.
  • DCT: Conditional reabsorption regulated by hormones (ADH and Aldosterone).

Counter Current Mechanism

  • Maintains osmotic gradient in the kidney for efficient urine concentration.
  • Flow of fluid in the Loop of Henle and blood in the Vasa Recta is in opposite directions.

Regulation of Kidney Function

  • ADH (Antidiuretic Hormone): Increases water reabsorption in DCT and collecting duct.
  • JG Cells: Release renin in response to decreased blood pressure or filtration rate, initiating the Renin-Angiotensin-Aldosterone System (RAAS).
  • Atrial Natriuretic Factor (ANF): Reduces blood pressure by promoting sodium and water excretion.

Micturition

  • The process of expelling urine from the body.
  • Controlled by the autonomic nervous system and involves coordination of bladder contraction and sphincter relaxation.

Disorders Related to Excretion

  1. Uremia: High urea in the blood due to kidney failure.
    • Treatment: Hemodialysis or kidney transplantation.
  2. Renal Calculi: Formation of kidney stones (calcium oxalate).
  3. Glomerulonephritis: Inflammation of the glomerulus affecting filtration.

Conclusion

  • Stress on the importance of NCERT for NEET preparation.
  • Encourage practice of previous year questions and NCERT-based questions.