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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Excretion and Osmoregulation Know More

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  • Excretion and its Importance to the Body
    The process by which non-gaseous nitrogenous wastes are eliminated from the body is called excretion. During excretion metabolic wastes from the cell, the tissue or the body of an organism are eliminated. The process of excretion regulates the pH and osmotic pressure of the cells of the body. Excretion also maintains the acid-base balance of the body. Excretion regulates the water content of the body, which is essential for the survival of an organism.
  • Functions of Renal Tubule
    The renal tubule plays an important role in selective reabsorption of glucose, water, salts, etc. The cells of the renal tubule absorb substances like ammonia, potassium, hydrogen ions, creatinine, etc, from the blood capillaries surrounding the tubule and discharge them into the filtrate of the tubule. This is called tubular secretion.
  • Functions of Uriniferous Tubule:
    The uriniferous tubule plays an important role in ultrapurification of blood containing excretory substances. The cells of uriniferous tubule reabsorb essential substances like glucose, water, salts, etc; when the filtrate passes through it. The urea absorbed by the cells of the uriniferous tubule is secreted by them into the lumen of the tubule. This process is called renal or tubular secretion.
  • Selective Reabsorption
    The glomerular filtrate contains plenty of water, glucose and salts. When this filtrate passes through the uriniferous tubule, its cells reabsorb the essential substances like glucose, water and certain salts. This process is called selective reabsorption.
  • Chemical Composition of Urine
    The chemical analysis of normal urine has shown the presence of number of organic and inorganic constituents. These constituents and their percentage in normal human urine are as follows:
    Organic Constituents

    Urea
    - 2.5%
    Uric acid
    - 0.05%
    Creatinine
    - 1%
    Glucose
    - nil
    Inorganic Constituents

    Water
    - 95%
    Sodium chloride
    - 1%
    Calcium and magnesium
    - 0.5%
    Ammonia
    - traces
    The salt content of urine varies according to the season. It is higher in winter and less in summer. This is because during summer, greater amount of salt is lost through sweating.
  • Differences Between Tubular Reabsorption and Tubular Secretion
    Tubular reabsorption is concerned with the selective absorption of useful substances from the glomerular filtrate. Tubular secretion is concerned with the removal of unwanted substances from the glomerular filtrate.
    Tubular reabsorption involves the participation of microvilli. Tubular secretion does not involve the participation of microvilli.
    In tubular reabsorption, useful substances like glucose, amino acids and some salts are reabsorbed and supplied back to the blood. In tubular secretion, unwanted substances like ammonia, sodium and potassium salts, hydrogen ions and creatinine are removed from the blood and discharged along with the urine. Tubular reabsorption occurs in proximal convoluted tubule, Henle's loop, distal convoluted tubule and collecting duct. Tubular secretion occurs in proximal and distal convoluted tubules only.
  • Role of Liver and Alimentary Canal as Excretory Organs
    Liver is an excretory organ because a variety of metabolic by-products are secreted in the liver. For example, bile pigments like bilirubin and biliverdin are formed in liver due to decomposition of dead and injured red blood corpuscles. It also forms toxins due to detoxification in the liver. Liver plays an important role in eliminating urea formed due to deamination of excess amino acids. The bile pigments and toxins are excreted into the alimentary canal from where they are eliminated along with the faecal matter. Owing to these functions, liver and alimentary canal are considered as excretory organs.

    Some Diseases Related to Excretion

    Uremia
    is excess of urea in the blood.
    Anuria
    is the failure of kidney to form urine.
    Painful urination is termed dysuria
    Polyuria
    is a condition when large amount of urine is excreted.
    Kidney stones
    are formed by the precipitation of uric acid and accumulation of oxalate crystals.
  • Paget's disease is a type of carcinoma of breast that involves the nipple or areola and large ducts.
  • Bright disease is inflamation of the kidney that involves glomeruli and is caused by infection of streptococci bacteria.

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