Excretory Products And Their Elimination Class 11 Notes Biology Chapter 19 - CBSE

Chapter : 19

What Are Excretory Products And Their Elimination ?

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    • The elimination of harmful and unwanted waste products derived from the organism during its own metabolism is known as excretion.
    • The excretory organs include kidneys, lungs, skin, intestine and liver.

    Excretory organs and the materials generated by them:

    Excretory Organs Excretory material generated
    Kidney Urine
    Lungs Carbon dioxide and water vapour.
    Skin Sweat and metabolic wastes.
    Liver Bile pigments bilirubin, biliverdin and urochrome are metabolic wastes of haemoglobin of dead red blood cells.
    Large Intestine Excess salts of calcium, magnesium, undigested food material and iron.
    Endocrine Glands These allow excess water to leave the body.
    Salivary Glands and Lacrimal Glands Small amount of nitrogenous wastes.

    Mechanism Of Urine Formation

    Urine is formed by the kidneys in the following three steps :

    Ultrafiltration

    Formation of a protein free filtrate from the plasma into the Bowman’s capsule through the glomerlus.

    Selective Reabsorption

    Some filtered materials are reabsorbed in the renal tubules.

    Secretion

    Collection of urine by the Pelvis from the tubules.

    Disorders Of The Kidney

    Uremia

    (Nephritis) Due to malfunctioning of kidney, urea level in blood increases.

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    Stone formation

    Due to precipitation of uric acid or accumulation of oxalate crystals, stones are formed in kidney.

    Diuresis

    The formation of excessive urine.

    Osmoregulation

    The regulation of solute movement and the water movement (which follows solutes by osmosis) is called osmoregulation. On the basis of osmoregulation, animals are either osmoconformers or osmoregulators.

    Renin-angiotensin System

    The renin-angiotensin system (RAS) is one of the major control systems for blood pressure and fluid balance. The major biologically active hormone generated by this system, angiotensin (Ang) II, is produced by sequential cleavage of peptides derived from the substrate molecule angiotensinogen (Agt).

    Atrial Natriuretic Factor (ANF)

    It is a 28 amino acid polypeptide hormone secreted mainly by the heart atria in response to atrial stretch. ANF acts on the kidney to increase sodium excretion and GFR, to antagonize renal vasoconstriction, and to inhibit renin secretion.

    ADH

    Vasopressin or Antidiuretic Hormone (ADH) or Arginine Vasopressin (AVP) is a nonapeptide synthesized in the hypothalamus. Science has known it to play essential roles in the control of the body's osmotic balance, blood pressure regulation, sodium homeostasis, and kidney functioning.

    Diabetes Insipidus

    It is a rare disorder that causes the body to make too much urine. While most people make 1 to 3 quarts of urine a day, people with diabetes insipidus can make up to 20 quarts of urine a day. People with this disorder need to urinate frequently, called polyuria.

    Role Of Other Organs In Excretion

    Lungs, liver and skin also play important role in the process of excretion. Lungs remove CO2 and water, liver eliminates bile containing substances like bilirubin, biliverdin, cholesterol and drugs, sweat glands in skin removes NaCl, urea and lactic acid and sebaceous glands eliminate substances like sterols, hydrocarbons and waxes as sebum.

    Disorders Of The Excretory System

    • Uremia: Accumulation of urea in blood due to malfunctioning of kidneys. This can lead to kidney failures. This problem can be remedied with the help of haemodialysis.
    • Renal failure: The condition where the glomerular filtration stops and both the kidney’s stop working is called renal failure. In case of acute failures, kidney transplant is the only option available.
    • Renal calculi: When stones or insoluble salts are formed within the kidney, the condition is called renal
      calculi.

    Renal Dialysis

    Renal dialysis is a device to treat kidney failure. This process uses an artificial kidney (hemodialyzer) to remove waste and extra fluid from the blood. The blood is removed from the body and filtered through the
    artificial kidney. The filtered blood is then returned to the body with the help of a dialysis machine. There are three main types of dialysis: in-center hemodialysis, home hemodialysis, and peritoneal dialysis.

    Kidney Transplantation

    A kidney transplant is a surgery to place a healthy kidney from a living or deceased donor into a person whose kidneys no longer function properly.

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