Excretory Products And Their Elimination

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Pattern: Excretion in Animals
Description: Animals require to remove the waste products formed in their body during different life processes. These are majorly nitrogenous wastes like ammonia, urea and uric acid.
  • The process of excreting ammonia is ammonotelism.
  • The process of excreting urea is ureotelism.
  • The process of excreting uric acid is uricotelism.
Different excretory organs are found across the Animal Kingdom. For example, simple excretory organs like flame cells in Platyhelminthes to complex structures like kidneys in mammals.
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Pattern: Human Excretory System
Description: Every living organism generates waste in its body and has a mechanism to expel it. In humans, the excretory system takes care of waste generation and elimination. It comprises of the following structures:
  • 2 Kidneys
  • 2 Ureters
  • 1 Urinary bladder
  • 1 Urethra
Apart from the above-mentioned organs, there are other accessory organs that perform excretion. They are:
  • Skin - eliminates compounds like NaCl, a small amount of urea, excess water, etc.
  • Lungs - remove the large amount of carbon dioxide and also significant quantities of water every day.
  • Liver - it helps in excretion of bile.
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Pattern: Structure of Kidney and Nephron
Description: Kidneys are divided into three regions - renal cortex, renal medulla and pelvis. The renal cortex is the outer layer. The renal medulla is the inner layer. And lastly, the renal pelvis carries the urine from the kidney to the ureter. The nephron is the functional unit of a kidney. Each kidney consists of around a million nephrons. They all function together to filter blood. It consists of the following parts:
  • Bowman's capsule - It is a cup-shaped structure.
  • Proximal Convoluted Tubule - The Bowman's capsule continues downwards to form the proximal tubule.
  • The loop of Henle - The proximal tubule leads to the formation of a u-shaped loop called the Loop of Henle. It has three parts: the descending limb, the u-shaped bend, and the ascending limb.
  • Distal Convoluted Tubule - The Loop of Henle continues into the distal convoluted tubule.
  • Collecting Duct- The distal convoluted tubule of many nephrons lead to the collecting ducts. The collecting ducts together form the renal pelvis. Through the renal pelvis, the urine passes into the ureter and then into the bladder.
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Pattern: Working of Nephron - Formation of Urine
Description: Urine is the liquid waste product of the human body. It contains urea, uric acid, salts, water and other waste products that are the result of various metabolic processes occurring in the body. It is formed in the kidneys. The structural and functional unit of the kidneys is called the nephrons. Millions of nephrons are involved in the process of urine formation. The formation of urine involves 3 steps:
  • Glomerular Filtration - occurs in the glomerular capillaries. Except for the blood cells and proteins, everything is pushed into the Bowman's capsule to form the ultrafiltrate. The glomerular filtration rate (GFR) is 125 mL/min or 180 Litres/day.
  • Tubular Reabsorption - At the level of the proximal convoluted tubule(PCT), some of the substances like sodium, chloride, potassium, glucose, amino acids, bicarbonate, and most of the water are reabsorbed. The distal convoluted tubule shows selective absorption of sodium ions and water and selective secretion of hydrogen and potassium ions.
  • Tubular Secretion - The peritubular capillaries that help in transporting the reabsorbed substances into the bloodstream.
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Pattern: Regulation of Kidney Function
Description: The kidneys are regulated efficiently by hormonal feedback mechanism. Any change in the blood volume or ion concentration activates the osmoreceptors of the body which stimulate the hypothalamus to release antidiuretic hormone (ADH) or vasopressin. ADH promotes water reabsorption from the latter parts of the tubule, thereby preventing diuresis. Another method by which regulation occurs is the Renin-Angiotensin mechanism by JGA. Atrial Natriuretic Factor (ANF) mechanism keeps a check on the renin-angiotensin mechanism.
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Pattern: Disorders of Kidney and Haemodialysis
Description: Some of the disorders of kidney are:
  • Kidney stones - also called renal calculi, are formed by the deposition of minerals and salts within the kidneys.
  • Kidney failure - also called renal failure, this is a condition when one or both the kidneys stop functioning. Kidney transplantation is the ultimate solution to kidney failure.
  • Uremia - This condition is characterized by an increase in blood urea levels. This occurs because the kidneys are unable to filter urea properly which leads to its accumulation and increased levels in the blood. In such cases, urea can be removed by dialysis which is a treatment that filters and purifies the blood using a machine.
  • Glomerulonephritis - Inflammation of glomeruli of kidney.
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