EXCRETION

• The biological process of removal of harmful nitrogenous metabolic waste from the body is called excretion.
• Unicellular organisms excrete by diffusion and multicellular organisms use specialized organ to perform same function.

Excretion in human beings

• A pair of kidneys, a pair of ureters, a urinary bladder and a urethra constitutes the human excretory system.
• Kidneys are present on either side of the backbone in the abdomen.
• Kidneys produce urine and urine from kidney passes through the ureters into the urinary bladder and remains stored their until it is released through the urethra.
• Urine is produced to filter out waste products from the blood.
• Nephrons are basic structural and functional unit of kidney.
• Cluster of thin walled blood capillaries called glomerulus in the nephron filtrate the urine and each cluster is associated with cup shaped end of a tube called Bowman’s capsule.
• Substances like glucose, amino acids, salts and a major amount of water is selectively reabsorbed from the initial filtrate as the urine flows along the tube.
• Reabsorption depends on the amount of excess water in the body and dissolved waste to be excreted.
• The urine from kidney enters the long tube called ureter.
• Ureter connects the kidney with the urinary bladder and urine from the kidney is passed to urinary bladder and stored in the bladder.
• When the pressure in the expanded bladder leads to the urge to urinate, the urine is passed out through urethra.