Describe the process of urine formation in kidneys

  • Urine is formed in the nephrons of kidneys.
  • Each kidney contains a large number of tiny filtration units called nephrons.
  • Blood at high pressure flows into these tubules by blood capillary’s called glomerulus which are surrounded by Bowman’s capsule.

The following steps are involved in the process of urine formation

  •  Blood enters the glomerulus through the afferent arterioles.
  •  It passes under high pressure that results in filtration of blood. Water and small molecules are forced out of glomerular capillary walls and Bowman’s capsule
  •  Large molecules remain in the blood of the glomerulus.
 Selective reabsorption
  •  Some molecules are selectively reabsorbed into the blood.
  •  The glomerular filtrate flows through the tubular parts of U-shaped Henle’s loop.
  •  The useful substances such as glucose amino acids and  salts which give energy are reabsorbed by a process called selective reabsorption.
  •  Hence the filtrate now contains Urea, Some salts and water.
  •  Reabsorption of solutes increases the water concentration of the filtrate.
  •  Water is then reabsorbed into blood by osmosis.
 Tubular secretion
  •  Some nitrogenous waste products and some other substances are removed from blood by parts of Henle’s loop and are passed to blood.
  •  The urine formed in each kidney enters a long tube called the ureter. Which connects the kidneys with the urinary bladder.
  • The urine thus formed is collected in the urinary bladder.
  •  Urine is stored in the urinary bladder until the pressure of the expanded bladder causes the urge to pass it out through the urethra.


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