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

Ultrafiltration
  •  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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