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 It is the primary step in urine formation. In this process, the excess fluid and waste
products from the kidney are filtered out of the blood into the urine collection
tubules of the kidney and eliminated out of the body.
 Blood flows in glomerulus under pressure due to narrowness of efferent arteriole.
As a result it undergoes ultrafiltration. All small volume solutes (e.g., urea, uric acid,
amino acids, hormones, glucose, Ions, vitamins) and water are filtered out and
enter the Bowman’s capsule.This product is called glomerular filtrate or initial
filtrate.
 The amount of filtrate produced by the kidneys every minute is known as
Glomerular Filtration Rate.

Tubular Reabsorption

It is the absorption of ions and molecules such as sodium ions, glucose, amino
acids, water etc. Water involves passive absorption, while glucose and sodium ions
are absorbed by an active process.

Secretion
Potassium ions, hydrogen ions, and ammonia are secreted out to maintain the
equilibrium between the body fluids.

The functions of the various tubules involved in the process are:

 Glomerulus filters the blood
 Proximal Convoluted Tubules reabsorb ions, water, and nutrients, removes
toxins, and maintains the pH of the filtrate.
 Loop of Henle helps in reabsorption of water and recovery of sodium chloride from
the filtrate.
 Distal Convoluted Tubules reabsorb and secrete selective ions and maintains the
pH of the blood.
 Collecting Duct, solutes, and water is reabsorbed from the filtrate by the collecting
duct.
 The urinary bladder is stretched and gets filled with urine formed in the nephrons.
 The receptors present on the walls of the urinary bladder send signals to
the Central Nervous System, thereby, allowing the relaxation of sphincter muscles
to release urine. This is known as micturition.