Urine is formed in the kidneys through a three step process: ultrafiltration, tubular reabsorption and secretion, and water absorption. During ultrafiltration, blood undergoes filtration through the glomerulus, forming a glomerular filtrate with a similar composition to plasma. As the filtrate passes through the renal tubules, materials like glucose and amino acids are reabsorbed into the blood while waste products like urea remain. Excess water is also reabsorbed, leaving behind a smaller volume of concentrated urine.
2. •Urine is formed in kidneys.
•Urine is formed in the kidneys in three major steps
Ultrafilration
Tubular reabsorption and Secretion
Water absorption.
3. ULTRAFILTRATION
Blood undergoes filtration through the pores of
the glomerulus.
The pressure inside the glomerulus is very high
as the size of the efferent vessel is leess than
that of the afferent vessel.This helps in filtration.
The glomerular filtrate formed by the process of
ultrafiltration is collected in the capsular space.
The composition of glomerular filtrate is similar
to that of plasma.
4. COMPONENTS OF GLOMERULAR FILTRATE
Water
Glucose
Amino acids
Ions of Sodium,Potassium and Calcium
Vitamins
Urea,Uric acid,Creatinine etc.
5. REABSORPTION AND SECRETION
When the glomerular filtrate is transported from
the capsular space to the collecting duct
through the renal tubule,materials which are to
be retained in the body like glucose,aminoacids
etc,are reabsorbed completely and
sodium,potassium and calcium ions and water
are reabsorbed partially into peritubular
capillaries.
Urea,Potassium,Hydrogen ions etc.,which are
seen in blood even after ultrafiltration is
secreted from peritubular capillaries in to the
renal tubules.
6. WATER ABSORPTION
Excess water seen in glomerular filtrate is
absorbed in the collecting duct.
As a result,the glomerular filtrate is change in
to urine.
Both the kidneys together produce about
127ml of glomerular filtrate per minute out of
which 126 ml is reabsorbed in to the blood.
The remaining part forms urine.
