Physiology of Urine Formation

Physiology of urine formation: There are mainly 3 processes involved in urine formation.

  1. Glomerular filtration  
  2. Tubular reabsorption  
  3. Tubular secretion.

Glomerular Filtration

It is the filtration of body fluids and solutes from the blood filtration are assisted by the difference between the blood pressure in the glomerulus, and the pressure of filtrate in the glomerular capsule. The volume of the filtrate by both kidneys in each minute is called Glomewar Filtration Rate (GFR) in a healthy individual GFR is 125ml/min i.c.80 liter of trade is formed each day by two kidneys but nearly all the filtrate is reached and 1-1.5its is excreted as urine.

GFR rate depends on the following factors:

  • Permeability of capillaries
  • Area of filtration
  • intra-capillary pressure
  • The osmotic pressure of the blood.

Tubular Reabsorption

Nearly 180 liters of filtrate is formed each day by two kidneys but nearly all the filtrate is reabsorbed and 7-1.5fts is excreted as urine. The following substances are reabsorbed by the rent tubules:


  • It is reabsorbed completely from the proximal tubules, galactose, fructose is all so reabsorbed.


  • More than 80% of water is reabsorbed and these stikes place in collecting tubules and proximal and distal tubules This reabsorption is controlled by antidiuretic the hormone of the posterior pituitary gland.


  • NaCl is reabsorbed in the proximal and distal tubules
  • Potassium, phosphate, and bicarbonate is completely reabsorbed in the proximal tubule
  • Aldosterone regulates the extracellular fluid volume by adjusting the amount of sodium reabsorbed by the blood from the kidneys
  •  Uric acid, Creatine, Amino acids, Beta-hydroxybutyric acid are reabsorbed from the loop of Henle.

Tubular Secretion

Further, the substances which are not found in the filtrate are also found in the urine these are directly excreted from the blood by the tubules through the enzyme mechanism, which is called tubulation. It is an active process in which substances like potassium, hydrogen, creatine, and drugs like penicillin, para amino-hippuric acid, etc are directly the tubular cells from the blood.

Make sure you also check our other amazing Article on : Anatomy of Nephron
Sharing Is Caring:

Leave a Comment