Question

What are the stages of urination?

Answer 1

Urination:

1. The discharge of urine from the body is known as urination or micturition.
2. Urine is released from the urinary bladder through the urethra outside the body.

Stages of Urination:

The process of urination is carried out in three main stages: Glomerular ultrafiltration, tubular reabsorption, and tubular secretion.

Glomerular ultrafiltration:

1. Urine formation starts when the blood is filtered by the glomerulus then enters the Bowman's capsule where the glomerular filtrate is formed.
2. The afferent arteriole that enters the glomerulus has a wide diameter which helps in increasing the blood pressure in the glomerulus as well as in filtration.
3. Glomerular filtrate contains all blood constituents except corpuscles and plasma proteins.

Tubular ultrafiltration:

1. The glomerular filtrate comes to the proximal tubule for the reabsorption of essential nutrients.
2. Nutrients like glucose, amino acids, water, sodium ions, potassium ions, chloride ions, bicarbonate ions, magnesium ions and calcium ions are reabsorbed.
3. The filtrate then goes to the collecting duct where anti-diuretic hormone (ADH) acts to reabsorbs the excess water.
4. Thus, the volume of water decreases.

Tubular secretion:

1. The glomerular filtrate comes to the proximal tubule where creatinine, and uric acid are secreted in it.
2. When the glomerular filtrate goes to the distal part where urea, potassium ions and hydrogen ions are secreted in the form of urine.