Question

Explain the steps involved in the formation of urine.

[Review question: Pg. No: 245]

Answer 1

Mechanism of Urine Formation:
The process of urine formation includes the following three stages.
1.Glomerular filtration
2.Tubular reabsorption
3.Tubular secretion

Glomerular filtration:

• Urine formation begins with the filtration of blood through epithelial walls of the glomerulus and Bowman’s capsule.
• The filtrate is called as the glomerular filtrate.
• Both essential and non-essential substances present in the blood are filtered.

Tubular reabsorption:

• The filtrate in the proximal tubule consists of essential substances such as glucose, amino acids, vitamins, sodium, potassium, bicarbonates and water that are reabsorbed into the blood by a process of selective reabsorption.

Tubular secretion:

• Substances such as H+ or K+ ions are secreted into the tubule. This tubular filtrate is finally known as urine, which is hypertonic in man.
• Finally the urine passes into collecting ducts to the pelvis and through the ureter into the urinary bladder.