Question

The mechanism of urine formation in nephron involves
A. ( i )- Glomerular filtration, ( ii )- Reabsorption, ( iii )- Secretion, ( iv )- Excretion
B. ( i )- Glomerular filtration, ( ii )- Secretion, ( iii )- Reabsorption, ( iv )- Excretion
C. ( i )- Secretion, ( ii )- Reabsorption, ( iii )- Glomerular filtration, ( iv )- Excretion
D. ( i )- Glomerular filtration, ( ii )- Reabsorption, ( iii )- Excretion, ( iv )- Secretion

Answer 1

A nephron is the kidney’s structural and functional unit. It is made up of a renal corpuscle and a renal tubule. The renal corpuscle is the initial filtering component of the nephron while the renal tubule processes and carries away the filtered fluid.

Complete answer:
This option (A) represents the correct sequence of urine formation prior to its excretion. The renal corpuscle of the nephron contains the glomerulus (tuft of capillaries) and the Bowman’s capsule surrounding these capillaries. The initial filtration process starts in the glomerulus which is also known as glomerular filtration. Then this filtered fluid passes into the renal tubule which causes the reabsorption of useful minerals and some water into the adjacent capillaries and at the same time waste ions and hydrogen ions pass from the capillaries into the tubule, known as secretion. These secreted ions along with the filtrate from the urine which is then excreted out.
The correct sequence of urine formation in nephron is:
Glomerular filtration $\to$ reabsorption $\to$ secretion $\to$ excretion.

Hence, the correct answer is option (A).

Note: Kidneys are the organ of the excretory system and they are known for filtering out the unwanted substances from the blood and producing urine which is then excreted out. Urine formation in the nephron involves three stages i.e., glomerular filtration, reabsorption, and secretion. These are the processes that ensure that only waste materials and excess water is excreted out of the body while the remaining useful substances are again reabsorbed after the filtration process. Urine, thus produced contains $95\%$ water and $5\%$ waste products.