Question

The mechanism of urine formation in nephron involves

• A. (i)- Glomerular filtration, (ii)- Reabsorption, (ii)- Secretion, (iv)- Excretion
• B. (i)- Glomerular filtration, (ii)- Secretion, (ii)- Reabsorption, (iv)- Excretion
• C. (i)- Secretion, (ii)- Reabsorption, (ii)- Glomerular filtration, (iv)- Excretion
• D. (i)- Glomerular filtration, (ii)- Reabsorption, (ii)- Excretion, (iv)- Secretion

Answer 1

Answer: (A)

(i)- Glomerular filtration, (ii)- Reabsorption, (ii)- Secretion, (iv)- Excretion

During filtration, blood enters the afferent renal arteriole and flows into the glomerulus where blood components such as water and nitrogenous waste will move towards the inside of the glomerulus, and non-filterable components such as cells will exit via the efferent arteriole. These filterable components accumulate in the glomerulus to form the glomerular filtrate. The next step is reabsorption, during which molecules and ions will be reabsorbed back into the circulatory system. What remains in the glomerulus after this process has taken place is known as the tubular fluid and this is what will pass through to the collecting duct to form urine. During secretion, some substances such as hydrogen ions, creatinine, and drugs will be removed from the blood through the peritubular capillary network into the distal convoluted tubule, or collecting duct. The end product of all these processes is urine; a collection of substances that has not been reabsorbed during glomerular filtration or tubular reabsorption. It is removed from the body through the process of excretion.