Question

 Assertion: The renal threshold of glucose is said to be 180 mg per 100 ml.
Reason: Glucose starts appearing in the urine when its blood level exceeds 180 mg per 100 ml of blood.
(a) Both Assertion and Reason are correct and the Reason is a correct explanation of Assertion.
(b) Both Assertion and Reason are correct but the Reason is not a correct explanation of Assertion.
(c) Assertion correct but Reason is incorrect.
(d) Both Assertion and Reason and incorrect.

Answer 1

Hint: Renal threshold is the highest concentration of the substance in blood which is fully reabsorbed from the glomerular filtrate. Glomerular filtration involves filtration of blood which takes place by glomerular capillary blood pressure.

Complete answer:
The substance that reabsorbs actively in the blood includes glucose and amino acid. When these substances are absorbed in the renal threshold value of 180 mg per 100 ml then they do not appear in urine but when the value exceeds glucose begin to appear in the blood.
In the mechanism of urine formation, tubular reabsorption involves active and passive mechanisms in which proximal and distal convoluted tubules, the loop of Henle, and collecting duct contribute absorption.

Additional Information: The proximal convoluted tubule is a major site of reabsorption where glucose, amino acids, vitamins, hormones, ions, water, and some urea get reabsorbed from the filtrate. Distal convoluted tubule function under the influence of aldosterone. Absorption of sodium, chlorine, and water takes place in this tubule. Aldosterone helps to make filtrate isotonic to blood plasma. Ascending loop of Henle absorbs sodium, potassium, and chloride ion with less amount of urea in which filtrate becomes hypotonic whereas in the descending loop of Henle reabsorption of water takes place without resorption of ions and filtrate become hypertonic. In collecting duct reabsorption a small amount of water and sodium takes place and the filtrate form is urine which is hypertonic to blood plasma.
So, the correct answer is ‘Both assertion and Reason are correct and the Reason is a correct explanation of Assertion’.

Note: The absorption of glucose, amino acids, and sodium, potassium ions take place by active transport. The reabsorption of water takes place by osmosis. Chlorine, urea, and other solutes reabsorbed by passive diffusion.