\ \ \ \ \ \ \ is completely reabsorbed by the renal tubules. - AIIMS BHOPAL NO- 2018( Shift-2nd)

AIIMS BHOPAL NO- 2018( Shift-2nd)

Applied Physiology

Easy

Appeared in: AIIMS BHOPAL NO- 2018( Shift-2nd)

Explanation

Under normal conditions, 100% of the glucose filtered by the glomerulus is reabsorbed back into the blood.
This reabsorption occurs primarily in the Proximal Convoluted Tubule (PCT) of the nephron.
The mechanism involves secondary active transport via Sodium-Glucose Cotransporters (SGLT).
Glucose is considered a 'threshold substance'; it is only excreted in the urine when blood levels surpass the reabsorptive capacity of the tubules (renal threshold of about 180 mg/dL).

Option A: Creatinine, a metabolic waste product, is filtered by the glomerulus but is not reabsorbed by the tubules. It is also actively secreted in small amounts.
Option B: While a large amount of potassium is reabsorbed, it is also actively secreted into the filtrate in the distal tubules and collecting ducts to regulate plasma potassium levels. Therefore, it is not 'completely' reabsorbed.
Option C: Uric acid undergoes complex handling by the kidney, which includes filtration, significant reabsorption (around 90%), and also secretion. It is not completely reabsorbed.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Renal tubular reabsorption of solutes as background academic context rather than a clinical decision trigger.
The presence of glucose in the urine (glycosuria) is a cardinal sign of hyperglycemia, most commonly associated with diabetes mellitus. A nurse performing a urinalysis would report this finding immediately.
Monitoring serum creatinine and creatinine clearance is a fundamental nursing responsibility for assessing a patient's kidney function, especially in those with renal disease or on nephrotoxic medications.
What if? If a patient's blood glucose level was 250 mg/dL (well above the typical renal threshold of 180-200 mg/dL), the glucose transporters would be saturated. In this case, the nurse would expect to find glucose in the urine, and the statement 'glucose is completely reabsorbed' would be false for this specific patient.

How to Approach the Question

First, identify the key concept in the question stem: 'completely reabsorbed' by the 'renal tubules'. This is a direct recall question about renal physiology.
Mentally review the renal handling of each substance listed in the options.
Recall that glucose is a nutrient the body aims to conserve. Under normal blood concentrations, it is entirely reclaimed from the filtrate.
Contrast this with waste products like creatinine, which the body aims to excrete, meaning it should not be reabsorbed.
Remember that electrolytes like potassium are finely regulated, involving both reabsorption and secretion to maintain balance, so reabsorption is not 'complete'.
Based on this physiological knowledge, conclude that glucose is the only substance that is completely reabsorbed under normal circumstances.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 46-48

E6 Medicine Harrison 22e Part 2 p. 273-275