In which part of nephron, glucose reabsorption takes place?

NIA - 29 January 2023

Applied Physiology

Easy

Appeared in: NIA - 29 January 2023

Explanation

The proximal tubule is responsible for reabsorbing virtually all of the glucose and amino acids from the glomerular filtrate.
Its epithelial cells are equipped with a dense brush border (microvilli) that massively increases the surface area for transport.
Glucose is reabsorbed via secondary active transport, using Sodium-Glucose Cotransporters (SGLT) that couple glucose movement to the favorable influx of sodium ions.
Under normal physiological conditions, this process is so efficient that no glucose is excreted in the urine.

Option B: The distal tubule's primary role is the fine-tuning of ion and water balance under hormonal control (aldosterone and ADH). It lacks the specific high-capacity transporters for glucose reabsorption.
Option C: The collecting duct's main function is to make final adjustments to the urine's water content, regulated by ADH, and to transport urea. It does not reabsorb glucose.
Option D: The Loop of Henle is critical for creating the osmotic gradient that allows for the concentration of urine. It reabsorbs water and salts but not glucose.

Clinical Relevance

Nursing practice connection: Knowing Renal physiology and tubular reabsorption in the nephron helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding glucose reabsorption is fundamental for interpreting urinalysis. The presence of glucose in urine (glycosuria) is a key sign of hyperglycemia, most commonly due to diabetes mellitus, where blood glucose levels exceed the kidney's reabsorptive capacity (renal threshold).
This knowledge is also the basis for a class of diabetes medications called SGLT2 inhibitors (e.g., dapagliflozin, canagliflozin). These drugs block glucose reabsorption in the proximal tubule, causing excess glucose to be excreted in the urine, thereby lowering blood glucose levels.
What if? A patient's blood glucose is 350 mg/dL. At this level, the SGLT transporters in the proximal tubule are completely saturated. The nurse would anticipate finding a significant amount of glucose in the patient's urine, confirming that the renal threshold has been far exceeded.

How to Approach the Question

Identify the core concept of the question: It asks for the specific location of glucose reabsorption within the nephron.
Recognize this as a factual recall question based on fundamental renal physiology.
Mentally trace the path of filtrate through the nephron: Glomerulus → Proximal Tubule → Loop of Henle → Distal Tubule → Collecting Duct.
Recall the primary function of each segment. The proximal tubule is the 'workhorse' of the nephron, responsible for the bulk reabsorption of essential substances filtered from the blood.
Evaluate the options: The proximal tubule is specialized for reabsorbing nearly 100% of glucose and amino acids. The other segments have more specialized roles in concentrating urine and fine-tuning electrolyte and water balance.
Conclude that the proximal tubule is the only segment equipped for high-capacity glucose reabsorption.

Concept Tested & Keywords

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