ln response to an increase in GFR, the proximal tubule and the loop of Henle demonstrate an increase in the rate of Na reabsorption. This phenomenon is called
**Core Concept**
The phenomenon of increased sodium reabsorption in the proximal tubule and loop of Henle in response to increased glomerular filtration rate (GFR) is a classic example of tubuloglomerular feedback. This mechanism helps maintain sodium balance and blood pressure homeostasis.
**Why the Correct Answer is Right**
When GFR increases, the macula densa cells in the distal convoluted tubule detect the higher sodium load. This triggers the release of adenosine and other signaling molecules that stimulate the juxtaglomerular cells to release renin. Renin initiates the renin-angiotensin-aldosterone system (RAAS), leading to increased angiotensin II and aldosterone levels. Angiotensin II constricts the afferent arterioles, reducing GFR, while aldosterone promotes sodium reabsorption in the collecting duct and increases sodium reabsorption in the proximal tubule and loop of Henle.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the phenomenon described. The sodium-potassium pump is an important mechanism for maintaining sodium balance, but it is not directly related to the increase in sodium reabsorption in response to increased GFR.
**Option B:** This option is incorrect because the sodium-glucose cotransporter is primarily responsible for glucose reabsorption in the proximal tubule, not sodium reabsorption.
**Option C:** This option is incorrect because the countercurrent multiplier system is a mechanism for concentrating or diluting the urine in the loop of Henle, but it is not directly related to the increase in sodium reabsorption in response to increased GFR.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that tubuloglomerular feedback is a key mechanism for maintaining sodium balance and blood pressure homeostasis. This feedback loop helps regulate GFR and sodium reabsorption in response to changes in sodium load, making it a critical concept for understanding hypertension and electrolyte disorders.
**Correct Answer: C. TGR5 (Tubuloglomerular feedback)**