According to myogenic hypothesis of renal autoregulation, the afferent arterioles contract in response to stretch induced by
**Core Concept**
The myogenic hypothesis of renal autoregulation proposes that changes in blood pressure lead to stretch in the smooth muscle cells of the afferent arterioles, triggering a reflex contraction to maintain constant renal blood flow. This mechanism is crucial for maintaining glomerular filtration rate (GFR) and preventing hypotension-induced renal dysfunction.
**Why the Correct Answer is Right**
The correct answer choice is related to the mechanism of stretch-induced contraction in the afferent arterioles. When blood pressure increases, it stretches the smooth muscle cells of the afferent arterioles, leading to an increase in intracellular calcium concentration. This increase in calcium triggers the contraction of the smooth muscle cells, which in turn causes a decrease in afferent arteriolar diameter and subsequent decrease in GFR. This mechanism helps to prevent excessive renal blood flow and maintain constant GFR.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the stimulus for contraction in the myogenic hypothesis. While increases in blood pressure do lead to stretch, the contraction is not directly caused by the increase in blood pressure itself, but rather by the stretch-induced increase in intracellular calcium.
**Option B:** This option is incorrect because it does not accurately describe the mechanism of renal autoregulation. Tonicity of the renal medulla is not a direct stimulus for contraction in the afferent arterioles.
**Option C:** This option is incorrect because it does not accurately describe the mechanism of renal autoregulation. Tubuloglomerular feedback is a separate mechanism that helps to regulate GFR, but it is not related to the myogenic hypothesis.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the myogenic hypothesis of renal autoregulation is a critical mechanism for maintaining constant GFR and preventing hypotension-induced renal dysfunction. Understanding this mechanism is essential for managing patients with hypertension, heart failure, and other conditions that can affect renal blood flow.
**Correct Answer:** C. Increased intravascular pressure