Scientists studying the kidney's response to hypoperfusion apply a clip to a pig's right renal artery that reduces blood flow to the kidney by about 70%. After 6 months, they perform a right nephrectomy and examine the glomeruli and tubules microscopically. Which of the following cell types would be most likely to undergo hyperplasia as a result of the clip placement?

Question

Scientists studying the kidney's response to hypoperfusion apply a clip to a pig's right renal artery that reduces blood flow to the kidney by about 70%.  After 6 months, they perform a right nephrectomy and examine the glomeruli and tubules microscopically.  Which of the following cell types would be most likely to undergo hyperplasia as a result of the clip placement?

Quizplus · Accepted Answer

11ec160b_3b5c_2aa9_9249_e774dab08195_MD0001_00 A markedly narrowed renal artery (eg, due to an atherosclerotic plaque or external clip) cannot supply the kidney with enough blood to maintain a normal glomerular filtration rate. The reduced blood flow is sensed by the juxtaglomerular (JG) apparatus, which consists of the macula densa, extraglomerular mesangial cells (ie, Lacis cells), and JG cells. Macula densa cells are tall, narrow cells located in the distal tubule that monitor salt content and tubular flow rate. This information is transmitted to nearby JG cells that are located mainly in the wall of the afferent arteriole. JG cells are modified smooth muscle cells with renin-containing zymogen granules. Significant renal hypoperfusion leads to a compensatory increase in renin secretion by JG cells. This activates the renin-angiotensin-aldosterone system, leading to increased levels of angiotensin II and aldosterone. Long-term renal hypoperfusion, such as caused by renal artery stenosis, leads the JG cells of the affected kidney(s) to undergo hyperplasia as a result of chronic stimulation. When renal artery stenosis is restricted to one side and the contralateral kidney functions normally, chronic kidney disease does not occur as the normal kidney is still able to efficiently filter and excrete waste products (eg, creatinine, urea). However, hypertension can occur in both unilateral and bilateral disease, as secretion of renin by one kidney will lead to systemic vasoconstriction and retention of salt and water by both kidneys. (Choices A, C, and E) The cuboidal cells of the proximal tubule, the intraglomerular mesangial cells (which are distinct from the extraglomerular mesangial [Lacis] cells), and the squamous cells of the thick ascending limb of the loop of Henle are not components of the JG apparatus and do not undergo hyperplasia in response to hypoperfusion. In fact, these tissues may atrophy in the clipped kidney due to ischemia. (Choice B) The endothelium is composed of a single layer of squamous cells that line blood vessel walls; endothelial cells do not undergo hyperplasia in response to hypoperfusion. Efferent arteriolar smooth muscle cells may undergo hypertrophy/hyperplasia with chronic angiotensin stimulation, but these lie within the arteriolar wall (underneath the endothelium). Educational objective: Renal artery stenosis causing significant renal hypoperfusion will result in a decreased glomerular filtration rate and activation of the renin-angiotensin-aldosterone system. This leads to increased renin release by modified smooth muscle (juxtaglomerular) cells in the walls of afferent glomerular arterioles. Chronic renal hypoperfusion can cause hyperplasia of the juxtaglomerular apparatus.

Scientists Studying the Kidney's Response to Hypoperfusion Apply a Clip