Question

Cells of macula densa produce
A) Erythropoietin
B) Renin
C) Angiotensinogen
D) Angiotensin

Answer 1

Hint:The macula densa, a part of the distal convoluted tubule of the nephron where distal convoluted tubule comes in contact with the afferent renal arteriole of the glomerulus.

Complete answer
The macula densa cells is a collection of specialized epithelial cells that respond to the sodium concentration in the fluid within the distal convoluted tubule and, perhaps, to the rate of fluid flow past them. An increase in sodium concentration in the tubular fluid leads to contraction of the afferent arteriole, reducing flow of blood to the glomerulus and the glomerular filtration rate. Juxtaglomerular cells originating from afferent arteriole smooth muscle cells contribute to a decrease in renin production when arterial blood pressure decreases. Via the renin-angiotensin-aldosterone pathway, renin raises blood pressure.

The influence on the volume of macula densa cells of changes in luminal fluid structure has remained a contentious issue. With associated increase in Na and osmolarity, both increases and decreases in macula densa cell volume have been observed. Macula densa cells acted like osmometers when NaCl concentration was maintained fixed, swelling with a decrease and shrinking with a rise in osmolarity.

Hence,the correct answer is option (B) i.e, Angiotensinogen.

Note:A specialized structure constituted by the distal convoluted tubule and the glomerular afferent arteriole is the juxtaglomerular apparatus. It is situated near the glomerular vascular pole and its primary purpose is to control blood pressure and the rate of glomerular filtration.