________ is a special sensitive region in kidney formed by cellular modifications in the distal convoluted tubule and afferent arteriole at the location of their contact.
AJuxta glomerular apparatus
BRenal capsule
CColumns of Bertini
DRenal pelvis
Answer:
A. Juxta glomerular apparatus
Read Explanation:
Juxtaglomerular Apparatus (JGA)
The structure described is the Juxtaglomerular Apparatus (JGA), a critical regulatory complex located where the distal convoluted tubule (DCT) makes physical contact with the afferent arteriole of the same nephron.
- Function: The JGA plays a pivotal role in the regulation of blood pressure and glomerular filtration rate (GFR). It acts as a sensor to monitor fluid composition and blood volume.
- Key Components: The apparatus is composed of three primary cell types:
- Macula Densa: Specialized epithelial cells in the wall of the distal convoluted tubule that act as chemoreceptors. They sense changes in sodium chloride (NaCl) concentration in the tubular fluid.
- Juxtaglomerular (JG) Cells: Modified smooth muscle cells located primarily in the wall of the afferent arteriole. These cells synthesize, store, and secrete the enzyme Renin.
- Extraglomerular Mesangial Cells: Located in the space between the arterioles and the macula densa, these cells facilitate communication between the macula densa and JG cells.
- Renin-Angiotensin-Aldosterone System (RAAS): When the macula densa senses a decrease in NaCl delivery (often indicating low blood pressure), it triggers the JG cells to release renin into the bloodstream. This activates the RAAS cascade, ultimately leading to vasoconstriction and increased sodium/water reabsorption, which raises systemic blood pressure.
- Autoregulation: The JGA is essential for tubuloglomerular feedback, a mechanism that adjusts the diameter of the afferent arteriole to maintain a constant GFR despite fluctuations in systemic blood pressure.