Juxtaglomerular Apparatus: Located near the vascular pole of a renal corpuscle at the point of contact between a distal convoluted tubule and an afferent arteriole, this includes juxtaglomerular (JG) cells, a macula densa, and extraglomerular mesangial cells. The JG cells, modified smooth muscle cells in the wall of the afferent arteriole, exhibit typical secretory ultrastructure and numerous PAS-positive cytoplasmic granules. Although the influence of the macula densa on the JG cells is poorly understood, below-normal blood volume, blood pressure, or levels of blood sodium causes the JG cells to secrete renin, This enzyme cleaves plasma angiotensinogen to produce angiotensin I, which is converted to its active form, angiotensin II, by enzymes in the lungs. Angiotensin II, a vasoconstrictor, increases blood pressure and stimulates aldosterone production by the adrenal cortex, thereby increasing chloride and sodium reabsorption by the distal tubule. Urinary system
Distal convoluted tubule
4. Distal convoluted tubule. This final segment of the nephron lies in the cortex. Its epithelial lining is low cuboidal, with no brush border, making its lumen appear wider. Its lining cells are more basophilic than those lining the proximal convoluted tubules. The lateral cell boundaries are indistinct as a result of extensive lateral membrane interdigitations with their neighbors. The distal tubule epithelium forms a disk of tightly packed columnar cells called a macula densa at the point near the vascular pole of a renal corpuscle where it contacts an afferent arteriole. This disk may monitor the osmolarity of the fluid in the tubule lumen
5. Cortical and juxtamedullary nephrons, renal corpuscles are found throughout the cortex. While most belong to the cortical nephrons, the 15% closest to the medulla belong to the juxtamedullary nephrons. The latter group has short thick descending limbs and longer thin limbs that extend deeper into the medulla. The juxtamedullary nephrons bear the primary responsibility for setting up the osmotic gradient in the medulla.