Proximal and distal tubules and the loop of Henle. A Proximal and distal tubules and the loop of Henle. A. Proximal and distal tubules in the cortex. The brush border of the proximal convoluted tubule (PCT) cells may accumulate as blebs in the lumen of the tubules during fixation. The distal convoluted tubule (DCT) cells lack a brush border. Solutes and fluid recovered by the tubules flow into capillaries and venules (asterisks) in the thin interstitial connective tissue. B. Proximal tubule transport processes. The proximal convoluted tubules utilize the sodium pump to generate a Na+ electrochemical potential that drives the reabsorption of solutes and water from the filtrate. Proteins that escape into the filtrate are specifically removed by endocytosis and degraded in lysosomes. Solutes and water that exit the basolateral membranes enter capillaries in the interstitial tissue. AAs, amino acids; ADP, adenosine diphosphate; ATP, adenosine triphosphate. C. The loop of Henle in the medulla. The thin limbs (tL) of the loop of Henle are lined with a simple low epithelium. The thick ascending limbs (TAL) are lined with a cuboidal epithelium. The collecting ducts (CD) are also present in the medulla and are lined with tall, narrow cells. D. Countercurrent multiplier system. Sodium pumps in the TAL actively remove Na+ from the filtrate (red arrow); Cl– follows passively. The sodium pumps continuously move a fraction of the Na+ that is inside the tubules out and generate a high Na+ concentration in the interstitial tissue outside the tubules. Source: URINARY SYSTEM, The Big Picture: Histology Citation: Ash R, Morton DA, Scott SA. The Big Picture: Histology; 2017 Available at: https://accessphysiotherapy.mhmedical.com/DownloadImage.aspx?image=/data/books/2058/ashhist_ch13_f002a-d.png&sec=155784796&BookID=2058&ChapterSecID=155784773&imagename= Accessed: October 21, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved