Histology Chapter 16 Urinary Tract PDF

Histology – Chapter 16 The Kidney and Urinary system Materials Edited, added and improved by Prof. Wael Abdel-Rahman Hassan Based on: Wheater's Functional Histology: A Text and Colour Atlas, By: Barbara Young, John W. Heat & Reso...

Histology – Chapter 16 The Kidney and Urinary system Materials Edited, added and improved by Prof. Wael Abdel-Rahman Hassan Based on: Wheater's Functional Histology: A Text and Colour Atlas, By: Barbara Young, John W. Heat & Resources at ELSEVIER Figure 16.1 The urinary system Downloaded from: StudentConsult (on 27 October 2007 03:49 PM) © 2005 Elsevier  Chapter 16. The Urinary System Kidney General Structure. The human kidney is made up of 10-18 lobes. A single lobe is made up of a medullary pyramid and a cortical part which is fused with those of other lobes to form a continuous cortex. The cortex contains the renal corpuscles and the proximal and distal parts of the tubules. The renal medulla is made up of multiple medullary pyramids separated by medullary extensions of the cortex. Each renal papilla is surrounded by a branch of the renal pelvis called a calyx; the whole urinary collecting system within the kidney being described as the pelvicalyceal system. The space between the branches of the pelvicalyceal system is filled with fatty supporting tissue and is known as the renal sinus. The nephron. The nephron is the functional unit of the kidney. It consists of two major components, the renal corpuscle and the renal tubule. The renal corpuscle is responsible for the filtration of plasma and is a combination of two structures, Bowman's capsule and the glomerulus. Bowman's capsule consists of a single layer of flattened cells resting on a basement membrane. The glomerulus is a globular network of anastomosing capillaries, which invaginates Bowman's capsule. Thus the capillary loops of the glomerulus are invested by the visceral layer of Bowman's capsule which is a highly specialized layer of epithelial cells called podocytes. The visceral layer is reflected around the vascular stalk of the glomerulus to become continuous with the parietal layer that constitutes Bowman's capsule proper. The space between the two layers is known as Bowman's space and is continuous with the lumen of the renal tubule. The afferent arteriole, which supplies the glomerulus, and the efferent arteriole, which drains it, enter and leave the corpuscle at the vascular pole that is usually situated opposite the entrance to Figure 16.4 Basic organisation of the nephron, collecting system the renal tubule, the urinary pole and renal vasculature The nephron and collecting system  The nephron The nephron is the functional unit of the kidney The Renal the Renal Tubules: Corpuscle: 1.PCT Bowman's capsule 2.Loop of Henle Glomerulus. 3.DCT 4.The collecting tubule, collecting duct, 5. ducts of Bellini pelvicalyceal system Renal tubules: 1- The proximal convoluted tubule (PCT) is the longest, most convoluted section of the tubule and is responsible for the reabsorption of approximately 65% of the ions and water of the glomerular filtrate. PCTs are confined to the renal cortex. 2- The loop of Henle includes the distal straight part of the proximal tubule, the pars recta, the thin descending and ascending limbs, and the thick ascending limb. See Table on next page. 3- The distal convoluted tubule (DCT) is a continuation of the thick limb of the loop of Henle after its return to the cortex. It is shorter and less convoluted than the PCT. 4- The collecting tubule is the straight terminal portion of the nephron; several collecting tubules converging to form a collecting duct. The collecting ducts descend through the cortex in parallel bundles called medullary rays, progressively merging in the medulla to form the large ducts of Bellini which open at the tips of the renal papillae to discharge urine into the pelvicalyceal system. Figure 16.6 Renal cortex H [amp ] E ×40 Downloaded from: StudentConsult (on 27 October 2007 03:49 PM) © 2005 Elsevier  Structural differences between proximal and distal convoluted In the proximal convoluted tubule (PCT), the simple cuboidal epithelium has a prominent blue stained brush border of tall microvilli, increasing the surface area of the plasma membrane some 20-fold. The cytoplasm of PCT epithelial cells stains intensely due to a high content of organelles, principally mitochondria. The cells are almost pyramidal in shape and the PCT lumen is narrow. The distal convoluted tubules (DCT): may be differentiated from proximal convoluted tubules by the absence of a brush border, a larger more clearly defined lumen, and paler cytoplasm (due to fewer organelles). In addition, sections of DCT are less numerous than sections of PCT since the DCT is much shorter than the PCT Figure 16.23 (a) Summary of activities of different parts of the tubule (b) Comparison of epithelial structure in different parts of the renal tubule Downloaded from: StudentConsult (on 27 October 2007 03:50 PM) © 2005 Elsevier