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Dr Rania Gabr To describe the microscopic structure of the kidney, ureter,urinary bladder and urethra Uriniferous tubules are Composed of: 1- Nephron : Renal corpuscle plus renal tubules 2-Collecting duct Involved in concentrating urine (1) Cortical nephrons are the most common type of nephrons. (2) Juxtamedullary nephrons account for approximately 20% of all nephrons; their corpuscles are found adjacent to the medulla. These nephrons are responsible for producing the urine-concentrating mechanism of the kidney. 4 Renal corpuscle › Glomerulus and glomerular capsule Glomerulus – tuft of capillaries Capillaries of glomerulus are fenestrated Glomerular (Bowman’s) capsule Parietal layer – simple squamous epithelium Visceral layer – consists of podocytes The podocytes possess processes called pedicles that wrap around the capillaries and interdigitate to form filtration slits approximately 25nm wide. In addition to capillary endothelial cells and podocytes, renal corpuscles also contain mesangial cells. The mesangial cells serve a phagocytic function and keep the basement membrane clear of debris. 8 Consist of 3 layers › 1- Fenestrated Capillary endothelium › 2- Basement membrane › 3- Foot processes of podocytes of glomerular capsule. 9 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 23.6c At the vascular pole, smooth muscle cells in the tunica media of the afferent glomerular arteriole are replaced by highly modified epithelioid cells containing cytoplasmic granules. These are the juxtaglomerular cells,. In the adjacent segments of distal convoluted tubules the cells that border the juxtaglomerular area, are narrow and more columnar than elsewhere in the tubule. This darker and more compact area is called macula densa. The juxtaglomerular cells and macula densa constitute the juxtaglomerular apparatus Filtrate proceeds to renal tubules from glomerulus › Proximal convoluted tubule › Loop of Henle Descending limb Thin segment Thick segment( Ascending limb) › Distal convoluted tubule The proximal convoluted tubule is formed of simple cuboidal to low columnar epithelium. They are large cells, each transverse section of PCT contain only 3-5 nuclei The apical surface is covered with microvilli creating a light microscopic brush border that increases the surface area for ion absorption. the walls formed by cuboidal epithelial cells Their Luminal surfaces have dense microvilli. 23 Descending limb › Proximal part: similar cells of the PCT › Thin segment: simple sequamous epithelium Ascending limb › Cuboidal epithelium or low columnar→ thick segment 24 P P D D Distal convoluted tubules are located within the cortex. They are approximately 1/3rd as long as their proximal counterparts. They contact the renal corpuscle forming the macula densa which is part of the juxtaglomerular apparatus The wall: cuboidal epithelium (like PCT) Thinner Lack micrivilli 27 Collecting tubules › Receive urine from distal convoluted tubules Figure 23.8 The collecting system starts in the cortex as a continuation of the distal convoluted tubules and descend through the medulla. As the ducts coalesce and increase in size, the cells of the tubes change from somewhat squamous to cuboidal to columnar and similarly become increasing stratified. They terminate at the tip of the renal pyramid as the papillary ducts . Long section of Collect tubules (CT) and PCT (P) CT P CT 30 Histology of ureter › Mucosa – transitional epithelium › Lamina propria: CT › Muscularis – two layers Inner longitudinal layer Outer circular layer › Adventitia – typical connective tissue Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 23.12 Ureter – folded mucus membrane Transitional Epithelium 33 Wall of bladder › Mucosa Transitional epithelium › Muscular layer Detrusor muscle: 3 layers of smooth muscles › Adventitia Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 23.15a, b 38 Epithelium of urethra › Transitional epithelium At the proximal end (near the bladder) › Stratified and pseudostratified columnar – mid urethra (in males) › Stratified squamous epithelium At the distal end (near the urethral opening) 41