SYSTEMIC HISTOLOGY URINARY SYSTEM II Mr. Babatunde, D.E Descending Pars Recta (straight portion) of Proximal Tubule Is also lined by a simple cuboidal epithelium having a prominent brush border. Cells are shorter and less elaborate in shape than those of the proximal convoluted tubule, but they have the same general features. This region of the nephron is often damaged in acute renal failure and mercury poisoning. This segment constitutes the initial part (thick descending limb) of the loop of Henle. Proximal convoluted tubule and thick descending limb of Henle’s loop Distal convuloted tubule and thick ascending limb of Henle’s loop Thin limb of Henle’s loop Collecting duct Figure 19–16. Cellular ultrastructure of the nephron, represented schematically. Cells of the thick ascending limb of Henle’s loop and the distal tubule are different in their ultrastructures and functions. Thin Limb of the Loop of Henle is composed of a descending limb, a loop, and an ascending limb, all of which are lined by a simple squamous epithelium. cells in this epithelium have nuclei that bulge into the lumen, and their surfaces possess only a few short microvilli. the thin limb has separated into four distinct segment based on shape of cells, their content of organelles, the depth of their tight junctions, and their water permeability. is the region that forms the middle part of the loop Henle. Proximal convoluted tubule and thick descending limb of Henle’s loop Distal convuloted tubule and thick ascending limb of Henle’s loop Thin limb of Henle’s loop Collecting duct Figure 19–16. Cellular ultrastructure of the nephron, represented schematically. Cells of the thick ascending limb of Henle’s loop and the distal tubule are different in their ultrastructures and functions. Ascending Thick Limb (straight portion) of Distal Tubule Is the third (and final) component of the loop of Henle. Is lined by a simple cuboidal epithelium containing only a few microvilli. Its nuclei occupy an apical position in the cells. Mitochondria are compartmentalized within the interdigitations formed by the basal and lateral infoldings. Cells transport ions from the lumen into the interstitium, and since this part of the nephron has a impermeability to water, the luminal fluid becomes hypotonic to the blood. Proximal convoluted tubule and thick descending limb of Henle’s loop Distal convuloted tubule and thick ascending limb of Henle’s loop Thin limb of Henle’s loop Ascending Thick Limb of Distal Tubule Collecting duct Figure 19–16. Cellular ultrastructure of the nephron, represented schematically. Cells of the thick ascending limb of Henle’s loop and the distal tubule are different in their ultrastructures and functions. Distal Convoluted Tubule Begins at the macula densa. Has microvilli much shorter than the proximal microvilli, and their nuclei occupy an apical position in the cytoplasm. Extensive lateral interdigitations compartmentalize mitochondria in basal cytoplasmic infoldings. Cells actively transport sodium ions from the filtrate into the interstitium. Proximal convoluted tubule and thick descending limb of Henle’s loop Distal convuloted tubule and thick ascending limb of Henle’s loop Thin limb of Henle’s loop Collecting duct Figure 19–16. Cellular ultrastructure of the nephron, represented schematically. Cells of the thick ascending limb of Henle’s loop and the distal tubule are different in their ultrastructures and functions. Figure 19—19. Region of the kidney consisting mainly of distal convoluted tubules (DCT) and thin segments of Henle’s loop (asterisks). Capillaries filled with blood appear in red. PT stain. Medium magnification. Figure 19—13. Renal cortex showing proximal (P) and distal (D) convoluted tubules. One can see sections through the vascular pole of 3 renal corpuscles where juxtaglomerular renin-secreting cells appear well stained (broken lines). PT stain. Medium magnification. 1. Macula Densa Is a specific region of the distal tubule, lying near the afferent glomerular arteriole. Is one component of the juxtaglomerular apparatus. Cells are tall, narrow, and lined up closely together to form a row of nuclei that appear as a “dense spot” by light microscopy. Cells are thought to monitor the fluid in the distal tubule and send a signal to the juxtaglomerular cells (modified smooth muscle cells) located in the afferent arteriole. Signaling could occur via gap junctions present between these two cells types. Figure 19—3. The renal corpuscle. The upper part of the drawing shows the vascular pole, with afferent and efferent arterioles and the macula densa. Note the juxtaglomerular cells in the wall of the afferent arteriole. Podocyte processes cover the outer surfaces of the glomerular capillaries; the part of the podocyte containing the nucleus protrudes into the urinary space. Note the flattened cells of the parietal layer of Bowman’s capsule. The lower part of the drawing shows the urinary pole and the proximal convoluted tubule. Figure 19—9. Photomicrograph of a renal cortex showing parts of 2 renal corpuscles, macula densa, and distal and proximal convoluted tubules. The collagen type IV of the basement membrane of the glomerular capillaries is clearly visible (arrows). The collagen of the parietal layer of the Bowman’s capsule and basal membrane of a distal tubule are shown by the arrowhead. Picrosirius stain. Medium magnification. Figure 19—21. Photomicrograph of renal cortex. A macula densa is clearly seen (arrow) at the vascular pole of a renal corpuscle. Picrosirius-hematoxylin (PSH) stain. Medium magnification. 2. Juxtaglomerular (JG) Apparatus is located at the vascular pole of the renal corpuscle. consists of four structures: modified smooth muscle cells of the afferent arteriole, of the efferent arteriole, the macula densa (of the distal tubule) and the extraglomerular mesangial cells. Function of Juxtaglomerular Apparatus in response to a decrease in extracellular fluid volume (perhaps detected by the macula densa) the JG cells release renin (an Enzyme). Figure 19—3. The renal corpuscle. The upper part of the drawing shows the vascular pole, with afferent and efferent arterioles and the macula densa. Note the juxtaglomerular cells in the wall of the afferent arteriole. Podocyte processes cover the outer surfaces of the glomerular capillaries; the part of the podocyte containing the nucleus protrudes into the urinary space. Note the flattened cells of the parietal layer of Bowman’s capsule. The lower part of the drawing shows the urinary pole and the proximal convoluted tubule. Figure 19—24. Photomicrograph of an afferent arteriole entering a renal corpuscle. The wall of this arteriole shows the renin-producing juxtaglomerular (JG) cells (broken line). At the upper right is a distal convoluted tubule (DCT) with many elongated mitochondria. PT stain. High magnification. Renin acts on angiotensinogen in the plasma, converting it to angiotensin I. in capillaries of the lung, angiotensin I is converted to angiotensin II, which causes release of aldosterone from the zona glomerulosa cells in the adrenal cortex. Aldosterone stimulates distal tubule cells to retain sodium ions. water follows the sodium, and the fluid volume is increased in the extracellular compartment (thus correcting the initial problem. Angiotensin II is also a potent vasoconstrictor, which acts to elevate the blood pressure. Distal tubule Macula densa Afferent arteriole Juxtaglomerular cells (modified smooth muscle) Juxtaglomerular cells Efferent arteriole Bowman’s capsule Vascular pole (Parietal layer) Bownan’s capsule (Visceral layer Podocytes) Parietal layer Urinary space Urinary pole Brush border Proximal convoluted tubule Figure 19—24. Photomicrograph of an afferent arteriole entering a renal corpuscle. The wall of this arteriole shows the renin-producing juxtaglomerular (JG) cells (broken line). At the upper right is a distal convoluted tubule (DCT) with many elongated mitochondria. PT stain. High magnification. 3. Collecting Tubules have different functions, depending on their location in the kidney. in the cortex and medulla they respond to antidiuretic hormone (ADH), also known as vasopressin. in the medulla they play a primary role in producing a concentrated urine (by establishing a gradient due to the transport of urea from the tubular fluid into the renal interstitium). Figure 19—22. Photomicrograph of renal medulla with 2 collecting ducts consisting of cuboidal cells resting on a basement membrane. In this hypertonic region of the kidney, because of the action of the hypophyseal antidiuretic hormone, water is reabsorbed, controlling the water balance of the body. PT stain. Medium magnification. Figure 19—23. Electron micrograph of a collecting tubule wall. M, mitochondria; NU, nucleolus. x15,000. C P Collecting tubule (C) Proximal tubule (P) C P Cortical Collecting Tubules are located primarily within the medullary ray, although a few arched collecting tubules exist with the cortical labyrinth. have two cell types, a light (principal) cell and a dark (intercalated) cell. 1) Light Cells are simple cuboidal in shape and have round centrally located nuclei. a single central cilium (flagellum) extends into the lumen from the surface of each light cell. 2) Dark Cells are fewer in number and have microplicae (folds) on their surface. apical cytoplasm of the dark cell contains many vesicles. Glomerulus Collecting tubule Medullary Collecting Tubule is similar in structure to the cortical collecting tubule. dark cells