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Urinary organs
Urinary organs A. Carretero, J. Ruberte, M. Navarro, V. Nacher and Y. Espada
The urinary organs contributes to the maintenance of body homeostasis by the producing of urine, through which are eliminated diverse metabolic waste products together with water and electrolytes. The urinary organs include the kidneys, the ureters, the urinary bladder and the urethra. The kidneys produce the urine by filtering the blood from the systemic circulation, whereas the ureters take the urine from the kidneys to the urinary bladder, where it is stored until it is eliminated through the urethra.
URINARY ORGANS OF THE MOUSE Caudal vena cava Aorta Adrenal gland
Left kidney
Ureter
Urinary bladder
Urethra
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■ ■ KIDNEYS The kidneys are paired organs, positioned in the retroperitoneal region, located dorsally in the roof of the abdominal wall, on both sides of the vertebral column. The right kidney is located more cranially than the left kidney and contacts the caudate lobe of the liver (Figs. 5-43, 7-1, 7-3 and 7-4). The kidneys are reddish-brown in color and described as «bean» shaped (Fig. 7-2). Both kidneys are surrounded by the adipose capsule, which functions as a protective layer (Fig. 7-3). They have a dorsal face, which contacts the roof of the abdomen, and a ventral face that contacts the abdominal viscera (Figs. 7-1 and 7-2). The cranial and caudal extremities of the kidneys are connected by a lateral convex border. In the concave medial border is situated the renal hilus. It is through the hilum that the ureter, blood vessels, and nerves enter and leave the kidney (Fig. 7-2). The fibrous capsule of the kidney is a sheet of dense connective tissue surrounding the renal parenchyma. The internal zone of the parenchyma forms the medulla and the most external zone is the cortex (Fig. 7-5). The renal medulla is divided into renal pyramids (Fig. 7-5). The base of the renal pyramids contacts the renal cortex and its vertex the renal pelvis. One renal pyramid and its associated renal cortex form a renal lobe. All the renal lobes finish by draining into the renal papilla, which in the case of the mouse is unique, although (Fig. 7-6) humans have several renal papilla. The renal lobes are not visible neither internally or externally, which gives a smooth outer surface to the kidney. The mouse renal papilla makes prominence in the renal pelvis, occupying almost two thirds of its volume (Fig. 7-6). Each kidney receives blood from a renal artery, which is a direct branch of the abdominal aorta. Usually, before entering the hilus, the renal artery originates two branches, one cranial and one caudal, that immediately penetrate the renal parenchyma (Fig. 7-7). Inside the kidney, these branches give rise the segmental arteries from which interlobar arteries originate and that form the limit of the renal pyramids (Figs. 7-8 to 7-10). Interlobar arteries are joined by the arcuate arteries that are located at the boundary between the medulla and renal cortex (Fig. 7-10). Arcuate arteries give rise to the interlobular arteries, which are distributed throughout the renal cortex
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(Fig. 7-10). The afferent glomerular arterioles arise from the interlobular artery (Fig. 7-10). Glomeruli are formed by a tangled ball of capillaries, which originate from afferent glomerular arterioles and converge into efferent glomerular arterioles (Fig. 7-10). Efferent arterioles finish in a capillary plexus that drains into the interlobular veins. In general, renal veins presented a path parallel to arteries and, consequently, they have the same names. The renal vein exits the renal hilus and opens directly into the caudal vena cava (Figs. 7-7 and 7-8). The functional unit of the kidney is the nephron, which is composed of the glomerular capsule (Bowman capsule), the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule. The glomerular capsule has two layers, an external or parietal, which is continuous with the proximal convoluted tubule, and an internal or visceral layer (Figs. 7-11 to 7-13). The external layer of the mouse glomerular capsule is sexually dimorphic (Fig. 7-11). In males, the external layer is a cuboidal epithelium, whereas in females it is a squamous epithelium. The internal layer of the glomerular capsule is formed by the podocytes, which rest on the surface of the glomerular capillaries (Fig. 7-13). The podocytes have cytoplasmic prolongations that are called pedicels (foot processes). There are two types of pedicels: pedicels of the fi rst-order, which are much thicker, and those of the second-order, which contact the basement membrane of the glomerular capillaries. However, the second-order pedicels are not continuous with the basement membrane, leaving spaces between them known as fi ltration slits (Fig. 7-13). The glomerular capillary endothelium is not continuous as well, defining large fenestrations for blood plasma filtration. Altogether, the fenestrated endothelium, the basement membrane, and the second order pedicels form the filtration barrier (Fig. 7-13). The glomerulus and glomerular capsule form the renal corpuscle, also known as the Malpighian corpuscle (Figs. 7.11 to 7-13). The renal corpuscles are located exclusively in the renal cortex and, usually, those located near the renal medulla are larger (Fig. 7-11). The majority of the cortex of the kidney is occupied by the proximal convoluted tubules since the length of the distal convoluted tubules is much smaller. The wall of the proximal convoluted tubules is lined by simple cuboidal epithelium, which have rounded nuclei, with a basal disposition, and microvilli on their apical pole. At the light microscope level, the microvilli are visible and can be seen forming a characteristic brush border that is positive for PAS staining (Fig. 7-12). The cells of the distal convoluted tubules have no microvilli and the cells of the loops of Henle are flattened (Figs. 7-14 and 7-15). The proximal and distal convoluted tubules are located exclusively in the renal cortex, whereas the loops of Henle are located both in the cortex and in the renal medulla (Figs. 7-14 and 7-15). The loops of Henle drain into the distal convoluted tubules, which in turn drain into the collecting ducts, the papillary ducts and finally into the renal pelvis through the area cribrosa (Fig. 7-15).
■ ■ URETER The ureter originates in the renal pelvis and leaves the kidney through the hilus, located at its medial border (Fig. 7-2). The ureter follows a caudal path that is retroperitoneal in the abdominal portion. At the level of the pelvic cavity, the ureter opens into the urinary bladder. Before opening, the ureter runs intermurally between the tunica muscularis and tunica mucosa of the urinary bladder. The ureteric orifice is the slit of the ureter at the lumen of the urinary bladder. The ureter is a simple tubular organ. It consists of a tunica adventitia, the tunica muscularis, and a tunica mucosa. The mucosa of the ureter consists of transitional epithelium and its lumen has a characteristic star shape (Fig. 7-16). Surrounding the adventitia is a layer of loose connective tissue and adipocytes.
■ ■ URINARY BLADDER The urinary bladder is a hollow musculo-membranous organ whose size and shape varies depending on the amount of urine that it contains (Figs. 7-17 to 7-19). In the urinary bladder it is possible to distinguish several parts: a vertex, which is located cranially; a body; and a neck that is continuous with the urethra (Fig. 7-18 and 7-19). The median and lateral vesical ligaments attach the urinary bladder at the floor and lateral walls of the pelvic cavity, respectively. In the fetus, the median vesicle ligament contains the urachus whereas the lateral ligaments contain the umbilical arteries. Both structures collapse at birth. The collapsed umbilical arteries then form the round ligaments, located at the free edge of the lateral ligaments. The tunica serosa of the urinary bladder is formed by the visceral peritoneum (Fig. 7-19) whereas the tunica muscularis is organized into three layers with a lot of connective tissue separating the muscle fiber bundles (Fig. 7-19). The inner and outer layers are composed of longitudinal muscle fi bers. Between them is found the intermediate layer that is formed by circular muscle fibers. The tunica mucosa of the urinary bladder has a transitional epithelium in which three types of cells are found: cuboidal basal cells, intermediate cells, which are the smallest of the three, and the superficial cells. The latter are larger and can cover a number of intermediate cells (Fig. 7-19). The lamina propria is also highly vascularized. When the bladder is empty the epithelium forms irregular folds that disappear on distension (Fig. 7-19).
■ ■ URETHRA In females, the urethra is exclusive of the urinary apparatus, whereas in males it is also part of the reproductive system. The topography and structure of the male and female urethra are discussed in Chapters 8 and 9, respectively.
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Figure 7-1. Topography of kidneys. Ventral view. A) Male. The digestive viscera were removed. B) Computed tomography images. 3D reconstruction. C) Female. The digestive viscera were removed. 1: Right kidney; 2: Left kidney; 3: Caudal vena cava; 4: Left renal vein; 5: Vesicular glands; 6: Left testicle; 7: Preputial glands; 8: Right deferent duct; 9: Urinary bladder; 10: Rib; 11: Lumbar vertebrae; 12: Coxal bone; 13: Sacrum; 14: Femur; 15: Spleen; 16: Pancreas; 17: Liver; 18: Left ovarian vein; 19: Right ovary; 20: Uterine horn.
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Figure 7-2. Left kidney. A) Dorsal view. B) Ventral view.
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1: Lateral border; 2: Medial border; 3: Cranial extremity; 4: Caudal extremity; 5: Dorsal surface; 6: Ureter; 7: Adrenal gland; 8: Hilus of kidney; 9: Ventral surface.
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Figure 7-3. Transverse sections of the abdominal cavity. Caudal view. A, B and C) Magnetic resonance images. D) Detail of kidneys. Arteries were injected with latex. 1: Right kidney; 2: Caudal vena cava; 3: Caudate lobe (liver); 4: Pancreas; 5: Spleen; 6: Stomach; 7: Lumbar vertebra; 8: Epaxial muscles; 9: Portal vein; 10: Left renal vein; 11: Left kidney; 12: Descending part (duodenum); 13: Jejunum; 14: Cecum; 15: Ascending colon; 16: Descending colon; 17: Adipose capsule (right kidney); 18: Adipose capsule (left kidney); 19: M. quadratus lumborum and m. psoas minor.
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Figure 7-4. Topography of kidneys. A) Abdominal horizontal section. B) Magnetic resonance image. Horizontal section. 1: Right kidney; 2: Left kidney; 3: Right lateral lobe of liver; 4: Left lateral lobe of liver; 5: Papillary process (caudate lobe); 6: Stomach; 7: Right lung; 8: Left lung; 9: Spleen.
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Figure 7-5. Kidney structure. Horizontal sections through the hilus of kidney. A) Non-fixed kidney. B) Scanning electron microscopy image. C) Histological section. Masson's trichrome stain. 1: Renal lobe; 2: Renal cortex; 3: Renal medulla; 4: Renal pyramid; 5: Interlobar artery; 6: Renal papilla; 7: Base of renal pyramid; 8: Arcuate artery; 9: Renal pelvis
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Figure 7-6. Kidney structure. A) Horizontal histological section. Hematoxylin-eosin stain. B) Ultrasound image. Horizontal section of an isolated kidney. C) Transverse histological section. Hematoxylin-eosin stain. D) Ultrasound image. Transverse section of an isolated kidney. 1: Renal cortex; 2: Renal medulla; 3; Renal papilla; 4: Renal pelvis; 5: Lateral border; 6: Medial border; 7: Cranial extremity; 8: Caudal extremity; 9: Adrenal gland; 10: Dorsal surface; 11: Ventral surface.
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Figure 7-7. Vascularization of kidneys. A) Vascular corrosion cast (Mercox®). Dorsal view. B) Ventrodorsal arteriography. Vascular injection with barium. C) Ventrodorsal venography. Vascular injection with barium. 1: Aorta; 2: Right renal artery; 3: Left renal artery; 4: Caudal vena cava; 5: Right kidney; 6: Left kidney; 7: Adrenal gland; 8: Segmental arteries; 9: Interlobar arteries; 10: Arcuate arteries; 11: Right deep circumflex iliac artery; 12: Left deep circumflex iliac artery; 13: Celiac artery; 14: Cranial mesenteric artery; 15: Right renal vein; 16: Left renal vein; 17: Segmental veins; 18: Interlobar veins; 19: Arcuate veins; 20: Right deep circumflex iliac vein; 21: Left deep circumflex iliac vein; 22: Hepatic veins.
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Figure 7-8. Vascularization of kidney. A) Ventrodorsal arteriography. Vascular injection with barium. B) Ventrodorsal venography. Vascular injection with barium. 1: Renal artery; 2: Segmental arteries; 3: Interlobar arteries; 4: Arcuate arteries; 5: Interlobular arteries; 6: Renal vein; 7: Segmental veins; 8: Interlobar veins; 9: Arcuate veins.
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Cranial Medial Figure 7-9. Vascularization of kidney. Horizontal sections. A) Non-fixed kidney. B) Ultrasound image. C) Power Doppler ultrasound image. 1: Segmental veins; 2: Interlobar veins; 3: Arcuate veins.
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Figure 7-10. Vascularization of kidney. A and B) Cleared vascular injection with latex (green). C) Vascular corrosion cast (Mercox®). Scanning electron microscopy image (Bar = 165μm). D) Glomerular vascular corrosion cast (Mercox®). Scanning electron microscopy image (Bar = 10μm). 1: Cranial branch (renal artery); 2: Caudal branch (renal artery); 3: Cranial segmental artery; 4: Middle segmental artery; 5: Caudal segmental artery; 6: Interlobar artery; 7: Arcuate artery; 8: Interlobular artery; 9: Glomeruli; 10: Afferent glomerular arteriole; 11: Glomerular capillary; 12: Efferent glomerular arteriole.
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Figure 7-11. Renal corpuscle structure. A) Renal cortex. Masson’s trichrome stain. B) Cortical glomerulus. Hematoxylin-eosin stain (400X). C) Juxtamedullary glomerulus. Hematoxylin-eosin stain (400X). D) Male glomerulus. Note the cuboidal epithelium in the parietal layer of glomerular capsule. Hematoxylin-eosin stain (400X). E) Female glomerulus. Note the squamous epithelium in the parietal layer of glomerular capsule. Hematoxylin-eosin stain (400X). 1: Outer zone of renal cortex; 2: Inner zone of renal cortex (juxtamedullary); 3: Interlobar vein; 4: Interlobar artery; 5: Vascular pole; 6: Urinary pole; 7: Glomerulus; 8: Parietal layer (glomerular capsule); 9: Visceral layer (glomerular capsule); 10: Urinary space ; 11: Glomerular capillaries.
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Figure 7-12. Renal corpuscle structure (400X). A) Hematoxylin-eosin stain. B) Masson’s trichrome stain. C) PAS-Harris’ hematoxylin stain. D) Confocal laser microscopy image. Basement membrane immunodetected with anti-collagen IV antibody (green). Nuclei counterstained with propidium iodide (red). E) Blue Heidenhain Azan stain. F) Methylene blue stain. Semithin section. 1: Parietal layer (glomerular capsule); 2: Visceral layer. Podocyte (glomerular capsule); 3: Urinary space; 4: Glomerulus; 5: Distal convoluted tubule; 6: Macula densa; 7: Afferent glomerular arteriole; 8: Extraglomerular mesangial cells; 9: Glomerular capillaries; 10: Basement membrane of the glomerular capsule; 11: Glomerular basement membrane; 12: Mesangial cells; 13: Brush border.
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14 Figure 7-13. Renal corpuscle ultrastructure. A) Scanning electron microscopy image (Bar = 11μm). B) Glomerular capillary. Electron scanning microscopy image (8,000X). C) Podocyte. Scanning electron microscopy image (Bar = 4μm). D) Podocyte. Transmission electron microscopy image (40,000X). E) Filtration membrane. Scanning electron microscopy image (Bar = 1μm). F) Filtration membrane. Transmission electron microscopy image (40,000X). 1: Parietal layer (glomerular capsule); 2: Visceral layer (glomerular capsule); 3: Urinary space; 4: Glomerular capillary; 5: Podocyte; 6: Erythrocyte; 7: Podocyte cell body; 8: First order pedicels; 9: Second order pedicels; 10: Filtration slit; 11: Endothelial cell nucleus; 12: Glomerular capillary fenestrations; 13: Glomerular basement membrane; 14: Filtration slit diaphragm.
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Figure 7-14. Renal tubule structure. A, B and C) Proximal convoluted tubule. Blue Heidenhain Azan stain (1,000X), methylene blue stain (1,000X) and transmission electron microscopy image (5,000X), respectively. D, E and F) Distal convoluted tubule. Blue Heidenhain Azan stain (1,000X), methylene blue stain (1,000X) and transmission electron microscopy image (3,000X), respectively. G, H and I) Collecting tubule. Blue Heidenhain Azan stain (1000X), methylene blue stain (1,000X) and transmission electron microscopy image (3,000X), respectively. J and K) Loop of Henle (1,000X). Hematoxylin-eosin stain and blue Heidenhain Azan stain, respectively. 1: Nucleus; 2: Cytoplasm; 3: Basement membrane; 4: Brush border; 5: Erythrocytes.
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Figure 7-15. Renal papilla and ureter. A) Renal papilla. Scanning electron microscopy image (Bar = 20μm). B) Papillary ducts (Bar = 30μm). C) Histological section of papillary ducts. Masson’s trichrome stain (400X). D) Histological section of ureter. Masson’s trichrome stain (400X). E) Magnification of the wall of ureter (1,000X). 1: Renal papilla; 2: Papillary ducts; 3: Renal pelvis; 4: Blood vessel; 5: Erythrocyte; 6: Ureter (lumen); 7: Tunica mucosa; 8: Transitional epithelium; 9: Lamina propria; 10: Tunica muscularis; 11: Inner longitudinal layer; 12: Middle circular layer; 13: Outer longitudinal layer; 14: Tunica adventitia.
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Figure 7-16. Topography of urinary bladder. A) The abdominal cavity was open and the small intestine was displaced. Ventral view. B) In vivo fluorescence image. Intravenous administration of Cy5.5. The fluorochrome accumulated in the bladder. Ventral view. C) Magnetic resonance image. Horizontal section. 1: Xiphoid procces (sternum); 2: Right costal arch; 3: Left costal arch; 4: Right medial lobe of liver; 5: Left medial lobe of liver; 6: Left lateral lobe of liver; 7: Duodenum; 8:Transverse colon; 9: Jejunum; 10: Mesentery; 11: Cecum; 12: Urinary bladder; 13: Left testicle; 14: Preputial glands; 15: Stomach; 16: Ascending colon; 17: Descending colon; 18: Right ventricle; 19: Left ventricle; 20: Hepatic veins.
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Figure 7-17. Position of urinary bladder in the abdominal cavity. A) A part of the small intestine was removed. B) The large intestine was removed. C) Ventrodorsal cystography. Urethral injection with barium. 1: Cecum; 2: Urinary bladder; 3: Preputial glands; 4: Left testicle; 5: Left kidney; 6: Right kidney; 7: Caudal vena cava; 8: Vesicular glands; 9: Left deferent duct; 10: Urethra; 11: Femur; 12: Ilium; 13: Wing (sacrum); 14: Lumbar vertebrae; 15: Caudal vertebrae.
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Figure 7-18. Location of urinary bladder in the abdominal and pelvic cavities. A) Laterolateral cystography. Urethral injection with barium. B) Ultrasound image. 1: Body of bladder; 2: Apex of bladder; 3: Neck of bladder; 4: Urethra; 5: Lumbar vertebra; 6: Caudal vertebrae; 7: Ilium; 8: Obturator foramen; 9: Right and left femur; 10: Patella; 11: Tibia.
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10 Figure 7-19. Urinary bladder structure. A and C) The urinary bladder was horizontally sectioned and its internal surface exposed. Scanning electron microscopy images (Bars = 450μm and 15.5μm, respectively). B, D and E) Horizontal histological section. Hematoxylin-eosin stain (2X, 200X and 400X, respectively). 1: Apex of bladder; 2: Body of bladder; 3: Neck of bladder; 4: Tunica subserosa; 5: Tunica muscularis; 6: Internal urethral opening; 7: Ureter; 8: Lumen; 9: Tunica mucosa; 10: Tunica adventitia; 11: Transitional epithelium; 12: Basal cell layer; 13: Intermediate cell layer; 14: Superficial cell layer.
The urinary organs contributes to the maintenance of body homeostasis by the producing of urine, through which are eliminated diverse metabolic waste products together with water and electrolytes. The urinary organs include the kidneys, the ureters, the urinary bladder and the urethra. The kidneys produce the urine by filtering the blood from the systemic circulation, whereas the ureters take the urine from the kidneys to the urinary bladder, where it is stored until it is eliminated through the urethra.
URINARY ORGANS OF THE MOUSE Caudal vena cava Aorta Adrenal gland
Left kidney
Ureter
Urinary bladder
Urethra
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■ ■ KIDNEYS The kidneys are paired organs, positioned in the retroperitoneal region, located dorsally in the roof of the abdominal wall, on both sides of the vertebral column. The right kidney is located more cranially than the left kidney and contacts the caudate lobe of the liver (Figs. 5-43, 7-1, 7-3 and 7-4). The kidneys are reddish-brown in color and described as «bean» shaped (Fig. 7-2). Both kidneys are surrounded by the adipose capsule, which functions as a protective layer (Fig. 7-3). They have a dorsal face, which contacts the roof of the abdomen, and a ventral face that contacts the abdominal viscera (Figs. 7-1 and 7-2). The cranial and caudal extremities of the kidneys are connected by a lateral convex border. In the concave medial border is situated the renal hilus. It is through the hilum that the ureter, blood vessels, and nerves enter and leave the kidney (Fig. 7-2). The fibrous capsule of the kidney is a sheet of dense connective tissue surrounding the renal parenchyma. The internal zone of the parenchyma forms the medulla and the most external zone is the cortex (Fig. 7-5). The renal medulla is divided into renal pyramids (Fig. 7-5). The base of the renal pyramids contacts the renal cortex and its vertex the renal pelvis. One renal pyramid and its associated renal cortex form a renal lobe. All the renal lobes finish by draining into the renal papilla, which in the case of the mouse is unique, although (Fig. 7-6) humans have several renal papilla. The renal lobes are not visible neither internally or externally, which gives a smooth outer surface to the kidney. The mouse renal papilla makes prominence in the renal pelvis, occupying almost two thirds of its volume (Fig. 7-6). Each kidney receives blood from a renal artery, which is a direct branch of the abdominal aorta. Usually, before entering the hilus, the renal artery originates two branches, one cranial and one caudal, that immediately penetrate the renal parenchyma (Fig. 7-7). Inside the kidney, these branches give rise the segmental arteries from which interlobar arteries originate and that form the limit of the renal pyramids (Figs. 7-8 to 7-10). Interlobar arteries are joined by the arcuate arteries that are located at the boundary between the medulla and renal cortex (Fig. 7-10). Arcuate arteries give rise to the interlobular arteries, which are distributed throughout the renal cortex
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(Fig. 7-10). The afferent glomerular arterioles arise from the interlobular artery (Fig. 7-10). Glomeruli are formed by a tangled ball of capillaries, which originate from afferent glomerular arterioles and converge into efferent glomerular arterioles (Fig. 7-10). Efferent arterioles finish in a capillary plexus that drains into the interlobular veins. In general, renal veins presented a path parallel to arteries and, consequently, they have the same names. The renal vein exits the renal hilus and opens directly into the caudal vena cava (Figs. 7-7 and 7-8). The functional unit of the kidney is the nephron, which is composed of the glomerular capsule (Bowman capsule), the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule. The glomerular capsule has two layers, an external or parietal, which is continuous with the proximal convoluted tubule, and an internal or visceral layer (Figs. 7-11 to 7-13). The external layer of the mouse glomerular capsule is sexually dimorphic (Fig. 7-11). In males, the external layer is a cuboidal epithelium, whereas in females it is a squamous epithelium. The internal layer of the glomerular capsule is formed by the podocytes, which rest on the surface of the glomerular capillaries (Fig. 7-13). The podocytes have cytoplasmic prolongations that are called pedicels (foot processes). There are two types of pedicels: pedicels of the fi rst-order, which are much thicker, and those of the second-order, which contact the basement membrane of the glomerular capillaries. However, the second-order pedicels are not continuous with the basement membrane, leaving spaces between them known as fi ltration slits (Fig. 7-13). The glomerular capillary endothelium is not continuous as well, defining large fenestrations for blood plasma filtration. Altogether, the fenestrated endothelium, the basement membrane, and the second order pedicels form the filtration barrier (Fig. 7-13). The glomerulus and glomerular capsule form the renal corpuscle, also known as the Malpighian corpuscle (Figs. 7.11 to 7-13). The renal corpuscles are located exclusively in the renal cortex and, usually, those located near the renal medulla are larger (Fig. 7-11). The majority of the cortex of the kidney is occupied by the proximal convoluted tubules since the length of the distal convoluted tubules is much smaller. The wall of the proximal convoluted tubules is lined by simple cuboidal epithelium, which have rounded nuclei, with a basal disposition, and microvilli on their apical pole. At the light microscope level, the microvilli are visible and can be seen forming a characteristic brush border that is positive for PAS staining (Fig. 7-12). The cells of the distal convoluted tubules have no microvilli and the cells of the loops of Henle are flattened (Figs. 7-14 and 7-15). The proximal and distal convoluted tubules are located exclusively in the renal cortex, whereas the loops of Henle are located both in the cortex and in the renal medulla (Figs. 7-14 and 7-15). The loops of Henle drain into the distal convoluted tubules, which in turn drain into the collecting ducts, the papillary ducts and finally into the renal pelvis through the area cribrosa (Fig. 7-15).
■ ■ URETER The ureter originates in the renal pelvis and leaves the kidney through the hilus, located at its medial border (Fig. 7-2). The ureter follows a caudal path that is retroperitoneal in the abdominal portion. At the level of the pelvic cavity, the ureter opens into the urinary bladder. Before opening, the ureter runs intermurally between the tunica muscularis and tunica mucosa of the urinary bladder. The ureteric orifice is the slit of the ureter at the lumen of the urinary bladder. The ureter is a simple tubular organ. It consists of a tunica adventitia, the tunica muscularis, and a tunica mucosa. The mucosa of the ureter consists of transitional epithelium and its lumen has a characteristic star shape (Fig. 7-16). Surrounding the adventitia is a layer of loose connective tissue and adipocytes.
■ ■ URINARY BLADDER The urinary bladder is a hollow musculo-membranous organ whose size and shape varies depending on the amount of urine that it contains (Figs. 7-17 to 7-19). In the urinary bladder it is possible to distinguish several parts: a vertex, which is located cranially; a body; and a neck that is continuous with the urethra (Fig. 7-18 and 7-19). The median and lateral vesical ligaments attach the urinary bladder at the floor and lateral walls of the pelvic cavity, respectively. In the fetus, the median vesicle ligament contains the urachus whereas the lateral ligaments contain the umbilical arteries. Both structures collapse at birth. The collapsed umbilical arteries then form the round ligaments, located at the free edge of the lateral ligaments. The tunica serosa of the urinary bladder is formed by the visceral peritoneum (Fig. 7-19) whereas the tunica muscularis is organized into three layers with a lot of connective tissue separating the muscle fiber bundles (Fig. 7-19). The inner and outer layers are composed of longitudinal muscle fi bers. Between them is found the intermediate layer that is formed by circular muscle fibers. The tunica mucosa of the urinary bladder has a transitional epithelium in which three types of cells are found: cuboidal basal cells, intermediate cells, which are the smallest of the three, and the superficial cells. The latter are larger and can cover a number of intermediate cells (Fig. 7-19). The lamina propria is also highly vascularized. When the bladder is empty the epithelium forms irregular folds that disappear on distension (Fig. 7-19).
■ ■ URETHRA In females, the urethra is exclusive of the urinary apparatus, whereas in males it is also part of the reproductive system. The topography and structure of the male and female urethra are discussed in Chapters 8 and 9, respectively.
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Figure 7-1. Topography of kidneys. Ventral view. A) Male. The digestive viscera were removed. B) Computed tomography images. 3D reconstruction. C) Female. The digestive viscera were removed. 1: Right kidney; 2: Left kidney; 3: Caudal vena cava; 4: Left renal vein; 5: Vesicular glands; 6: Left testicle; 7: Preputial glands; 8: Right deferent duct; 9: Urinary bladder; 10: Rib; 11: Lumbar vertebrae; 12: Coxal bone; 13: Sacrum; 14: Femur; 15: Spleen; 16: Pancreas; 17: Liver; 18: Left ovarian vein; 19: Right ovary; 20: Uterine horn.
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Figure 7-2. Left kidney. A) Dorsal view. B) Ventral view.
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Figure 7-3. Transverse sections of the abdominal cavity. Caudal view. A, B and C) Magnetic resonance images. D) Detail of kidneys. Arteries were injected with latex. 1: Right kidney; 2: Caudal vena cava; 3: Caudate lobe (liver); 4: Pancreas; 5: Spleen; 6: Stomach; 7: Lumbar vertebra; 8: Epaxial muscles; 9: Portal vein; 10: Left renal vein; 11: Left kidney; 12: Descending part (duodenum); 13: Jejunum; 14: Cecum; 15: Ascending colon; 16: Descending colon; 17: Adipose capsule (right kidney); 18: Adipose capsule (left kidney); 19: M. quadratus lumborum and m. psoas minor.
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Figure 7-4. Topography of kidneys. A) Abdominal horizontal section. B) Magnetic resonance image. Horizontal section. 1: Right kidney; 2: Left kidney; 3: Right lateral lobe of liver; 4: Left lateral lobe of liver; 5: Papillary process (caudate lobe); 6: Stomach; 7: Right lung; 8: Left lung; 9: Spleen.
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Figure 7-5. Kidney structure. Horizontal sections through the hilus of kidney. A) Non-fixed kidney. B) Scanning electron microscopy image. C) Histological section. Masson's trichrome stain. 1: Renal lobe; 2: Renal cortex; 3: Renal medulla; 4: Renal pyramid; 5: Interlobar artery; 6: Renal papilla; 7: Base of renal pyramid; 8: Arcuate artery; 9: Renal pelvis
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Figure 7-6. Kidney structure. A) Horizontal histological section. Hematoxylin-eosin stain. B) Ultrasound image. Horizontal section of an isolated kidney. C) Transverse histological section. Hematoxylin-eosin stain. D) Ultrasound image. Transverse section of an isolated kidney. 1: Renal cortex; 2: Renal medulla; 3; Renal papilla; 4: Renal pelvis; 5: Lateral border; 6: Medial border; 7: Cranial extremity; 8: Caudal extremity; 9: Adrenal gland; 10: Dorsal surface; 11: Ventral surface.
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Figure 7-7. Vascularization of kidneys. A) Vascular corrosion cast (Mercox®). Dorsal view. B) Ventrodorsal arteriography. Vascular injection with barium. C) Ventrodorsal venography. Vascular injection with barium. 1: Aorta; 2: Right renal artery; 3: Left renal artery; 4: Caudal vena cava; 5: Right kidney; 6: Left kidney; 7: Adrenal gland; 8: Segmental arteries; 9: Interlobar arteries; 10: Arcuate arteries; 11: Right deep circumflex iliac artery; 12: Left deep circumflex iliac artery; 13: Celiac artery; 14: Cranial mesenteric artery; 15: Right renal vein; 16: Left renal vein; 17: Segmental veins; 18: Interlobar veins; 19: Arcuate veins; 20: Right deep circumflex iliac vein; 21: Left deep circumflex iliac vein; 22: Hepatic veins.
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Figure 7-8. Vascularization of kidney. A) Ventrodorsal arteriography. Vascular injection with barium. B) Ventrodorsal venography. Vascular injection with barium. 1: Renal artery; 2: Segmental arteries; 3: Interlobar arteries; 4: Arcuate arteries; 5: Interlobular arteries; 6: Renal vein; 7: Segmental veins; 8: Interlobar veins; 9: Arcuate veins.
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Figure 7-10. Vascularization of kidney. A and B) Cleared vascular injection with latex (green). C) Vascular corrosion cast (Mercox®). Scanning electron microscopy image (Bar = 165μm). D) Glomerular vascular corrosion cast (Mercox®). Scanning electron microscopy image (Bar = 10μm). 1: Cranial branch (renal artery); 2: Caudal branch (renal artery); 3: Cranial segmental artery; 4: Middle segmental artery; 5: Caudal segmental artery; 6: Interlobar artery; 7: Arcuate artery; 8: Interlobular artery; 9: Glomeruli; 10: Afferent glomerular arteriole; 11: Glomerular capillary; 12: Efferent glomerular arteriole.
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Figure 7-11. Renal corpuscle structure. A) Renal cortex. Masson’s trichrome stain. B) Cortical glomerulus. Hematoxylin-eosin stain (400X). C) Juxtamedullary glomerulus. Hematoxylin-eosin stain (400X). D) Male glomerulus. Note the cuboidal epithelium in the parietal layer of glomerular capsule. Hematoxylin-eosin stain (400X). E) Female glomerulus. Note the squamous epithelium in the parietal layer of glomerular capsule. Hematoxylin-eosin stain (400X). 1: Outer zone of renal cortex; 2: Inner zone of renal cortex (juxtamedullary); 3: Interlobar vein; 4: Interlobar artery; 5: Vascular pole; 6: Urinary pole; 7: Glomerulus; 8: Parietal layer (glomerular capsule); 9: Visceral layer (glomerular capsule); 10: Urinary space ; 11: Glomerular capillaries.
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Figure 7-12. Renal corpuscle structure (400X). A) Hematoxylin-eosin stain. B) Masson’s trichrome stain. C) PAS-Harris’ hematoxylin stain. D) Confocal laser microscopy image. Basement membrane immunodetected with anti-collagen IV antibody (green). Nuclei counterstained with propidium iodide (red). E) Blue Heidenhain Azan stain. F) Methylene blue stain. Semithin section. 1: Parietal layer (glomerular capsule); 2: Visceral layer. Podocyte (glomerular capsule); 3: Urinary space; 4: Glomerulus; 5: Distal convoluted tubule; 6: Macula densa; 7: Afferent glomerular arteriole; 8: Extraglomerular mesangial cells; 9: Glomerular capillaries; 10: Basement membrane of the glomerular capsule; 11: Glomerular basement membrane; 12: Mesangial cells; 13: Brush border.
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Figure 7-15. Renal papilla and ureter. A) Renal papilla. Scanning electron microscopy image (Bar = 20μm). B) Papillary ducts (Bar = 30μm). C) Histological section of papillary ducts. Masson’s trichrome stain (400X). D) Histological section of ureter. Masson’s trichrome stain (400X). E) Magnification of the wall of ureter (1,000X). 1: Renal papilla; 2: Papillary ducts; 3: Renal pelvis; 4: Blood vessel; 5: Erythrocyte; 6: Ureter (lumen); 7: Tunica mucosa; 8: Transitional epithelium; 9: Lamina propria; 10: Tunica muscularis; 11: Inner longitudinal layer; 12: Middle circular layer; 13: Outer longitudinal layer; 14: Tunica adventitia.
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Figure 7-16. Topography of urinary bladder. A) The abdominal cavity was open and the small intestine was displaced. Ventral view. B) In vivo fluorescence image. Intravenous administration of Cy5.5. The fluorochrome accumulated in the bladder. Ventral view. C) Magnetic resonance image. Horizontal section. 1: Xiphoid procces (sternum); 2: Right costal arch; 3: Left costal arch; 4: Right medial lobe of liver; 5: Left medial lobe of liver; 6: Left lateral lobe of liver; 7: Duodenum; 8:Transverse colon; 9: Jejunum; 10: Mesentery; 11: Cecum; 12: Urinary bladder; 13: Left testicle; 14: Preputial glands; 15: Stomach; 16: Ascending colon; 17: Descending colon; 18: Right ventricle; 19: Left ventricle; 20: Hepatic veins.
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Figure 7-17. Position of urinary bladder in the abdominal cavity. A) A part of the small intestine was removed. B) The large intestine was removed. C) Ventrodorsal cystography. Urethral injection with barium. 1: Cecum; 2: Urinary bladder; 3: Preputial glands; 4: Left testicle; 5: Left kidney; 6: Right kidney; 7: Caudal vena cava; 8: Vesicular glands; 9: Left deferent duct; 10: Urethra; 11: Femur; 12: Ilium; 13: Wing (sacrum); 14: Lumbar vertebrae; 15: Caudal vertebrae.
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Figure 7-18. Location of urinary bladder in the abdominal and pelvic cavities. A) Laterolateral cystography. Urethral injection with barium. B) Ultrasound image. 1: Body of bladder; 2: Apex of bladder; 3: Neck of bladder; 4: Urethra; 5: Lumbar vertebra; 6: Caudal vertebrae; 7: Ilium; 8: Obturator foramen; 9: Right and left femur; 10: Patella; 11: Tibia.
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10 Figure 7-19. Urinary bladder structure. A and C) The urinary bladder was horizontally sectioned and its internal surface exposed. Scanning electron microscopy images (Bars = 450μm and 15.5μm, respectively). B, D and E) Horizontal histological section. Hematoxylin-eosin stain (2X, 200X and 400X, respectively). 1: Apex of bladder; 2: Body of bladder; 3: Neck of bladder; 4: Tunica subserosa; 5: Tunica muscularis; 6: Internal urethral opening; 7: Ureter; 8: Lumen; 9: Tunica mucosa; 10: Tunica adventitia; 11: Transitional epithelium; 12: Basal cell layer; 13: Intermediate cell layer; 14: Superficial cell layer.