Abdomen Anatomy PDF

● ● terminates at the esophagogastric junction, where ingested matter enters the cardial orifice of the stomach (Fig. 5.21B). It is located to the left of the midline at the level of the 7th left costal cartilage and the T11 vertebra. The esophagus is retroperitoneal during its short abdominal cours...

● ● terminates at the esophagogastric junction, where ingested matter enters the cardial orifice of the stomach (Fig. 5.21B). It is located to the left of the midline at the level of the 7th left costal cartilage and the T11 vertebra. The esophagus is retroperitoneal during its short abdominal course. ● ● has circular and external longitudinal layers of muscle. In its superior third, the external layer consists of voluntary striated muscle, the inferior third is composed of smooth muscle, and the middle third is made up of both types of muscle. FIGURE 5.20. View OriginalDownload Slide (.ppt) Esophagus. A. Lymphatic drainage. B. Arterial supply. FIGURE 5.21. View OriginalDownload Slide (.ppt) Esophagus (terminal part), stomach, and proximal duodenum. A. Parts of stomach. B. Internal surface of stomach. C. Radiograph of stomach and duodenum after barium ingestion. Arrows, peristaltic wave. D. Illustration and photograph of coronal section of region of esophagogastric junction. D, diaphragm; E, esophagus; ST, stomach; Z, esophagogastric junction (Z-line). C Courtesy of Dr. E.L. Lansdown, Professor of Medical Imaging, University of Toronto, Ontario, Canada. The esophagogastric junction is marked internally by the abrupt transition from esophageal to gastric mucosa, referred to clinically as the Z-line (Fig. 5.21D). Just superior to this junction, the diaphragmatic musculature forming the esophageal hiatus functions as a physiological inferior esophageal sphincter that contracts and relaxes. Radiological studies show that food or liquid may be stopped here momentarily and that the sphincter mechanism is normally efficient in preventing reflux of gastric contents into the esophagus. The abdominal part of the esophagus has its ● ● arterial supply from the esophageal branches of the left gastric artery (Fig. 5.20B), a branch of the celiac trunk, and the left inferior phrenic artery ● ● venous drainage primarily to the portal venous system through the left gastric vein (Fig. 5.22B), whereas the proximal thoracic part of the esophagus drains primarily into the systemic venous system through the esophageal veins entering the azygos vein (see Chapter 4). However, the veins of the two parts of the esophagus communicate and provide a clinically important portosystemic anastomosis. Stomach The stomach acts as a food blender and reservoir; its chief function is acidic and mechanical digestion. The gastric juice gradually converts a mass of food into a semiliquid mixture, chyme (G. juice), which passes into the duodenum. Parts and Curvature of Stomach The shape of the stomach is dynamic (changing in shape as it functions) and highly variable from person to person (see Fig. SA5.2B). The stomach has four parts and two curvatures (Fig. 5.21): ● ● The short cardia surrounds the cardial orifice, the trumpet-shaped opening of the esophagus into the stomach. ● ● The fundus of the stomach is the dilated superior part of the stomach that is related to the left dome of the diaphragm and is limited inferiorly by the horizontal plane of the cardial orifice. The superior part of the fundus usually reaches the level of the left 5th intercostal space. The cardial notch is between the esophagus and the fundus. The fundus may be dilated by gas (especially in the upright position), fluid, food, or any combination of these. ● ● The body of the stomach, the major part of the stomach, lies between the fundus and the pyloric antrum. (Histologists/pathologists often treat the fundus and body as synonyms; hence, the mucosa of the fundus and body is composed of “fundic glands.”) ● ● The pyloric part of the stomach is the distal funnel-shaped region; its wide part, the pyloric antrum, leads into the pyloric canal, its narrow part. The pylorus, the distal sphincteric region, is a thickening of the circular layer of smooth muscle, which controls discharge of the stomach contents through the pyloric orifice into the duodenum. ● ● The lesser curvature forms the shorter concave border of the stomach; the angular incisure (notch) is the sharp indentation approximately two thirds of the distance along the lesser curvature that approximates the junction of the body and pyloric part of the stomach. ● ● The greater curvature forms the longer convex border of the stomach. Interior of Stomach When contracted, the gastric mucosa is thrown into mostly longitudinal gastric folds (rugae) (Fig. 5.21B,C). These are most marked toward the pyloric part and along the greater curvature. A gastric canal (furrow) forms temporarily during swallowing between the longitudinal gastric folds along the lesser curvature. Saliva and small quantities of masticated food and other fluids pass through the gastric canal to the pyloric canal when the stomach is mostly empty. Vasculature and Nerves of Stomach The stomach has ● ● a rich arterial supply, arising from the celiac trunk and its branches (Fig. 5.22A and Table 5.5). Most of the blood is supplied by anastomoses formed along the lesser curvature by the right and left gastric arteries and, along the greater curvature, by the right and left gastro-omental artery (gastro-epiploic artery). The fundus and upper body of stomach receive blood from the short and posterior gastric arteries, branches of the splenic artery. ● ● ● ○ supplied by its branch, the inferior pancreaticoduodenal artery. The superior and inferior pancreaticoduodenal arteries form an anastomotic loop between the celiac trunk and the SMA; consequently, there is potential for collateral circulation here. ● ● duodenal veins, which follow the arteries and drain into the hepatic portal vein (Figs. 5.19C, 5.22B, and 5.27); some veins drain directly and others indirectly through the superior mesenteric and splenic veins. ● ● lymphatic vessels, which follow the arteries in a retrograde direction. The anterior lymphatic vessels drain into the pancreaticoduodenal lymph nodes located along the superior and inferior pancreaticoduodenal arteries and into the pyloric lymph nodes, which lie along the gastroduodenal artery (Fig. 5.23A). The posterior lymphatic vessels pass posterior to the head of the pancreas and drain into the superior mesenteric lymph nodes. Efferent lymphatic vessels from the duodenal lymph nodes drain into the celiac lymph nodes. ● ● parasympathetic innervation from the vagus and sympathetic innervation from the greater and lesser splanchnic nerves by way of the celiac and superior mesenteric plexuses and then via peri-arterial plexuses extending to the pancreaticoduodenal arteries (Fig. 5.23B). FIGURE 5.26. View OriginalDownload Slide (.ppt) Arterial supply of gastrointestinal tract. FIGURE 5.27. View OriginalDownload Slide (.ppt) Venous drainage of abdominal part of gastrointestinal tract. The hepatic portal vein drains blood rich in nutrients but reduced in oxygen from the stomach, intestines, spleen, pancreas, and gallbladder to the liver. INSERT TABLE 5.6 The cecum, the first part of the large intestine, is continuous with the ascending colon. It is a blind intestinal pouch in the right lower quadrant, where it lies in the iliac fossa inferior to the junction of the terminal ileum and cecum. The cecum is usually almost entirely enveloped by peritoneum and can be lifted freely; however, the cecum has no mesentery. The ileum enters the cecum obliquely and partly invaginates into it, forming the ileal orifice (Fig. 5.30B). The vermiform (L. worm-like) appendix, a blind intestinal diverticulum, extends from the posteromedial aspect of the cecum inferior to the ileocecal junction. The appendix varies in length and has a short triangular mesentery, the meso-appendix, which derives from the posterior side of the mesentery of the terminal ileum (Fig. 5.30B). The meso-appendix attaches to the cecum and the proximal part of the appendix. The position of the appendix is variable, but it is usually retrocecal (posterior to the cecum). The base of the appendix most often lies deep to a point that is one third of the way along the oblique line joining the right anterior superior iliac spine to the umbilicus (spino-umbilical or McBurney point). The cecum is supplied by the ileocolic artery, the terminal branch of the SMA. The appendix is supplied by the appendicular artery, a branch of the ileocolic artery (Figs. 5.30B and 5.31A and Table 5.6). A tributary of the SMV, the ileocolic vein, drains blood from the cecum and appendix (Fig. 5.27). The lymphatic vessels from the cecum and appendix pass to lymph nodes in the meso-appendix and to the ileocolic lymph nodes that lie along the ileocolic artery (Fig. 5.31C). Efferent lymphatic vessels pass to the superior mesenteric lymph nodes. The nerve supply to the cecum and appendix derives from sympathetic and parasympathetic nerves from the superior mesenteric plexus (Fig. 5.31D). The sympathetic nerve fibers originate in the lower thoracic part of the spinal cord (T10–T12), and the parasympathetic nerve fibers derive from the vagus nerves. Afferent nerve fibers from the appendix accompany the sympathetic nerves to the T10 segment of the spinal cord. Laparoscopic appendectomy has become a standard procedure used to remove the appendix via small incisions. The peritoneal cavity is first inflated with carbon dioxide gas, distending the abdominal wall, to provide viewing and working space. The laparoscope is passed through the incision in the anterolateral abdominal wall (e.g., near or through the umbilicus). One or two other small incisions (“ports”) are required for surgical (instrument) access to the appendix and related vessels. An appendectomy may be performed through a transverse or gridiron (muscle-splitting) incision centered at the McBurney point in the right lower quadrant, if indicated. In unusual cases of malrotation of the intestine, or failure of descent of the cecum, the appendix is not in the lower right quadrant (LRQ). When the cecum is high (subhepatic cecum), the appendix is in the right hypochondriac region and the pain localizes there, not in the LRQ (see Fig. B5.10). Colitis, Colectomy, and Ileostomy Chronic inflammation of the colon (ulcerativecolitis, Crohn disease) is characterized by severe inflammation and ulceration of the colon and rectum. In some cases, a colectomy is performed, during which the terminal ileum and colon as well as the rectum and anal canal are removed. An ileostomy is then constructed to establish an artificial cutaneous opening between the ileum and the skin of the anterolateral abdominal wall. Following a partial colectomy, a colostomy or sigmoidostomy is performed to create an artificial cutaneous opening for the terminal part of the colon. Colonoscopy The interior surface of the colon can be observed and photographed in a procedure called colonoscopy, or coloscopy, using a long fiberoptic endoscope (colonoscope) inserted into the colon through the anus and rectum. Small instruments can be passed through the colonoscope to perform minor operative procedures, such as biopsies or removal of polyps. Most tumors of the large intestine occur in the rectum; approximately 12% of them appear near the rectosigmoid junction. The interior of the sigmoid colon is observed with a sigmoidoscope, a shorter endoscope, in a procedure called sigmoidoscopy. Spleen The spleen, a mobile ovoid lymphatic organ, lies intraperitoneally in the left upper quadrant. The spleen is entirely surrounded by peritoneum except at the hilum (Fig. 5.33), where the splenic branches of the splenic artery and vein enter and leave. It is associated posteriorly with the left 9th through 11th ribs and separated from them by the diaphragm and the costodiaphragmatic recess, the cleft-like extension of the pleural cavity between the diaphragm and the lower part of the thoracic cage (Fig. SA5.3B). The spleen normally does not descend inferior to the costal region; it rests on the left colic flexure. The spleen varies considerably in size, weight, and shape; however, it is usually about 12 cm long and 7 cm wide, roughly the size and shape of a clenched fist. right and left livers, respectively. Within each lobe, the secondary and tertiary branches of the hepatic portal vein and hepatic artery are consistent enough to form hepatic segments (Fig. 5.39). Between the segments are the right, intermediate (middle), and left hepatic veins, which drain parts of adjacent segments. The hepatic veins open into the IVC just inferior to the diaphragm (Fig. 5.39A). The attachment of these veins to the IVC helps hold the liver in position. The liver is a major lymph-producing organ; between one quarter and one half of the lymph received by the thoracic duct comes from the liver. The lymphatic vessels of the liver occur as superficial lymphatics in the subperitoneal fibrous capsule of the liver (Glisson capsule), which form its outer surface, and as deep lymphatics in the connective tissue that accompany the ramifications of the portal triad and hepatic veins. Superficial lymphatics from the anterior aspects of the diaphragmatic and visceral surfaces and the deep lymphatic vessels accompanying the interlobular portal triads converge toward the porta hepatis and drain to the hepatic lymph nodes scattered along the hepatic vessels and ducts in the lesser omentum (Fig. 5.40A). Efferent lymphatic vessels from these lymph nodes drain into the celiac lymph nodes, which in turn drain into the cisterna chyli at the inferior end of the thoracic duct. Superficial lymphatics from the posterior aspects of the diaphragmatic and visceral surfaces of the liver drain toward the bare area of the liver. Here, they drain into phrenic lymph nodes or join deep lymphatics that have accompanied the hepatic veins converging on the IVC and then pass with this large vein through the diaphragm to drain into the posterior mediastinal lymph nodes. Efferent vessels from these nodes join the right lymphatic and thoracic ducts. A few lymphatic vessels also drain to the left gastric nodes, along the falciform ligament to the parasternal lymph nodes and along the round ligament of the liver to the lymphatics of the anterior abdominal wall. The nerves of the liver derive from the hepatic nerve plexus (Fig. 5.40B), the largest derivative of the celiac plexus. The hepatic plexus accompanies the branches of the hepatic artery and hepatic portal vein to the liver. It consists of sympathetic fibers from the celiac plexus and parasympathetic fibers from the anterior and posterior vagal trunks. FIGURE 5.40. View OriginalDownload Slide (.ppt) Lymphatic drainage and innervation of liver. A. Lymphatic drainage. B. Innervation. inferomedially anterior to the psoas major and the tips of the transverse processes of the lumbar vertebrae (see Fig. SA5.5A) and cross the external iliac artery just beyond the bifurcation of the common iliac artery. They then run along the lateral wall of the pelvis to enter the urinary bladder (Fig. 5.51). The ureters are normally constricted to a variable degree in three places: (1) at the junction of the ureters and renal pelves, (2) where the ureters cross the brim of the pelvic inlet, and (3) during their passage through the wall of the urinary bladder. These constricted areas are potential sites of obstruction by ureteric (kidney) stones. FIGURE 5.49. View OriginalDownload Slide (.ppt) Blood supply of kidneys and ureters. A. Renal segments and segmental arteries. Only the superior and inferior arteries supply the whole thickness of the kidney. B. Blood supply of ureters. Photo courtesy of Dr. Joel A. Vilensky, Indiana University School of Medicine, Fort Wayne, Indiana, and Dr. Edward C. Weber, The Imaging Center, Fort Wayne, Indiana. FIGURE 5.50. View OriginalDownload Slide (.ppt) Internal structure of kidney and suprarenal gland. FIGURE 5.51. View OriginalDownload Slide (.ppt) Normal constrictions of ureters demonstrated by retrograde pyelogram. A. Contrast medium was injected into the ureters from a flexible endoscope (urethroscope) in the bladder. B. Sites at which relative constrictions in the ureters normally appear: (1) ureteropelvic junction, (2) crossing external iliac vessels and/or pelvic brim, and (3) as ureter traverses bladder wall. sympathetic ganglia (Figs. 5.54 and 5.55 and Table 5.8). The peri-arterial extensions of these plexuses deliver postsynaptic sympathetic fibers and the continuations of parasympathetic fibers to the abdominal viscera, where intrinsic parasympathetic ganglia occur. FIGURE 5.54. View OriginalDownload Slide (.ppt) Autonomic nerves of posterior abdominal wall. A. Origin and distribution of pre- and postsynaptic sympathetic and parasympathetic fibers, and the ganglia involved in supplying abdominal viscera are shown. B. The fibers supplying the intrinsic plexuses of abdominal viscera are demonstrated. FIGURE 5.55. View OriginalDownload Slide (.ppt) Splanchnic nerves, nerve plexuses, and sympathetic ganglia in abdomen. TABLE 5.8. Autonomic Innervation of Abdominal Viscera (Splanchnic Nerves) Splanchnic Nerves Autonomic Fiber Typea A. Postsynaptic Cardiopulmon ary (cervical and upper thoracic) System Origin Destination Sympathetic FINISH TABLE 5.8 three leaves, resembling a wide cloverleaf. Although it lies near the center of the diaphragm, the central tendon is closer to the anterior part of the thorax. The superior aspect of the central tendon is fused with the inferior surface of the fibrous pericardium (Fig. 5.58C). The surrounding muscular part of the diaphragm forms a continuous sheet; however, for descriptive purposes it is divided into three parts based on the peripheral attachments (Fig. 5.58A): ● ● A sternal part, consisting of two muscular slips that attach to the posterior aspect of the xiphoid process of the sternum; this part is not always present. ● ● A costal part, consisting of wide muscular slips that attach to the internal surfaces of the inferior six costal cartilages and their adjoining ribs on each side; this part forms the domes of the diaphragm. ● ● A lumbar part, arising from two aponeurotic arches, the medial and lateral arcuate ligaments, and the three superior lumbar vertebrae; this part forms right and left muscular crura that ascend to the central tendon. The crura of the diaphragm are musculotendinous bundles that arise from the anterior surfaces of the bodies of the superior three lumbar vertebrae, the anterior longitudinal ligament, and the IV discs (Fig. 5.58A). The right crus, larger and longer than the left crus, arises from the first three or four lumbar vertebrae, whereas the left crus arises from only the first two or three. The crura are united by the median arcuate ligament, which passes over the anterior surface of the aorta. The diaphragm is also attached on each side to the medial and lateral arcuate ligaments, which are thickenings of the fascia covering the psoas and quadratus lumborum muscles, respectively. Diaphragmatic Apertures The diaphragmatic apertures permit structures (e.g., esophagus, vessels, nerves, and lymphatics) to pass between the thorax and the abdomen (Figs. 5.58, 5.59, and 5.60). The three large apertures for the IVC, esophagus, and aorta are the caval opening, esophageal hiatus, and aortic hiatus, respectively. FIGURE 5.60. View OriginalDownload Slide (.ppt) Diaphragmatic apertures. FIGURE 5.63. View OriginalDownload Slide (.ppt) Muscles of posterior abdominal wall. A. Iliopsoas. B. Quadratus lumborum. The attachments, nerve supply, and main actions of these muscles are summarized in Table 5.9. TABLE 5.9. Main Muscles of Posterior Abdominal Wall Muscle Superior Attachments Inferior Attachment(s) Innervation Actions Psoas majora Transverse processes of lumbar vertebrae; sides of bodies of T12–S1 vertebrae and intervening IV discs By a strong tendon to lesser trochanter of femur Lumbar plexus via anterior branches of nerves L2–L4 Acting inferiorly with iliacus, flexes thigh; acting superiorly, flexes vertebral column laterally to balance the trunk; when sitting, acts inferiorly with iliacus to flex trunk Iliacusa Superior two thirds of iliac fossa, ala of sacrum, and anterior sacro-iliac ligaments Lesser trochanter of femur and shaft inferior to it and to psoas major tendon Femoral nerve (L2–L4) Flexes thigh and stabilizes hip joint; acts with psoas major Quadratus lumborum Medial half of inferior border of 12th rib and tips of lumbar transverse processes Iliolumbar ligament and internal lip of iliac crest FIGURE 5.72. View OriginalDownload Slide (.ppt) Other abdominal imaging. A. 3-D reconstruction of abdominal CT scan. D, duodenum; HP, head of pancreas; PV, portal vein; SM, small intestine; SMV, superior mesenteric vein; ST, stomach; SV, splenic vein. B. Magnetic resonance angiogram (MRA). Ao, aorta; CA, celiac trunk; K, kidney; LRA, left renal artery; RRA, right renal artery; SA, splenic artery; SMA, superior mesenteric artery; ST, stomach. C. Single-contrast radiograph of colon after a barium enema. Letters are identified in D. D. Overview of characteristics of the large intestine. A Courtesy of M. Asch, University of Toronto, Ontario, Canada. B Dean D, Herbener TE. Cross-sectional Human Anatomy. 2000. C Courtesy of Dr. C.S. Ho, University of Toronto, Ontario, Canada. Go to http://thePoint.lww.com/ for helpful study tools, including USMLE-style questions, case studies, images, and more!