{"id":114,"date":"2020-03-09T17:52:29","date_gmt":"2020-03-09T17:52:29","guid":{"rendered":"https:\/\/integrations.pressbooks.network\/anatomy\/chapter\/abdominal-organs\/"},"modified":"2020-06-11T01:46:03","modified_gmt":"2020-06-11T01:46:03","slug":"abdominal-organs","status":"publish","type":"chapter","link":"https:\/\/integrations.pressbooks.network\/anatomy\/chapter\/abdominal-organs\/","title":{"raw":"Abdominal Organs","rendered":"Abdominal Organs"},"content":{"raw":"<div>\n<div>\n<h3>Chapter Section<\/h3>\n<a href=\"#diaphragm\"><strong>Thoracoabdominal Diaphragm<\/strong><\/a>\n\n<strong>Abdominal Organs<\/strong>\n<p style=\"padding-left: 40px\"><a href=\"#GI\">Gastrointestinal Tract and Associated Organs<\/a><\/p>\n<p style=\"padding-left: 40px\"><a href=\"#urinary\">Urinary Tract<\/a><\/p>\n\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\n<h3 class=\"textbox__title\">Learning Objectives<\/h3>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n \t<li>Locate the thoracoabdominal diaphragm and identify the three major foramina within it.<\/li>\n \t<li>Describe the changes in thoracic and abdominal volume and pressure that occur with contraction of the diaphragm.<\/li>\n \t<li>Describe the relative positions and general functions of the organs within the abdomen.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<h1><a id=\"diaphragm\" href=\"\"><\/a>Thoracoabdominal Diaphragm<\/h1>\n<div>Recall that the thoracoabdominal diaphragm is a sheet of skeletal muscle dividing the thorax from the abdominal cavity. Looking at an inferior view of the thoracoabdominal diaphragm, it is apparent that the central part of the diaphragm is tendinous, while its outer edges are muscular.\u00a0 There are three large <strong>hiatuses<\/strong> (holes) in the diaphragm.\u00a0 The hiatuses allow the passage of structures between the thorax and abdomen.<\/div>\n<ul>\n \t<li>The <strong>vena caval foramen<\/strong> is within the central tendon of the diaphragm, at T8.\u00a0 The inferior vena cava passes through it, along with the right phrenic nerve.\u00a0 Because this foramen is within the central tendon, it will get larger when the diaphragm contracts, because the central tendon is pulled taut.\u00a0 This helps venous return to the heart by increasing the diameter of the inferior vena cava.<\/li>\n \t<li>The <strong>esophageal hiatus<\/strong> is within the muscular part of the diaphragm, at T10.\u00a0 The esophagus and vagal trunks pass through it.\u00a0 This hiatus gets smaller in diameter when the diaphragm contracts, which helps to prevent esophageal reflux.<\/li>\n \t<li>The <strong>aortic hiatus<\/strong> is at T12 and is actually an opening that is <em>behind<\/em> the diaphragm.\u00a0 The aorta runs right behind a ligamentous area at the posterior midline of the diaphragm and is just anterior to the vertebral bodies.\u00a0 This anatomy protects the aorta from diaphragmatic contractions.\u00a0 The thoracic duct travels through the diaphragm with the aorta.<\/li>\n<\/ul>\n[caption id=\"attachment_2380\" align=\"aligncenter\" width=\"550\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/DiaphragmForamina.png\"><img class=\" wp-image-96\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-1024x553.png\" alt=\"\" width=\"550\" height=\"297\"><\/a> The three major hiatuses in the thoracoabdominal diaphragm. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.[\/caption]\n\n<\/div>\nThis video shows an interesting clinical case of phrenic nerve injury, its consequences, and the results of a nerve repair!\nhttps:\/\/www.youtube.com\/watch?v=CSTFZ_mpJC4\n\n<hr>\n\n<h5>KNOWLEDGE CHECK<\/h5>\n[h5p id=\"4\"]\n<p style=\"text-align: right\"><a href=\"#LO\">Back to Top<\/a><\/p>\n\n\n<hr>\n\n<h1>Abdominal Organs<\/h1>\n<h3><a id=\"GI\" href=\"\"><\/a>Gastrointestinal Tract and Associated Organs<\/h3>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"562\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/GITract.jpg\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-97 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-1024x747.jpg\" alt=\"\" width=\"562\" height=\"410\"><\/a> Organs of the digestive system.\u00a0 From Marieb et al., Human Anatomy, 7th edition, Pearson, 2014.[\/caption]\n\nThe gastrointestinal (GI) tract is a single tube, extending from the oral cavity, pharynx, and esophagus, through the stomach, small intestine, and large intestine, ending in the rectum and anus.\u00a0 Each segment of the GI tract is regionally specialized for particular digestive functions. In addition to the tube itself, there are three important glands that empty into the small intestine: the liver, gall bladder, and pancreas.\n\nAt every level of the GI tract, one of the major functions is propulsion: ingested food must be moved inferiorly to continue the digestive process.\u00a0 Certain parts of the digestive system are responsible for mechanical digestion: physically breaking up ingested food into smaller particles.\u00a0 Most regions of the digestive tract also have critical roles in chemical digestion: secreting enzymes and other chemicals to break chemical bonds and transform ingested food into absorbable particles.\n<p style=\"text-align: right\"><a href=\"#LO\">Back to Top<\/a><\/p>\n\n<h4>Abdominal Quadrants<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"776\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Abdominal_Quadrant_Regions.jpg\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-98\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Abdominal_Quadrant_Regions-1024x528.jpg\" alt=\"\" width=\"776\" height=\"400\"><\/a> Two ways of dividing the abdomen into regions. From https:\/\/med.libretexts.org\/Bookshelves\/Anatomy_and_Physiology\/Book%3A_Anatomy_and_Physiology_(Boundless)\/1%3A_Introduction_to_Anatomy_and_Physiology\/1.4%3A_Mapping_the_Body\/1.4F%3A_Abdominopelvic_Regions[\/caption]\n\nIn order to make it easier to describe the anatomy and to assess patients' conditions, the abdomen can be divided into regions, according to various systems.\u00a0 Two common systems are shown in the figure above.\u00a0 The abdomen can be divided into nine regions (at left) or into four quadrants (at right).\u00a0 For the purposes of this class, we will divide the abdomen into four quadrants:\u00a0 right upper, left upper, right lower, and left lower quadrants.\u00a0 You should understand the position of the organs of the abdomen in relation to these quadrants.\n<ul>\n \t<li>The <strong>right upper quadrant<\/strong> contains the liver and associated structures and most of the duodenum.<\/li>\n \t<li>The <strong>left upper quadrant<\/strong> contains the spleen and much of the stomach.<\/li>\n \t<li>The <strong>right lower quadrant<\/strong> contains the appendix.<\/li>\n \t<li>The <strong>left lower quadrant<\/strong> contains the sigmoid colon.<\/li>\n<\/ul>\n<h4>Peritoneum and Regions Within the Abdomen<\/h4>\nJust as the thoracic organs are surrounded by sacs (the pericaridal and pleural sacs), the abdomen contains a sac called the <strong>peritoneum<\/strong> that surrounds many of the abdominal organs.\u00a0 The peritoneum has the same basic functions as the pericardial and pleural sacs: secretes a small amount of fluid into its cavity to help organs move relative to other structures, reflections act as a corridor for blood vessels to travel from the aorta to the organ.\u00a0 The parts of the peritoneum are also referred to in the same way as the sacs in the thorax: <strong>visceral peritoneum<\/strong> lines the organ itself, <strong>parietal peritoneum<\/strong> lines the body wall.\u00a0 However, the peritoneum surrounds not one organ, but many (very oddly shaped) organs, and this causes the peritoneal sac to be much more complex in shape than the pericaridal or pleural sacs.\n\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"1020\"]<img class=\"size-full wp-image-99\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled.jpg\" alt=\"abdominal organs and mesenteries\" width=\"1020\" height=\"1080\"> Abdominal Organs and Mesenteries. Image from Marieb et al., Human Anatomy, 7th Edition, Pearson Education, 2014.[\/caption]\n\n&nbsp;\n\nMesenteries (reflections from parietal to visceral peritoneum) provide pathways for vessels and nerves to reach the organs.\u00a0 Each mesentery is named based on the organ to which it is attached.\u00a0 For example:\n<ul>\n \t<li><strong>mesointestine<\/strong> (aka <strong>mesentery proper<\/strong>): small intestine<\/li>\n \t<li><strong>transverse mesocolon<\/strong>: transverse colon<\/li>\n \t<li><strong>sigmoid mesocolon<\/strong>: sigmoid colon<\/li>\n<\/ul>\nThere are regions of the mesenteries that also get named because they have a special significance:\n<ul>\n \t<li><strong>greater omentum<\/strong>: large overgrowth of the mesentery that connects the stomach and the transverse mesocolon, looks like a large apron filled with variable amounts of fat<\/li>\n \t<li><strong>lesser omentum<\/strong>: mesentery connecting liver to stomach, encloses a small sac posterior to it known as the lesser sac<\/li>\n \t<li><strong>hepatoduodenal ligament<\/strong>: part of the lesser omentum that transmits the proper hepatic artery, hepatic portal vein, and common bile duct (see below for more details on all of these structures)<\/li>\n \t<li><strong>falciform ligament<\/strong>: extends between anterior body wall and liver, contained the umbilical vein during fetal life (now know as the round ligament of the liver)<\/li>\n<\/ul>\n[caption id=\"\" align=\"aligncenter\" width=\"549\"]<img src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image7.png\" alt=\"sagittal view of mesenteries\" width=\"549\" height=\"408\"> Sagittal view of the mesenteries surrounding the digestive organs. Image from Marieb et al., Human Anatomy, 7th Edition, Pearson Education, 2014.[\/caption]\n<h4>Stomach<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"691\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Stomachh.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-101\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-1024x686.png\" alt=\"\" width=\"691\" height=\"463\"><\/a> The stomach lies in the superior abdomen just inferior to the diaphragm. Modified from Marieb et al., Human Anatomy, 7th edition, Pearson, 2014.[\/caption]\n\nThe <strong>stomach<\/strong> is the widest part of the GI tract. Food from the esophagus enters the stomach through the <strong>cardiac sphincter<\/strong> which is just inferior to the diaphragm.\u00a0 The large volume and expandability of the stomach allows it to store food after eating and slowly release it to the small intestine. Normal capacity of the stomach is about one liter, though it can purportedly be stretched to a whopping four liters of capacity!\n\nThe <strong>pyloric sphincter<\/strong> regulates the movement of food from the stomach to the proximal part of the small intestine (the <strong>duodenum<\/strong>).\u00a0 Unlike the cardiac sphincter, the pyloric sphincter is highly functional and regulates the movement of food past the stomach.\n\nThe stomach has several functions:\n<ul>\n \t<li>Storage of food: The large capacity of the stomach allows us to eat larger amounts at one time. The stomach releases ingested food slowly to the small intestine, which allows for more complete digestion and absorption of nutrients.<\/li>\n \t<li>Mechanical digestion: Contraction of three layers of smooth muscle in the wall of the stomach grinds ingested food into smaller particles and mixes it with stomach secretions.<\/li>\n \t<li>Chemical digestion: Cells in the epithelial lining of the stomach secrete hydrochloric acid, which helps break food into smaller pieces, and pepsin, an enzyme which digests proteins.<\/li>\n<\/ul>\nThe slurry of digested food and gastric juices that leaves the stomach is called <strong>chyme<\/strong>.\n\n<a href=\"#LO\">Back to Top<\/a>\n<h4>Small Intestine<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"382\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/small-intestine.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-102\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine.png\" alt=\"\" width=\"382\" height=\"439\"><\/a> Small intestine within the abdomen. The large intestine and greater omentum have been reflected superiorly. From Netter Presenter.[\/caption]\n\nThere are three regions of the small intestine: the <strong>duodenum<\/strong>, <strong>jejunum<\/strong>, and <strong>ileum<\/strong>.\u00a0 Though they are distinct histologically, the three segments of the small intestine are not distinguishable grossly.\u00a0 You should know them by location.\n<ul>\n \t<li>The <strong>duodenum<\/strong> is the C-shaped segment continuous with the stomach; it is wrapped around the head of the pancreas in the posterior abdomen.\u00a0 It is consists of the first twelve inches (or so) of the small intestine and receives all of the secretions from the liver, gall bladder, and pancreas. Its lining contains bicarbonate-secreting glands (<em>Brunner's glands<\/em>) to neutralize the acidic chyme from the stomach.<\/li>\n \t<li>The <strong>jejunum<\/strong> is located mostly in the upper left quadrant of the abdomen. This middle section of the small intestine has extensive folds to facilitate both secretion of digestive enzymes and absorption of nutrients by the cells lining its walls.<\/li>\n \t<li>The <strong>ileum<\/strong> empties into the cecum of the large intestine and is located mostly in the lower right quadrant.\u00a0 It has abundant immune cells in its walls (<em>Peyer's patches<\/em>). The ileum ends at the junction with the large intestine (the <strong>ileocecal junction<\/strong>).<\/li>\n<\/ul>\nAll three segments of the small intestine are important for both chemical digestion and absorption of nutrients.\u00a0 Cells lining the small intestine secrete digestive enzymes (which break down fats, proteins, and carbohydrates) as well as absorb nutrients from the lumen of the gut.\u00a0 Deep to the epithelial lining of the small intestine are dense networks of blood and lymphatic capillaries.\u00a0 Fats are absorbed into the lymphatic capillaries and then travel through the lymphatic system to the thoracic duct, which returns them to the venous circulation of the body.\u00a0 Proteins and carbohydrates are absorbed into the blood capillaries. Blood from these capillary beds travels to the liver, via the hepatic portal circulation (<a href=\"#portalvein\">below<\/a>). The liver will process proteins and carbohydrates for use by the cells of the body.\n\n<a href=\"#LO\">Back to Top<\/a>\n<h4>Liver, Gall Bladder, and Pancreas<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"554\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Liver-GB.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-103 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB.png\" alt=\"\" width=\"554\" height=\"423\"><\/a> Orientation of liver, gall bladder, and pancreas.\u00a0 Their ducts all empty into the duodenum. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.[\/caption]\n\nThe <strong>liver<\/strong> is the largest gland in the body and it has many functions (most of which are beyond the scope of this class).\u00a0 Cells of the liver (<em>hepatocytes<\/em>) process the nutrients (proteins and carbohydrates) and toxins absorbed by the digestive tract, metabolize waste products from red blood cell destruction in the spleen, and produce bile.\n\n<strong>Bile<\/strong> is a substance which emulsifies fats, breaking them into smaller pieces in order to make them more susceptible to enzymatic digestion.\u00a0 Hepatocytes produce bile constantly. Bile leaves the liver through the <strong>common hepatic duct<\/strong>.\u00a0 If bile is not needed in the duodenum to digest fats immediately, it will travel into the <strong>gall bladder<\/strong> through the <strong>cystic duct<\/strong> where it will be stored until needed.\u00a0 When fat reaches the small intestine, the gall bladder is stimulated to release bile.\u00a0 Bile travels through the <strong>common bile duct<\/strong> to the duodenum.\u00a0 (The common bile duct carries bile from both the liver and the gallbladder.\u00a0 See figure below.)\n\nTo reach the duodenum, the common bile duct passes through the <strong>head of the pancreas<\/strong>.\u00a0 The pancreas is a long gland located posterior to the stomach.\u00a0 The head of the pancreas is surrounded by the duodenum.\u00a0 The pancreas is both an exocrine and endocrine organ.\u00a0 Its endocrine function is to secrete insulin and glucagon into the bloodstream.\u00a0 These hormones regulate blood glucose levels by affecting the release and storage of glucose from cells of the liver.\u00a0 Its exocrine function is to secrete digestive enzymes, through the<strong> pancreatic duct<\/strong>, into the duodenum.\u00a0 These pancreatic enzymes are critical to chemical digestion in the small intestine, breaking down fats, proteins, and carbohydrates into components that can be absorbed by the epithelium that lines the small intestine.\n\nThe <strong>pancreatic duct <\/strong>is a tube that runs through the length of the pancreas.\u00a0 Within the head of the pancreas, the common bile duct and the pancreatic duct join together briefly and empty into the duodenum through a common opening.\u00a0 Because the two duct systems share a common opening to the duodenum, gallstones (which form in the gall bladder) can potentially block both the secretion of bile and the secretion of pancreatic enzymes into the duodenum, depending on where the gallstones lodge.\n\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"654\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Ducts.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-104 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-1024x669.png\" alt=\"\" width=\"654\" height=\"427\"><\/a> The ducts from the liver, gall bladder, and pancreas empty into the duodenum through a common opening. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.[\/caption]\n\n<a href=\"#LO\">Back to Top<\/a>\n<h4>Large Intestine (Colon) &amp; Rectum<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"648\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Colon.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-105 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-1024x683.png\" alt=\"\" width=\"648\" height=\"432\"><\/a> The large intestine begins at the cecum and ends at the rectum and anal canal. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.[\/caption]\n\nThe ileum of the small intestine empties into the large intestine (<strong>colon<\/strong>) at the <strong>cecum<\/strong> (through the <strong>ileocecal junction,<\/strong> in the lower right quadrant of the abdomen).\u00a0 Hanging off of the inferior part of the cecum is the <strong>appendix<\/strong>, a small appendage which is filled with lymphatic tissue (lymphocytes, macrophages, and supporting tissues).\u00a0 Food passes from the cecum through the <strong>ascending, transverse, descending, and sigmoid colons<\/strong>.\u00a0 The junction between the ascending and transverse colons is called the <strong>hepatic flexure<\/strong>; the junction between the transverse colon and the descending colon is called the <strong>splenic flexure<\/strong>.\u00a0 The sigmoid colon passes into the pelvis where it becomes the <strong>rectum<\/strong>.\u00a0 Fecal waste leaves the body through the <strong>anal canal<\/strong> and the <strong>anus<\/strong>.\n\nThe primary function of the large intestine is the absorption of water and vitamins.\n\nThe passage of fecal waste out of the body is regulated by two sets of sphincter muscles in the anal canal.\u00a0 The <strong>internal anal sphincter<\/strong> is made of smooth muscle and is under involuntary control.\u00a0 Generally, sympathetic innervation keeps this sphincter closed and parasympathetic stimulation relaxes it.\u00a0 The <strong>external anal sphincter<\/strong> is made of skeletal muscle and is under voluntary control.\u00a0 This skeletal muscle sphincter is innervated by the pudendal nerve, which is comprised of ventral rami from S2, S3, and S4 spinal levels.\n\n<a href=\"#LO\">Back to Top<\/a>\n<h4>Spleen<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"558\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/spleen-1.png\"><img class=\" wp-image-106\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-1024x574.png\" alt=\"\" width=\"558\" height=\"313\"><\/a> The spleen is located in the left upper quadrant of the abdomen.\u00a0 Modified from Netter Presenter.[\/caption]\n\nThe <strong>spleen<\/strong> is an organ of both the immune and circulatory systems located in the posterior recess of the superior left abdomen, near the tail of the pancreas. Although it is not a digestive organ, the spleen is supplied by the arteries which also supply the organs of the digestive system.\u00a0 Importantly, the spleen's venous drainage passes through the hepatic portal system (below).\n\nOne of the important functions of the spleen is to destroy old red blood cells.\u00a0 This process produces bilirubin, a waste product. Bilirubin travels to the liver via the hepatic portal vein and is recycled by hepatocytes as a component of bile. As described above, bile is released to the small intestine where it emulsifies fats.\n\nThe spleen is also a reservoir for blood.\u00a0 The blood supply to the spleen is huge and damage to the spleen can cause major blood loss.\u00a0 Since the organ is difficult to repair, it is often removed if it is damaged.\n\n<a href=\"#LO\">Back to Top<\/a>\n\n&nbsp;\n\n<hr>\n\n<h5>KNOWLEDGE CHECKS<\/h5>\n[h5p id=\"5\"]\n\n[h5p id=\"6\"]\n\n[h5p id=\"7\"]\n\n[h5p id=\"8\"]\n\n[h5p id=\"9\"]\n\n[h5p id=\"10\"]\n\n<a href=\"#LO\">Back to Top<\/a>\n<h4>Arteries of the Digestive System<\/h4>\n[caption id=\"\" align=\"aligncenter\" width=\"403\"]<img src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image1.jpeg\" alt=\"Artery supply to the digestive system\" width=\"403\" height=\"452\"> Three unpaired branches of the abdominal aorta supply the organs of the digestive system. Modified from Snell, Clinical Anatomy for Medical Students, 5th edition, Little Brown, 1995.[\/caption]\n\nThe blood supply to the gut tube is related to its development. Early in the embryo, the developing gut tube is supplied with blood by three unpaired branches of the abdominal aorta. The <strong>celiac trunk<\/strong> supplies the foregut (stomach to duodenum); the <strong>superior mesenteric artery<\/strong>\u00a0 supplies the midgut (duodenum to transverse colon); and the <strong>inferior mesenteric artery<\/strong> supplies the hindgut (descending colon to anus).\u00a0 There are anastomoses between these three arteries in areas that join foregut to midgut and midgut to hindgut.\u00a0 These patterns of circulation, established very early in development, persist throughout the formation of the convoluted gut tube and into the adult.\n\nThe main arteries to the digestive system have extensive branching.\u00a0 The names of all of the many (many!) branches is beyond the scope of this course, but we will dissect some of them to get a sense of the vast branching patterns.\u00a0<em> Branches that you definitely need to know are in bold (and are included in the lab as well). <\/em>\n\n<strong>Celiac Trunk<\/strong>\n\nThe <strong>celiac trunk<\/strong> supplies the stomach, spleen, liver, and parts of the duodenum.\u00a0 The liver receives arterial blood from a branch of the celiac trunk called the <strong>proper hepatic artery <\/strong>(see Venous Drainage of the Gut and Spleen below for the other part of the liver's blood supply).\u00a0 The spleen receives blood from a very distinctively curly artery (like a pig tail!) called the <strong>splenic artery<\/strong>.\u00a0 The stomach receives blood from multiple branches of the celiac trunk.\u00a0 If you see \"gastro\" in the name of an artery, it goes to the stomach.\n\n&nbsp;\n\n[caption id=\"\" align=\"aligncenter\" width=\"652\"]<img src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image2.jpeg\" alt=\"celiac trunk\" width=\"652\" height=\"429\"> Branches of the celiac trunk supply the liver, spleen, stomach and part of the pancreas and esophagus. Modified from Hollinshead, Textbook of Anatomy, 4th edition, HarperCollin, 1985.[\/caption]\n\n&nbsp;\n\nhttps:\/\/mediaspace.wisc.edu\/id\/1_mpwbeg4f?width=649&amp;amp;amp;amp;height=401&amp;amp;amp;amp;playerId=34298521\n\n&nbsp;\n<div><strong>Superior Mesenteric Artery<\/strong><\/div>\n<div><\/div>\n<div>The <strong>superior mesenteric artery<\/strong> branches from the aorta approximately 1 inch inferior to the celiac trunk and supplies the part of the pancreas, small intestine, ascending colon, and transverse colon.\u00a0 Branches to the small intestine are called<strong> intestinal branches<\/strong>, and are found in the mesentery proper.\u00a0 The intestinal branches form extensive anatomoses called <strong>arcades<\/strong> within the mesentery proper.\u00a0 From the arcades, <strong>vasa recta<\/strong> run directly in to the small intestine.\u00a0 Branches to the large intestine all have \"colic\" in their names, and extend from the superior mesenteric artery to different regions of the large intestine.\u00a0 The <strong>marginal artery<\/strong> runs along the large intestine to provide anatomosis between the colic arteries from the superior mesenteric arteries and colic arteries from the inferior mesenteric artery.<\/div>\n<div><\/div>\n<div>\n\n[caption id=\"\" align=\"aligncenter\" width=\"544\"]<img src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image3.jpeg\" alt=\"superior mesenteric artery\" width=\"544\" height=\"532\"> Branches of the superior mesenteric artery supply most of the small intestine and parts of the pancreas and colon.\u00a0 Modified from Snell, Clinical Anatomy for Medical Students, 5th edition, Little Brown, 1995.[\/caption]\n\n&nbsp;\n\n<\/div>\nhttps:\/\/mediaspace.wisc.edu\/id\/1_gnn61sni?width=649&amp;amp;height=401&amp;amp;playerId=34298521\n\nInferior Mesenteric Artery\n\nThe <strong>inferior mesenteric artery<\/strong> branches from the aorta just superior to the aortic bifurcation (near L3-L4 vertebral bodies).\u00a0 The inferior mesenteric artery supplies the descending colon, sigmoid colon, and rectum.\u00a0 Branches from the inferior mesenteric artery are named after the location on the colon they supply.\u00a0 For example, branches to the sigmoid colon are called <strong>sigmoid arteries<\/strong>.\n\n&nbsp;\n\n[caption id=\"\" align=\"aligncenter\" width=\"494\"]<img src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image4.jpeg\" alt=\"inferior mesenteric artery\" width=\"494\" height=\"488\"> Branches of the inferior mesenteric artery supply the descending and sigmoid colon as well as the superior rectum. Modified from Snell, Clinical Anatomy for Medical Students, 5th edition, Little Brown, 1995.[\/caption]\n\n&nbsp;\n\nhttps:\/\/mediaspace.wisc.edu\/id\/1_99lsmcuc?width=649&amp;amp;height=401&amp;amp;playerId=34298521\n<h4><a id=\"portalvein\" href=\"\"><\/a>Venous Drainage of the Gut Tract and Spleen<\/h4>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"337\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/HepaticPortalVein.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-111 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein.png\" alt=\"\" width=\"337\" height=\"357\"><\/a> All of the veins which drain the organs of the digestive tract, as well as those that drain the spleen, empty into the hepatic portal vein.\u00a0 Modified from Netter Presenter.[\/caption]\n\nThe return of venous blood from the GI tract involves a <strong>portal system<\/strong>: a system of veins that connects two capillary beds. In this case, the first set of capillary beds are within the walls of the gut tube (where nutrients are absorbed) and in the spleen (which destroys red blood cells); the second set of capillary beds is within the liver (where the absorbed nutrients, as well as bilirubin from the spleen, are processed).\n\nAll of the venous drainage from the capillary beds of the GI tract and spleen ends up in the <strong>hepatic portal vein<\/strong>, a huge vein leading into the liver. After being processed in the capillaries of the liver, blood leaves the liver through the <strong>hepatic veins<\/strong> and enters the <strong>inferior vena cava<\/strong> (and the systemic circulation).\n\n<a href=\"#LO\">Back to Top<\/a>\n\n<hr>\n\n<h3><a id=\"urinary\" href=\"\"><\/a>Urinary Tract<\/h3>\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"454\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/PosteriorAbWall.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-112 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-1024x712.png\" alt=\"\" width=\"454\" height=\"316\"><\/a> Structures of the posterior abdomen include the kidney and ureters as well as some muscles that move the lower limb. Modified from Netter Presenter.[\/caption]\n\nThe <strong>kidneys<\/strong> are located in the superior abdomen, posterior to all of the organs of the digestive system. Although they are not large organs, the kidneys receive 25% of the cardiac output of blood, a testament to their critical function in maintaining appropriate blood volume, pressure, and concentration.\u00a0 All of the kidney's vasculature as well as the <strong>ureter<\/strong> enter or exit the organ from the medial side (at the hilus of the kidney).\u00a0 Usually there is a single <strong>renal artery and vein<\/strong>, as well as a single ureter. The large renal arteries branch directly off the aorta; the renal veins empty into the inferior vena cava.\n\nThe <strong>adrenal (suprarenal) glands<\/strong> sit on top of the kidneys, but are not functionally associated with them.\u00a0 These endocrine glands secrete epinephrine and norepinephrine into the blood stream to elicit a systemic sympathetic response.\u00a0 They also secrete corticosteroids and androgens, among other hormones.\n\nThe <strong>ureters<\/strong> are extremely muscular tubes (smooth muscle). Peristaltic contractions of the walls of the ureters move urine from the kidneys to the urinary bladder. Urine is not altered as it travels down the ureter.\u00a0 The ureters pierce the posterior wall of the <strong>urinary bladder<\/strong>. Their oblique course through the muscular wall of the bladder acts as a valve, closing off the ureteric opening when the bladder is full. This prevents urine from backing up from the urinary bladder to the kidneys.\n\nThe urinary bladder is located in the pelvis, but can extend into the lower abdomen when it is distended. Since it stores urine until it is possible (or necessary) to eliminate it, the urinary bladder can stretch to many times its resting size. The epithelium lining the urinary bladder is able to stretch as the organ distends. The organ has extremely thick muscular walls (smooth muscle), which contract to eliminate urine.\n\nAt the base of the bladder, at the junction with the <strong>urethra<\/strong>, is an involuntary <strong>internal urethral sphincter<\/strong> (made of smooth muscle) which prevents the bladder from emptying; it contracts involuntarily (so we don\u2019t have to think about it).\u00a0 Sympathetics generally keep the sphincter closed; parasympathetic stimulation relaxes the sphincter.\n\n[caption id=\"attachment_99\" align=\"aligncenter\" width=\"706\"]<a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/urethra.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-113 \" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-1024x409.png\" alt=\"\" width=\"706\" height=\"282\"><\/a> The female and male urethrae. Both pass through a skeletal muscle (voluntary) sphincter in the urogenital diaphragm. Modified from Netter Presenter.[\/caption]\n\nUrine leaves the bladder through the urethra.\u00a0 In females, the urethra is fairly short. It passes through a sheet of skeletal muscle (the <em>urogenital diaphragm<\/em>) which contains the <strong>external urethral sphincter<\/strong> (skeletal muscle; a voluntary sphincter).\u00a0 In males, the urethra is much longer and consists of 3 distinct segments:\n<ul>\n \t<li>the <strong>prostatic urethra<\/strong> (which passes through the prostate gland)<\/li>\n \t<li>the <strong>membranous urethra<\/strong> (which passes through the urogenital diaphragm &amp; is the site of the external urethral sphincter)<\/li>\n \t<li>the<strong> penile urethra<\/strong> (which passes through the erectile tissue of the penis).<\/li>\n<\/ul>\nMore about this when we talk about the pelvis!!\n\nThere are two important muscles in the posterior abdomen which are involved in moving the lower limb:\u00a0 <strong>psoas major<\/strong> and <strong>quadratus lumborum<\/strong>. We will discuss them with the lower limb.\n\n<hr>\n\n<h4>KNOWLEDGE CHECKS<\/h4>\n[h5p id=\"11\"]\n\n[h5p id=\"12\"]","rendered":"<div>\n<div>\n<h3>Chapter Section<\/h3>\n<p><a href=\"#diaphragm\"><strong>Thoracoabdominal Diaphragm<\/strong><\/a><\/p>\n<p><strong>Abdominal Organs<\/strong><\/p>\n<p style=\"padding-left: 40px\"><a href=\"#GI\">Gastrointestinal Tract and Associated Organs<\/a><\/p>\n<p style=\"padding-left: 40px\"><a href=\"#urinary\">Urinary Tract<\/a><\/p>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<h3 class=\"textbox__title\">Learning Objectives<\/h3>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>Locate the thoracoabdominal diaphragm and identify the three major foramina within it.<\/li>\n<li>Describe the changes in thoracic and abdominal volume and pressure that occur with contraction of the diaphragm.<\/li>\n<li>Describe the relative positions and general functions of the organs within the abdomen.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<h1><a id=\"diaphragm\" href=\"\"><\/a>Thoracoabdominal Diaphragm<\/h1>\n<div>Recall that the thoracoabdominal diaphragm is a sheet of skeletal muscle dividing the thorax from the abdominal cavity. Looking at an inferior view of the thoracoabdominal diaphragm, it is apparent that the central part of the diaphragm is tendinous, while its outer edges are muscular.\u00a0 There are three large <strong>hiatuses<\/strong> (holes) in the diaphragm.\u00a0 The hiatuses allow the passage of structures between the thorax and abdomen.<\/div>\n<ul>\n<li>The <strong>vena caval foramen<\/strong> is within the central tendon of the diaphragm, at T8.\u00a0 The inferior vena cava passes through it, along with the right phrenic nerve.\u00a0 Because this foramen is within the central tendon, it will get larger when the diaphragm contracts, because the central tendon is pulled taut.\u00a0 This helps venous return to the heart by increasing the diameter of the inferior vena cava.<\/li>\n<li>The <strong>esophageal hiatus<\/strong> is within the muscular part of the diaphragm, at T10.\u00a0 The esophagus and vagal trunks pass through it.\u00a0 This hiatus gets smaller in diameter when the diaphragm contracts, which helps to prevent esophageal reflux.<\/li>\n<li>The <strong>aortic hiatus<\/strong> is at T12 and is actually an opening that is <em>behind<\/em> the diaphragm.\u00a0 The aorta runs right behind a ligamentous area at the posterior midline of the diaphragm and is just anterior to the vertebral bodies.\u00a0 This anatomy protects the aorta from diaphragmatic contractions.\u00a0 The thoracic duct travels through the diaphragm with the aorta.<\/li>\n<\/ul>\n<figure id=\"attachment_2380\" aria-describedby=\"caption-attachment-2380\" style=\"width: 550px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/DiaphragmForamina.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-96\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-1024x553.png\" alt=\"\" width=\"550\" height=\"297\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-1024x553.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-300x162.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-768x414.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-65x35.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-225x121.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina-350x189.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2017\/02\/DiaphragmForamina.png 1425w\" sizes=\"auto, (max-width: 550px) 100vw, 550px\" \/><\/a><figcaption id=\"caption-attachment-2380\" class=\"wp-caption-text\">The three major hiatuses in the thoracoabdominal diaphragm. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.<\/figcaption><\/figure>\n<\/div>\n<p>This video shows an interesting clinical case of phrenic nerve injury, its consequences, and the results of a nerve repair!<br \/>\n<iframe loading=\"lazy\" id=\"oembed-1\" title=\"Phrenic Nerve Injury Treatment | UCLA Plastic and Reconstructive Surgery\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/CSTFZ_mpJC4?feature=oembed&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<hr \/>\n<h5>KNOWLEDGE CHECK<\/h5>\n<div id=\"h5p-4\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-4\" class=\"h5p-iframe\" data-content-id=\"4\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Thorax - diaphragmatic hiatuses\"><\/iframe><\/div>\n<\/div>\n<p style=\"text-align: right\"><a href=\"#LO\">Back to Top<\/a><\/p>\n<hr \/>\n<h1>Abdominal Organs<\/h1>\n<h3><a id=\"GI\" href=\"\"><\/a>Gastrointestinal Tract and Associated Organs<\/h3>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 562px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/GITract.jpg\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-97\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-1024x747.jpg\" alt=\"\" width=\"562\" height=\"410\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-1024x747.jpg 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-300x219.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-768x560.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-65x47.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-225x164.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract-350x255.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/GITract.jpg 1296w\" sizes=\"auto, (max-width: 562px) 100vw, 562px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">Organs of the digestive system.\u00a0 From Marieb et al., Human Anatomy, 7th edition, Pearson, 2014.<\/figcaption><\/figure>\n<p>The gastrointestinal (GI) tract is a single tube, extending from the oral cavity, pharynx, and esophagus, through the stomach, small intestine, and large intestine, ending in the rectum and anus.\u00a0 Each segment of the GI tract is regionally specialized for particular digestive functions. In addition to the tube itself, there are three important glands that empty into the small intestine: the liver, gall bladder, and pancreas.<\/p>\n<p>At every level of the GI tract, one of the major functions is propulsion: ingested food must be moved inferiorly to continue the digestive process.\u00a0 Certain parts of the digestive system are responsible for mechanical digestion: physically breaking up ingested food into smaller particles.\u00a0 Most regions of the digestive tract also have critical roles in chemical digestion: secreting enzymes and other chemicals to break chemical bonds and transform ingested food into absorbable particles.<\/p>\n<p style=\"text-align: right\"><a href=\"#LO\">Back to Top<\/a><\/p>\n<h4>Abdominal Quadrants<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 776px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Abdominal_Quadrant_Regions.jpg\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-98\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Abdominal_Quadrant_Regions-1024x528.jpg\" alt=\"\" width=\"776\" height=\"400\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">Two ways of dividing the abdomen into regions. From https:\/\/med.libretexts.org\/Bookshelves\/Anatomy_and_Physiology\/Book%3A_Anatomy_and_Physiology_(Boundless)\/1%3A_Introduction_to_Anatomy_and_Physiology\/1.4%3A_Mapping_the_Body\/1.4F%3A_Abdominopelvic_Regions<\/figcaption><\/figure>\n<p>In order to make it easier to describe the anatomy and to assess patients&#8217; conditions, the abdomen can be divided into regions, according to various systems.\u00a0 Two common systems are shown in the figure above.\u00a0 The abdomen can be divided into nine regions (at left) or into four quadrants (at right).\u00a0 For the purposes of this class, we will divide the abdomen into four quadrants:\u00a0 right upper, left upper, right lower, and left lower quadrants.\u00a0 You should understand the position of the organs of the abdomen in relation to these quadrants.<\/p>\n<ul>\n<li>The <strong>right upper quadrant<\/strong> contains the liver and associated structures and most of the duodenum.<\/li>\n<li>The <strong>left upper quadrant<\/strong> contains the spleen and much of the stomach.<\/li>\n<li>The <strong>right lower quadrant<\/strong> contains the appendix.<\/li>\n<li>The <strong>left lower quadrant<\/strong> contains the sigmoid colon.<\/li>\n<\/ul>\n<h4>Peritoneum and Regions Within the Abdomen<\/h4>\n<p>Just as the thoracic organs are surrounded by sacs (the pericaridal and pleural sacs), the abdomen contains a sac called the <strong>peritoneum<\/strong> that surrounds many of the abdominal organs.\u00a0 The peritoneum has the same basic functions as the pericardial and pleural sacs: secretes a small amount of fluid into its cavity to help organs move relative to other structures, reflections act as a corridor for blood vessels to travel from the aorta to the organ.\u00a0 The parts of the peritoneum are also referred to in the same way as the sacs in the thorax: <strong>visceral peritoneum<\/strong> lines the organ itself, <strong>parietal peritoneum<\/strong> lines the body wall.\u00a0 However, the peritoneum surrounds not one organ, but many (very oddly shaped) organs, and this causes the peritoneal sac to be much more complex in shape than the pericaridal or pleural sacs.<\/p>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 1020px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-99\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled.jpg\" alt=\"abdominal organs and mesenteries\" width=\"1020\" height=\"1080\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled.jpg 1020w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled-283x300.jpg 283w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled-967x1024.jpg 967w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled-768x813.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled-65x69.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled-225x238.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/figure_23_04_labeled-350x371.jpg 350w\" sizes=\"auto, (max-width: 1020px) 100vw, 1020px\" \/><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">Abdominal Organs and Mesenteries. Image from Marieb et al., Human Anatomy, 7th Edition, Pearson Education, 2014.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>Mesenteries (reflections from parietal to visceral peritoneum) provide pathways for vessels and nerves to reach the organs.\u00a0 Each mesentery is named based on the organ to which it is attached.\u00a0 For example:<\/p>\n<ul>\n<li><strong>mesointestine<\/strong> (aka <strong>mesentery proper<\/strong>): small intestine<\/li>\n<li><strong>transverse mesocolon<\/strong>: transverse colon<\/li>\n<li><strong>sigmoid mesocolon<\/strong>: sigmoid colon<\/li>\n<\/ul>\n<p>There are regions of the mesenteries that also get named because they have a special significance:<\/p>\n<ul>\n<li><strong>greater omentum<\/strong>: large overgrowth of the mesentery that connects the stomach and the transverse mesocolon, looks like a large apron filled with variable amounts of fat<\/li>\n<li><strong>lesser omentum<\/strong>: mesentery connecting liver to stomach, encloses a small sac posterior to it known as the lesser sac<\/li>\n<li><strong>hepatoduodenal ligament<\/strong>: part of the lesser omentum that transmits the proper hepatic artery, hepatic portal vein, and common bile duct (see below for more details on all of these structures)<\/li>\n<li><strong>falciform ligament<\/strong>: extends between anterior body wall and liver, contained the umbilical vein during fetal life (now know as the round ligament of the liver)<\/li>\n<\/ul>\n<figure style=\"width: 549px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image7.png\" alt=\"sagittal view of mesenteries\" width=\"549\" height=\"408\" \/><figcaption class=\"wp-caption-text\">Sagittal view of the mesenteries surrounding the digestive organs. Image from Marieb et al., Human Anatomy, 7th Edition, Pearson Education, 2014.<\/figcaption><\/figure>\n<h4>Stomach<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 691px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Stomachh.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-101\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-1024x686.png\" alt=\"\" width=\"691\" height=\"463\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-1024x686.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-300x201.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-768x515.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-65x44.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-225x151.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh-350x235.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Stomachh.png 1473w\" sizes=\"auto, (max-width: 691px) 100vw, 691px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">The stomach lies in the superior abdomen just inferior to the diaphragm. Modified from Marieb et al., Human Anatomy, 7th edition, Pearson, 2014.<\/figcaption><\/figure>\n<p>The <strong>stomach<\/strong> is the widest part of the GI tract. Food from the esophagus enters the stomach through the <strong>cardiac sphincter<\/strong> which is just inferior to the diaphragm.\u00a0 The large volume and expandability of the stomach allows it to store food after eating and slowly release it to the small intestine. Normal capacity of the stomach is about one liter, though it can purportedly be stretched to a whopping four liters of capacity!<\/p>\n<p>The <strong>pyloric sphincter<\/strong> regulates the movement of food from the stomach to the proximal part of the small intestine (the <strong>duodenum<\/strong>).\u00a0 Unlike the cardiac sphincter, the pyloric sphincter is highly functional and regulates the movement of food past the stomach.<\/p>\n<p>The stomach has several functions:<\/p>\n<ul>\n<li>Storage of food: The large capacity of the stomach allows us to eat larger amounts at one time. The stomach releases ingested food slowly to the small intestine, which allows for more complete digestion and absorption of nutrients.<\/li>\n<li>Mechanical digestion: Contraction of three layers of smooth muscle in the wall of the stomach grinds ingested food into smaller particles and mixes it with stomach secretions.<\/li>\n<li>Chemical digestion: Cells in the epithelial lining of the stomach secrete hydrochloric acid, which helps break food into smaller pieces, and pepsin, an enzyme which digests proteins.<\/li>\n<\/ul>\n<p>The slurry of digested food and gastric juices that leaves the stomach is called <strong>chyme<\/strong>.<\/p>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<h4>Small Intestine<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 382px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/small-intestine.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-102\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine.png\" alt=\"\" width=\"382\" height=\"439\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine.png 738w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine-261x300.png 261w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine-65x75.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine-225x259.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/small-intestine-350x403.png 350w\" sizes=\"auto, (max-width: 382px) 100vw, 382px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">Small intestine within the abdomen. The large intestine and greater omentum have been reflected superiorly. From Netter Presenter.<\/figcaption><\/figure>\n<p>There are three regions of the small intestine: the <strong>duodenum<\/strong>, <strong>jejunum<\/strong>, and <strong>ileum<\/strong>.\u00a0 Though they are distinct histologically, the three segments of the small intestine are not distinguishable grossly.\u00a0 You should know them by location.<\/p>\n<ul>\n<li>The <strong>duodenum<\/strong> is the C-shaped segment continuous with the stomach; it is wrapped around the head of the pancreas in the posterior abdomen.\u00a0 It is consists of the first twelve inches (or so) of the small intestine and receives all of the secretions from the liver, gall bladder, and pancreas. Its lining contains bicarbonate-secreting glands (<em>Brunner&#8217;s glands<\/em>) to neutralize the acidic chyme from the stomach.<\/li>\n<li>The <strong>jejunum<\/strong> is located mostly in the upper left quadrant of the abdomen. This middle section of the small intestine has extensive folds to facilitate both secretion of digestive enzymes and absorption of nutrients by the cells lining its walls.<\/li>\n<li>The <strong>ileum<\/strong> empties into the cecum of the large intestine and is located mostly in the lower right quadrant.\u00a0 It has abundant immune cells in its walls (<em>Peyer&#8217;s patches<\/em>). The ileum ends at the junction with the large intestine (the <strong>ileocecal junction<\/strong>).<\/li>\n<\/ul>\n<p>All three segments of the small intestine are important for both chemical digestion and absorption of nutrients.\u00a0 Cells lining the small intestine secrete digestive enzymes (which break down fats, proteins, and carbohydrates) as well as absorb nutrients from the lumen of the gut.\u00a0 Deep to the epithelial lining of the small intestine are dense networks of blood and lymphatic capillaries.\u00a0 Fats are absorbed into the lymphatic capillaries and then travel through the lymphatic system to the thoracic duct, which returns them to the venous circulation of the body.\u00a0 Proteins and carbohydrates are absorbed into the blood capillaries. Blood from these capillary beds travels to the liver, via the hepatic portal circulation (<a href=\"#portalvein\">below<\/a>). The liver will process proteins and carbohydrates for use by the cells of the body.<\/p>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<h4>Liver, Gall Bladder, and Pancreas<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 554px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Liver-GB.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-103\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB.png\" alt=\"\" width=\"554\" height=\"423\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB.png 950w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB-300x229.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB-768x586.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB-65x50.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB-225x172.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Liver-GB-350x267.png 350w\" sizes=\"auto, (max-width: 554px) 100vw, 554px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">Orientation of liver, gall bladder, and pancreas.\u00a0 Their ducts all empty into the duodenum. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.<\/figcaption><\/figure>\n<p>The <strong>liver<\/strong> is the largest gland in the body and it has many functions (most of which are beyond the scope of this class).\u00a0 Cells of the liver (<em>hepatocytes<\/em>) process the nutrients (proteins and carbohydrates) and toxins absorbed by the digestive tract, metabolize waste products from red blood cell destruction in the spleen, and produce bile.<\/p>\n<p><strong>Bile<\/strong> is a substance which emulsifies fats, breaking them into smaller pieces in order to make them more susceptible to enzymatic digestion.\u00a0 Hepatocytes produce bile constantly. Bile leaves the liver through the <strong>common hepatic duct<\/strong>.\u00a0 If bile is not needed in the duodenum to digest fats immediately, it will travel into the <strong>gall bladder<\/strong> through the <strong>cystic duct<\/strong> where it will be stored until needed.\u00a0 When fat reaches the small intestine, the gall bladder is stimulated to release bile.\u00a0 Bile travels through the <strong>common bile duct<\/strong> to the duodenum.\u00a0 (The common bile duct carries bile from both the liver and the gallbladder.\u00a0 See figure below.)<\/p>\n<p>To reach the duodenum, the common bile duct passes through the <strong>head of the pancreas<\/strong>.\u00a0 The pancreas is a long gland located posterior to the stomach.\u00a0 The head of the pancreas is surrounded by the duodenum.\u00a0 The pancreas is both an exocrine and endocrine organ.\u00a0 Its endocrine function is to secrete insulin and glucagon into the bloodstream.\u00a0 These hormones regulate blood glucose levels by affecting the release and storage of glucose from cells of the liver.\u00a0 Its exocrine function is to secrete digestive enzymes, through the<strong> pancreatic duct<\/strong>, into the duodenum.\u00a0 These pancreatic enzymes are critical to chemical digestion in the small intestine, breaking down fats, proteins, and carbohydrates into components that can be absorbed by the epithelium that lines the small intestine.<\/p>\n<p>The <strong>pancreatic duct <\/strong>is a tube that runs through the length of the pancreas.\u00a0 Within the head of the pancreas, the common bile duct and the pancreatic duct join together briefly and empty into the duodenum through a common opening.\u00a0 Because the two duct systems share a common opening to the duodenum, gallstones (which form in the gall bladder) can potentially block both the secretion of bile and the secretion of pancreatic enzymes into the duodenum, depending on where the gallstones lodge.<\/p>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 654px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Ducts.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-104\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-1024x669.png\" alt=\"\" width=\"654\" height=\"427\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-1024x669.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-300x196.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-768x502.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-65x42.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-225x147.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts-350x229.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Ducts.png 1175w\" sizes=\"auto, (max-width: 654px) 100vw, 654px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">The ducts from the liver, gall bladder, and pancreas empty into the duodenum through a common opening. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.<\/figcaption><\/figure>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<h4>Large Intestine (Colon) &amp; Rectum<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 648px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/Colon.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-105\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-1024x683.png\" alt=\"\" width=\"648\" height=\"432\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-1024x683.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-300x200.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-768x512.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-65x43.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-225x150.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon-350x233.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/Colon.png 1438w\" sizes=\"auto, (max-width: 648px) 100vw, 648px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">The large intestine begins at the cecum and ends at the rectum and anal canal. Modified from Schuenke et al., Atlas of Anatomy, Thieme Medical Publishers, 2007.<\/figcaption><\/figure>\n<p>The ileum of the small intestine empties into the large intestine (<strong>colon<\/strong>) at the <strong>cecum<\/strong> (through the <strong>ileocecal junction,<\/strong> in the lower right quadrant of the abdomen).\u00a0 Hanging off of the inferior part of the cecum is the <strong>appendix<\/strong>, a small appendage which is filled with lymphatic tissue (lymphocytes, macrophages, and supporting tissues).\u00a0 Food passes from the cecum through the <strong>ascending, transverse, descending, and sigmoid colons<\/strong>.\u00a0 The junction between the ascending and transverse colons is called the <strong>hepatic flexure<\/strong>; the junction between the transverse colon and the descending colon is called the <strong>splenic flexure<\/strong>.\u00a0 The sigmoid colon passes into the pelvis where it becomes the <strong>rectum<\/strong>.\u00a0 Fecal waste leaves the body through the <strong>anal canal<\/strong> and the <strong>anus<\/strong>.<\/p>\n<p>The primary function of the large intestine is the absorption of water and vitamins.<\/p>\n<p>The passage of fecal waste out of the body is regulated by two sets of sphincter muscles in the anal canal.\u00a0 The <strong>internal anal sphincter<\/strong> is made of smooth muscle and is under involuntary control.\u00a0 Generally, sympathetic innervation keeps this sphincter closed and parasympathetic stimulation relaxes it.\u00a0 The <strong>external anal sphincter<\/strong> is made of skeletal muscle and is under voluntary control.\u00a0 This skeletal muscle sphincter is innervated by the pudendal nerve, which is comprised of ventral rami from S2, S3, and S4 spinal levels.<\/p>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<h4>Spleen<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 558px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/spleen-1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-106\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-1024x574.png\" alt=\"\" width=\"558\" height=\"313\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-1024x574.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-300x168.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-768x431.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-65x36.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-225x126.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1-350x196.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/spleen-1.png 1291w\" sizes=\"auto, (max-width: 558px) 100vw, 558px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">The spleen is located in the left upper quadrant of the abdomen.\u00a0 Modified from Netter Presenter.<\/figcaption><\/figure>\n<p>The <strong>spleen<\/strong> is an organ of both the immune and circulatory systems located in the posterior recess of the superior left abdomen, near the tail of the pancreas. Although it is not a digestive organ, the spleen is supplied by the arteries which also supply the organs of the digestive system.\u00a0 Importantly, the spleen&#8217;s venous drainage passes through the hepatic portal system (below).<\/p>\n<p>One of the important functions of the spleen is to destroy old red blood cells.\u00a0 This process produces bilirubin, a waste product. Bilirubin travels to the liver via the hepatic portal vein and is recycled by hepatocytes as a component of bile. As described above, bile is released to the small intestine where it emulsifies fats.<\/p>\n<p>The spleen is also a reservoir for blood.\u00a0 The blood supply to the spleen is huge and damage to the spleen can cause major blood loss.\u00a0 Since the organ is difficult to repair, it is often removed if it is damaged.<\/p>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<p>&nbsp;<\/p>\n<hr \/>\n<h5>KNOWLEDGE CHECKS<\/h5>\n<div id=\"h5p-5\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-5\" class=\"h5p-iframe\" data-content-id=\"5\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Abdomen - order digestive organs\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-6\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-6\" class=\"h5p-iframe\" data-content-id=\"6\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Abdomen - glands\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-7\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-7\" class=\"h5p-iframe\" data-content-id=\"7\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Abdomen - ducts\/gallstones\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-8\">\n<div class=\"h5p-content\" data-content-id=\"8\"><\/div>\n<\/div>\n<div id=\"h5p-9\">\n<div class=\"h5p-content\" data-content-id=\"9\"><\/div>\n<\/div>\n<div id=\"h5p-10\">\n<div class=\"h5p-content\" data-content-id=\"10\"><\/div>\n<\/div>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<h4>Arteries of the Digestive System<\/h4>\n<figure style=\"width: 403px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image1.jpeg\" alt=\"Artery supply to the digestive system\" width=\"403\" height=\"452\" \/><figcaption class=\"wp-caption-text\">Three unpaired branches of the abdominal aorta supply the organs of the digestive system. Modified from Snell, Clinical Anatomy for Medical Students, 5th edition, Little Brown, 1995.<\/figcaption><\/figure>\n<p>The blood supply to the gut tube is related to its development. Early in the embryo, the developing gut tube is supplied with blood by three unpaired branches of the abdominal aorta. The <strong>celiac trunk<\/strong> supplies the foregut (stomach to duodenum); the <strong>superior mesenteric artery<\/strong>\u00a0 supplies the midgut (duodenum to transverse colon); and the <strong>inferior mesenteric artery<\/strong> supplies the hindgut (descending colon to anus).\u00a0 There are anastomoses between these three arteries in areas that join foregut to midgut and midgut to hindgut.\u00a0 These patterns of circulation, established very early in development, persist throughout the formation of the convoluted gut tube and into the adult.<\/p>\n<p>The main arteries to the digestive system have extensive branching.\u00a0 The names of all of the many (many!) branches is beyond the scope of this course, but we will dissect some of them to get a sense of the vast branching patterns.\u00a0<em> Branches that you definitely need to know are in bold (and are included in the lab as well). <\/em><\/p>\n<p><strong>Celiac Trunk<\/strong><\/p>\n<p>The <strong>celiac trunk<\/strong> supplies the stomach, spleen, liver, and parts of the duodenum.\u00a0 The liver receives arterial blood from a branch of the celiac trunk called the <strong>proper hepatic artery <\/strong>(see Venous Drainage of the Gut and Spleen below for the other part of the liver&#8217;s blood supply).\u00a0 The spleen receives blood from a very distinctively curly artery (like a pig tail!) called the <strong>splenic artery<\/strong>.\u00a0 The stomach receives blood from multiple branches of the celiac trunk.\u00a0 If you see &#8220;gastro&#8221; in the name of an artery, it goes to the stomach.<\/p>\n<p>&nbsp;<\/p>\n<figure style=\"width: 652px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image2.jpeg\" alt=\"celiac trunk\" width=\"652\" height=\"429\" \/><figcaption class=\"wp-caption-text\">Branches of the celiac trunk supply the liver, spleen, stomach and part of the pancreas and esophagus. Modified from Hollinshead, Textbook of Anatomy, 4th edition, HarperCollin, 1985.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><iframe loading=\"lazy\" id=\"kaltura_player\" title=\"CeliacTrunkOverview\" src=\"https:\/\/cdnapisec.kaltura.com\/p\/1660902\/sp\/166090200\/embedIframeJs\/uiconf_id\/25717641\/partner_id\/1660902?iframeembed=true&#38;playerId=kaltura_player&#38;entry_id=1_mpwbeg4f&#38;flashvars[streamerType]=auto&#38;flashvars[localizationCode]=en_US&#38;flashvars[sideBarContainer.plugin]=true&#38;flashvars[sideBarContainer.position]=left&#38;flashvars[sideBarContainer.clickToClose]=true&#38;flashvars[chapters.plugin]=true&#38;flashvars[chapters.layout]=vertical&#38;flashvars[chapters.thumbnailRotator]=false&#38;flashvars[streamSelector.plugin]=true&#38;flashvars[EmbedPlayer.SpinnerTarget]=videoHolder&#38;flashvars[dualScreen.plugin]=true&#38;flashvars[Kaltura.addCrossoriginToIframe]=true&#38;wid=1_5viuxy38\" width=\"649\" height=\"401\" allowfullscreen=\"allowfullscreen\" frameborder=\"0\"><\/iframe><\/p>\n<p>&nbsp;<\/p>\n<div><strong>Superior Mesenteric Artery<\/strong><\/div>\n<div><\/div>\n<div>The <strong>superior mesenteric artery<\/strong> branches from the aorta approximately 1 inch inferior to the celiac trunk and supplies the part of the pancreas, small intestine, ascending colon, and transverse colon.\u00a0 Branches to the small intestine are called<strong> intestinal branches<\/strong>, and are found in the mesentery proper.\u00a0 The intestinal branches form extensive anatomoses called <strong>arcades<\/strong> within the mesentery proper.\u00a0 From the arcades, <strong>vasa recta<\/strong> run directly in to the small intestine.\u00a0 Branches to the large intestine all have &#8220;colic&#8221; in their names, and extend from the superior mesenteric artery to different regions of the large intestine.\u00a0 The <strong>marginal artery<\/strong> runs along the large intestine to provide anatomosis between the colic arteries from the superior mesenteric arteries and colic arteries from the inferior mesenteric artery.<\/div>\n<div><\/div>\n<div>\n<figure style=\"width: 544px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image3.jpeg\" alt=\"superior mesenteric artery\" width=\"544\" height=\"532\" \/><figcaption class=\"wp-caption-text\">Branches of the superior mesenteric artery supply most of the small intestine and parts of the pancreas and colon.\u00a0 Modified from Snell, Clinical Anatomy for Medical Students, 5th edition, Little Brown, 1995.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<\/div>\n<p><iframe loading=\"lazy\" id=\"kaltura_player\" title=\"SMAOverview\" src=\"https:\/\/cdnapisec.kaltura.com\/p\/1660902\/sp\/166090200\/embedIframeJs\/uiconf_id\/25717641\/partner_id\/1660902?iframeembed=true&#38;playerId=kaltura_player&#38;entry_id=1_gnn61sni&#38;flashvars[streamerType]=auto&#38;flashvars[localizationCode]=en_US&#38;flashvars[sideBarContainer.plugin]=true&#38;flashvars[sideBarContainer.position]=left&#38;flashvars[sideBarContainer.clickToClose]=true&#38;flashvars[chapters.plugin]=true&#38;flashvars[chapters.layout]=vertical&#38;flashvars[chapters.thumbnailRotator]=false&#38;flashvars[streamSelector.plugin]=true&#38;flashvars[EmbedPlayer.SpinnerTarget]=videoHolder&#38;flashvars[dualScreen.plugin]=true&#38;flashvars[Kaltura.addCrossoriginToIframe]=true&#38;wid=1_ikyaa5md\" width=\"649\" height=\"401\" allowfullscreen=\"allowfullscreen\" frameborder=\"0\"><\/iframe><\/p>\n<p>Inferior Mesenteric Artery<\/p>\n<p>The <strong>inferior mesenteric artery<\/strong> branches from the aorta just superior to the aortic bifurcation (near L3-L4 vertebral bodies).\u00a0 The inferior mesenteric artery supplies the descending colon, sigmoid colon, and rectum.\u00a0 Branches from the inferior mesenteric artery are named after the location on the colon they supply.\u00a0 For example, branches to the sigmoid colon are called <strong>sigmoid arteries<\/strong>.<\/p>\n<p>&nbsp;<\/p>\n<figure style=\"width: 494px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/image4.jpeg\" alt=\"inferior mesenteric artery\" width=\"494\" height=\"488\" \/><figcaption class=\"wp-caption-text\">Branches of the inferior mesenteric artery supply the descending and sigmoid colon as well as the superior rectum. Modified from Snell, Clinical Anatomy for Medical Students, 5th edition, Little Brown, 1995.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><iframe loading=\"lazy\" id=\"kaltura_player\" title=\"IMAOverview\" src=\"https:\/\/cdnapisec.kaltura.com\/p\/1660902\/sp\/166090200\/embedIframeJs\/uiconf_id\/25717641\/partner_id\/1660902?iframeembed=true&#38;playerId=kaltura_player&#38;entry_id=1_99lsmcuc&#38;flashvars[streamerType]=auto&#38;flashvars[localizationCode]=en_US&#38;flashvars[sideBarContainer.plugin]=true&#38;flashvars[sideBarContainer.position]=left&#38;flashvars[sideBarContainer.clickToClose]=true&#38;flashvars[chapters.plugin]=true&#38;flashvars[chapters.layout]=vertical&#38;flashvars[chapters.thumbnailRotator]=false&#38;flashvars[streamSelector.plugin]=true&#38;flashvars[EmbedPlayer.SpinnerTarget]=videoHolder&#38;flashvars[dualScreen.plugin]=true&#38;flashvars[Kaltura.addCrossoriginToIframe]=true&#38;wid=1_vzau7jon\" width=\"649\" height=\"401\" allowfullscreen=\"allowfullscreen\" frameborder=\"0\"><\/iframe><\/p>\n<h4><a id=\"portalvein\" href=\"\"><\/a>Venous Drainage of the Gut Tract and Spleen<\/h4>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 337px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/HepaticPortalVein.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-111\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein.png\" alt=\"\" width=\"337\" height=\"357\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein.png 751w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein-283x300.png 283w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein-65x69.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein-225x238.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/HepaticPortalVein-350x371.png 350w\" sizes=\"auto, (max-width: 337px) 100vw, 337px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">All of the veins which drain the organs of the digestive tract, as well as those that drain the spleen, empty into the hepatic portal vein.\u00a0 Modified from Netter Presenter.<\/figcaption><\/figure>\n<p>The return of venous blood from the GI tract involves a <strong>portal system<\/strong>: a system of veins that connects two capillary beds. In this case, the first set of capillary beds are within the walls of the gut tube (where nutrients are absorbed) and in the spleen (which destroys red blood cells); the second set of capillary beds is within the liver (where the absorbed nutrients, as well as bilirubin from the spleen, are processed).<\/p>\n<p>All of the venous drainage from the capillary beds of the GI tract and spleen ends up in the <strong>hepatic portal vein<\/strong>, a huge vein leading into the liver. After being processed in the capillaries of the liver, blood leaves the liver through the <strong>hepatic veins<\/strong> and enters the <strong>inferior vena cava<\/strong> (and the systemic circulation).<\/p>\n<p><a href=\"#LO\">Back to Top<\/a><\/p>\n<hr \/>\n<h3><a id=\"urinary\" href=\"\"><\/a>Urinary Tract<\/h3>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 454px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/PosteriorAbWall.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-112\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-1024x712.png\" alt=\"\" width=\"454\" height=\"316\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-1024x712.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-300x209.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-768x534.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-65x45.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-225x156.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall-350x243.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/PosteriorAbWall.png 1100w\" sizes=\"auto, (max-width: 454px) 100vw, 454px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">Structures of the posterior abdomen include the kidney and ureters as well as some muscles that move the lower limb. Modified from Netter Presenter.<\/figcaption><\/figure>\n<p>The <strong>kidneys<\/strong> are located in the superior abdomen, posterior to all of the organs of the digestive system. Although they are not large organs, the kidneys receive 25% of the cardiac output of blood, a testament to their critical function in maintaining appropriate blood volume, pressure, and concentration.\u00a0 All of the kidney&#8217;s vasculature as well as the <strong>ureter<\/strong> enter or exit the organ from the medial side (at the hilus of the kidney).\u00a0 Usually there is a single <strong>renal artery and vein<\/strong>, as well as a single ureter. The large renal arteries branch directly off the aorta; the renal veins empty into the inferior vena cava.<\/p>\n<p>The <strong>adrenal (suprarenal) glands<\/strong> sit on top of the kidneys, but are not functionally associated with them.\u00a0 These endocrine glands secrete epinephrine and norepinephrine into the blood stream to elicit a systemic sympathetic response.\u00a0 They also secrete corticosteroids and androgens, among other hormones.<\/p>\n<p>The <strong>ureters<\/strong> are extremely muscular tubes (smooth muscle). Peristaltic contractions of the walls of the ureters move urine from the kidneys to the urinary bladder. Urine is not altered as it travels down the ureter.\u00a0 The ureters pierce the posterior wall of the <strong>urinary bladder<\/strong>. Their oblique course through the muscular wall of the bladder acts as a valve, closing off the ureteric opening when the bladder is full. This prevents urine from backing up from the urinary bladder to the kidneys.<\/p>\n<p>The urinary bladder is located in the pelvis, but can extend into the lower abdomen when it is distended. Since it stores urine until it is possible (or necessary) to eliminate it, the urinary bladder can stretch to many times its resting size. The epithelium lining the urinary bladder is able to stretch as the organ distends. The organ has extremely thick muscular walls (smooth muscle), which contract to eliminate urine.<\/p>\n<p>At the base of the bladder, at the junction with the <strong>urethra<\/strong>, is an involuntary <strong>internal urethral sphincter<\/strong> (made of smooth muscle) which prevents the bladder from emptying; it contracts involuntarily (so we don\u2019t have to think about it).\u00a0 Sympathetics generally keep the sphincter closed; parasympathetic stimulation relaxes the sphincter.<\/p>\n<figure id=\"attachment_99\" aria-describedby=\"caption-attachment-99\" style=\"width: 706px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/wisc.pb.unizin.org\/app\/uploads\/sites\/7\/2019\/02\/urethra.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-113\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-1024x409.png\" alt=\"\" width=\"706\" height=\"282\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-1024x409.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-300x120.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-768x307.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-65x26.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-225x90.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra-350x140.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/114\/2020\/06\/urethra.png 1456w\" sizes=\"auto, (max-width: 706px) 100vw, 706px\" \/><\/a><figcaption id=\"caption-attachment-99\" class=\"wp-caption-text\">The female and male urethrae. Both pass through a skeletal muscle (voluntary) sphincter in the urogenital diaphragm. Modified from Netter Presenter.<\/figcaption><\/figure>\n<p>Urine leaves the bladder through the urethra.\u00a0 In females, the urethra is fairly short. It passes through a sheet of skeletal muscle (the <em>urogenital diaphragm<\/em>) which contains the <strong>external urethral sphincter<\/strong> (skeletal muscle; a voluntary sphincter).\u00a0 In males, the urethra is much longer and consists of 3 distinct segments:<\/p>\n<ul>\n<li>the <strong>prostatic urethra<\/strong> (which passes through the prostate gland)<\/li>\n<li>the <strong>membranous urethra<\/strong> (which passes through the urogenital diaphragm &amp; is the site of the external urethral sphincter)<\/li>\n<li>the<strong> penile urethra<\/strong> (which passes through the erectile tissue of the penis).<\/li>\n<\/ul>\n<p>More about this when we talk about the pelvis!!<\/p>\n<p>There are two important muscles in the posterior abdomen which are involved in moving the lower limb:\u00a0 <strong>psoas major<\/strong> and <strong>quadratus lumborum<\/strong>. We will discuss them with the lower limb.<\/p>\n<hr \/>\n<h4>KNOWLEDGE CHECKS<\/h4>\n<div id=\"h5p-11\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-11\" class=\"h5p-iframe\" data-content-id=\"11\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Abdomen - urinary organs\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-12\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-12\" class=\"h5p-iframe\" data-content-id=\"12\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Abdomen - sphincters and venous drainage\"><\/iframe><\/div>\n<\/div>\n","protected":false},"author":14,"menu_order":1,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-114","chapter","type-chapter","status-publish","hentry"],"part":95,"_links":{"self":[{"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/chapters\/114","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/wp\/v2\/users\/14"}],"version-history":[{"count":2,"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/chapters\/114\/revisions"}],"predecessor-version":[{"id":161,"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/chapters\/114\/revisions\/161"}],"part":[{"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/parts\/95"}],"metadata":[{"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/chapters\/114\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/wp\/v2\/media?parent=114"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/pressbooks\/v2\/chapter-type?post=114"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/wp\/v2\/contributor?post=114"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/anatomy\/wp-json\/wp\/v2\/license?post=114"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}