GROSS ANATOMY OF THE FOREGUT, MIDGUT, AND HINDGUT REGIONS (Grant's Dissector (16th Ed.) pp. 110-131) TODAY’S GOALS: 1. Identify the coverings and contents of the scrotum, spermatic cord, and testis, and the anatomy related to a vasectomy procedure 2. Explore the abdominal contents in situ 3. Understand the important peritoneal relationships I. Peritoneal Reflections DISSECTION NOTES: Reflect the anterior abdominal wall (Dissector p. 111, Fig. 4.16) to enable access to the abdominal cavity and its contents. Make a vertical incision through the linea alba just to the left of the midline from the xiphoid process to the pubis. Separate the anterior wall from the abdominal contents with your hand. Carefully cut the abdominal wall along the right costal margin and continue the incision inferiorly in the midaxillary line to the iliac crest. Note the falciform ligament as you begin reflecting this flap from the right upper Quadrant. It connects the abdominal wall from the umbilicus to the surface of the liver. Cut it close to the abdominal wall and reflect the right abdominal wall inferiorly. This preserves the relationships of the iliac vessels and structures passing to the umbilicus from the pelvis. On the left, cut the abdominal wall just superior to the inguinal ligament and reflect the wall laterally. On the inner surface of the right anterior abdominal wall flap note the following peritoneal folds (Dissector p. 112, Fig. 4.17): • Median umbilical fold/ligament: contains the urachus, a remnant of the allantoic duct; extends from the apex of the bladder to the umbilicus • Medial umbilical fold/ligament: contains the obliterated umbilical artery (paired) • Lateral umbilical fold/ligament: consists of peritoneum covering the inferior epigastric vessels (paired) Examine the area just lateral to the lateral umbilical fold and identify a slight depression in the peritoneal lining. This marks the location of the deep inguinal ring. II. Inspection of Abdominal Cavity and Viscera (Inspect. Do not dissect at this time.) The abdominal and pelvic cavities, like other body cavities, are lined by serous membranes that secrete a clear, serous fluid to permit movement of organs. This membrane is a continuous sheet that is given different terms depending on structures it covers. Peritoneum that covers the inner surface of the abdominal and pelvic walls is called parietal peritoneum; that which covers surfaces of organs is called visceral peritoneum. The potential space between these layers containing a small amount of serous fluid is the peritoneal cavity. Identify the peritoneal folds: • Greater omentum (Dissector p. 114, Figs. 4.18, 4.19): this peritoneal fold forms a broad fat-filled apron that hangs from the borders of the greater curvature of the stomach and transverse colon, covering most of the intestines • Lesser omentum (Dissector p. 118, Fig. 4.24): a peritoneal extension between the inferior surface of the liver and the first part of the duodenum and lesser curvature of the stomach. Based on these connections, it is divided into two ligaments: the hepatogastric ligament and the hepatoduodenal ligament. 13 Understand the ‘sac within a sac’ concept. (Dissector p. 115, 116, Fig. 4.20, 4.22) • Greater peritoneal sac: the main part of the peritoneal cavity, i.e., the space first entered when the abdominal wall flaps were reflected • Lesser peritoneal sac: also called the omental bursa; a small sac within the peritoneal cavity behind the lesser omentum • Epiploic foramen (foramen of Winslow): the “entrance” to the omental bursa just posterior to the free edge of the hepatoduodenal ligament Abdominal Viscera In Situ (Dissector p. 114, Figs. 4.18, 4.19) Understand the difference between retroperitoneal and peritoneal structures. Starting at the abdominal end of the esophagus, follow the gastrointestinal tract distally and identify its components (Dissector 131, Fig. 4.44). Stomach • lesser curvature with attached lesser omentum • greater curvature with attached greater omentum • also find the gastrocolic and gastrosplenic (gastrolienal) ligaments • pylorus – junction between the stomach with the duodenum Small Intestine • duodenum – its first part is mobile (intraperitoneal); its 2nd, 3rd, and most of the 4th portions are secondarily retroperitoneal; the distal end of the 4th part is mobile near the duodenojejunal flexure (location of the ligament of Treitz, a surgical landmark) • jejunum – intraperitoneal. Is suspended by the mesentery of the small intestine, which extends from the posterior abdominal wall to the ileocecal junction • ileum – intraperitoneal. Is continuous with the jejunum and also suspended by the mesentery of the small intestine; it connects to the ascending colon at the cecum Large Intestine • cecum – a blind-ended pouch and the first part of ascending colon. It is located at the junction with the ileum and from it extends a narrow fingerlike projection, the vermiform appendix; the appendix is attached to the posterior abdominal wall by the mesoappendix • ascending colon – secondarily retroperitoneal. It is continuous with the transverse colon at the right colic or hepatic flexure • transverse colon – intraperitoneal (via transverse mesocolon) and very mobile; extends from the right colic flexure to the left colic or splenic flexure; it is also attached to the greater omentum • descending colon – secondarily retroperitoneal. It is continuous distally with the sigmoid colon • sigmoid colon – intraperitoneal ( via sigmoid mesocolon which connects the sigmoid colon to the posterior abdominal wall). The sigmoid colon is a mobile, “S”-shaped portion of the large intestine that descends into the pelvic cavity as the rectum 14 Liver (Fig. 4.21) • falciform ligament – a double layer of parietal peritoneum that spans the space between the inner surface of the anterior abdominal wall and the anterior surface of the liver. It contains the ligamentum teres (round ligament of the liver), a remnant of the left umbilical vein in its inferior free margin. It divides the liver into right and left anatomic lobes. Gallbladder • Emerges from under the cover of the inferior border of the liver at the junction of the right costal margin and rectus abdominis muscle Peritoneal Gutters 1. Passages formed by folds of peritoneum around abdominal viscera 2. Paracolic gutters – lateral gutters formed between the ascending and descending parts of the colon and the lateral walls of the abdomen 3. Mesenteric gutters – formed by the oblique course of the root of the small intestine mesentery from the duodenojejunal flexure to the distal ileum Q. What is located or normally present in the peritoneal cavity, or for that matter, in the pleural or pericardial cavities? PEER TEACHING GUIDE: Organize your narrative to minimally include: 1. Demonstration and/or discussion of the fascial coverings and contents of the spermatic cord. 2. Demonstration and/or discussion of the coverings of the testis, including the two layers of the tunica vaginalis. 3. Demonstration of the internal anatomy of the testis, including the tunica albuginea, septae/lobules, seminiferous tubules, and the different parts of the duct system. 4. Demonstration of the peritoneal folds on the inner surface of the anterior abdominal wall and discussion of the contents contained within each. 5. Provide a “tour” of the abdominal viscera in situ and a demonstration of the following peritoneal structures: greater and lesser omentum, falciform ligament, the mesentery, sigmoid mesocolon, and their relevant relationships. Demonstration of the greater and lesser peritoneal sacs and the passageway (i.e., epiploic foramen) connecting them. 15 CELIAC TRUNK AND FOREGUT DERIVATIVES (Grant's Dissector [16th Ed.] pp. 117-122) Today’s Goals: 1. Inspect the stomach and its parts 2. Dissect the structures (portal triad) in the hepatoduodenal ligament 3. Dissect the branches emanating from the celiac trunk (one of the unpaired arteries of the abdominal aorta) 4. Inspect the liver, its surfaces and lobes 5. Mobilize the spleen and observe its surfaces 6. Inspect the gallbladder DISSECTION NOTES: Before proceeding with dissection, refer to the Dissector p. 117, Fig, 4.23 and review the parts of the stomach: Greater and Lesser Curvatures Cardia Fundus Body Pylorus and the liver (Dissector p. 121, Fig, 4.29): Right lobe Separated by the falciform ligament Left lobe Diaphragmatic surface Visceral surface and porta hepatis (gateway for nerves, vessels, and lymphatics to/from the liver) Inferior border A. Portal Triad Structures and Celiac Trunk (Dissector p. 118, Figs. 4.24 and 4.25) Access to the celiac trunk and its branches is best achieved by initially dissecting through the anterior peritoneal layer of the hepatoduodenal ligament. Locate the hepatoduodenal ligament (right free border of the lesser omentum). Q. What are the contents of the hepatoduodenal ligament and their spatial relationships to one another? Open the hepatoduodenal ligament and identify the portal triad structures: bile duct, hepatic artery proper, hepatic portal vein. The bile duct is formed by the union of the cystic duct and common hepatic duct. The common hepatic duct, in turn, is formed by the union of the right and left hepatic ducts. Identify each of these structures by dissecting the tissue around them. The tough “stringy” material you encounter in this process are autonomic nerve fibers to the liver. Lymphatic vessels and hepatic lymph nodes are also contained within the hepatoduodenal ligament. Clean the hepatic artery proper in