GI Tract Anatomy PDF

ESOPHAGUS • Tubular structure about 25 cm long. • Begins at the level of C6. • Pierces the diaphragm atT10. • It is divided into 3 parts: • 1- Cervical. • 2- Thoracic. • 3- Abdominal. CERVICALPART •Posteriorly Vertebral column. •Laterally: Lobes of the thyroid gland. •Anteriorly: Trachea and t...

ESOPHAGUS • Tubular structure about 25 cm long. • Begins at the level of C6. • Pierces the diaphragm atT10. • It is divided into 3 parts: • 1- Cervical. • 2- Thoracic. • 3- Abdominal. CERVICALPART •Posteriorly Vertebral column. •Laterally: Lobes of the thyroid gland. •Anteriorly: Trachea and the recurrent laryngeal nerves. THORACICPART •In the thorax, it passes downward and to the left through superior then to posterior mediastinum •At the level of the sternal angle, the aortic arch pushes the esophagus again to the midline. POSTERIOR RELATIONS ANTERIOR RELATIONS • • • • • Trachea Left recurrent laryngeal nerve Left principal bronchus Pericardium Left atrium • • • • • Bodies of the thoracic vertebrae Thoracic duct Azygos vein Intercostal arteries Descending thoracic aorta (at the lower end) ABDOMINALPART • In the Abdomen, the esophagus descends for 1.3 cm and joins the stomach. • Anteriorly, left lobe of the liver. • Posteriorly, left crus of the diaphragm. •Fibers from the right crus of the diaphragm form a sling around the esophagus. •At the opening of the diaphragm, the esophagus is accompanied by: • The two vagi nerves • Branches of the left gastric vessels • Lymphatic vessels. ESOPHAGEALCONSTRICTIONS The esophagus has 3 anatomic constrictions. • The first is at the junction with the pharynx (pharyngeoesophageal junction). • The second is at the crossing with the aortic arch and the left main bronchus. • The third is at the junction with the stomach. They have a considerable clinical importance. • Why? 1. They may cause difficulties in passing an endoscope. 2. In case of swallowing of caustic liquids (mostly in children), this is where the burning is the worst and strictures develop. 3. The esophageal strictures are common sites for the development of esophageal carcinoma. ARTERIALSUPPLY •Upper third by the inferior thyroid artery. •The middle third by the thoracic aorta. •The lower third by the left gastric artery. VENOUS DRAINAGE VENOUSDRAINAGE •The upper third drains in into the inferior thyroid veins. •The middle third into the azygos veins. •The lower third into the left gastric vein, which is a tributary of the portal vein. •(Clinical correlate: Esophageal varices.) CARDIACORIFICE •It is the site of the gastro- esophageal sphincter. •It is a physiological rather than an anatomical, sphincter. •Consists of a circular layer of smooth muscle (under vagal and hormonal control). •Function: •Prevents (GER) regurgitation (reflux) •Clinical correlate. Notice the abrupt mucosal transition from esophagus to stomach (Z- line) Stomach • The stomach is the most dilated part of the gastrointestinal tract and has a J-like shape • Positioned between the abdominal esophagus and the small intestine • The stomach is in the epigastric, umbilical, and left hypochondrium regions of the abdomen. Stomach • The stomach is the most dilated part of the gastrointestinal tract and has a J-like shape • Positioned between the abdominal esophagus and the small intestine • The stomach is in the epigastric, umbilical, and left hypochondrium regions of the abdomen. Stomach • The stomach is devided into four regions: Cardia Fundus Body Pyloric part • The stomach has some distintinctive features: Greater and lesser curvatures Cardial notch Angular incisure Arterial supply to the stomach • the left gastric artery from the celiac trunk, • the right gastric artery, often from the hepatic artery proper, • the right gastro-omental artery from the gastroduodenal artery, • the left gastro-omental artery from the splenic artery, and • the posterior gastric artery from the splenic artery (variant and not always present). Small Intestine Small Intestine Definition A part of the GI tract which extends from the stomach (pyloric orifice) to the large intestine (ileal orifice) Function Final stages of food digestion Absorption of nutrients and water Parts Duodenum, jejunum, ileum All three parts are covered with the greater omentum anteriorly Blood supply Arteries: celiac trunk, superior mesenteric artery Veins: hepatic portal vein, superior mesenteric vein Clinical relations Diarrhea, obstructive disorders, infectious diseases, neoplastic growths, congenital conditions, duodenal ulcer Function • Absorption, carbohydrates and proteins are absorbed in the duodenum and jejunum respectively. • The jejunum also functions to absorb most fats. • The ileum function involves absorption of vitamin B12, bile salts and all digestion products which were not absorbed in duodenum and jejunum. • All three small intestine segments absorb water and electrolytes. Duodenum • 25 cm long • Shortest part of the intestine • The proximal 2.5cm is intraperitoneal – The remainder is retroperitoneal • Form: An elongated ´C´that lies between the level of L1 and L3 • The head & uncinate process of the pancreas lie within the concavity (The ¨C¨) • The duodenum lies above the level of the umbilicus. Duodenum Sections First part Superior part Continuation from the pylorus to transpyloric plane The duodenal bulb is the first part Mobile, and connected to the liver by the hepatoduodenal ligament Ends at the superior duodenal flexure. Second part Descending part Begins at the superior duodenal flexure. Makes a sharp turn medially into the inferior duodenal flexure, the end of the descending part The pancreatic duct and common bile duct enter the descending duodenum, through the major duodenal papilla. Third part Horizontal part inferior part Begins at the inferior duodenal flexure and passes transversely to the left, passing in front of the inferior vena cava, abdominal aorta and the vertebral column. Fourth part Ascending part Passes upward, joining with the jejunum at the duodenojejunal flexure. Jejunum • The jejunum represents the proximal two-fifths. • Begins at the duodenojejunal flexure. • Intraperitoneal • The wall of the jejunum is thicker and its lumen is wider than in ileum • Additionally, the inner mucosal lining of the jejunum is characterized by numerous prominent folds that circle the lumen (plicae circulares). • The less prominent arterial arcades and longer vasa recta (straight arteries) compared with those of the ileum are a unique characteristic of the jejunum. Ileum • The ileum makes up the distal three fifths of the small intestine • Mostly in the right lower quadrant. • The ileum has thinner walls, fewer and less prominent mucosal folds (plicae circulares), shorter vasa recta, more mesenteric fat, and more arterial arcades, has an external diameter of about 3 cm, an internal diameter of about 2.5 cm. Jejunum: lymphatic drainage & innervation • The lymphatic system of the small intestine regulates tissue fluid homeostasis, participates in immune surveillance, and transports dietary fat and fatsoluble vitamins from the gut lumen. • The jejunum is innervated by parasympathetic and sympathetic fibers via the superior mesenteric plexus. The visceral sensation of pain arising from the jejunum is poorly localized and is usually referred to the periumbilical region. • The ileum terminates at the ileal orifice (ileocecal junction) where the cecum of the large intestine begins. • At the ileocecal junction, the lamina muscularis of the ileum protrudes into the lumen of the cecum forming a structure called the ileocecal fold. • These muscular fibers form a muscular ring within the fold called the ileocecal sphincter which controls the emptying of ileal content into the large intestine Large Intestine Large intestine: colon • The large intestine extends from the distal end of the ileum to the anus • Distance of approximately 1.5 m in adults. (4.9ft) • It absorbs fluids and salts from the gut contents, thus forming feces • Consists of the cecum, appendix, colon, rectum, and anal canal. The large intestine has several distinct anatomical characteristics; the omental appendices, teniae coli and haustra: Omental or epiploic appendages are fat filled pouches of peritoneum that are attached externally to the walls of the large intestine. Teniae coli are three longitudinal bands of smooth muscle located underneath the peritoneum that extend along certain sections of the large intestine. Their contractions facilitate the peristaltic action. Haustra are sacculations that occur along the large intestine, providing it with its characteristic ‘baggy’ aspect. Layers: -Taenia Libera -Taenia mesocolica -Taenia omentalis Cecum • The cecum is the first part of the large intestine. • It is inferior to the ileocecal opening and in the right iliac fossa. • The cecum is continuous with the ascending colon at the entrance of the ileum and is usually in contact with the anterior abdominal wall. • The appendix is attached to the posteromedial wall of the cecum, just inferior to the end of the ileum. Appendix • The APPENDIX is a narrow, hollow, blind-ended tube connected to the cecum. • It has large aggregations of lymphoid tissue in its walls and is suspended from the terminal ileum by the mesoappendix, which contains the appendicular vessels. Rectum & anal canal • Extending from the sigmoid colon is the rectum. • The rectosigmoid junction is usually described as being at the level of vertebra SIII or at the end of the sigmoid mesocolon because the rectum is a retroperitoneal structure. Rectum & anal canal VASCULATURE The arterial supply to the rectum and anal canal includes: • The superior rectal artery from the inferior mesenteric artery. • The middle rectal artery from the internal iliac artery. • The inferior rectal artery from the internal pudendal artery (from the internal iliac artery). Anal Canal 2.5 to 3.5 cm long  Begins anorectal ring  Ends at the intersphincteric groove.  Externally, is surrounded by the internal and external anal sphincter muscles. The superior half of the anal canal contains a series of longitudinal ridges called the anal columns (of Morgagni), which extend from the anorectal junction superiorly to the anal valves inferiorly. The anal valves form an irregular line called the dentate or pectinate line (important anatomic landmark.)