GI+Track+and+Associated+Organs

=**GI Track and Associated Organs**=

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 * Be able to describe the following viscera of the abdominal cavity and their major anatomical components and relationships.**

**Esophagus**

 * 1. Abdominal part of esophagus**

The esophagus passes through esophageal hiatus where diaphragm fibers split apart to allow entry into abdominal cavity. It is anchored to the diaphragm firmly by phrenicoesophageal ligaments. The inferior esophageal sphincter has circular muscle bands and is controlled by part of the diaphragm. The esophagogastric junction is where mucosal epithelium changes over to gastric epithelium, forming a Z-line. Anterior / posterior vagal trunks also pass through hiatus to give branches to stomach.

Clinical correlation: Hiatal hernia is passage of part of the stomach through the hiatus into the thoracic cavity, often results in Pyrosis (heartburn). This is caused by loosening of the phrenicoesophageal ligaments which holds the esophagus at the hiatus at the level of the esophagogastric junction z-line. As the herniation progresses, the sphincter function is lost and stomach acid enters the esophagus. This condition can be treated by surgically pushing the stomach back below the hiatus and tightening the hiatus opening.

**Stomach**

 * 2A. Identify**

__Cardiac and pylorus orifices__ Cardiac orifice is the entrance to the stomach from the esaphagus, the pylorus orifice is the exit of the stomach to the duodenum.

The right crus anchors the diaphragm to the vertebrae, allowing muscle contraction to close the cardiac orifice. The phrenicoesophageal ligament anchors to esophagus at the diaphragm hiatus at the esophagogastric junction z-line. Vagal trunks follow the esophagus down through the hiatus; some split and become gastric trunks and innervate the stomach, while others continue on to other visceral organs.

__Relationship with greater and lesser omentum__ The greater omentum attaches to the greater curvature of the stomach, anteroinferiorly. The lesser omentum attaches to the lesser curvature of the stomach posterosuperiorly, and the inferior portion of the liver. The greater omentum contains the gastrocolic ligament, the gastrophrenic ligament, and the gastrosplenic ligament. The lesser omentum houses the hepatogastric and the hepatoduodenal ligaments.

__Anterior and posterior surfaces__ The anterior surface faces the greater sac while the posterior surface faces the lesser sac of the peritoneum.

__Fundus and cardiac notch__ The fundus is the superior enlargment of the stomach to the left of the esophagus, separated from the esophagus by the cardiac notch.

__Body and angular incisure__ The body is the central portion of the stomach that ends at the acute turn known as the angular incisure, located at the base of the lesser curvature of the stomach. The inferior border of the body is the pyloric antrum, the superior border is the fundus, and the medial border is the cardia.

__Pyloric antrum__ Pyloric antrum is region of the stomach proximal to the pyloric canal, inferior to the body of the stomach.

__Pylorus, pyloric sphincter, pyloric canal__ The pylorus contains the pyloric sphincter and lies just distal to the pyloric canal.

__Mucous membrane appearance, gastric folds (rugae)__ Increase surface area in the stomach resulting from gastric folds (rugae) with canals between the folds. Also helps direct agitated food towards the pyloric antrum.

__Muscles of stomach wall__ The muscles of the stomach wall are threefold: internal specialized oblique muscle, circular smooth muscle in the middle, longitudinal smooth muscle on the external surface. This circular smooth muscle is especially pronounced at the pyloric orifice where it is greatly thickened to form the pyloric sphincter.

When the smooth muscle of the gastric mucosa is contracted, it is thrown into longitudinal gastric folds and gastric canals. Gastric canals form because of the firm attachment of the gastric mucosa to the muscular layer.

Anteriorly, the stomach is related to the diaphragm, the left lobe of the liver, and the anterior abdominal wall. The anterior portion of the stomach helps define the posterior border of the greater sac.
 * 2B. Describe relations of stomach with adjacent structures.**

Posteriorly, the stomach is related to the omental foramen and the pancreas. The posterior surface of the stomach forms most of the anterior wall of the lesser sac, connected to the greater sac by the omental foramen.

The bed of the stomach on which the stomach rests in supine position from superior to inferior are the left dome of the diaphragm, the spleen, left kidney and suprarenal gland, splenic artery, pancreas, and transverse mesocolon and colon.

all 3 branches of celiac trunk supply it. -left gastric a. supplies lesser curvature (in lesser omentum) -splenic a. travels behind stomach to supply the spleen and also branches to fundus of stomach via short gastric arteries. -left gastro-omental artery (branch of splenic) travels inferiorly down the greater curvature of the stomach, supplying the body. -Common hepatic a. gives off gastroduodenal a. which gives off right gastro-omental which supplies greater curvature and anastomoses with left gastro-omental. -Right gastric a. comes off of proper hepatic a. and supplies lesser curvature (within lesser omentum).
 * 2C. Describe the blood supply of the stomach**

**Small Intestine**

 * 3A. Identify and distinguish the 3 major divisions of the small intestine: duodenum, jejunum, and ilium.**

The duodenum is the first part of the small intestine, approximately 12 finger lengths in length. It contains four regions, superior, descending, horizontal, and ascending regions, and is arranged in a C-shape, looping inferiorly and then superiorly below the stomach. Along the descending region, the major and minor duodenal papilla open up. Both major and minor duodenal papilla secrete digestive enzymes from the pancreas, but only the major papilla secretes bile. The bile duct and main pancreatic duct come together to form the hepatopancreatic ampulla, which then enters the duodenum through a sphincter-like valve, the major duodenal papilla. The inside surface of the duodenum is covered with circular folds called plicae to increase its surface area. Lastly, at the acute angle or flexure between the apex of the ascending duodenum and jejunum, the suspensory ligament of duodenum (Treitz) anchors the duodenum to the diaphragm, continuous with the right crus.

The jejunum and the ileum make up the next 7 and 10-12 feet of intestine with a gradual change between the two parts of intestine. Generally, the jejunum is thicker, with less fat, numerous plicae, and few Peyer’s patches, compared to the ileum. Additionally, the arteries of the jejunum are arranged with few arcades and long vasa recta extending to the length of jejunum while the ileum arteries have many arcades and short vasa recta. The jejunum tends to appear more pink than the ileum due to increased vascularization.


 * 3B. Describe the blood supply of the small intestine.**

The blood supply of the duodenum comes primarily from the gastroduodenal artery branch from the celiac artery and the superior mesenteric artery. The gastroduodenal artery branches off to give the supraduodenal artery and the superior pancreaticoduodenal artery which supply the duodenum proximal to the entry of the bile duct in the descending part of the duodenum. The superior mesenteric artery gives off the inferior pacreaticoduodenal artery which supplies the duodenum distal to the entry of the bile duct. The superior and inferior pancreaticoduodenal arteries wrap around the duodenum like upper and lower “fangs.” The duodenal veins follow the arteries and drain into the portal vein either directly or through the superior mesenteric and splenic veins.

__Clinical correlate: Arteriomesenteric Occlusion of Duodenum__ The superior mesenteric artery can squeeze the duodenum up against the aorta, causing a blockage. This typically happens in a tall patient with a long trunk with weak abdominal muscles: the intestines hanging down put tension on the mesenteric artery, squeezing the duodenum. Treatment involves lying down after a meal or working out the abdominal muscles.

The superior mesenteric artery supplies the jejunum and the ileum. The superior mesenteric artery arises from the abdominal aorta at the L1 vertebrae level, 1 cm inferior to the celiac trunk and runs between layers of mesentery, sending 15-18 branches to the jejunum and ileum. These arteries united to form arterial arcades which give rise to straight arteries, the vasa recta. The superior mesenteric vein drains the jejunum and ileum and lies anterior and to the right of the superior mesenteric artery in the root of the mesentery. The superior mesenteric vein ends posterior to the neck of the pancreas where it unites with the splenic vein to form the portal vein.

**Large Intestine**

 * 4A. Identify the various parts, their location, and relationships to other abdominal structures.**

The large intestine includes the cecum and appendix, the ascending, transverse, descending, and sigmoid colon, the rectum, and the anal canal. Its main function is the absorption of water and the formation of fecal material.

The cecum is the proximal part of the large intestine and is continuous with the ascending colon. It is connected with the ileum by the ileocecal orifice and also contains the opening for the orifice of the appendix.

The ascending colon is separated from the anteriolateral abdominal wall by the greater omentum.

The large intestine has a number of distinguishing features: The Teniae Coli, three longitudinal bands of smooth muscle running the length of the colon(mesocolic, omental, and free); the Haustra, outpouching sacculated portions of the colon wall retained by the teniae coli; Omental appendices, lobular fatty projections from the teniae coli, and the Semilunar folds, lateral bands of tissue separating the outpouchings of the haustra.

The left colic flexure (splenic flexure) is the site for attachment of the phrenicocolic ligament, which connects the colon to the diaphragm.

The rectum lacks the teniae coli, haustra, and visceral peritoneum, exposing just the longitudinal smooth muscle.


 * 4B. Describe the blood supply of the large intestine.**

The superior mesenteric artery supplies the cecum and appendix, ascending colon, and greater part of the transverse colon. The inferior mesenteric artery supplies the distal part of the transverse colon, descending colon, and the rectum.

Branches of the superior mesenteric artery and the structures they supply include: -The middle colic artery, supplying the proximal transverse colon -The right colic artery, supplying the ascending colon -The ileocolic artery, supplying the ileocecal junction and the cecum, and -The marginal artery of Drummond, providing a redundant anastomic supply to the area infused by the branches above.

Branches of the inferior mesenteric artery and the structures they supply include: -The left colic artery, supplying the distal transverse colon and the descending colon -The sigmoidal artery, supplying the sigmoid colon, and -The superior rectal artery, supplying the rectum.

The superior and inferior mesenteric veins follow their respective arteries. The inferior mesenteric vein merges with the splenic vein which then merges with the superior mesenteric vein to form the portal vein.


 * 4C. Identify the appendix and its relationships.**

The appendix arises from the posteriomedial aspect of the cecum inferior to the ileocecal junction 65% of the time. 32% of the time, the appendix will be in pelvic orientation. The teniae coli from the cecum converge at the appendi to form the ileocecal valve. The blood supply of the cecum and appendix is provided by the ileocecal artery and the appendicular artery.


 * 4D. Describe the teniae coli, omental appendices, haustra, and semilunar folds.**

__Teniae Coli__ The teniae coli are 3 bands of longtitudinal smooth muscle that run the length of large intestine. They converge at the appendix. The three bands are: Mesocolic, Omental, and Free.

__Omental Appendices__ Little lobules of fat that project along the exterior wall of large intestine, associated with teniae coli.

__Haustra__ Bulges in the wall, corresponding to compartments in the lumen of the large intestine, that are created by the presence of teniae coli. They are separated by semilunar folds and, together, act with smooth muscle to regulate movement of materials.

__Semilunar folds__ Ridges that separate adjacent haustra. See Haustra.


 * 4E. Understand the location and relationships of the colic flexures.**

The junction between the ascending and transverse colon is called the right colic or hepatic flexure while the junction between the transverse and descending colon is called the left colic or splenic flexure.

The left colic flexure is more superior, more acute, and less mobile than the right colic flexure and lies anterior to the inferior part of the left kidney, attaching to the diaphragm through the phrenicocolic ligament.

**Liver**

 * 5A. Define its major function.**

The liver has metabolic activies, stores glycogen, and secretes bile.

Anatomical lobes (determined by ligaments): Right, Left, Caudate (superior posterior), Quadrate (inferior posterior) Functional lobes (determined by blood supply):Right, Left See p. 41
 * 5B. Describe the lobes of the liver.**

The liver is in the right upper quadrant closely associated with the Gallbladder, overlies the stomach and is above the right kidney and colon.
 * 5C. Define the relations of the liver to other abdominal structures.**

Porta Hepatis is where the bile duct, hepatic artery, portal vein enter the liver on the posterior surface.
 * 5D. Describe the porta hepatis and its contents.**

Peritoneal ligaments: - The falciform ligament extends from the liver to the anterior abdominal wall and the diaphragm. - The ligamentum teres is the obliterated remnant of the left umbilical vein, lying in the free edge of the falciform ligament and extending from the groove for the ligamentum teres to the umbilicus. Its posterior continuation is the groove created by the ligamentum venosum (remnants of the sinus venosus). - The superior (anterior) and inferior (posterior) layers of the coronary ligament are reflections of the peritoneum, which surround the bare area of the liver. - The left and right triangular ligaments are where the layers of the coronary ligament meet to the left and right respectively. - The falciform, coronary and triangular ligaments are derived from that part of the ventral mesogastrium connecting the liver to the body wall. - The gastrohepatic and hepatoduodenal ligaments are derived from that part of the ventral mesogastrium connecting the stomach and the liver. - The gastrosplenic and gastrophrenic, as well as the lienorenal and phrenicolienal ligaments are derived from the dorsal mesogastrium.
 * 5E. Describe the peritoneal ligament and the bile ducts of the liver.**

Bile ducts: R and L hepatic ducts join to form the common hepatic duct which is joined by the cystic duct of the gallbladder to form the Bile Duct.

Blood supply is 70% coming in through portal vein(hepatocytes) and 30% coming from Hepatic artery(stroma of liver, bile ducts). Three hepatic veins drain to the inferior vena cava in the bare area.
 * 5F. Describe the blood supply of the liver.**

**Gall Bladder**

 * 6. Describe its location, relationships, functions, and duct system.**

The gall balder is located in the fossa on the right lobe of the liver. It is divided up into the fundus, the body, and the neck. The fundus projects out beyond the free edge of liver. The body is the main part. The neck is the narrowing, s-curved bit that goes into the duct and contains ridges that make up the spiral valve – these ridges keep the cystic duct patent. Backflow pressure from the closing of the sphincters at the main pancreatic duct and the hepatopancreatic ampulla prevents further flow of bile from the cystic duct.

Bile from the liver comes from the left and right hepatic ducts which merge to the common hepatic duct. When there is no food present, the bile is shunted to the gall bladder via cystic duct for storage and concentration.

The bile duct is formed when the cystic duct merges with the common hepatic duct. The main pancreatic duct joins the bile duct to form the hepatopancreatic ampulla which empties into the major duodenual papilla. Bile flow is controlled by the sphincter of Oddi.

The accessory pancreatic duct empties into the minor duodenal papilla and contains only digestive enzymes, no bile.

**Pancreas**

 * 7A. Describe its location, relationships, functions, and duct system.**

The pancreas lies retroperitoneally and inferolaterally across the posterior abdominal wall, posterior to the stomach between the duodenum on the right and the spleen on the left. The head of the pancreas originates from behind the superior mesenteric vessels inferiorly, while its tail traverses their anterior side.

It has both exocrine function (pancreatic enzymes from acinar cells) and endocrine function (insulin, glucagon, etc. from pancreatic islets).

The main pancreatic duct begins at the tail of the pancreas and runs through to the head where it turns inferiorly and joins with the bile duct and empties into the major duodenal papilla via the hepatopancreatic ampulla. The accessory duct empties through the minor duodenal papilla.


 * 7B. Define its parts.**

The pancreas has 4 parts: the head, neck, body, and tail. The head of the pancreas is right up against the C-shaped curve of the duodenum to the right of the superior mesenteric artery and vein and rests posteriorly against the inferior vena cava, right renal artery and vein, and left renal vein. The unctinate process is the part of the head posterior to the superior mesenteric artery and vein.

The neck of the pancreas is short and is anterior to the superior mesenteric vessels, adjacent to the pylorus of the stomach. The superior mesenteric vein joins the splenic vein just posterior to the neck, forming the portal vein.

The body of the pancreas continues from the neck and goes to the left of the superior mesenteric vessels. The posterior surface contacts the aorta, superior mesenteric vein, left suprarenal gland,and left kidney and renal vessels.

The tail of the pancreas lies anterior to the left kidney, and is closely related to the hilum of the spleen and the left colic flexure.


 * 7C. Describe its blood supply.**

The dorsal and greater pancreatic arteries are derived from the splenic artery which anastomoses with the pancreatic branches of the gastroduodenal a. Up to 10 branches of the splenic artery supply the body and tail while the anterior and posterior superior pancreaticoduodenal arteries from the superior mesenteric artery supply the head, anastomosing with the anterior and posterior superior pancreaticoduodenal arteries. The pancreatic veins empty into the splenic vein, which then unites with the superior mesenteric vein to form the portal vein.

**Spleen**
The Spleen is a intraperitoneal organ closely related to tail of pancreas. It filters blood, removes old RBCs, screens for foreign materials, and stimulates an immune response. The organ is very delicate, has a thin fibrous capsule composed of dense irregular CT, and internal trabeculae. The structure of the spleen is designed to allow for rapid contraction and expansion. It is located in the LUQ, or the left hypochondrium. The medial face of the speen is intimate with four organs: the stomach superiorly, the colon inferiorly, the tail of the pancreas near the hilum and the left kidney posteriorly.
 * 8A. Describe its location, relationships, and functions.**

The hilum of the spleen consists of two ligaments, the splenorenal and gastrosplenic, surrounding the splenic artery and vein.

If the internal structure is damaged, blood will pool in the spleen and cause expansion during hemorrhaging possibly rupturing resulting in massive bleeding into peritoneal cavity flowing into greater sac.

Hilum of spleen is the attachment point for ligaments and splenic artery and vein. The splenic artery also supplies pancreas.
 * 8B. Describe its blood supply.**

Clinical correlate: Greater curvature of the spleen is right up against diaphragm. Stab wound at 9th intercostal space will injure spleen and cause hemo/pneumothorax.