(9) Portal Vein The portal vein is formed by the confluence of the inferior mesenteric, superior mesenteric, and splenic veins. It is ensheathed along with the common hepatic artery and common bile duct in the hepaticoduodenal ligament and form the portal triad entering through the portal hepatis. The portal veins brings nutrients absorbed from the intestines into the liver where the cells process the nutrients. The portal vein is located anterior to the inferior vena cava. The portal vein is a site of thrombosis in patients at high risk for clotting.
(10) Superior Mesenteric Artery This artery is the second branch of the abdominal aorta (the first is the celiac trunk). The vessel travels through the pancreas in between the head and the uncinate process. The artery is located to the left of the superior mesenteric vein. As was discussed in embryology, the vessel provides blood to the mid-gut. This includes the duodenum, jejunum, and ileum.
(10*) Superior Mesenteric Vein The superior mesenteric vein drains the blood coming from the small intestine and empties it into the portal vein. The SMV joins with the splenic vein and inferior mesenteric vein to form the portal vein. This vein also travels through the pancreas between the head and uncinate process to the right of the superior mesenteric artery.
(11) Ascending Colon This is the first part of the colon and it lies on the right side of the abdomen. Only the transverse and part of the ascending colon are considered to be intra-peritoneal organs. The colon has fat filled tags called appendices epiploicae on its its surface. On X-ray, the colon is identified by the sacculations called haustra scattered all along the colon. These two features separate the large from the small intestine. Both the small intestine and ascending colon derive their blood supply from the superior mesenteric artery and are therefore classified as midgut organs. The first part of the ascending colon is the cecum which sits at the junction of the colon and ileum of small intestine. The cecum has a valve that prevents back flow of fecal material into the small intestine, but this valve is often incompetent. The cecum also has attached to it the vermiform appendix which is attached to the cecum at its posterior and medial aspect. There is open communication between the appendix and cecum which if plugged can cause appendicitis. The arterial blood supply to the cecum comes from the ileocecal branch of the superior mesenteric artery. The arterial supply to the ascending colon comes from the ileocolic and the right colic branches of the superior mesenteric artery.
(12) Descending Colon This part of the colon is also retroperitoneal and derives its blood supply from the left colic branch of the inferior mesenteric artery. The descending, part of the transverse, and sigmoid colon make up the embryological hindgut. The hindgut takes it blood supply form the inferior mesenteric artery. The descending colon is located on the left side of the abdomen and lies along the left paracolic gutter. This part of the colon is connected to the posterior abdominal wall from the splenic flexure to the pelvis. Its function is in storing stool and absorbing water from the stool to form solid feces.
(13) Transverse Colon This part of the colon is intraperitoneal because it is suspended by the part of the mesentery called the transverse mesocolon. It begins at the hepatic flexure and ends at the splenic flexure. The hepatic flexure is where the ascending turns into the transverse colon. The splenic flexure is where the transverse turns into the descending colon. The transverse colon is the longest part of the colon. It may dip down to the pelvis. The blood supply to this part of the colon comes from the middle colic artery, a branch of the superior mesenteric artery.
(14) Stomach The stomach is made up of the cardia, fundus, body, antrum and pylorus The cardia is the intersection of the stomach and esophagus. The fundus is the most superior part of the stomach. On X-ray, air is usually seen in the fundus, allowing the identification of the stomach by finding this gastric "bubble". Both the stomach and the esophagus are considered to be foregut organs. The stomach lies in the left hypogastric and epigastric regions. When it is full of food, the stomach may extend down as far as into the pelvis.The blood supply comes from the left gastric, splenic, as well as common hepatic arteries, all branches of the celiac plexus. The blood supply is rich with anastamoses so that ligation of a single blood supply to the stomach usually does not result in ischemia. The parietal cells that reside in the fundus of the stomach secrete a substance known as gastric intrinsic factor which is important in the absorption of vitamin B12. Gastric ulcers usually occur in the lesser curvature of the stomach and require biopsy to rule out cancer if the ulcer does not heal after 6 weeks of conventional treatment. The fundus of the stomach can herniate into the thorax. The paraesophageal type hernia can cause intense pain. The appearance on X-ray is the presence of the stomach bubble lying in the thorax. This condition usually requires surgical repair.
(15) Distal Stomach As described above. The distal stomach consists of both the pylorus, antrum, and part of the body. The antrum forms the beginning of the distal stomach. The pylorus is the 3 cm canal of the stomach that leads to the duodenum. The pylorus can become hypertrophied in a condition called congenital hypertrophic pyloric stenosis. This condition can present in babies between 4 to 12 weeks old as non-bilious projectile vomiting.
(16) Right Kidney The right kidney is a retroperitoneal organ that is located in the posterior abdomen. The right kidney is situated 2-8 cm lower than its left counterpart because of the large liver which sits superior to it. It is related to the 12th rib posteriorly and to the liver, duodenum, and hepatic flexure of the colon anteriorly. The kidney is surrounded by a distinct layer of fascia (called Gerota's renal fascia) that separates the fat surrounding the kidney into the perinephric and paranephric fat. The kidney is surrounded by a fibrous capsule that is easily removed from the kidney. This capsule protects the body from the spread of infection occurring within the kidney.
The structure of the kidney is complex. Each of the pyramids in the medulla come together to form the papilla. There are 9-14 pyramids in the medulla. The pyramid is home to the Henle's loops and collecting ducts. Each of the papillae come together to form the minor calyx which join to form 4-6 major calyces. The calyces form the renal pelvis which drains into the ureter. The kidney gets its blood supply from the renal artery, a branch of the abdominal aorta. The right renal artery travels posterior to the IVC to reach the right kidney. The renal artery enters the capsule then divides into segmental branches which divide into the interlobar branches into arcuate branches into interlobular branches to afferent glomerular arterioles. The function of the kidney is to regulate the electrolyte and water balance in the body.
(17) Left Kidney As described above. The left kidney is higher than the right kidney. The left renal vein is long and has to cross the aorta anteriorly to reach the left kidney. The left kidney rises to as high as the 11th thoracic rib posteriorly. The kidney has relations with the pancreas, splenic flexure, spleen anteriorly.
(18) Inferior Mesenteric Artery (Not visualized on the provided images of the upper abdomen) The inferior mesenteric artery provides blood supply to the embryological hindgut organs including the distal transverse colon, descending colon and sigmoid colon. It is the third branch of the abdominal aorta after the celiac and superior mesenteric branches. This vessels branches into the left colic, rectosigmoid, sigmoid, and superior rectal arteries. The ascending branches of the left colic artery forms anastomosis with the middle colic artery (a branch of the superior mesenteric artery) to form the marginal artery of Drummond.
(19) Duodenum, 2nd part The duodenum is the first part of the small intestine. It is also the shortest part. It is divided into four parts. The first part is encased in the hepatoduodenal ligament. The second part, or descending part, sits behind the transverse colon and anterior to the right kidney and inferior to the liver. It is a retroperitoneal structure. The second part also contains the ampulla into which the pancreatic duct and common bile duct drain. The first, second, third parts of the duodenum form a C-loop around the head of the pancreas. The blood supply to the duodenum comes from the superior pancreaticoduodenal arteries, branches of the celiac artery, and the inferior pancreaticoduodenal arteries, which are branches of the superior mesenteric arteries.
(19*) Duodenum, 3rd part The third part of the duodenum is the transverse part that is about 2 inches in length. It connects to the fourth and last part of the duodenum, which is held in place by the ligament of Treitz. This ligament connects the duodenum to the right crus of the diaphragm.
(20) Left Renal Vein The left renal vein courses between the aorta and superior mesenteric artery to join the inferior vena cava. The left gonadal vein will drain into to left renal vein. The right gonadal vein drains directly into the inferior venal cava.
(20*) Left Renal Artery The left renal vein originates from the abdominal aorta at about L1 or L2, below the origin of the superior mesenteric artery.
(21) Rt. Renal Vein
The right renal vein is anterior to the right renal artery. It is shorter than the left vein.
(21*) Rt. Renal Artery
As with the left renal artery, the right renal artery originates from the aorta at about L1 or L2. This vessels passes posterior to the IVC.
(22) Small Intestine
The small intestine is the longest part of the gastrointestinal tract, usually measuring 6-7 meters. It forms the embryological midgut and is supplied by the superior mesenteric artery. It is divided into duodenum, jejunum, and ileum. On abdominal x-ray, the small bowel is located in the center of the abdomen whereas the colon is located at the superior and lateral edge of the abdomen. The small intestine is identified by valvulae circulares or circular folds of mucosa on barium x-ray study. It is sometimes referred to as the small bowel. On this cross sectional image, the small bowel is identified by white coloration due to filling of the barium contrast agent. The organ is responsible for the digestion and absorption of nutrients such as protein and carbohydrates. The terminal ileum is responsible for the absorption of vitamin B12, fatty acids, bile salts. Most digestion of food occurs in the small instestine. In small bowel obstruction caused by either hernias or adhesions, the abdominal x-ray shows multiple dilated loops of small intestine with air-fluid levels as the patient is asked to sit upright.
(+) Splenic Artery
This artery is one of three branches of the celiac trunk. It is also the largest branch of the celiac trunk due to the high amount of blood flow to the speen. It travels posterior to the fundus of the stomach and gives a branch called the left gastro-omental artery before entering the hilum of the spleen. The splenic artery divides into five or more branches in the splenorenal ligament before entering the hilum of the spleen. The left gastro-omental artery supplies blood to the greater curvature of the stomach. This artery can be a site of aneurysm formation. This aneurysm may be identified by egg-shell calcifications on the abdominal x-ray. Pregnancy is a predisposition to the formation of splenic artery aneurysm.
(x) Common Hepatic Artery
This artery is also a branch of the celiac trunk and it supplies the liver as well as the stomach and duodenum. It gives a gastroduodenal branch which supplies the duodenum with blood. This branch also wraps around the greater curvature of the stomach, supplying it with blood, and anastomoses with the left gastro-omental artery, which is a branch of the splenic artery. Another branch of the common hepatic artery is the proper hepatic artery, which supplies blood to the liver. One branch of the proper hepatic artery is the right gastric artery. This vessel supplies blood to the lesser curvature of the stomach and forms an anastomosis with the left gastric artery, which is a branch of the celiac trunk.
(#) Celiac Trunk Soon after entering the abdomen, the celiac trunk originates from the anterior aspect of the aorta. It has three major branches: the common hepatic artery, the splenic artery and the left gastrtic artery.
(*) Splenic Vein
The splenic vein is formed by several veins that drain the spleen at the hilum. It travels posterior to the body and tail of the pancreas. It joins the inferior mesenteric vein and then merges with superior mesenteric vein to form the portal vein. Splenic vein thrombosis is a disease where there is occlusion of the splenic vein by a thrombus. The result of splenic vein thrombosis is portal hypertension and formation of gastric varices. The most common cause of splenic vein thrombosis is pancreatitis.
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