Abdomen - Summary

Abdomen Summary Inguinal RegionThe inguinal triangle is bounded by the lateral edge of the rectus abdominis (linea semilunaris), the inferior epigastric vessels, and the inguinal ligament. The superficial inguinal ring is in the aponeurosis of the external abdominal oblique muscle and lies just lateral to the pubic tubercle. The deep inguinal ring lies in the transversalis fascia, just lateral to the inferior epigastric vessels. The inguinal canal transmits the spermatic cord or the round ligament of the uterus and the genital branch of the genitofemoral nerve. The spermatic cord is composed of the ductus deferens, testicular, cremasteric, and deferential arteries; pampiniform plexus of testicular veins; genital branch of the genitofemoral and cremastric nerves; the testicular sympathetic plexus; and lymph vessels. The spermatic cord is surrounded by external spermatic fascia , which derived from the aponeurosis of the external oblique abdominal muscle, the cremasteric fascia (cremaster muscle and fascia) originating from the internal oblique abdominal muscle, and the internal spermatic fascia , which derived from the transversalis fascia Umbilical FoldThe median umbilical fold or ligament contains the fibrous remnant of the obliterated urachus , the medial umbilical fold contains the fibrous remnant of the obliterated umbilical artery , and the lateral umbilical fold contains the inferior epigastric vessels. Peritoneal ReflexionsThe lesser omentum contains the right and left gastric vessels, and its right free margin forms the anterior wall of the epiploic foramen and contains the proper hepatic artery, bile duct, and portal vein. The greater omentum contains the right and left gastroepiploic vessels; the mesentery proper contains the superior mesenteric vessels and its branches and tributaries; the transverse mesocolon contains the middle colic vessels; the sigmoid mesocolon contains the sigmoid vessels; and the mesoappendix contains the appendicular vessels. The lienogastric (gastrosplenic) ligament contains the short gastric and left gastroepiploic vessels; lienorenal (splenorenal) ligament contains the splenic vessels and the tail of the pancreas; and the free margin of the falciform ligament contains the ligamentum teres hepatis , which is the fibrous remnant of the left umbilical vein, and the paraumbilical vein , which connects the left branch of the portal vein with the subcutaneous veins in the region of the umbilicus. Retroperitoneal organs or structures include the duodenum (2nd, 3rd, and 4th parts), pancreas except a small portion of its tail, ascending colon, descending colon, kidney, ureter, suprarenal gland, renal, suprarenal vessels, gonadal vessels, abdominal aorta, inferior vena cava. StomachThe stomach has the cardiac part, fundus, body, pyloric antrum, and pyloric canal. The rugae are longitudinal folds of mucous membrane and form the gastric canals along the lesser curvature, and these canals direct fluids toward the pylorus. The stomach produces hydrochloric acid, which destroys many organisms in food and drink; pepsin which converts proteins to polypeptides; and the hormone gastrin, which is produced in its pyloric antrum and stimulates gastric acid secretion. Small IntestineThe small intestine consists of the duodenum , which is a C-shaped tube surrounding the head of pancreas and is retroperitoneal except for the beginning of the first part. Its descending (second) part contains the junction of the foregut and midgut, where the bile duct and main pancreatic ducts open into the greater papilla. The duodenojejunal junction is fixed in position by the suspensory ligament of Treitz, a surgical landmark. The jejunum makes up the proximal two fifths of the small intestine; is emptier, larger in diameter, thicker walled; and has tall and closely packed plica circulares. The ileum is longer than the jejunum and its mesentery contains more prominent arterial arcades and shorter vasa recta. Its lower part contains Peyer's patches (aggregations of lymphoid tissue). Large IntestineThe large intestine consists of the cecum, appendix, colon, rectum, and anal canal and functions to convert the liquid contents of the ileum into semisolid feces by absorbing water and electrolytes as sodium and potassium. The colon has the ascending and descending colons, which are retroperitoneal, and transverse and sigmoid colons, which are surrounded by peritoneum. The ascending and transverse colons are supplied by the superior mesenteric artery and the vagus nerve; the descending and sigmoid colons supplied by the inferior mesenteric artery and the pelvic splanchnic nerves. The colons are characterised by presence of the teniae coli , sacculations or haustra , and epiploic appendages. The appendix has large aggregations of lymphoid tissue in its wall, and its base lies deep to McBurney's point , which occurs at the junction of the lateral one third of a line between the right anterior-superior iliac spine and the umbilicus. This is the site of maximum tenderness in acute appendicitis. Liver The liver is the largest visceral organ and plays an important role in bile production and secretion; detoxification; storage of carbohydrate as glycogen; storage of vitamins, iron, and copper; protein synthesis; and production of heparin and bile pigments from breakdown of hemoglobin. The liver is divided, based on hepatic drainage and blood supply, into the right and left lobe by the fossae for the gallbladder and the IVC. On the visceral surface of the liver, there is an H-shaped group of fissures including fissures for the ligamentum teres hepatic, the ligamentum venosum, the gallbladder, and the IVC. The porta hepatis is a transverse fissure between the quadrate and caudate lobes and lodges the hepatic ducts, hepatic arteries, branches of the portal vein, hepatic nerves, and lymphatic vessels. The liver contains the portal triad, which consists of the following: (a) branches of the hepatic artery which brings oxygen and nutrients to the liver, (b) branches of the portal vein bring nutrient-rich and oxygen poor blood to the liver, and (c) hepatic ducts carry bile in the opposite direction of the blood flow and function to emulsify fat in the digestive system. Gallbladder The gallbladder is located at the junction of the right ninth costal cartilage and lateral border of the rectus abdominis, which is the site of maximum tenderness in acute inflammation of the gallbladder. It receives bile, concentrates it (by absorbing water and salts), stores it, and releases it. It receives blood from the cystic artery arising from the right hepatic artery within the cystohepatic triangle, which is formed by the visceral surface of the liver, the cystic duct, and the common hepatic duct. Pancreas The pancreas is a retroperitoneal organ except for a small portion of its tail, which lies in the lieno-renal ligament. It is both an exocrine gland , which produces digestive enzymes, and an endocrine gland which secretes insulin, glucagon, and somatostatin. For bile passage , the right and left hepatic ducts unite to form the common hepatic duct , which joins the cystic duct to form the bile duct. The bile duct descends behind the first part of the duodenum and runs through the head of the pancreas and joins the main pancreatic duct to form the hepatopancreatic duct , which enters the second part of the duodenum at the greater papilla. Spleen The spleen is a large vascular lymphatic organ and is developed in the dorsal mesogastrium and supported by the lienogastric (splenogastric) and lienorenal (splenorenal) ligaments. The spleen is composed of white pulp, which consists of lymphatic nodules and diffuse lymphatic tissue, and red pulp, which consists of venous sinusoids. It is hematopoietic in early life, later it destroys aged or worn-out red blood cells, and then removes them. The spleen filters blood (lymph nodes filter the lymph), stores blood and platelets, produces lymphocytes and antibodies , and is involved in body defense against foreign particles (removal of blood-borne antigens as its immune function). The hemoglobin is broken down into (a) the globin (protein part), which is hydrolyzed to amino acid that are reused for protein synthesis; (b) iron , which is released from heme and transported to the bone marrow where it is reused in erythropoiesis; and (c) iron-free heme , which is metabolised to bilirubin in the liver and excreted in the bile. Celiac Trunk The celiac trunk arises from the abdominal aorta and divides into the left gastric, splenic, and common hepatic arteries. The common hepatic artery divides into the proper hepatic and gastroduodenal arteries. The proper hepatic artery divides into the right and left hepatic arteries; the right hepatic artery gives off the cystic artery. The gastroduodenal artery divides into the superior pancreaticoduodenal and left gastroepiploic arteries. The splenic artery gives off the dorsal pancreatic, left gastroepiploic, and short gastric arteries. Superior and Inferior Mesenteric Arteries The superior mesenteric artery gives off the inferior pancreaticoduodenal artery, the middle colic artery supplies the transverse colon, right colic artery supplies the ascending colon, the ileocolic artery, and the jejuna and ileal arteries. The inferior mesenteric artery gives rise to the left colic, sigmoid, and superior rectal arteries. Portal Vein The portal vein is formed by the union of the splenic vein and the superior mesenteric vein and receives the right and left gastric vein. The inferior mesenteric vein joins the splenic vein or the superior mesenteric vein or the junction of these veins. The portal vein carries deoxygenated blood containing nutrients and toxins and carries three times as much blood as the hepatic artery. The important portal-caval (systemic) anastomoses occur between (a) the left gastric vein and the esophageal vein of the azygos vein; (b) the superior rectal vein and the middle and inferior rectal vein (c) the paraumbilical veins and radicles of the epigastric (superficial and inferior) veins; and (d) the retrocolic veins and twigs of the renal, suprarenal, and gonadal veins. Kidney and Ureter The kidney is retroperitoneal in position and extends from T12 to L3, and the right kidney lies a little lower than the left. It is invested by a fibrous renal capsule and is surrounded by the renal fascia that divides the fat into two regions. The perirenal fat lies between the renal capsule and renal fascia, and the pararenal fat lies external to the renal fascia. The kidney consists of the medulla and the cortex, containing 1 to 2 million nephrons, which are the anatomic and functional units. Each nephron consists of a renal corpuscle , a proximal convoluted tubule, Henle's loop, and a distal convoluted tubule. The renal corpuscle consists of a tuft of capillaries, the glomerulus , surrounded by a glomerular capsule , which is the invaginated blind end of the nephron. The kidney produces and excretes urine (by which metabolic waste products are eliminated), main electrolyte (ionic) balance and pH, and produces vasoactive substances (angiotensin II) that regulate blood pressure. The cortex contains renal corpuscles and proximal and distal convoluted tubules. The medulla consists of 8 to 12 renal pyramids, which contain straight tubules (Henle's loops) and collecting tubules. An apex of the renal pyramid, the renal papilla, fits into the cup-shaped minor calyce on which the collecting tubules open. The minor calyces receive urine from the collecting tubules and empty into two or three major calyx, which in turn empty into the renal pelvis. The right renal artery arises from the abdominal aorta, is longer and a little lower than the left, and passes posterior to the IVC; the left artery passes posterior to the left renal vein. The ureter is a muscular tube that extends from the kidney to the urinary bladder. It may be obstructed by renal calculi (kidney stones) where it joins the renal pelvis (ureteropelvic junction), where it crosses the pelvic brim over the distal end of the common iliac artery, or where it enters the wall of the urinary bladder (ureterovesicular junction). Suprarenal Gland The suprarenal (adrenal) gland is a retroperitoneal organ lying on the superomedial aspect of the kidney and is surrounded by a capsule and renal fascia. Its cortex is essential to life and produces steroid hormones, and its medulla is derived from embryological neural crest cells, receives preganglionic sympathetic nerve fibers directly, and secretes epinephrin and norepinephrine. The gland receives arteries from three sources: the superior suprarenal artery from the inferior phrenic artery, the middle suprarenal from the abdominal aorta, and the inferior suprarenal artery from the artery. It is drained via the suprarenal vein, which empties into the IVC on the right and the renal vein on the left. Posterior Abdominal Blood Vessels and Lymphatics The suprarenal and gonadal veins drain into the IVC on the right and the renal vein on the left. The azygos vein is connected to the IVC, but the hemiazygos vein is connected to the left renal vein. The cisterna chyli is the lower dilated end of the thoracic duct and lies just to the right and posterior to the aorta, usually between two crura of the diaphragm. It is formed by the intestinal and lumbar lymphatic trunks. Diaphragm The diaphragm arises from the xiphoid process, lower six costal cartilages, and medial and lateral lumbocostal arches and vertebrae and inserts into the central tendon. It is the principal muscle of inspiration and receives somatic motor fibers solely from the phrenic nerve; its central part receives sensory fibers from the phrenic nerve, whereas the peripheral part receives sensory fibers from the intercostal nerves. It has (a) the vena caval hiatus , which lies in the central tendon at the level of T8 and transmits the IVC and the right phrenic nerve; (b) the esophageal hiatus , which lies in the muscular part of the diaphragm at the level of T10 and transmits the esophagus and vagus nerve; and (c) the aortic hiatus which lies between the two crura at the level of T12 and transmits the aorta, thoracic duct, azygos and sometimes greater splanchnic nerve. ◄.....Go back to the Gross Anatomy homepage