Abdominal Cavity Anatomy

Abdominal Cavity

• The abdominal cavity contains the abdomen proper and the lesser pelvis, extending from the diaphragm to the base of the pelvis.
• Musculature maintains the position of abdominal and pelvic structures.
• Bony structures bound the abdomen, including ribs, iliac crests, pelvic girdle, and vertebrae.
• Significant bony landmarks include the xiphoid process, subcostal margin, anterior iliac crests, and symphysis pubis.
• The abdomen proper houses a large portion of the digestive tract, liver, gallbladder, pancreas, spleen, kidneys, and adrenal glands, along with blood and lymph vessels, lymph nodes, and nerves.
• The lesser pelvis includes digestive tract coils, blood and lymph vessels, lymph nodes, nerves, and structures related to urology and gynecology.
• The abdomen is divided into nine regions: epigastric, right and left hypochondriac, umbilical, right and left lumbar, hypogastric/pubic, and right and left inguinal/iliac.
• It is also described in terms of quadrants: right and left upper and lower quadrants.

Surface Features

• The umbilicus is generally at the level of the disk between the third and fourth lumbar vertebrae.
• The linea alba is a median groove formed by the joining of abdominal aponeuroses.
• Semilunar lines of Spieghel demarcate the lateral margins of the rectus abdominis muscles.
• Abdominocrural creases are located between the thigh and abdomen.

Abdominal Musculature

• Anterior muscles commonly encountered are the external and internal oblique, transverse abdominis, and rectus abdominis.
• The oblique groups and transverse abdominis (flat muscles) attach to the lower ribs and iliac crests.
• The rectus abdominis is a vertical strap-like muscle from the costal margin and xiphoid process to the symphysis pubis.
• Abdominal muscles are wrapped in fibrous fascia.
• The transverse abdominis and obliques have aponeuroses forming the sheath around the rectus abdominis and the linea alba.

Peritoneum

• The peritoneum is the fibrous tissue lining the abdominal cavity and organs.
• The parietal peritoneum lines the abdominal walls, pelvis, and diaphragm, loosely attached for easy stripping.
• The visceral peritoneum covers the organs of the peritoneal cavity and is continuous with their walls.
• The primary function is to provide a slippery surface for viscera movement.
• A small amount of fluid is normally present within the abdominal cavity.
• The peritoneum is semipermeable, allowing water and solute diffusion. Its large surface area (1.7 m2) can cause fluid shifts in trauma or infection.
• The parietal peritoneum's somatic nerves account for localized pain sensation.
• Afferent nerves innervate the visceral peritoneum, transmitting sensations of vague pain.

Retroperitoneum

• The retroperitoneum is a plane posterior to the abdominal parietal peritoneum, from the diaphragm to the pelvis.
• It is bounded anteriorly by the peritoneum, posteriorly by the spine, laterally by the psoas and quadratus lumborum muscles, superiorly by the 12th ribs and diaphragm, and inferiorly by the pelvis.
• The retroperitoneum consists of the anterior pararenal (pancreas, duodenum, colon), perirenal (urologic and vascular structures), and posterior pararenal (no organs) regions.

Alimentary Canal

• The alimentary canal is a digestive passageway from the mouth to the anus, with similar wall structures throughout.
• It includes pharyngeal, esophageal, gastric, and intestinal portions.

Esophagus

• The esophagus is a 24 cm hollow tube connecting the pharynx to the stomach.
• It is divided into upper, middle, and lower thirds, maintaining closure via sphincters at each end.
• The pharyngoesophageal sphincter closes the upper esophagus (2-3 cm in length).
• The esophagogastric (cardiac) sphincter closes the distal esophagus.
• Blood supply is from the inferior thyroid artery (upper), bronchial and intercostal arteries (middle), and celiac artery (lower).
• Venous drainage is via right and left gastrics, and lymphatic drainage is associated with the internal jugular, tracheal, intercostal, diaphragmatic, and gastric nodes.
• Innervation includes parasympathetic fibers from the vagus nerve and sympathetic nerves from the cervical and thoracic ganglia.

Stomach

• The stomach is a sac-like structure in the epigastric, umbilical, and left hypochondriac regions.
• Sections include the cardia, fundus, corpus, antrum, and pylorus.
• The cardia is at the esophagogastric junction, corpus is the largest region, fundus is above the corpus, antrum is below extending to the pylorus.
• The stomach has two curves: the lesser (superior) and greater (inferior).
• The musculature consists of three layers: incomplete inner, complete middle circular, and outer longitudinal.
• The middle layer plays a dominant role in gastric emptying.
• A thick band of muscle, the pyloric sphincter, separates the pylorus from the duodenum.
• Blood supply is via the left gastric artery, left gastroepiploic and short gastric branches of the splenic artery, and the gastroduodenal artery.
• Five veins drain the stomach: left gastric, right gastric, short gastrics, and left and right gastroepiploics.
• Parasympathetic innervation is by the left (anterior) and right (posterior) vagal nerve trunks.
• Sympathetic innervation comes from thoracic roots 7 to 9, supplying vasomotor control and the main pathway for gastric pain.
• Digestive functions: mucous secretions of the cardia ease passage of food, fundus produces hydrochloric acid, corpus produces acid, pepsinogen, and mucus, antrum secretes mucus and gastrin, and pylorus stores chyme before it enters the duodenum.

Small Intestine

• The small intestine begins at the pyloric sphincter and has three sections: duodenum, jejunum, and ileum.
• The jejunum and ileum are termed the mesenteric small intestine.
• It is approximately 6 to 7 meters long, with a luminal diameter of 3 to 5 cm.
• The small intestine digests foodstuff, absorbs nutrients, and produces necessary acids and enzymes.
• Blood supply to the duodenum is from the right gastric, supraduodenal, right gastroepiploic, and superior and inferior pancreaticoduodenal arteries.
• The adjoining venous system ends in the splenic, superior mesenteric, and portal veins.
• Innervation to the small intestine is via the celiac plexus, vagus, and thoracic splanchnic nerves, which influence peristalsis, sphincter activity, and intestinal secretions.
• Lymph drainage originates at mucosal and muscularis levels, draining to the mesentery.

Duodenum

• The duodenum is the first segment of the small intestine, horseshoe-shaped, about 30 cm long and 3 to 5 cm wide.
• It is subdivided into four portions.
• The first portion (duodenal cap) is a 5cm cone lined with longitudinal mucosal folds and is the most mobile segment; it contains the hepatoduodenal ligament.
• The duodenal cap is the most frequent site of peptic ulcers.
• The second portion is 10-12 cm long, retroperitoneal, descending to the right of midline and associated with the pancreas; it contains the hepatopancreatic ampulla of Vater.
• The third portion runs horizontally (15cm long) from right to left over the descending aorta and the inferior vena cava (IVC) and is retroperitoneal.
• The fourth portion is 8 cm long, passing upward to the left of the aorta, terminating at the ligament of Treitz, marking the start of the mesenteric small intestine.

Jejunum and Ileum

• The mesenteric small intestine is longer in men than in women, averaging 5 meters.
• The proximal two-fifths is the jejunum, and the distal three-fifths is the ileum.
• The jejunum occupies the left upper abdominal cavity, and the ileum lies in the right abdomen and pelvis.
• The jejunum has a thicker wall and wider lumen than the ileum; the ileum displays more mesenteric vascularity and fat.
• The mesenteric small intestine’s lumen gradually narrows from the duodenum to the distal ileum.
• Walls are composed of five layers: mucosa, submucosa, muscularis propria, subserosa, and serosa.
• Villi line the lumen aiding in nutrient absorption and secretion; the jejunum has longer, more frondlike villi than the ileum.
• Epithelial cells produce disaccharides and amino peptidases. Goblet cells secrete mucus, and Paneth cells produce lysosomal enzymes.
• Villi contain columnar absorption cells.
• The submucosa, a network of loose connective tissue, is rich in blood vessels, nerves, and lymphatics.
• The muscularis propria has inner circular and outer longitudinal layers of nonstriated muscle, thickest in the duodenum.
• The serosa is the visceral peritoneum, an extension of the mesentery.

Mesentery

• Mesenteries are peritoneal folds, including the mesentery of the small intestine, mesoappendix, transverse mesocolon, and sigmoid mesocolon.
• They contain blood vessels, nerves, and lymph vessels serving the adjoining organs.
• The small intestine’s mesentery attaches the posterior wall of the abdominal cavity, extending diagonally downward 15 cm.
• This mesentery fans out to meet the small intestine's length, changing in length from 20 cm at the jejunum to 5 cm at the ileum.
• The arterial structure increases in complexity, demonstrating "end arteries" and looping vascular "arcades."
• The small intestine requires more than 12 branches of the superior mesenteric artery (SMA).
• The mesoappendix is a triangular fold attaching the appendix to the ileal mesentery and carries appendicular vessels.
• The transverse mesocolon carries the middle colic vessels and attaches to the posterior abdominal wall around the pancreas.
• The sigmoid mesocolon secures the sigmoid colon to the pelvis, carrying sigmoid and superior rectal vessels and the left ureter.

Colon

• The colon averages 90 to 125 cm in length, ranging from 8.5 to 2.5 cm in lumen diameter.
• It is divided into the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.
• The wall consists of mucosa, submucosa, muscularis, and serosa.
• The mucosa is similar to the small intestine but contains more goblet cells and lacks villi.
• The inner muscularis has circular rings, the outer longitudinal muscularis propria is arranged in three separate taenia (coli).
• The colon absorbs water and electrolytes, compacts fecal waste, and produces vitamin K.
• The left colon is primarily a storage unit.
• Approximately 2 liters of water enters the colon, of which it absorbs all but 150 to 200 mL.
• The cecum, ascending colon, and right transverse colon are supplied by the ileocolic, right colic, and middle colic branches of the SMA.
• The left transverse colon, descending colon, sigmoid, and rectum are supplied by the superior left colic, sigmoid, and superior rectal branches of the IMA.
• Venous return is by veins with the same names as the arteries. Lymphatic drainage courses alongside the arterial supply to the cisterna chyli.
• Innervation is primarily autonomic from the celiac, superior mesenteric, intermesenteric, and hypogastric plexuses, as well as fibers from the splanchnic and vagus nerves, and sacral segments.

Cecum

• The cecum is a mobile pouch in the right lower abdominal cavity, wider (8.5 cm) than long (6.5 cm), with no mesenteric attachment.
• The ileum terminates at the ileocecal junction at the superior aspect of the cecum with a semilunar valve.

Appendix

• The vermiform appendix is attached to the cecum.
• It's a worm-like blind tube, 0.8 cm wide and 8.5-22.5 cm long.
• Usually retrocecal, its tip can be in various positions. It derives its blood supply from the mesoappendix.

Ascending Colon

• The ascending colon is approximately 20 cm long.
• It begins at the ileocecal junction, extending upward along the right side of the abdominal cavity to the lower pole of the right kidney.
• It ends in a hepatic flexure at the inferior surface of the liver.
• The ascending colon is fixed retroperitoneally to the posterior abdominal wall.

Transverse Colon

• The transverse colon begins at the hepatic flexure, traverses the anterior abdomen in an upward curve, and attaches to the undersurface of the diaphragm at the level of the 10th and 11th ribs.
• It is connected to the diaphragm by the phrenocolic ligament.
• The transverse colon is the longest (40-50 cm) and most mobile segment.
• Haustra are outpouchings of the colon wall.
• The splenic flexure is acute, causing the transverse colon to overlap the descending colon.

Descending Colon

• The descending colon begins at the splenic flexure and routes inferiorly along the lateral border of the left kidney toward the pelvis.
• It is 30 cm long, has the heaviest muscle layer and thinnest lumen, and is covered with peritoneum on its anterior two-thirds.

Sigmoid Colon

• The sigmoid colon is the primary site of colon cancer and most susceptible to volvulus.
• It can vary from 15 to 50 cm and is attached to a generous mesentery.
• Named for its shape resembling the Greek letter sigma and has regularly spaced, fat-laden epiploic appendices on its serosal layer.

Rectum

• The rectum is a 10-12 cm long, curved tube with a "zig-zagged" lumen and three interior folds (valves of Houston).
• It descends along the sacrococcygeal concavity and has an anteroposterior curve to join the anus.
• The taenia arrangement changes to a continuous muscle layer in the rectum.

Anus

• The anal canal is 3 cm long, surrounded by anal sphincters.
• The internal sphincter is a continuation of the circular smooth muscle layer of the rectum.
• The external sphincter forms a collar around the anus and intermingles with the levator ani.
• The upper half of the anus is lined with mucosa and transitions from columnar epithelium to stratified squamous epithelium.
• Membranes connecting the papillae form the anal valves, with recesses above termed anal sinuses (crypts).
• Except in the lower anus, innervation is both sympathetic and parasympathetic.
• Sympathetic innervation is from the lumbar trunk and the superior hypogastric plexus.
• Parasympathetic supply is via the pelvic splanchnic nerve.
• The external sphincter is controlled by the inferior rectal branch of the pudendal nerve and motor fibers from the fourth sacral segment of the spinal cord.

Omenta

• The omenta include the lesser and greater omentum.
• The lesser omentum is continuous with the peritoneum, covers the stomach and first 2 cm of the duodenum, connects the duodenum to the liver forming the hepatoduodenal ligament and ascending as a double fold to the porta hepatis.
• It encloses the hepatic artery, portal vein, bile duct, lymph vessels, lymph nodes, and nerves.
• The foramen of Winslow communicates between the lesser omentum and the peritoneal cavity.
• The greater omentum is a double sheet folded on itself to form four layers descending from the greater curvature of the stomach and cap of the duodenum.
• It stores fat and limits peritoneal infection.

Pancreas

• The pancreas is an elongated, flattened, gray-tan organ weighing 70-120g.
• It is divided into the head, body, and tail.
• The head is within the duodenal curve.
• The neck adjoins the pylorus and merges into the body.
• The tail is narrow and reaches the gastric surface of the spleen.
• The parenchyma is divided into lobules of acini (exocrine secreting glands).
• Acinar secretions break down fats, proteins, carbohydrates, nucleic acids, and digestive secretions and maintains a neutral intraluminal pH.
• Islets of Langerhans are endocrine secreting glands which secrete glucagon, insulin, somatostatin secretin, and pancreatic peptide.
• The pancreas has a rich arterial supply from branches of the celiac and superior mesenteric arteries as well as the splenic artery.
• Pancreatic and pancreaticoduodenal veins drain the pancreas into the splenic, portal, and superior mesenteric veins.
• Innervation is by the vagus and splanchnic nerves by way of the hepatic and celiac plexuses.

Spleen

• The spleen is the largest mass of lymphatic tissue, in the left upper quadrant of the abdomen.
• It's shaped by the stomach, left kidney, splenic flexure of the colon, and tail of the pancreas.
• It generally measures 12 cm long, 7 cm thick, and 3-4 cm wide, weighing 150-200 g.
• Suspended by the gastrosplenic, splenorenal, splenophrenic, and pancreaticosplenic ligaments.
• The spleen has red pulp (vascular) and white pulp (lymph tissue).
• The filtration mechanism of the red pulp serves as an erythrocyte storage area in youth and holds 35-80% of the adult body’s platelets.
• The white pulp contains lymphocytes and macrophages.
• Blood supply is via the splenic artery from the celiac trunk.
• The splenic vein is joined by the superior and inferior mesenteric veins to form the portal vein.
• Inner vation is from the medial and anterior parts of the celiac plexus and the vagus nerve.
• Lymphatic drainage arises from the splenic capsule and hilum and empties into the pancreaticosplenic and celiac nodes.

Liver

• The liver is the largest parenchymal organ in the abdomen, weighing 1,200-1,500 g, at 2% of adult body weight.
• It lies in the right upper quadrant under the protection of the thorax.
• It is divided into right and left sides by the falciform ligament and fissures and has four lobes: right, left, quadrate, and caudate.
• The liver is covered by Glisson’s capsule.
• The liver has a double blood supply.
• The hepatic artery, which provides all the oxygen, carries 25% of the blood. The portal vein provides nutrients and carries 75% of the blood.
• The point at which the hepatic artery and portal vein enter, and the bile duct exits, is termed the porta hepatis.
• Lobules are polyhedral units (0.7 x 2.0 mm) with various cells that metabolize lipids, proteins, carbohydrates, and hormones, store vitamins, produce cytotoxins, degrade microorganisms and drugs, harbor immunoglobulin-producing cells, and secrete bile.
• Hepatocytes carry the major metabolic activities.
• Kupffer cells take up bacteria, endotoxins, and cellular debris.
• Pit cells possess natural killer activity.
• Lipocytes produce fibronectin, laminin, chondroitin sulfate, hyaluronic acid, and collagen.
• The liver performs functions such as producing bile, metabolizing carbohydrates, fats, and proteins, storing sugar as glycogen, storing fat-soluble vitamins, detoxifying harmful substances, and synthesizing prothrombin and fibrinogen.
• The liver drains via the right and left hepatic veins into the inferior vena cava.
• Bile collects in ductules, drains into the right and left hepatic ducts which merge to form the common hepatic duct (CHD).
• Hepatic innervation contains sympathetic and parasympathetic fibers.
• Lymph drainage is into the portal system.

Biliary Tract

• The biliary tract connects the liver and the duodenum, consisting of the gallbladder, cystic duct, CHD, and the CBD.
• It transports, stores, and releases bile.
• The gallbladder stores bile and is a bluish, pear-shaped bag which is generally 9 cm long with a bile storage capacity of approximately 50 mL.
• The gallbladder is divided into the fundus, body, infundibulum, and neck.
• The cystic duct connects the neck of the gallbladder to the CBD and has 10-14 crescentic folds that appear as a spiral valve (valves of Heister).
• The CBD is formed by a junction of the cystic and hepatic ducts.
• The sphincter of Oddi controls the flow of bile into the duodenum.
• The blood supply to the gallbladder is through the cystic artery, right hepatic artery, and the posterior superior pancreaticoduodenal artery.
• The gallbladder receives parasympathetic vagal innervation from the plexus common to the alimentary canal.
• Sympathetic innervation reaches the gallbladder and bile ducts via the splanchnic nerve and hepatic plexus.

General Surgery Instrumentation

• Instrumentation varies with geographic location, hospital capability, and surgeon preference.
• The major laparotomy set is the foundation set for many surgical procedures.
• Retractors, forceps, clamps, and hemostats vary widely in type and size.