Peritoneal Cavity and Organ Arrangement

• The peritoneal canal runs from the respiratory diaphragm down to the floor of the pelvis.

Peritoneum Layers

• The serosa, known as the visceral peritoneum, adheres to organs and is continuous with the parietal peritoneum.
• The parietal peritoneum lines the abdominal cavity walls.

Intraperitoneal Organs

• These organs lie within the peritoneal cavity and are completely surrounded by the visceral peritoneum.
• Examples include the stomach and liver.

Retroperitoneal Organs

• The parietal peritoneum covers these organs on their anterior surface.
• Examples include the kidneys, ureters, and abdominal aorta.

Mesenteries

• They consist of fused, double sheets of visceral peritoneum.
• Mesenteries stabilize organ positions and related blood vessels/nerves.
• The mesentery proper suspends most of the small intestine (except the duodenum).
• The mesocolon attaches to the large intestine.
• The lesser omentum is the mesentery between the stomach and liver, while the greater omentum extends from the stomach to the transverse colon and hangs anterior to the small intestine.

Esophagus

• The esophagus is a hollow, musculoelastic tube that lies behind the trachea.
• It transports food and liquids to the stomach.
• The esophagus passes through the thoracic cavity along the dorsal mediastinum wall, entering the peritoneal cavity via the esophageal hiatus.

Stomach

• The stomach is a dilated, sac-like part of the gastrointestinal tract with variable size and configuration.
• Regions include the Cardiac, Fundus, Body and Pyloric.

Small Intestine Segments

• The duodenum is about 25 cm long and largely retroperitoneal.
• The jejunum is about 2.5 meters long and suspended by a mesentery.
• The ileum is about 3.5 meters long and suspended by a mesentery.
• The jejunum occupies the left upper quadrant of the abdomen and is larger in diameter than the ileum.
• The jejunum has thicker walls and less fat in its mesentery than the ileum.
• The jejunum's arterial branches have fewer arcades and longer vasa recta.
• Higher and more numerous mucosal folds in the jejunum increase its surface area for absorption.
• The ileocecal junction, with the ileocecal valve, marks the end of the small intestine, controlling passage into the cecum.

Large Intestine

• The large intestine is approximately 1.5 meters long.
• The cecum is a pouch connected to the ascending colon and ileum, sitting below the ileocecal junction.
• The cecum is surrounded, but not suspended, by a mesentery.
• The appendix is a narrow muscular tube of variable length, containing lymphoid nodules, suspended by the mesoappendix.
• The ascending colon is secondarily retroperitoneal, ascending on the right flank to reach the liver and bends as the right colic (hepatic) flexure.
• The transverse colon is suspended by the transverse mesocolon, running from the right hypochondrium to the left, forming the left colic (splenic) flexure.
• The descending colon is secondarily retroperitoneal, descending on the left flank to join the sigmoid colon in the left groin region.
• The sigmoid colon is suspended by the sigmoid mesocolon, forming a loop that joins the midline rectum in the pelvis.
• The superior two thirds of the rectum are retroperitoneal, and the rectum and anal canal extend from the middle sacrum to the anus.

Blood Supply to Intestines

• The superior mesenteric artery supplies blood to the cecum, ascending colon, appendix, and most of the transverse colon.
• The inferior mesenteric artery supplies blood to the distal transverse colon, descending colon, sigmoid colon, rectum, and anal canal.
• The internal iliac and internal pudendal arteries supply the distal rectum, anal canal, and rectal branches.

Liver

• The liver is the largest solid organ in the body, divided into four lobes.
• The right lobe is the largest, and the left lobe lies to the left of the falciform ligament.
• The quadrate lobe lies between the gallbladder and round ligament of the liver.
• The caudate lobe lies between the inferior vena cava (IVC), ligamentum venosum, and porta hepatis.

Liver Functions

• The liver receives venous drainage from the GI tract, accessory organs, and spleen via the portal vein.
• It stores energy sources (glycogen, fat, protein, and vitamins) and produces cellular fuels (glucose, fatty acids, and ketoacids).
• The liver produces plasma proteins, clotting factors, lymph, metabolizes toxins/drugs, and modifies hormones.
• The liver produces bile acids, excretes substances (bilirubin), stores iron/vitamins, and phagocytizes foreign materials from the bowel.

Gallbladder & Extrahepatic Ducts

• The gallbladder consists of the fundus, body, infundibulum, and neck, storing and concentrating bile.
• Bile from hepatocytes passes through right and left hepatic ducts, then the common hepatic duct.
• Bile then enters the cystic duct for storage in the gallbladder.
• Upon stimulation (vagal efferents and cholecystokinin), bile exits the gallbladder via the cystic duct.
• Bile passes inferiorly through the common bile duct which then enters the hepatopancreatic ampulla (of Vater), encircled by the sphincter of Oddi.
• Bile empties into the duodenum's second part via the major duodenal papilla.

Pancreas

• The pancreas lies posterior to the stomach in the posterior wall and is an exocrine/endocrine organ.
• Except the tail, the pancreas is secondarily retroperitoneal and the tail touches the spleen.
• The head nestles in the duodenum's C-shaped curve, overlying the abdominal aorta, renal vessels, and IVC.
• The uncinate process is posterior to the superior mesenteric vessels.
• The neck is anterior to the superior mesenteric vessels, aorta, IVC, and deep to the pylorus.
• The body extends above the duodenojejunal flexure and across the left kidney's superior part.
• The tail crosses from the left kidney to the hilum of the spleen in the splenorenal ligament.

Spleen

• It's in the left upper quadrant (hypochondriac region), tucked posterolateral to the stomach.
• The spleen is a large lymph node, enlarging during infections.
• Functions include lymphocyte proliferation (B and T cells), immune surveillance/response, and blood filtration.
• The spleen destroys old or damaged red blood cells and platelets and recycles iron/globin.
• The spleen provides reservoir for blood and source of RBCs during early fetal life.

Kidneys and Adrenal Glands

• The kidneys and adrenal glands are retroperitoneal organs with a rich arterial supply.
• Each kidney has a renal capsule, perirenal (perinephric) fat, renal (Gerota's) fascia, and pararenal (paranephric) fat.

GI Embryonic regions

• The GI tract derives from three embryonic gut regions.
• The foregut gives rise to the abdominal esophagus, stomach, proximal duodenum, liver, gallbladder, and pancreas.
• The midgut gives rise to the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal two thirds of the transverse colon.
• The hindgut gives rise to the distal third of the transverse colon, descending colon, sigmoid colon, rectum, and proximal anal canal.

Superior Mesenteric Artery (SMA) Branches

• The IMA major branches include the inferior pancreaticoduodenal, jejunal, and ileal, middle colic, right colic, and ileocolic arteries.

Inferior Mesenteric Artery (IMA) Branches

• The major branches include the left colic, sigmoid, and superior rectal arteries.

Celiac Trunk

• The celiac trunk has both significant and secondary branches.