5.0 Peritoneum and Sacs and Viscera (Exam 3)

• The peritoneum is a continuous layer of fascia located between the parietal peritoneum and the muscles of the abdomino-pelvic walls
• The layer is referred to regionally by different names based on the layer it underlies
• The part adhering to the anterior body wall is the transversalis fascia
• The peritoneum is a single layer of mesothelial cells (squamous epithelium) that secrete a small amount of peritoneal fluid (lubricant)

Parietal Peritoneum

• Parietal peritoneum lines the body wall
• It is highly sensitive, innervated by the phrenic and thoracoabdominal (segmental ventral rami) nerves

Visceral Peritoneum

• Visceral peritoneum (serosa) reflects over the surface of viscera
• It is insensitive because it is not innervated

Retroperitoneal Organs

• Organs held against the posterior abdominal wall behind the peritoneum are retroperitoneal

Functions of the Peritoneum

• Reduces friction to facilitate free movement
• Resists infection by exuding fluid and cells to fight off infection
• Stores fat

Arrangement of the Peritoneum

• Mesentery: double layer of peritoneum enclosing an organ and connects it to the abdominal wall
• Mesocolon: mesentery of the colon
• Omentum: double-layered sheet of peritoneum
• Recess: peritoneal fold forming a blind pouch that opens into the peritoneal cavity

Peritoneal Sacs

• The greater sac is the larger portion of the abdominal cavity

Lesser Sac

• The lesser sac is a smaller compartment formed posterior to the stomach by a pouch-like evagination of the dorsal mesentery of the stomach
• The lesser sac extends down into the greater omentum

Communication of Sacs

• The two sacs communicate through the epiploic foramen
• The epiploic foramen is found under the free edge of the lesser omentum

Supracolic Compartment

• The Supracolic compartment is anterior to the greater omentum
• The Supracolic compartment is superior to the transverse colon
• The Supracolic compartment is limited superiorly by the inferior aspect of the diaphragm
• It is difficult to palpate the various organs in the Supracolic compartment
• Organs of the supracolic compartment include the last 1/2" of esophagus, stomach, 1st part of duodenum, liver, gallbladder and spleen
• The falciform ligament prevents passing right to left across the anterior surface of the liver

Infracolic Compartment

• Identifying the infracolic peritoneal compartment requires reflecting the greater omentum superiorly over the costal margin
• Paracolic gutters exist laterally, on either side of the abdominal cavity
• The right paracolic gutter communicates with the supracolic compartment, specifically the lesser sac via the epiploic foramen
• The locations of the listed infracolic compartments are: left subhepatic space (lesser sac), right lateral paracolic gutter, right medial paracolic gutter, left medial paracolic gutter, and left lateral paracolic gutter

Greater Omentum

• A sheet-like peritoneal fold hangs from the greater curvature of the stomach
• The greater omentum hangs down in front of the transverse colon to which it is attached posteriorly

Lesser Omentum

• The lesser omentum connects the lesser curvature and first part of the duodenum to the liver
• The gastro-epiploic foramen falls under the lesser omentum's free edge
• The common bile duct, portal vein, and hepatic artery (from lateral to medial) run in the free edge

Esophagus

• The esophagus passes into the abdomen through the muscular part of the diaphragm (left of the midline surrounded by a muscle fiber loop form de right crus) at the T9-10 level
• Accompanying the esophagus are the anterior and posterior vagal trunks
• The esophagus meets the cardiac region of the stomach at the gastroesophageal junction
• Anatomically, the functional sphincter makes up the last inch or so of the esophagus where there is no anatomical sphincter
• A hiatal hernia involves the cardiac portion of the stomach moving up into the thorax

Stomach

• The stomach is often J-shaped in tall people, while shorter individuals generally exhibit the steer horn configuration
• Ultimately, the shape of the stomach depends on the degree to which it is filled
• Peritoneum (serosa) covers the stomach, continuing out into the greater and lesser omenta from the greater and lesser curvatures
• The gastroesophageal and gastroduodenal junctions are relatively fixed by piercing the diaphragm and the duodenum passing retroperitoneally

Important Relationships of the Stomach

• The anterior and superior surfaces of the Stomach face the anterior abdominal wall, left costal margin and diaphragm
• The left surface of the Stomach faces the spleen
• The right surface of the Stomach faces the quadrate and left lobes of the liver
• The posterior surface of the Stomach faces the diaphragm, left suprarenal gland, upper pole of left kidney, pancreas and left colic flexure
• The bed of the stomach is separated from the peritoneum

Duodenum

• The first 12" of the small intestine
• The duodenum is continuous with the stomach at the pylorus and with the jejunum at the duodenojejunal junction
• Only about the first centimeter is mobile and attached to the lesser omentum
• The remainder of the duodenum is retroperitoneal

Liver

• The anterior, superior, lateral, and posterior surfaces are molded by the diaphragm, hence the name diaphragmatic surface
• The posteroinferior (visceral) surface slopes forward and downward to a sharp inferior border
• Anatomically, the liver is divided into right and left lobes via the attachment of the falciform ligament
• The inferior surface exhibits two further lobes on the anatomical right side, which are the caudate and quadrate lobes
• Visceral peritoneum covers the liver except for the bare area and where the gallbladder lies adjacent to its inferior surface
• The falciform ligament connects the liver with the anterior abdominal wall, and the lesser omentum connects it with the stomach
• Both the falciform ligament and lesser omentum are considered forms of mesentery
• The falciform ligament extends up the liver's anterior surface and then splits into a left triangular and (right) coronary ligament
• The coronary ligament terminates by becoming the right triangular ligament
• Prior to the right triangular ligament returning to join with the left, it encircles a substantial part of the posterior surface of the liver and vena cava, leaving them uncovered by peritoneum and forming the bare area of the liver

Gallbladder and Biliary Tree

• The gallbladder has a fundus that extends past the inferior border of the liver
• The gallbladder body tapers to a neck that blends into the cystic duct
• The cystic duct exhibits spiral mucosal folds, forming the spiral valve
• The cystic duct joins with the common hepatic duct (composed of fused right and left hepatic ducts) to form the biliary duct
• The biliary duct unites with the pancreatic duct at the hepato-pancreatic ampulla, which opens into the duodenum lumen via the duodenal papilla
• The sphincter of the ampulla is a thickening of the ampulla wall

Small Intestine

• The small intestine has three parts: duodenum, jejunum, and ileum
• The duodenum is predominantly retroperitoneal and thus fixed
• The jejunum and ileum are suspended by the mesentery from the posterior abdominal wall and are highly mobile
• The duodenojejunal junction occurs at the point of the duodenum emerging from being retroperitoneal
• The junction between the jejunum and ileum is indiscernible
• 3/5 of the 20 feet of small intestine (aside from the duodenum) is jejunum, and the remainder is ileum
• Jejunum generally exhibits "mesenteric windows" where fat is kept away from the intestinal wall, however in the ileum, fat approaches the intestinal wall

Large intestine

• Resembles a 3 1/2 sided picture frame
• Starts in the right iliac fossa at the ileocecal junction
• Terminates in the anus
• The large intestine includes the vermiform appendix, colon (ascending, transverse, descending, and sigmoid), rectum, and anal canal
• The outer layer of longitudinal muscle is incomplete in the colon (separated into 3 evenly spaced longitudinal bands called taeniae coli)
• Taeniae are shorter than the colon, collecting it into haustra
• Each haustral compartment facilitates water resorption from feces
• The taeniae blend into the smooth muscle layer over the appendix and rectum
• Fat creeps onto the colon wall, attaching to the taeniae as tags of fat appendages epiploicae

Retroperitoneal Organs

• Organs in this section are retroperitoneal, with the exception of possible partial mesenterization of the ascending and descending colon

Major Structures (Retroperitoneal)

• Descending (abdominal) aorta
• Duodenum
• Kidneys
• Ureters
• Inferior vena cava
• Pancreas
• Suprarenal glands
• Ascending/descending colon
• Structures associated with the posterior abdominal wall such as the: quadratus lumborum, posas major/minor, illacus and components of the Lumbar plexus

Duodenum Sections

• Divided into 4 sections: 1st (superior), 2nd (descending), 3rd (horizontal), and 4th (ascending)
• First section passes posteriorly to the right and terminates at the duodenal bulb.

Second Section

• The second section passes inferiorly alongside the vertebral column.

Third Section

• The third section is horizontal - crosses the vertebral column at the level of L3

Fourth Section

• The fourth section ascends the superiorly to the duodeno-jejunal junction at L2
• The C-shape concavity contains the head and neck of the pancreas and lies on the hilus and vessels of the right kidney
• The biliary duct and hepatic portal vein lie posterior to the superior part of the duodenum
• The superior mesenteric vessels pass anterior to the horizontal part
• The interior shows mucosal folds (plicae circularis) and the duodenal papillae, where secretions from the pancreas and gallbladder are released into the duodenal lumen

Location of Pancreas

• The Pancreas is on the abdominal wall roughly L1
• The head of the pancreas is nestled in the concavity of the duodenum anterior to the inferior vena cava and left renal vein
• The biliary duct passes through the head
• A small portion of the head is tucked under the superior mesenteric vein and is referred to as the uncincate process
• The neck joins to the head and lies anterior to the superior mesenteric vessels and portal vein
• The body extends as far left as the hilus of the left kidney crossing anterior to the aorta and the left renal vein
• The tail leaves the posterior abdominal wall in lienorenal ligament on the hilus of the spleen
• The main pancreatic duct traverses the organ and opens into the 2nd part of the duodenum, joined by the biliary duct
• The splenic artery is embedded in the superior aspect of the pancreas

Ascending/Descending Colon

• These are generally held against the posterior abdominal wall by the peritoneum (retroperitoneal), these regions can exhibit varying degrees of mesenterization, up to and including that exhibited by the sigmoid colon (sigmoid mesocolon)

Explore the anatomy and function of the peritoneum, including its layers, primary functions, and key structures like the greater and lesser sacs. Learn about the visceral and parietal peritoneum and related clinical considerations.