Peritoneum+and+Major+Vessels

=**Objectives**=


 * 1. Define the peritoneum and peritoneal cavity.**

Peritoneum is a large thin transparent sheet of serous membrane which lines the walls of the abdominopelvic cavity and is reflected on the viscera. The peritoneal cavity is a potential space between adjacent layers of peritoneum usually containing a small amount of fluid.


 * 2. Understand what distinguishes parietal from visceral peritoneum.**

The parietal peritoneum lines the abdominal and pelvic walls. The visceral peritoneum covers the abdominal and pelvic organs.


 * 3. Describe the shape and extent of the peritoneal cavity.**

The peritoneal cavity is subdivided by the greater and lesser omentum into two sacs called the greater and lesser sacs. The omental foramen connects the two sacs. This is a closed space in males but communicates with the exterior in females (the fallopian tubes of the female reproductive tract communicate with the outside, suggesting a possible advanced education of the female immune system).


 * 4. Know what borders of the greater and lesser sac are.**

The greater sac is the main and larger part of the peritoneal cavity. The lesser sac lies posterior to the stomach and adjoining structures. These two sacs are connected by the omental foramen.


 * 5. Describe the components of the greater and lesser omentums.**

The omentum is a double layer of peritoneum attached to the stomach and proximal part of the duodenum.

The lesser omentum attaches the stomach along the lesser curvature to the liver. It is subdivided into the hepatogastric and hepatoduodenal ligaments.

The greater omentum attaches to the stomach along the greater curvature to the posterior abdominal wall. It is subdivided into the gastrophrenic, gastrosplenic, and gastrocolic ligaments.


 * 6. Know what forms the borders of the epiploic foramen. What spaces does it connect.**

The epiploic or omental formamen connects the greater and lesser abdominal sacs. This opening is posterior to the free edge of the lesser omentum (hepatoduodenal ligament) and can be located by running a finger along the gallbladder to the free edge of the lesser omentum. The hepatoduodenal ligament contains the bile duct, hepatic artery and portal vein.

The boundaries of the omental foramen are:

__Anteriorly__ Portal vein, hepatic artery, and bile duct contained in the hepatoduodenal ligament (free edge of the lesser omentum)

__Posteriorly__ Inferior vena cava, and right crus of diaphragm, covered with parietal peritoneum (retroperitoneal).

__Superiorly__ Caudate lobe of the liver, covered with visceral peritoneum.

__Inferiorly__ Superior or first part of the duodenum, portal vein, hepatic artery, and bile duct.


 * 7. Know what organs and structures within the abdomen are intraperitoneal (peritoneal) and which are primarily and secondary retroperitoneal.**

__Intraperitoneal__ Stomach Liver Jejunum Ilium Cecum Appendix Transverse Colon Sigmoid Colon Spleen

__Primary Retroperitoneal__ Esophagus Rectum Kidneys Suprarenal glands

__Secondary Retroperitoneal__ Pancreas Duodenum Ascending Colon Descending Colon


 * 8. Be able to describe and give examples of peritoneal folds and recesses.**

Peritoneal folds are ridges on the surface of the body wall covered with parietal peritoneum. These ridges are produced by an underlying vessel, duct, or obliterated fetal vessel. There are five folds: two lateral umbilical folds formed by the inferior epigastric vessels, two medial umbilical folds formed by the obliterated umbilical artery, and one median umbilical fold formed by the urachus.

Peritoneal recesses are a pouch of peritoneum formed by peritoneal folds or ligaments. There is a hepatorenal pouch in the superior part of the abdomen and a rectovesical pouch in males, and a retrouterine pouch in females in the inferior part of the abdomen. When a person lies on his/her back, fluid tends to accumulate in these pouches.


 * 9. Distinguish between mesentery, mesocolon, greater omentum, lesser omentum, and the various peritoneal ligaments.**

__Mesentery__ A double layer of peritoneum that connects an intraperitoneal organ to the posterior abdominal wall. It has a connective tissue core with blood vessels, nerves, and lymphatics that travel to and from the intraperitoneal organ. Organs with a mesentery are freely movable.

__Mesocolon__ The mesentery of the large intesting is the mesocolon.

__Greater Omentum__ The greater omentum attaches to the stomach along the greater curvature and the proximal part of the duodenum to the posterior abdominal wall. It is subdivided into the gastrophrenic, gastroplenic, and gastrocolic ligaments. It is a prominent peritoneal fold that hangs down like an apron and folds back and attaches to the anterior surface of the transverse colon and its mesentery.

__Lesser Omentum__ The lesser omentum attaches the stomach along the lesser curvature to the liver. It is subdivided into the hepatogastric and hepatoduodenal ligaments.

__Peritoneal Ligaments__ Consists of a double layer of peritoneum which connect organs to other organs or organs to the abdominal wall.

The liver is connected to the anterior abdominal wall by the falciform ligament, the stomach by the gastrohepatic ligament, and the duodenum by the hepatoduodenal ligament. The gastrohepatic and hepatoduodenal ligament are part of the lesser omentum.

The stomach is connected to the inferior surface of the diaphragm by the gastrophrenic ligament, the spleen by the gastrosplenic ligament, and the transverse colon by the gastrocolic ligament. The greater omentum and the gastrosplenic ligament are continuous.


 * 10. List and describe the peritoneal gutters.**

The attachments of the mesentery as well as the positions of the ascending and descending colon to the posterior abdominal wall form four “gutters” that can conduct materials (blood, ascites, infectious agents, tumor cells, bile, etc.) to other regions of the abdominal cavity.

__Right Paracolic Gutter__ Materials from the hepatorenal pouch and the supracolic compartment of the abdomen (above the transfer colon) conduct towards the infracolic compartment through the right paracolic gutter because the phrenicocolic ligament on the left side blocks flow to the left paracolic gutter.

__Left Paracolic Gutter__ Drains only the left paracolic side in the infracolic compartment because materials from the supracolic compartment are blocked by the phrenicocolic ligament and flow through the right paracolic gutter instead.

__Right Infracolic Space__ A “dead space” that can allow fluid to fill up because it is blocked by mesentery. When fluid overflows, it then flows into the left infracolic space and down towards the rectovesical/rectouterine pouch.

__Left Infracolic Space__ Flows directly towards the rectovesical/rectouterine pouch.


 * 11. Describe the peritoneal reflections located on the anterior abdominal wall.**

The coronary ligaments are two peritoneal reflections on the diaphragmatic surface of the liver, and the posterior side of the liver formed by the greater and lesser sacs respectively. The two coronary ligaments come anteriorly and unite to become continuous with the falciform ligament which is the only peritoneal reflection that anchors to the anterior abdominal wall.

Additionally, the gastrocolic ligament of the greater omentum is another peritoneal reflection that runs along the anterior abdominal wall.

The three main unpaired branches of the abdominal aorta are the celiac artery, the superior mesenteric artery, and the inferior mesenteric artery.
 * 12. List all the three unpaired branches of the abdominal aorta. Know the terminal branches of these main arteries.**

The celiac artery gives off the left gastric artery, supplying the stomach. It then branches into the splenic artery and the common hepatic artery. The splenic artery branches into the short gastric arteries, the left gastro-omental atery, and the pancreatic arteries. The common hepatic artery gives off the gastroduodenal artery and continues as the proper hepatic artery. The gastroduodenal artery splits into the superduodenal artery, the superior pacreaticoduodenal artery, and the right gastro-omental artery. The proper hepatic artery branches inot the right gastric artery, and the left and right hepatic arteries.

The superior mesenteric artery gives off five branches to supply the ascending colon, and the transverse colon: the inferior pacreaticoduodenal, instestinal branches, ileocolic, right colic and middle colic arteries. These arteries anastomose in the marginal artery of Drummond to provide redundant blood supply to the intestines, allowing a person to survive occlusions in the blood supply of the intestines.

The inferior mesenteric artery gives off three branches to supply the descending colon, sigmoid colon, and superior portion of the rectum: the left colic, sigmoidal, and superior rectal arteries. The superior rectal artery is always the last, most medial artery.


 * 13. Describe the venous drainage for the abdomen. What is the hepatic portal system?**

Venous drainage for the abdomen occurs through the hepatic portal system where blood passes through two capillary beds in the intestine and the liver before returning to the heart. This pathway allows unprocesses nutrients, etc. absorbed from the intestines to enter the liver for processing before entering systemic circulation.

The hepatic portal venous system begins at the venous ends of the capillaries in the organs of the GI tract and ends at the venous sinusoids in the liver. The portal vein is formed by the joining of the splenic vein with the superior mesenteric vein. The inferior mesenteric vein usually joins the splenic vein.


 * 14. What is a portal-systemic anastomoses? Where do these occur in the body and what is their clinical significance.**

A portal-systemic anastomosis is a connection between the venous drainage of the portal system with the systemic system. Portal hypertension can occur when portal circulation through the liver is obstructed by liver disease (cirrhosis) or tumor. Because portal system veins do not have valves, the rising pressure would cause blood to find alternative pathways to reach the systemic system, bypassing the liver and causing varicosities (enlarged veins).

Treatment of portal hypertension can be by producing a shunt surgically between the portal vein and the inferior vena cava to reduce the pressure.

__Esophageal varices__ Between esophageal branch of left gastric portal vein and esophageal branches to azygous (systemic veins). Because the enlarged vein bulges into the esophagus, a large bolus traveling down the esophagus could tear the vein open and result in death by exsanguination, which is totally not cool.

__Hemorrhoids__ Between superior rectal branch of inferior mesenteric vein (portal) and the middle / inferior rectal vein to the internal iliac (systemic).

__Caput Medusae__ Between paraumbilical branch of portal v. (in falciform ligament) and the superior / inferior epigastric veins (systemic).

__Retroperitoneal Varices (veins of Retzius)__ Between colic / duodenal / pancreatic veins and the lumbar / renal veins to the inferior vena cava (systemic).