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Abdominal-Peritoneal Cavities
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Fall 1999 Moore, pp152-85 Lecture 17 Dr. C. Dlugos
ABDOMINAL - PERITONEAL CAVITIES General Overview: The abdominopelvic cavity is the largest cavity of the body and is bounded cranially by the diaphragm and caudally by the levator ani and coccygeus muscles. The abdominal cavity is divided into two parts: 1) the abdominal cavity proper and 2) the pelvic cavity. The contents of the abdominal cavity include viscera, blood vessels and nerves, and the peritoneum. The abdominal cavity extends into the rib cage so that many abdominal organs particularly foregut deriviatives are protected by the ribs. The greater or false pelvis protects the lower abdominal organs. The anterior and lateral abdominal walls contain crisscrossing muscle fibers which protect and bolster this region which contains soft and vital viscera.
Objectives: 1. To become familiar with the planes and regions of the abdomen. 2. To understand the peritoneum, and its relationships with the abdominal organs.
Planes: A. There are two horizontal planes and two vertical planes which divide the abdomen into six regions or compartments. These regions are important for the localization of organs and pain (Moore, Fig. 2-1 A,B, p177).
a. right hypochondriac (liver), epigastric (stomach) , left hypochondriac (spleen) regions b. right lumbar (right kidney), umbilical (transverse colon) and left lumbar regions (left kidney) regions
The peritoneal cavity: formed from the intraembryonic coelomic cavity (Sadler Fig.14.2, p244). The gut starts as a simple tube which, when mature, fills most of the abdominal cavity limiting the peritoneal cavity to a potential space between the parietal peritoneum and the visceral peritoneum. No organs are contained within the peritoneal cavity and the terms abdominal and peritoneal cavity are not synonymous.
Terms related to peritoneum: 1. Mesentery – a double layer of peritoneum which encloses an organ and connects it to body wall, blood vessels supplying that organ lie within the mesentery. Mesentaries result from the evagination of the peritoneum by an organ (Moore Fig.2.12., p212)
4. Recesses - subdivision of the peritoneal cavity, usually blind ended sacs, such as the subphrenic and the hepatorenal recess. The hepatorenal pouch is bounded by the the liver, the right kidney, the colon, and the duodenum, and represents the lowest point of the peritoneal cavity when a patient is lying down. The retrocecal recess is important since the vermiform appendix usually lies in this recess.
2. Omental bursa or lesser sac: is a subdivision of the peritoneal cavity between stomach and posterior abdominal wall. This sac allows for distension of the stomach and communicates with the peritoneal cavity proper through the epiploic foramen of Winslow (omental foramen). (Moore,Fig. 2.24.p216).The omental bursa is bounded on its lateral side by the gastrosplenic and lienorenal ligament. The stomach is located anterior to the bursa, the pancreas posterior to it. The omental bursa includes: 1) a superior recess, between the liver and the diaphragm, 2) a main portion, behind the stomach,and 3) an inferior recess between the double layers of the gastrocolic ligament. The inferior recess is obliterated in the adult.
Modifications of parietal peritoneum in anterior body wall
Named mesenteries (double layer) attaching to posterior body wall Functions: transport vessels, nerves, and lymphatics, allow for mobility of the intestine. Examples of mesenteries include:
Omentum- derived from the primitive mesentery and functions to attach the stomach and proximal duodenum to the body wall, parts of the omenta were subdivided by early anatomists into named ligaments. Fig2.21. p213).
1.Greater omentum- originally 4 layers, inner two disintegrate, fat filled apron in humans, suspended from greater curvature of stomach, localizes infections "policeman of GI tract", gastrocolic ligament is its major portion.The gastrosplenic and gastrophrenic ligaments comprise smaller portions. The greater omentum is a derivative of the dorsal mesentery.
2. Lesser omentum: derived from the ventral mesentery of the embryo with the falciform ligament, attaches to lesser curvature and dorsal surface of stomach (hepatogastric and hepatoduodenal ligaments).
Peritoneal gutters: (Moore 2.23 B, Dissector Fig. 2.39, p64,). Four depressions or pathways for the conduction of fluid and infections which are formed by the attachments of the mesenteries of the small intestine, ascending and descending colon. These include the right lateral paracolic gutter, the left lateral paracolic gutter, the gutter to the right of the mesentery and the gutter to the left of the mesentery. The lateral right paracolic gutter is especially important since it serves as a pathway for infection from the hepatorenal pouch into the pelvis.
Ligaments 1. organ to organ attachments, some specific regions of the omenta 2. Examples: gastrosplenic-stomach to spleen gastrophrenic-stomach to diaphragm
Esophagus: (Moore, Fig 2.30.,p225). The esophagus pierces the diaphragm at the esophageal hiatus at vertebral level T10. The abdominal portion of the esophagus comprises a 1 cm segment which grooves the left lobe of the liver before it enters the stomach at the cardiac orifice. Within the abdomen, the esophagus is covered with peritoneum on its anterior and lateral borders and is surrounded by the esophageal plexus. Arterial supply of abdominal portion: esophageal branches from the left gastric artery of celiac trunk and left inferior phrenic artery
Stomach: (Moore Fig 2.31., p226). The stomach is situated in the left upper quandrant of the abdomen, partially covered by the ribs. It is grossly divided into four regions and has two curved surfaces.
Surfaces: Greater curvature; left border of the stomach,notched where the esophagus enters it, the cardiac notch, greater omentum attaches to it
Lesser curvature: right border, at its pyloric end is the angular notch Regions:
Duodenum:(Moore, Table 2.7. p239). The duodenum, a C-shaped loop, is about twelve finger breadths long and is divided into four parts: a superior part (1), a descending part (2), a horizontal part (3), and an ascending part (4). Parts 2 and 3 are completely retroperitoneal. The duodenum originates at vertebral level L1. The second part or the descending portion descends to L3. The third portion, the horizontal portion remains at L3 and the ascending portion rises to L2. The first two portions of the duodenum are derived from the embroyologic foregut and are supplied by the celiac artery. The last two parts of the duodenum are supplied by branches of the superior mesenteric artery and are part of the embroyological midgut. Specific features of the parts include: 1. superior region, also called the duodenal bulb 2. descending region,The common bile duct and the main pancreatic duct enter the descending portion of the duodenum at the ampulla of Vater. (hepoatopancreatic ampulla), an outgrowth on the outside of the duodenum. The major duodenal papilla , marks the opening of these ducts on the inside of the duodenum.. 3. The superior and descending region of the duodenum are the site of duodenal ulcers which occur above the major duodenal papilla. Arterial supply: Embryology, both foregut and midgut, branches of celiac and superior mesenteric arteries
Jejunum and Ileum: ( Moore,Fig. 2.38, p242-243 , Fig. 2.39. p245, Table 2.8, p244). The jejunum and ileum are suspended by the mesentery which is directed obliquely, inferior, and to the right from the duodenal jejunal flexure to the left side of L2 vertebrae and to the right sacroiliac joint (next to midbody of L5). The jejunum and ileum are 6-7m long and are covered by the greater omentum. The jejunum lies mostly in the umbilical region of the abdomen, the ileum occupies the hypogastric and inguinal regions. The jejunum and thje ileum can be distinguished from one another by the features listed below : 1. The jejunum is more muscular than the ileum 2. the arrangement of blood vessels within the mesentery is different in both organs. Intestinal arteries form the superior mesenteric form arterial arcades from which straight vessels called vasa recta arise. In the ileum, the arterial arcades are more complex and the vasa recta shorter than in the jejunum. 3. Plicae circulares:- spiral folds of mucous membrane are more pronounced in the jejunum and more spaced in the ileum Arterial supply: branches of superior mesenteric arteries
Large Intestine: (Moore, Fig. 2.42, p249 and Fig. 2.43, p250) about 1.5 m long comprised of cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. The transverse colon has a mesentery as does the sigmoid colon. The large intestine commences at the ileocecal junction. The descending colon becomes the sigmoid colon when it crosses the pelvic brim. The large intestine has a greater diameter and some gross features which distinguish it from the small intestine. These features include: 1 taenia coli-longitudinal muscle layer is incomplete, forms three stripes on surface 2. haustra-sacculations of the large intestine 3. appendices epiploicae-fat-filled peritoneal sacs, can become filled with waste in diverticulutis There are two flexures present in the large intestine: 1. hepatic flexure-ascending to transverse colon 2. splenic flexure-transverse colon to descending colon Arterial supply: branches of superior and inferior mesenteric arteries .
Note: Specific arterial supply to individual organs will be discussed in the next lecture since it is easier to learn the major branches of an artery supplying a region before you learn the specific branches. You are, however, responsible for the specific branches. Helpful correlations between the embryo and the adult:
Foregut derivatives Pharynx, lungs, bronchi, and trachea, esophagus, stomach , superior and descending duodenum, liver, gallbladder, and pancreas Arterial supply: celiac artery for all foregut derivatives in the abdomen
Midgut derivitives Horizontal and ascending duodenum, jejunum, ileum, ascending colon, transverse colon Arterial supply: superior mesenteric artery
Hindgut derivatives: Descending colon, sigmoid colon, rectum, anal canal to pectinate line Arterial supply: inferior mesenteric artery
Derivatives of the ventral mesentery: Falciform ligament, lesser omentum (hepatogastric and hepatoduodenal ligments )
Derivatives of the dorsal mesentery: Greater omentum: gastrocolic, gastrosplenic, gastrophrenic ligaments Lienorenal ligament Mesentery of jejunum and ileum Mesocolon : transverse and sigmoid Mesoduodenum: lost in the adult |