Gross Anatomy: Peritoneal Cavity Notes 2024 PDF

Gross Anatomy: Peritoneal Cavity Page 1 of 20 Dr. Dennis J. Goebel LEARNING OBJECTIVES 1. Define the peritoneum and the peritoneal cavity. 2. Describe the general features of the peritoneum including its layers, spaces, cavities, and male...

Gross Anatomy: Peritoneal Cavity Page 1 of 20 Dr. Dennis J. Goebel LEARNING OBJECTIVES 1. Define the peritoneum and the peritoneal cavity. 2. Describe the general features of the peritoneum including its layers, spaces, cavities, and male/female differences. 3. Describe the specialized structures using descriptive anatomical terminology formed by the peritoneum including: mesentery, omentum, ligaments, folds, as well as descriptive definitions in reference to intraperitoneal, retroperitoneal structures/organs. 4. Describe the subdivisions of the peritoneal cavity: greater vs. lesser sacs and their relationship with the epiploic foramen. 5. List the features of the peritoneal cavity: peritoneal recesses, paracolic gutters. 6. Describe the sensory (visceral and somatic) innervation of the peritoneum. 7. Describe the functions of the peritoneum. 8. Summarize the reflections of parietal peritoneum transitioning to the visceral peritoneum as related to the abdominal organs. 9. Describe the 2 clinical systems for defining positions of abdominal contents. 10. Apply anatomical knowledge to discuss clinical relevancies of the peritoneal cavity. Gross Anatomy: Peritoneal Cavity Page 2 of 20 Dr. Dennis J. Goebel Session Outline I. Overview of the peritoneum II. General features of the peritoneum A. Consist of two layers 1. Parietal peritoneum 2. Visceral peritoneum B. The peritoneal cavity 1. Defined as a potential space 2. Occupies the abdominal and pelvic cavities 3. Closed in the male, 4. Open in the female III. Specialized structures formed by the peritoneum A. Defining mesentery, omentum, ligament and peritoneal folds 1. Mesentery 2. Omentum a. Greater omentum b. Lesser omentum 3. Peritoneal ligaments 4. Peritoneal folds B. Descriptive definitions 1. Intraperitoneal (peritoneal) 2. Retroperitoneal IV. Subdivisions of the peritoneal cavity A. Defining the greater and lesser sacs 1. Greater sac a. Subdivisions of the greater sac i. Supracolic compartment ii. Infracolic compartment b. Infracolic compartment 2. Lesser sac (omental bursa) a. Boundaries of the lesser sac i. Superior ii. Left iii. Inferiorly iv. Posteriorly v. Anteriorly b. Infracolic compartment 3. Epiploic foramen a. Boundaries of the epiploic foramen i. Superior ii. Left iii. Inferiorly iv. Posteriorly Gross Anatomy: Peritoneal Cavity Page 3 of 20 Dr. Dennis J. Goebel V. Features of the peritoneal cavity A. Peritoneal recesses B. Paracolic gutters VI. Sensory source and modalities of the peritoneum A. Parietal peritoneum B. Visceral peritoneum VII. Functions of the peritoneum VIII. The big picture IX. Two clinical systems for defining the regional anatomical positioning of abdominal contents X. Clinical relevance A. Peritonitis B. Peritoneal adhesions C. Ascites D. Intraperitoneal injections H. Herniation of intraperitoneal-abdominal structures Supplemental Reading Gray’s Anatomy for Students, 4rd Ed. (2020) Drake, Vogl, Mitchell. Chapter 4 Abdomen (Scroll to Section on Abdominal Viscera). Gross Anatomy: Peritoneal Cavity Page 4 of 20 Dr. Dennis J. Goebel THE PERITONEUM I. Overview of the peritoneum: The peritoneum is a single layer of squamous epithelium (mesothelium) that is derived from the mesoderm layer of the developing embryo. It forms a serous membrane, which invests most of the digestive and reproductive organs, as well as covering the walls of the abdominal and pelvic cavities (Figure 1). The complete coverage of all organs by the peritoneum in the abdominal and pelvic cavities creates a mesothelial-lined cavity (or sac) called the peritoneal cavity. The peritoneal cavity is void of “exposed” (uncovered) organs. Thus, with the exception of the fimbriae and the opening of the uterine tube in the female (which are not covered by peritoneum, see below), the peritoneal cavity exists as a potential space that contains only serous fluid and occasional macrophages, in the healthy person. Figure 1: Gray’s 4.10 To fully understand the anatomy of the peritoneum in the adult, it is important to know how this tissue invests the abdominal organs during development (note, this material will be covered (in detail) in a separate embryology lecture given later in this unit). However, a prelude to this material deserves mentioning here, in order to conceptualize how the peritoneal and pelvic cavities form, and how the abdominal and pelvic viscera are invested and suspended off of the anterior and posterior abdominal walls by peritoneum. As the developing embryo elongates and the primitive gut begins to close, the future abdominal and pelvic cavities are divided rostral-caudally by a double lined mesothelium (called the dorsal-mesogastrium, dorsal-mesoduodenum and dorsal-mesocolon) that has its origin at the base of the aorta, and its insertion at midline above the umbilicus on the ventral surface (called the ventral-mesogastrium. See Figure 2 on the next page). Between the two layers of mesothelium, the primitive gut-tube is located, along with primordial clusters of cells (found in the dorsal mesogastrium give rise to the pancreas and spleen), while another cluster of cells found in between the two layers of the ventral mesogastrium gives rise to the liver (Figure 2). As the gut closes off, the intestinal tract and associated organs continue to elongate and fold, bringing with them their respective arterial, lymphatic and nerve supply from the body wall to the developing organs, between the two sheets of mesothelium. Figure 2: Langman’s Medical Embryology 12th Ed. Gross Anatomy: Peritoneal Cavity Page 5 of 20 Dr. Dennis J. Goebel II. General features of the peritoneum A. Consist of two layers: 1. The parietal peritoneum lines the abdominal and pelvic walls (Figure 1 on previous page). 2. The visceral peritoneum invests the viscera of the abdominal & pelvic organs. B. The Peritoneal cavity 1. Defined as a potential space occupied only by fluid that lies between the parietal and visceral peritoneal layers. 2. Occupies the full extent of the abdominal and pelvic cavities. 3. The peritoneal cavity is closed in the male: There is no natural communication between the peritoneal cavity and the outside environment in the male. 4. The peritoneal cavity is open in the female: Note, the opening of the uterine tube is not covered by peritoneum (this accommodates the transport of the ovulated egg from the peritoneal cavity into the uterine tubes). Because of this, there is direct communication from the peritoneal cavity to the outside environment in the female, via uterine tube-uterus-cervix-vagina. This can serve as a direct route for the spread of infection from the female perineum into the peritoneal cavity. 5. The parietal peritoneum is separated from the body wall by extra peritoneal connective tissue. III. Specialized structures formed by the peritoneum: A. Defining a mesentery, an omentum, a ligament and peritoneal folds 1. A mesentery is a double layer of peritoneum that extends from body wall, to enclose and suspend part/all of an organ into the peritoneal cavity (Figure 3). a. An organ that is suspended by a mesentery is mobile. Examples: “the mesentery”, the transverse mesocolon, the mesoappendix and the sigmoid mesocolon. b. A mesentery accommodates the passage of arteries, veins, lymphatics and nerves, between the two sheets of the mesothelium, from the body wall to the suspended visceral organ. Figure 3: Gray’s 4.52 Gross Anatomy: Peritoneal Cavity Page 6 of 20 Dr. Dennis J. Goebel 2. An omentum is a double-layered fold of peritoneum (a mesentery) that suspends the stomach and the first part of the duodenum, to another abdominal organ (Figure 4). By definition, there are 2 omentums: a. The greater omentum attaches to the greater curvature of the stomach and the first part of the duodenum) and inserts onto the transverse colon. (See Figures 5 & 6). Figure 4: Gray’s 4.52 (modified) b. The lesser omentum attaches along the lesser curvature of the stomach and first part of the duodenum, and inserts onto the visceral surface (inferior surface) of the liver. See Figures 5 & 6. Gross Anatomy: Peritoneal Cavity Page 7 of 20 Dr. Dennis J. Goebel Figure 6: N 321 3. A peritoneal ligament is descriptive anatomical terminology used to describe regional sections of a mesentery or omentum that connects an organ with any adjacent organ or body wall (Figure 7). Examples include the hepatoduodenal and hepatogastric ligaments, which subdivide the lesser omentum, (See Figure 5 on the previous page), the gastrosplenic ligament, splenorenal ligament, gastrophrenic ligament (See Figure 14), the falciform ligament and the coronary ligaments (see Figure 9) of the liver. These will be described in detail in future Figure 7:Gray’s 4.52 (modified) enrichment presentations. a. The lesser omentum is subdivided into the hepato-duodenal ligament (portion connecting the liver to the first part of the duodenum) and the Hepatogastric ligament (portion of the lesser omentum connecting the liver to the lesser curvature of the stomach). See Figure 5. Gross Anatomy: Peritoneal Cavity Page 8 of 20 Dr. Dennis J. Goebel 4. A Peritoneal fold is a reflection of peritoneum that overlies a structure associated with the body wall. This results in the formation of a defined border over the covered structure. Examples include median-(remnant of the urachus), medial-(remnants of the umbilical arteries; rt & left) and lateral-umbilical folds (inferior epigastric arteries; rt & left). See Figure 8. Figure8:8:Gray’s Figure N 2494.52 (modified) B. Descriptive definitions: 1. Intraperitoneal- (also called peritoneal) defines any organ or structure that is suspended by a mesentery, omentum or ligament into the abdominal or pelvic cavity (see Figure 9). (Examples include the stomach, spleen, liver, portions of the transverse colon and sigmoid colon, the jejunum and ilium, and the gallbladder. Gray's, Fig. 4.52a & b Figure 9: Gray’s 4.52 (modified) (modified) Gross Anatomy: Peritoneal Cavity Page 9 of 20 Dr. Dennis J. Goebel 2. Retroperitoneal- (Behind the peritoneum) defines any region of a visceral organ that has one surface covered by visceral peritoneum and the opposing surface associated with the body wall. (See Figure 9). Examples include the ascending and descending colon, the rectum, and parts of the pancreas and duodenum and the urinary bladder (See Figure 10). Figure 10: N271 IV. Subdivisions of the peritoneal cavity. A. Defining the greater and lesser sacs: 1. The greater sac (Figure 11 on next page) is the larger of the two peritoneal-lined spaces. Access to the greater sac of the peritoneal cavity can be done by surgically opening the anterior abdominal wall. This allows direct access to the liver, the anterior surface of the stomach, the spleen, the colon, the majority of the small intestines (jejunum and ileum), the uterus and the majority of retroperitoneal structures located in the abdomen and pelvis. a. The Greater sac is subdivided into two compartments: i. Supracolic compartment: This area is superior to the transverse colon and its mesentery, and is partially under cover of the costal margin and the diaphragm. Structures related to the supracolic compartment include the liver, stomach and spleen (See Figures 11 & 12). ii. Infracolic compartment: This region is located inferior to the transverse colon and its mesentery, and leads inferiorly into the pelvic cavity. Examples of organs related to the infracolic compartment include the jejunum, ilium and the entire large intestine (Figures 11 & 12). Gross Anatomy: Peritoneal Cavity Page 10 of 20 Dr. Dennis J. Goebel Figure 11: N321 2. LESSER SAC: (also known as the omental bursa) is an enclosed compartment located posterior to the stomach, which is walled off by a series of ligaments, mesenteries and omentums. a. The boundaries of the lesser sac are: (See Figure 12 & 13) i. Superior, the posterior part of the coronary ligament of the liver, part of the gastrophrenic ligament and the diaphragm. ii. Left, the part of the gastrophrenic, splenorenal and gastrosplenic ligaments. Gross Anatomy: Peritoneal Cavity Page 11 of 20 Dr. Dennis J. Goebel iii. Inferiorly, the transverse mesocolon, the greater omentum and the transverse colon. iv. Posteriorly, the posterior abdominal wall and retroperitoneal structures including the pancreas, left adrenal gland and the left kidney. v. Anteriorly, the lesser omentum (e.g., Hepatoduodenal and Hepatogastric ligaments) and the posterior surface of the stomach. Figure 12: DJG Gross Anatomy: Peritoneal Cavity Page 12 of 20 Dr. Dennis J. Goebel Figure 13: N266 3. Epiploic foramen: In the normal individual, the lesser sac has a single natural outlet that communicates with the greater sac, called the epiploic foramen (Figures 12, 13 and 14). The epiploic foramen is located on the upper right side of the peritoneal cavity, and has defined boundaries (Figures 13 & 14). a. Boundaries of the epiploic foramen: i. Anteriorly, the hepatoduodenal ligament (containing the portal vein, common bile duct and proper hepatic artery) ii. Superiorly, the caudate lobe of the liver iii. Inferiorly, the first part of the duodenum iv. Posteriorly, the vena cava and right crus of the diaphragm. Gross Anatomy: Peritoneal Cavity Page 13 of 20 Dr. Dennis J. Goebel Figure 14: N 327, 4th Ed. V. FEATURES OF THE PERITONEAL CAVITY A. Peritoneal recesses: are blind pouches formed by folds of peritoneum which open into the peritoneal cavity. These recesses are mostly associated with structures that are transitioning between being retroperitoneal to peritoneal. 1. Examples include the paraduodenal-, superior-duodenal fossa, the inferior-duodenal fossa and the retroduodenal recess (Figure 15 on next page). These recesses occur where the duodenum transitions from being retroperitoneal to peritoneal. More on this in a later enrichment session. 2. The intersigmoid recess (Figure 16A on next page) and the retrocecal recess (Figure 16B on next page). Gross Anatomy: Peritoneal Cavity Page 14 of 20 Dr. Dennis J. Goebel Retroduodenal Figure 15: N 264a A B Netter 265b Netter 273b Figure 16 273b) B. Paracolic gutters (Figure 17): Are peritoneal-lined depression that form between the lateral sides of the ascending and descending colon and the posterior/lateral abdominal wall. These depressions form a channel, whereby fluids can easily flow from the abdominal cavity into the pelvic cavity, or vice versa. Gross Anatomy: Peritoneal Cavity Page 15 of 20 Dr. Dennis J. Goebel Rectum Netter 265a (retroperitoneal) Figure 17: N265 VI. SENSORY SOURCE AND MODALITIES OF THE PERITONEUM A. The parietal peritoneum is sensitive to touch, pain and temperature. Sensory innervation is provided by intercostal, lumbar and sacral nerves. Sensory innervation to the peritoneal surface of the thoracic diaphragm is provided by: 1. Intercostal nerves to the costal margin of the diaphragm. 2. Phrenic N. (C3-C5) to the central diaphragm. B. Visceral Peritoneum is insensitive to mechanical sensations, such as touch and temperature; however this layer, like the visceral pericardium and visceral pleura, is sensitive to stretch. VII. FUNCTIONS OF THE PERITONEUM The peritoneum serves several functions. Its primary function is to secrete a serous fluid, which aids to minimize friction of the moving intraperitoneal structures in the abdominal and pelvic cavities. It resists infection by extruding macrophages, and other immune cells into the peritoneal cavity, and has the ability to form adhesions to wall off an infection or a damaged organ (the greater omentum is notorious for this). Lastly, the surface area of the peritoneum is only second to the surface area of the skin, and has a very rapid absorption capacity for transporting injected liquids, metabolites, and injectable drugs, into the blood stream. Gross Anatomy: Peritoneal Cavity Page 16 of 20 Dr. Dennis J. Goebel VIII. THE BIG PICTURE: The reflection of the parietal peritoneum transitioning to the visceral peritoneum is elegantly visualized in Figure 18. Here, you can clearly see where the coronary ligament suspends the liver off of the thoracic diaphragm. Also, you can see where the esophagus enters the abdominal cavity and gives rise to the gastrophrenic ligament, which then transitions into the splenorenal ligament. Spanning from left to right on the anterior surface of the pancreas, you can see the origin of the transverse mesocolon. Inferior to this, you can see the superior mesenteric artery (not labeled) and the peritoneum reflection (transition from parietal to visceral) giving rise to “the mesentery”. On the right and left sides, you can see where the ascending and descending colon (which are retroperitoneal structure) were removed, and on the lower left side, where the sigmoid mesocolon was removed, and the cut blood vessels that supply the sigmoid colon are shown. Figure 18: N268  Gross Anatomy: Peritoneal Cavity Page 17 of 20 Dr. Dennis J. Goebel VIII. Two clinical systems for defining the positioning of abdominal contents A. Four-quadrant pattern: This gives rise to 4 spaces defined by a horizontal plane (called the transumbilical plane) and vertical plane (called the median plane) through the umbilicus. We will use this classification for this course. These two planes subdivide the peritoneal cavity into 4 compartments and define a right and left upper quadrant (above the transumbilical plane) and the right and left lower quadrant (located below the transumbilical plane). See Figure 20A B. Nine-region organization pattern: This is often used in the clinics, and subdivides the abdominal and pelvic regions into 9 segments. These segments are defined by two vertical planes bisecting the clavicles (called rt. & left mid-clavicular planes) and by two horizontal planes, a subcostal plane (superior) and a transtubercular plane (inferior). The 9 regions are arranged in three vertical columns (rt & left and central) and from a superior to inferior orientation. In the central column, the three regions are called the Epigastric, Umbilical and Pubic regions. The right and left lateral columns have corresponding Hypochondrium, Lateral lumbar (Flank) and Inguinal (Groin) regions. See Figure 20B). A B Figure 19 Gross Anatomy: Peritoneal Cavity Page 18 of 20 Dr. Dennis J. Goebel IX. CLINICAL RELEVANCE A. Peritonitis: Inflammation of the peritoneum is known as peritonitis. A ruptured appendix or perforated bowel causes of peritonitis, and is life threatening. B. Peritoneal adhesions: Inflammation or trauma (e.g., post-surgical) to the visceral or parietal peritoneum may result in adhesions. Adhesions may reduce mobility of the viscera and produce tension that can result in peritoneal pain (visceral, parietal, or both). Look for these in your “first patient”. C. Ascites: Excess accumulation of fluid within the peritoneal cavity is called ascites, and is related to metastatic cancer growth within the peritoneal cavity. D. Rapid drug or metabolite uptake via intraperitoneal inject (i.p. injection): The mesothelium layers (both visceral and parietal layers) have a very large surface area which are capable of facilitating rapid uptake of intraperitoneal (i.p.) injectable fluids, containing metabolites or pharmacological agents, into the blood stream. E. Herniation of intraperitoneal-abdominal structures: The jejunum and ileum are extremely mobile and have the ability to blunt-dissect their way out (e.g., herniate) of the abdominal and pelvic cavities. Common places of herniation include the inguinal, umbilical, diaphragmatic and femoral regions. In addition, the epiploic foramen and peritoneal recesses, such as the paraduodenal recess, are also sites (see Fig 20) where the small intestine can dissect its way out of the peritoneal cavity. In extreme cases, the small intestine can become strangulated in their confines, which can lead to a number of life-threatening issues that will require surgical intervention. Fig 20. Intra-abdominal hernias Epiploic hernia1 Internal hernia 1Ross et al., Abdominal Imaging, Hamm, B and Ros, P.R. (2013) Springer (Berlin/Heidelberg). Gross Anatomy: Peritoneal Cavity Page 19 of 20 Dr. Dennis J. Goebel Figure 21: To be used in my lecture Thoracic Diaphragm Transverse part of the Duodenum Gross Anatomy: Peritoneal Cavity Page 20 of 20 Dr. Dennis J. Goebel Sources for Figures in the notes: Drake, Vogl and Mitchell, Gray's Anatomy for Students, 4rd Edition, Churchill & Livingstone, Philadelphia, © 2020. Sadler, Langman's Medical Embryology, 5th Ed.,Williams & Wilkins, Baltimore, © 1985. Netter, Atlas of Human Anatomy, 6th Ed., Saunders, Philadelphia, © 2014.