MD124 Anatomy of the Abdomen (Viscera & Peritoneum) 2023-2024 PDF

MD124: Gastrointestinal System Abdominal Viscera & Peritoneum Academic Year 2023-2024 Alexander Black Learning Objectives Objectives Learning After studying this material, you will be able to: ✓ Outline the abdominal viscera in situ and their relationship to the alimentary system: ✓ Differentiate pa...

MD124: Gastrointestinal System Abdominal Viscera & Peritoneum Academic Year 2023-2024 Alexander Black Learning Objectives Objectives Learning After studying this material, you will be able to: ✓ Outline the abdominal viscera in situ and their relationship to the alimentary system: ✓ Differentiate parietal peritoneum from visceral peritoneum ✓ Distinguish intraperitoneal versus extraperitoneal organs and classify: intraperitoneal, retroperitoneal (primary 1° and secondary 2°) and infraperitoneal (a.k.a subperitoneal) ✓ Describe the following abdominal structures associated or derived from the peritoneum:  Greater omentum  Lesser omentum  Lesser sac a.k.a. Omental bursa – differentiate from the Greater sac ✓ Identify the boundaries of the omental (epiploic) foramen ✓ Define the supracolic viscera (distal esophagus, stomach, spleen, liver, gallbladder, pancreas and proximal duodenum) and relate the relevant surface anatomy, close anatomical relationships with other structures, arterial supply, venous drainage, innervation, lymphatic drainage and associated ligaments within the abdominal cavity ✓ Describe the anatomical relationships of the infracolic viscera: small intestine (distal duodenum, jejunum and ileum), large intestine (cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon), rectum and the anal cana READING: Grays Student: 303-310 Acland: 5.2.1 & 5.2.2 Overview: Mechanical breakdown and propulsion Peristalsis Segmentation Digestion: Gastric acid Bile Pancreatic juices Absorption Nutrients Water Function of Abdominal Viscera Preview: Development of the Gut Tube Amniotic cavity Amniotic cavity Visceral (splanchnic) mesoderm Endoderm Parietal (somatic) mesoderm Parietal mesoderm Visceral mesoderm Ectoderm Ectoderm Connection between gut & yolk sac Yolk sac Coelom (forming the body cavity) Body cavity (a.k.a. Peritoneal cavity) Gut tube Endoderm ~ Day 24 ~ Day 21 DORSAL MESENTERY ~ Day 28 Transverse Sections Lateral plate mesoderm divides: 1. 2. Cloacal membrane Visceral (splanchnic) layer Parietal (somatic) layer Amnion grows faster than the yolk sac causing the lateral body walls to fold down towards midline and fuse together to form a cavity. Dorsal mesentery suspends the gut tube from the dorsal (posterior) wall into the peritoneal cavity. Oropharyngeal membrane Development of the Gut Tube Preview: Amniotic cavity Oropharyngeal membrane Hindgut Foregut Remnant of oropharyngeal membrane Heart tube Pericardial cavity Septum transversum Yolk sac ~ Day 21 Midsagittal Sections Liver bud Midgut Connecting stalk Heart tube Lung bud Cloacal membrane Allantois Allantois VENTRAL MESENTERY Yolk sac Vitelline duct ~ Day 28 ~ Day 24 Cephalocaudal folding also helps to close the gut tube The ventral mesentery is formed from the septum transversum - ventral mesentery is a mass of mesenchyme below the diaphragm and between the stomach and ventral (anterior) body wall Cloacal membrane Oropharyngeal membrane The primitive gut starts as a simple straight tube however increased GI growth in relation to a limited body cavity at the 10th week results in: ▪ ▪ Looping & twisting Rotation & displacement ▪ ▪ Retroperitoneal structures Physiological umbilical herniation ▪ Formation of recesses Preview: Embryology of the Peritoneum Mesenteries and ligaments Ventral mesentery: provide pathways for vessels, nerves, and lymphatics to travel back and ▪ Only found between the foregut and the upper portion of the duodenum. ▪ Ventral mesentery is pulled towards the right side of the body! ▪ Associated with the liver & lesser curvature of the stomach forth between abdominal organs “Mesentery” Defined as a membranous fold attaching an organ to the body wall Liver Lesser omentum Diaphragm Falciform ligament (ventral) Dorsal mesogastrium Celiac trunk (ventral) Dorsal mesoduodenum Vitelline duct Dorsal mesentery: ▪ Extends continuously from the foregut to the end of the hindgut. ▪ Dorsal mesentery is pulled towards the left side of the body! ▪ Associated with the posterior abdominal wall Superior mesenteric a. Mesentery proper Allantois (dorsal) Inferior mesenteric a. Cloaca Umbilical artery Dorsal mesocolon Preview: Development of the Omental Bursa Lesser peritoneal sac Greater peritoneal sac Stomach Pancreas (a.k.a. Omental bursa) Duodenum Mesentery of the transverse colon Lesser peritoneal sac (Omental bursa) Greater omentum Mesentery proper Bulging of the dorsal mesogastrium (a.k.a. Greater omentum) Double layers of peritoneum fuse together Small intestine Sagittal View Anterior view Transverse view A L R P Liver Ventral mesentery Lesser omentum Stomach (rotating) Left kidney Dorsal mesentery Liver Gastrosplenic lig. Spleen Splenorenal (lienorenal) lig. Lesser sac (Omental bursa) Peritoneal Cavity Left lobe of liver When the anterior abdominal wall is reflected to expose the contents of the abdominal cavity, everything that can be seen is covered in peritoneum No structures lie between the parietal and visceral layers of peritoneum as this “space” is the peritoneal cavity In life, fluid occupies this potential space to allow movement and mobility of certain organs Peritoneal cavity can be divided into: Greater sac – main compartment Lesser sac – hidden from view All abdominal viscera have a relationship to the peritoneum Peritoneum: Abdominal cavity covering Covers and lines the internal walls of the abdomen → Pain is well localized (very sensitive) → Served by the same neurovasculature as the adjacent wall/structure Transverse colon Liver Parietal layer of peritoneum Visceral layer of peritoneum Covers and invests abdominal organs that protrude into the peritoneal cavity Stomach → Pain is generalized (is referred) → Served by the same neurovasculatureas the organ it is covering Portalv. IVC Intervertebral disc T12 IVC Right Peritoneal cavity Normally a “potential” fluid-filled space between the parietal and visceral peritoneum Kidney Peritoneal structures Formed from more than one layer ofperitoneum → greater omentum, lesser omentum, mesentery, peritoneal ligament Division of the Peritoneal Cavity: Greater sac The peritoneal cavity is a space between parietal & visceral peritoneum, it can be divided into two “sacs” Greater Sac: ▪ Main compartment of the peritoneal cavity ▪ Extends from the: Diaphragm to Pelvis ▪ Remember NO organs are in this potential space! Diaphragm Falciform ligament Males → Peritoneal cavity is completely closed Transverse colon Females →There is an opening in the peritoneum through the uterine tubes Greater omentum Sac: A cavity within an organism that is enclosed by a membrane and contains air, liquid or solid structures Division of the Peritoneal Cavity: Greater sac Males → Peritoneal cavity is completely closed to the external environment Females →The peritoneal cavity can connect to external environment via the internal reproductive organs Division of the Peritoneal Cavity: Lesser sac Pancreas Cut edges of the Lesser Sac: (deep to the peritoneum) greater omentum ▪ Also known as the omental bursa ▪ Remember NO organs here either! ▪ Forms due to the twisting and rotation of the gut. ▪ Small compartment that is lined with peritoneum and is positioned: ▪ Posterior to → Stomach & greater omentum ▪ Anterior to → Parietal peritoneum & pancreas The omental foramen is an opening that provides a direct communication between the greater & lesser sacs and can also be known as: ▪ ▪ Epiploic foramen Foramen of Winslow Bursa: Latin word for bag or purse and is defined as being a fluid-filled sac or sac-like cavity Knowledge of this area is important Boundaries of the Omental Foramen Anterior border: Diaphragm Hepatogastric ligament Hepatoduodenal ligament: The free edge of the lesser omentum Contains the portal triad 1. 2. 3. Hepatoduodenal ligament Common bile duct Hepatic portal vein Hepatic artery proper Greater omentum Posterior border: Inferior vena cava Right crus of the diaphragm Left Kidney Right Kidney Superior border: (Caudate lobe of) the liver Inferior border: IVC 1st part of the duodenum Duodenum Transverse colon Greater omentum Stomach Spleen Structures associated with, or derived from, peritoneum 1. Mesentery: defined as a double layer of peritoneum resulting from the invagination of the peritoneum by organs. 2. Omenta (Greater and Lesser): are extensions of peritoneum that form ligamentous “aprons” that extend from the stomach & proximal duodenum to adjacent organs. 3. Peritoneal ligaments: defined as a membranous fold (a.k.a. double layer of peritoneum) that supports an organ by helping to keep it in anatomical position. 4. Peritoneal recesses: defined as potential spaces in the abdominal cavity where excess fluid may collect. 5. Peritoneal fossae: are depressions in the anterior abdominal wall that are lateral to the three respective umbilical folds. 1. Mesentery Mesenteries (and ligaments) provide pathways for vessels, nerves, and lymphatics to pass between abdominal organs ▪ Greater omentum (reflected) Mesentery helps to provide a continuous connection between the visceral and parietal peritoneum ▪ Transverse mesocolon Ileum (cut) Jejunum (cut) Mesentery proper (cut) Sigmoid mesocolon Lateral umbilical fold Arcuate line Contains fat as well as the arteries, veins, lymphatic vessels, and nerves that supply the abdominal organs ▪ Also functions to connect organs to the posterior abdominal wall ▪ Named according to the organs they connect:  Mesoesophagus (embryonic)  Mesogastrium (embryonic)  The “Mesentery” proper (of small bowel)  Mesoappendix  Transverse mesocolon  Sigmoid mesocolon 2. Omenta (singular = omentum) Lesser Omentum: Greater Omentum: ▪ DOUBLE layered peritoneal fold ▪ Connects the liver to the LESSER curvature of the stomach and the first part of the duodenum ▪ FOUR layered peritoneal fold Connects transverse colon to GREATER curvature of stomach Hangs down and is able to move within the peritoneal cavity Can be divided into two ligaments: 1. 2. Hepatogastric → Thin and membranous portion Hepatoduodenal → Thick free edgecontaining the portal triad “Abdominal Policeman” Can wrap around organs to localise inflammation and prevent peritoneal adhesions 3. Peritoneal Ligaments Gastrophrenic lig. Gastrosplenic lig. Ligaments can connect: Organs to another organ An organ to the abdominal wall Splenorenal lig. *Phrenicocolic lig. ▪ Gastrocolic lig. Coronary ligament (limited by left/right triangular ligaments) ▪ Falciform ligament ▪ Round ligament of liver (a.k.a. ligamentum teres hepatis) ▪ Hepatogastric ligament ▪ Hepatogastric ligament ▪ Gastrophrenic ligament ▪ Gastrosplenic ligament Hepatoduodenal ligament (a.k.a. thick edge lesser omentum) Liver ▪ Gastrocolic ligament Gastrosplenic ligament (a.k.a. gastrolienal ligament) (a.k.a. gastrolienal ligament) (a.k.a. membranous lesser omentum) ▪ ▪ ▪ Splenorenal ligament (a.k.a. lienorenal ligament) *Note there is also a phrenicocolic ligament Stomach Spleen 4. Peritoneal Recesses Paracolic gutters: Groove or space between the abdominal wall and the lateral aspect of the ascending or descending colon Allows communication between the supracolic and infracolic regions of the greater sac Right paracolic gutter Left paracolic gutter Important for peritoneal fluid flow Diaphragm Subphrenic recesses: Located below the diaphragm Separated into left and right by the falciform lig. Potential site for fluid collection Right subphrenic space Coronary Left subphrenic space ligament Subhepatic space: (anterior) Bare area Liver (posterior) Hepatorenal recess: Potential site for fluid collection Coronary lig. Coronary lig. Immediately inferior to the liver Extension of the subhepatic space between the visceral surface of the liver and the right kidney Lung Round lig. of liver Falciform ligament Posterior abdominal mm. Hepatorenal recess Diaphragmatic surface of the liver Visceral surface of the liver Anterior subphrenic recess Subhepatic space Abdominal Organs: Relationships to the peritoneum Intra-peritoneal Organs Visceral peritoneum Parietal peritoneum Intraperitoneal organs: Defined as being almost entirely wrapped in visceral peritoneum Usually suspended by mesentery in the abdominal cavity Highly MOBILE organs Stomach Liver Spleen Tail of the pancreas Duodenum: 1st part Jejunum Ileum Cecum & appendix Transverse colon Sigmoid colon Uterus Uterine tubes Retro-peritoneal Organs Retro-peritoneal Organs Retroperitoneal organ: Defined as lying behind the peritoneal cavity with only part of its surface covered by peritoneum. 1° - Primary retroperitoneal structures are retroperitoneal from the start of their development. 2° - Secondary retroperitoneal structures were once suspended within the abdominal cavity by mesentery but migrated posteriorly to end up behind the peritoneum. 1° Duodenum: 2nd, 3rd & 4th parts 2° Suprarenal (adrenal) glands Ureters Pancreas: Head, neck and body Kidneys Ascending Colon Aorta and IVC Descending colon Esophagus Rectum: Proximal 1/3rd Mnemonic for retroperitoneal organs: SAD PUCKER Infra(/extra)-peritoneal Organs Infraperitoneal organ: Defined as being beneath the peritoneal cavity a.k.a. Subperitoneal Only part of its surface is covered by peritoneum Rectum: Distal 2/3rds Urinary bladder Organizing Abdominal Viscera: Compartments In the abdominal cavity, the transverse mesocolon can be used to delineate the boundary between supracolic and infracolic abdominal compartments: ▪ Supracolic viscera: Supracolic: Visceral structures below the diaphragm and above the transverse mesocolon ▪ Infracolic viscera:  Distal esophagus  Stomach  Duodenum: 2nd, 3rd & 4th parts  Duodenum: 1st & part of 2nd  Jejunum  Pancreas  Ileum  Spleen  Liver  Gallbladder  Small intestine  Cecum  Appendix  Large colon  Rectum  Anus Organizing Abdominal Viscera – Arterial Supply Foregut Distal esophagus Stomach Spleen* Pancreas Liver Gallbladder Duodenum: 1st & (proximal)2nd part Duodenum: (distal)2nd, 3rd & 4th parts Jejunum Ileum Cecum Appendix Ascending colon Transverse colon: Proximal 2/3rds Hindgut Branches from the abdominal aorta at the level of T12 Superior mesenteric a. Midgut Celiac trunk Transverse colon: Distal 1/3rd Descending colon Sigmoid colon Rectum & Anal Canal (upper half only): Branches from the abdominal aorta at the level of L1 Inferior mesenteric a. Branches from the abdominal aorta at the level of L3 Arterial Supply - Preview Cross sectional Anatomy - Preview