Embryology of Coelomic Cavity and peritoneum Prof Abdulameer

Embryology of Coelomic Cavity and peritoneum Prof. Abdulameer Al-Nuaimi E-mail: a. al-nuaimi@sheffield. ac. uk E. mail: abdulameerh@yahoo. com

Anal canal www. google. co. uk/search?

Gastrointestinal tract Parts Blood supply Components Foregut Celiac artery Pharynx, oesophagus, stomach, proximal half of duodenum and the derivatives (liver, biliary apparatus and pancreas) Midgut Superior mesenteric artery Small intestine (distal half of duodenum, jejunum and ileum), caecum, vermiform appendix, ascending colon and right 2/3 of the transverse colon Hindgut Inferior mesenteric artery Left 1/3 of the transverse colon, descending colon, sigmoid colon, rectum and anal canal

Oropharyngeal membrane Located at the cranial end of the embryonic disc, it consists of a small region of tightly adherent ectoderm and endoderm cells, there is no intervening mesoderm, it represents the future opening of the oral cavity Cloacal membrane Formed at the caudal end of the embryonic disc It consists of tightly adherent ectoderm and endoderm cells, there is no intervening mesoderm. When this membrane appears, the posterior wall of the yolk sac forms a small diverticulum, the Allantois which extends into the connecting stalk Langman’s Medical Embryology Sagittal Section www. google. co. uk/search? YOLK SAC Endoderm

Folding of the embryo during the fourth week, the embryo passes in cephalocaudal and lateral folding. Folding of the embryo is influenced and directed by the expression of specific genes, in addition to that is the disproportionate growth of different parts of the embryo The Cranial area of the embryo contains the Oropharyngeal Membrane, the Cardiogenic area (the heart) and Septum transversum, Cephalocaudal Folding brings the Oropharyngeal membrane, cardiogenic area and septum transversum ventraly, forming the ventral surface of the future face, neck and chest. It brings the heart into its thoracic position and septum transversum to the diaphragm. Cloacal membrane is brought anteriorly

Cephalocaudal folding of the Embryo Sagittal sections , the cranial area Langman’s Medical Embryology www. google. co. uk/search?

(Langman’s Medical Embryology) Parietal mesoderm Yolk sac Visceral mesoderm Yolk sac

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Parietal Mesoderm Visceral mesoderm Cross Sect. Parietal Mesoderm Visceral mesoderm Lat. Fold Formation of body wall Langman’s Medical Embryolog

The primitive gut is derived from the Endoderm and Visceral Mesoderm as follows The Endoderm gives rise to 1 - Epithelial lining of digestive tract 2 - Hepatocytes of liver 3 - Endocrine and Exocrine cells of Pancreas Visceral Mesoderm gives rise to 1 -Muscle, Connective tissue and peritoneal components of the wall of the gut 2 - Connective tissue for the glands

The Primitive gut, is a blind-ended tube and is described as Foregut, Midgut and Hindgut. The Midgut, remains connected temporarily to the yolk sac by means of Vitelline duct (yolk stalk) Foregut extends from Oropharyngeal membrane Midgut: from Liver bud end of Rt. 2/3 of Transverse Colon. Hindgut: from beginning of Lt. 1/3 of Transverse Colon Cloacal membrane Yolk sac www. google. co. uk/search? Liver bud. Vitelline duct

Posterior abdominal wall Extraperitoneal Partly covered organ with peritoneum Intraperitoneal organ Dorsal mesentery Abdominal cavity Ventral mesentery Anterior abdominal wall Peritoneum Dorsal mesentery Development of Peritoneum and Mesenteries

Mesenteries Parts of the gut tube are suspended from the dorsal and ventral body walls by Mesenteries. The latter are double layers of peritoneum that surround the organ and connect it to the body wall, such organ is called intraperitoneal When an organ is sitting directly on posterior abdominal wall and covered by peritoneum on its anterior surface only, it is called extraperitoneal (retroperitoneal) organ. Ligaments: are double layers of peritoneum pass from one organ to another or from an organ to the body wall. Mesenteries and ligaments provide pathway for blood vessels, lymphatics and nerves to go to and come from the abdominal viscera. Folds and Omenta are other forms of peritoneal layers By the 5 th week, the lower part of the foregut, midgut and major part of hindgut are suspended from posterior abdominal wall by dorsal mesentery. Dorsal mesentery extends from the lower part of Oesophagus to the Cloacal region.

Ventral Mesentery: Is present only in the region of the Foregut (terminal part of the oesophagus, the stomach and the upper part of duodenum). Thus the foregut has a dorsal and ventral mesenteries, while the midgut and hindgut have got only a dorsal mesentery. The ventral mesentery is derived from Septum Transversum. ; its free lower margin contains, the Hepatic art. , Portal V. and Bile duct. Liver develops in the ventral mesentry and divides it into Lesser Omentum and Falciform Ligament. Post. Abdominal wall Extraperitoneal organ Dorsal Mesentery Intra peritoneal organ Ventral Mesentery Cross section www. google. co. uk/search? Longitudinal Section

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Development of alimentary tract passes in stage of elongation. Most parts increase in length especially between four fixed regions. The points of fixation are GIT Diaphragm A- The point where the oesophagus A passes through the developing foregut diaphragm B- The point where the proximal B part of the duodenum lying on Midgut the posterior abdominal wall C- The point at junction between C the mid and hind gut Hindgut D- The point where the rectum passes through the pelvic D Pelvic diaphragm Diaphragm Points of fixation of GIT 2/5/2022

Development of Stomach appears as a fusiform dilatation in the foregut at age of the 4 th week. Its appearance and position changes greatly as a result of the different rate of growth in various regions of its wall and also due to its rotation around a longitudinal and anteroposterior axis. The stomach rotates 90° in clockwise direction around its longitudinal axis, thus its Lt. side becomes anterior and its Rt. Side becomes posterior. Simultaneously its nerves also change their position, hence, the Lt. Vagus nerve now is anterior and the Rt. Vagus is posterior. During this rotation, its left wall grows faster than the right side, this gives rise to the development of Greater and Lesser curvatures.

Rotation of stomach around an anteroposterior axis Upper and lower ends of stomach originally lie in the midline, but during further development, the stomach rotates around anteroposterior axis in a way that its pyloric end moves to the right and upward and its cardiac end moves to the left and slightly downward, thus the stomach axis extends from upper left to lower right. Ventral mesentery Liver Lesser curvature Dorsal mesentery Greater curvature Duodenum Rotation of Stomach www. google. co. uk/search?

Formation of Lesser Sac (Omental Bursa) Stomach has dorsal and ventral mesenteries; due to the axial rotation and disproportionate growth of the stomach during the fifth week of development, there is a change in the position of these mesenteries. Longitudinal rotation pulls the dorsal mesentery to the left and creating a space behind the stomach, this space is called Omental Bursa or Lesser Sac At the same time, the ventral mesentery is pulled to the right. The Spleen develops as a mesodermal proliferation in the left layer of the dorsal mesentery of stomach. With continued rotation of the stomach, the dorsal mesentery of stomach lengthens, and the portion between the spleen and dorsal midline swings to the left and fuses with the peritoneum of the posterior abdominal wall. The fused two layers (posterior leaf of the dorsal gastric mesentery and the peritoneum covering the posterior abdominal wall) degenerate.

Posterior Lt. Kidney Spleen Stomach Liver Lesser Sac Lienorenal Ligament Gastrolienal Ligament Lesser Omentum Falciform Ligament Anterior The spleen was connected to the posterior abdominal wall at the midline, but it has changed the position of its connection, it is now connected to the posterior abdominal wall in the region of the left kidney by the mesentery called Lienorenal Ligament and is connected to the stomach by the Gastrolienal ligament.

Omental bursa (Lesser Sac) L Lesser Omentum free margin Contains Portal V. , Hepatic Art. and Bile duct S S L Falciform Ligament L. O (Lesser Sac) Less. Sac Tran. Sec. in the body Lesser Omentum Long. Sec. Development of Omental bursa (Lesser Sac) Ant. View www. google. co. uk/search?

Formation of Greater Omentum When the stomach rotates along the anteroposterior axis, the dorsal Gastric mesentery (Mesogastrium) bulges down. It continues to grow down forming a double layered sac in front of transverse colon and small intestine (like an apron). The four layers of this apron fuse together, forming the Greater Omentum hanging from the greater curvature of the stomach. The posterior layer of the greater omentum also fuses with the mesentery of the transverse colon. www. google. co. uk/search? duodenum TC mesocolon Sagittal Sections

Falciform Ligament Liver Lesser Omentum Stomach Epiploic Foramen Greater Omentum Anterior view www. google. co. uk/search?

www. google. co. uk/search? Falcif Lig. Epiploic Foramen C. P. H. TMC Lig. Teres Great Omen Les Om Trans Meso Colon Greater Omentum Anterior views Ventral mesentery of foregut Gives rise to lesser omentum and Falciform Ligament. The free margin of Falciform ligament contains the umbilical vein which is obliterated after birth to form the Ligamentum Teres.

Free margin of Lesser Omentum contains 1 - Common Bile duct 2 - Hepatic artery 3 - Portal vein The Free margin of Lesser Omentum forms the anterior boundary of the Epiploic Foramen (Foramen of Winslow), which is the opening connecting the Lesser Sac with the rest of the peritoneal cavity (Greater Sac).

Greater Omentum, Lesser Omentum, Greater Sac and Lesser Sac. Greater Omentum: is part of the dorsal mesentery of stomach, which is hanging down from its greater curvature. Lesser Omentum: is part of the ventral mesentery of stomach, it is attached superiorly to the liver and to the lesser curvature of stomach inferiorly Greater Sac: is that part of peritoneal cavity you enter, when you open the anterior abdominal wall and the parietal peritoneum. Lesser Sac: is that part of peritoneal cavity, which is trapped behind the stomach and liver.

Liver Sagittal Section in the abdomen Lesser Omentum Lesser Sac Greater Sac Lt. Kidney D Spleen An. Ad. Wall Liver TC Mesocolon Pos. A. Wall Anter. view Greater and Lesser Omentum www. google. co. uk/search?

Diaphragm Ant. Abd. Wall Umbilical vein Greater Sac Liver Stomach Peritoneum Spleen Lt. Kidney Umblicus Falciform Ligament Lienorenal lig. Post. Abd. Wall Gastrosplenic Lig. Greater Sac H. A Lesser Omentum Dorsal and Ventral Mesenteries of Foregut Prof. Abdulameer Al-Nuaimi

Falciform Lig. Liver Diaphragm Umblicus Umbilical vein Lesser Omentum Less. Sac L. Spleen S Lt. Kidney Post. Abd. Wall Greater Sac Dorsal Mesentery (Greater Omentum) Rotation of Stomach Prof. Abdulameer Al-Nuaimi

Falciform Lig. Diaphragm L. Ant. Abd. Wall www. google. co. uk/search? L. Less. Sac Spleen Lesser Omentum Kidney S Pos. Ad. Wall Greater Sac T. C S. I. Greater Omentum Formation of Greater and Lesser Omentums and Sacs Prof. Abdulameer Al-Nuaimi

Parietal peritoneum GS Ant. view L L. Om S Cross Section in the abdomen G. Om Greater and Lesser Sac www. google. co. uk/search?

Summary The primitive gut is formed as a result of the folding of the embryo. Foregut has dorsal and ventral mesentery. Liver develops in the ventral mesentery and the spleen develops in the dorsal mesentery. Stomach rotates along two axes, this leads to the formation of lesser and greater omentums, and lesser and greater sacs.

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