RCSI Embryology of Gut tube 1 PDF

Embryology of Gut tube 1 Class Year 2, Semester 1 Lecturer Fiona Cronin Department of Anatomy [email protected] Date 08-10-2024  Learning outcomes Describe the normal development of the oesophagus and stomach Discuss the main oeso...

Embryology of Gut tube 1 Class Year 2, Semester 1 Lecturer Fiona Cronin Department of Anatomy [email protected] Date 08-10-2024  Learning outcomes Describe the normal development of the oesophagus and stomach Discuss the main oesophageal and gastric congenital (developmental) abnormalities and how they present in neonates Describe the development of the diaphragm and explain how congenital hernias occur Describe how the dorsal and ventral mesogastria develop into named peritoneal structures in the adult and be able to identify these Describe the development of the spleen and its haemopoietic function in the embryo Discuss how an accessory spleen may develop and the clinical significance of this  GASTRULATION Formation of the 3 germ layers from Epiblast Primitive streak REVIEW Amnioblasts Epiblast Invaginating mesoderm cells: Yolk sac Hypoblast Some of the invaginated cells displace hypoblast and form the embryonic ENDODERM Amnioblasts Others lie between epiblast and the newly formed endoderm ECTODERM These cells form intraembryonic or embryonic MESODERM MESODERM Remaining cells of the epiblast will ENDODERM form the embryonic ECTODERM Yolk sac  Yolk sac Body stalk Amniotic sac Generation of blood cells (in wall of sac) Yolk sac Origin of primordial 19 days germ cells Midgut Hindgut Foregut Amniotic sac 24 days Primitive heart Yolk sac 24 days  Body folding Longitudinal folding (cranio-caudal) Endodermal layer becomes incorporated into the body of the embryo → gut tube Communication with yolk sac narrows – vitelline duct Midgut Midgut Foregut Hindgut Foregut Hindgut Amniotic Amniotic sac sac Amniotic sac (Secondary) yolk sac Yolk sac Vitelline duct Primitive heart Yolk sac 19 days 24 days 28 days  Body folding Transverse folding Surface ectoderm and amniotic cavity fold around laterally the gut tube becomes evident  Developing PERICARDIAL CAVITY nervous system These two parts of the coelom are called the PERIOCARDIOPLEURAL FOREGUT CANALS. They will form the PLEURAL CAVITIES for the lungs MIDGUT Developing PERITONEAL CAVITY HINDGUT In these two diagrams, red = gut, purple = coelom and brown = CNS Very little room is available for the lungs at this stage because other things must get priority; the lungs are not needed until after birth.  Neural tube Paraxial mesoderm Eye Heart Cut edge of aminion  Model Formation of the Umbilicus MO3 Folding is completed, about halfway through the embryonic period, with the formation of the umbilicus. The structures in the umbilicus include the VITELLINE DUCT leading to the remains of the yolk sac, the ALLANTOIS, two UMBILICAL ARTERIES and one UMBILICAL VEIN. With further growth the wall of the amniotic cavity fuses onto these structures, and the embryo now floats VITELLINE within the amniotic sac, linked by the DUCT umbilical cord to the developing placenta. ALLANTOIS UMBILICAL ARTERIES UMBILICAL VEIN  Overview of gut development: early stages Buccopharingeal membrane Dorsal aorta As a result of the folding after 4 wks there is Respiratory bud Posterior wall formation of the GUT TUBE or PRIMITIVE INTESTINE which is lined by PRIMITIVE INTESTINE endoderm. Heart primordium This tube is connected with Septum transversum two other cavities lined by the same epithelium which are largely located outside the embryo. Thes two cavities are: YOLK SAC (connected via Vitelline duct vitelline duct) and ALLANTOIS. allantois Cloacal membrane  Overview of gut development: division Dorsal aorta with the 3 branches for the GIT Pharyngeal gut: buccal membrane → respiratory diverticle (mouth cavity - head and neck). Foregut: up to the hepatic Pharyngeal gut bud: oesophagus – Respiratory bud stomach – first half of duodenum – liver and FOREGUT pancreas. → Territory of coeliac trunk Septum transversum Midgut: up to the left third of the transverse colon MIDGUT → Territory of superior mesenteric artery Hindgut: up to the cloaca → Territory of inferior mesenteric artery HINDGUT The pattern of arterial supply is determined early in development; therefore Cloacal membrane very rarely variable Cloaca  Three main branches of dorsal aorta supplying the gut tube Coeliac trunk supplies foregut below the diaphragm Superior mesenteric artery supplies midgut Inferior mesenteric artery supplies hindgut http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf  Endoderm give rise to: epithelial lining of the digestive tract specific cells of the glands – hepatocytes, exocrine & endocrine cells of pancreas Splanchnic intraembryonic mesoderm give rise to: stroma (connective tissue) muscle visceral layer of peritoneum  Mesenteries Dorsal mesentery – greater omentum (dorsal mesogastrium, dorsal mesoduodenum, mesentery proper, dorsal mesocolon Ventral mesentery – derived from septum transversum which divides into lesser omentum and falciform ligament  Septum transversum Mesodermal tissue Extends from thorax to stalk of yolk sac Derivatives Ventral mesentery Contributes to Liver Diaphragm The Diaphragm is Formed from: The septum transversum – Central tendon Myotomes of C3, C4 and C5, which bring them nerve supply with them, the phrenic nerve A contribution from the body wall – Pleuroperitoneal membrane A contribution from the dorsal mesentery Peripheral Attachments of the Diaphragm: Lumbar vertebrae: right and left crurae, and arcuate ligaments The costal cartilages of ribs 7 – 10 Ribs 11 and 12 The xiphisternum Central Attachments of the Diaphragm: The central tendon fuses with the fibrous pericardium  INFERIOR VENA CAVA OESOPHAGUS AORTA Diaphragmatic hernias are of two sorts: CONGENITAL and ACQUIRED  Congenital Hernias When the coelom becomes divided into three separate cavities, the diaphragm closes the continuity between the pleural and the peritoneal cavities. Sometimes the closure is incomplete, especially on the left side where there is no liver to provide support. The opening is called the FORAMEN OF BOCHDALEK. The abdominal viscera can herniate through this foramen into the pleural cavity, giving rise to the more common form of congenital diaphragmatic hernia, called a HERNIA OF BOCHDALEK. The incidence of congenital diaphragmatic hernia is about 1:2,000 births, and in about 85% of cases the condition occurs on the left side. Very rarely the diaphragm fails to fuse anteriorly with the xiphisternum and ribs leaving an irregular opening through which a HERNIA OF MORGAGNI may occur. It account for only 3% of all congenital diaphragmatic hernias. The other congenital condition that can occur in this region is a CONGENITAL SHORT OESOPHAGUS, which anchors the stomach partly into the thorax. The stomach then has a ‘Figure 8’ appearance caused by the constricting effect of the diaphragm. Vincent Bochdalek (1801-1883) was a Czech anatomist. His name is pronounced BOK-DA-LEK Giovanni Morgagni (1682-1771) was a well-known Italian anatomist and pathologist Congenital Diaphragmatic Hernia The lung that is directly affected will typically be under-developed due to the pressure of abdominal contents in the thoracic cavity. Because of this, the pulmonary arteries will not develop normally leading to pulmonary hypertension. The heart and the other lung will be indirectly affected by a midline shift of the thoracic contents. A baby born with congenital diaphragmatic hernia will probably have severe respiratory problems. Illustration © Regents of the University of Michigan  Acquired hernias are much more common Oesophagus HERNIA Diaphragm Stomach Peritoneum Stomach SLIDING HIATUS HERNIA PARA-OESOPHAGEAL HIATUS HERNIA FOREGUT http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf Lung development (foregut derivatives) Respiratory diverticulum buds off foregut Tracheo-oesophageal ridges deepen Trachea & oesophagus separate (remain joined only at larynx) Diverticulum splits to form two lung (bronchial) buds  split further into lobes lateral anterio anteri r or Esophagus  Tracheo-oesophageal malformations Tracheoesophageal fistula Fluid (milk) runs into lungs when feeding! Cough / turn blue when feeding Oesophageal atresia Fluid (milk) has nowhere to go when feeding… So comes back up – gently ⚫ No strong muscular contractions as the stomach is not involved ⚫ Like a cup overflowing… Tracheo-oesophageal malformations Most common form (> 80%)  Clinical Vignette A 5-week-old male neonate presents to the emergency department with his parents. Parents report a two days history of projectile vomiting. No history of fever, diarrhea or constipation. Mother denies bilious or bloody emesis. Physical examination reveals normal vital signs with no distress. The abdomen is soft, not distended, non-tender and no palpable mass. Ultrasound showed the pyloric muscle to be abnormally thickened. The neonate was admitted to hospital for rehydration and surgery  Stomach Rapid cell growth – tube  sac More rapid posteriorly, along the greater curvature Gives the stomach its distinctive shape Stomach rotates 90o http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf  Formation of omental bursa/ lesser sac Spleen primordium appears as a mesodermal proliferation between two leaves of the dorsal mesogastrium http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf  Clinical correlates Cells at outflow grow to form pyloric sphincter… Hypertrophy of pyloric sphincter - pyloric stenosis Projectile vomiting!!!- 6 – 8 weeks* Hard “chestnut” at epigastrium after feeding Pyloric stenosis  Clinical Vignette A female infant was born prematurely at 32 weeks gestation to a 39-year-old woman whose pregnancy was complicated by polyhydramnios. The baby began to vomit within few hours after birth, the vomitus contained bile. Marked dilatation of the epigastrium also was noted. Radiographs of the stomach showed gas in the stomach and superior part of duodenum, but no other intestinal gas was observed http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf http://staff.um.edu.mt/acus1/Gastro-intestinal.pdf  Clinical correlates Duodenal atresia If fails to recanalise - Duodenal atresia (or stenosis) Abdominal distension, vomiting and absent bowel movements Vomiting may be bilious or non-bilious, depending on level  Spleen Forms within dorsal mesentery Initially isolated islands, which then coalesce Moves to left as stomach & dorsal mesogastrium rotate Accessory spleen may be present in 10% of population Relevant post-splenectomy References Acknowledgement Prof. Robin Prof. Fabio Quondamatteo