Development of digestive and respiratory systems M.A.Kai-Kai. Learning Objectives UNDERSTANDING: development of the gut tube from the splanchnopleure. the diverticula of the gut tubepharyngeal, foregut, midgut and hindgut. the derivatives of the diverticulalung buds, thymus, gastrointestinal tract, liver and pancreas. morphogenesis of the stomach and intestines by --rotations and positional shifts that result in the definitive positions of the GI-tract. Morphogenesis of the respiratory system the laryngotracheal groove, the lung bud, the laryngotracheal tube, branching of the bronchi Formation Of The Gut Tube(1) •Folding of somatopleure and splanchnopleure of a flat 12 day dog embryobody folds •The cranial,caudal and lateral flexures/body folds. •Rapid growth of the cranial end results in enlarged head process. •Lateral body folds grow downwards and ventrally towards midline. Formation Of The Gut Tube(2) •Body folds(BF) consists of inner splanchopleure and outer somatopleure. BF meet in ventral midline forming inner endodermal gut tube opened at the umbilicus (pig The Intestinal Portal Tube Differentiation Of Gut Tube Notochord PHARYNX MIDGUT FOREGUT Amnion Brain Amniotic cavity HINDGUT stomach Pd Cloacal plate Bladder Oral plate Lung bud D Liver Heart Pericardial cavity Yolk sac Median section through 18 days gestation of pig Ca. Cr. V Derivatives Of The Gut tube/Oesophagus Gut tube consists of three layers. 2 --inner epithelium(1) derived from 2 endoderm forms the different 1 3 functional cells of the mucosa of the GI-tract. T.S of oesophagus --the hepatocytes of the liver and secretory cells of pancreas. --the middle layer(2) of 3 mesoderm forms the stroma, supporting cells and the striated and smooth muscle. --the outer layer(3) is 3 mesoderm and visceral Splanchnic mesoderm peritoneum forms the outer Submucosal and muscular layers Endoderm Epithelial surface connective tissue Morphogenesis Of The Gut tube Development of the gut involves processes of: Elongation by rapid differential mitosis and enlargement., Herniation of part of the gut into the umbilical stalk. Rotation of several local regions of the gut. Histogenesis and functional maturation. Pharyngeal and Foregut region Pharynx Pharynx and oesophagus. The short rostral tip of the pharyngeal region form the pharynx The caudal part of pharyngeal region and rostral foregut forms the oesophagus. Oesophagus elongates to match growth of Bronchial Cr. cervical,and thoracic and abdominal regions. bud Failure to maintain growth rate results in Ca. a short oesophagus resulting in hiatal diaphragmatic hernia pocketing of stomach Oesophagus between pleuro-peritoneal membranes Schematic diagram of ventral view of gut tube showing development of pharynx and oesophagus D Dorsal mesogastrium Oesophagus Oesophagus Caudal Cranial Stomach A Ventral Mesogastrium/ Lesser omentum Duodenum Cystic diverticulum/ gallbladder Hepatic diverticulum/liver Ventral mesogastrium (i) A. Lateral B Dorsal mesogastrium/fold of peritoneum form body wall forms greater omentum Cr. Pylorus Ca. Duodenum Morphogenesis Of The Foregut. The Monogastric Stomach: The Dog view of the gut tube. The embryonic stomach is suspended dorsally and ventrally by the dorsal and ventral mesogastrium, a derivative of the splanchnopleure. (ii).The stomach rotates(180o) twice, 90o each in counterclock direction (iii) B. At end of rotation stomach lies transverse in the abdomen.With differential growth stomach forms large fundus and narrow pylorus.Stenotic pylorus common in dogs. (iv). Dorsal mesogastrium grows caudally, forms 2-layered sac, the greater omentum and omental bursa.Ventral mesogastrium forms the lesser omentum and connects the liver to the lesser curvature. Morphogenesis Of The Foregut-hindgut Derivatives and development of the intestines in carnivores The distal foregut -->develops into cranial duodenum, liver, and pancreas. The midgut--> caudal duodenum, jejunum. ileum, caecum, colon (ascending). The hindgut-->colon (transverse, descending), cloaca. The cloaca--> rectum, bladder, urogenital sinus stomach Peritoneum (contains allantoic connection) Dorsal aorta Mitosis and growth of foregut forms the intestinal loop. Gut tube is suspended by dorsal mesentery through which passes the cranial mesenteric artery(CMA). CMA acts as axis for looping of the intestines. Caudal limb develops a diverticulum,the caecum. Hindgut forms distal colon,rectum and cloaca. Intestinal loop enlongates, and rotates twice(360o) clockwise around cranial mesenteric artery. Morphogenesis Of The Foregut-hindgut Morphogenesis Of The Intestinal Loop Long intestinal loop herniates into the coelomic Ca cavity of the umbilical cord. Abdominal cavity expands to accommodate the intestine the midgut returns to the body cavity. Sequence of withdrawal of loop determines final position of the intestines. Foregut Midgut (SmallAmnion intestines) Amniotic cavity Cranial limb returns Pharynx first and forms the small intestines Caudal limb follows and forms part of the small intestine and the (Large intestines) large intestines Brain Yolk sac Heart D Cr V Chorion Notochord Herniated loop Development 0f pancreas, liver and gall bladder Stomach Oesophagus Dorsal pancreatic diverticulum Dorsal mesogastrium Duodenum Diaphragm Ventral pancreatic diverticulum Hepatic Diverticulum/ liver Blood vessels Diaphragm Ventral mesogastrium Cystic Diverticulum/gall bladder Development Of The Respiratory Diverticulum (A).The L-T groove forms on ventral floor, at level of 4th pharyngeal arch Laryngo-tracheal Grove(L-T) (B). L-T gives rise to larynx and trachea Foregut A Tracheo-oesophageal groove B Pharynx Oesophagus Larynx D Trachea V Pharynx Pharynx ( C ). Bifurcation of lung Tracheo-oesophageal bud , forms about 14 septum bifurcations Ca. Cr C Trachea Cr. Ca. Bronchial bud Oesophagus A and B, lateral view C, ventral view Ventral Views of branching of trachea into principal bronchi and lobar bronchi C RIGHT LEFT Pharynx Trachea Parietal pleura Principal bronchi Pleural cavity Pleuroperitoneal canal Visceral pleura Cr. Endoderm Respiratory epithelium, glands of trachea,bronchi, larynx and lungs Mesoderm Cartilage,muscle,blood vessels and connective tissues of trachea bronchi,larynx and lungs D Parietal pleura Trachea Principal bronchi lobar bronchi Viscera pleura Ca. LEFT RIGHT (dorsal view) Cranial lobe Trachea B Species differences in lobes of lungs Middle lobe Caudal lobe Accessory lobe Canine lungs Terminal bronchioles Minor differences Right lung has four lobes in Most species cranial, middle,accessory and caudal lobes Left lung has three lobes cranial(2parts) and caudal lobes Mesoderm C Alveolar cells Cr. Terminal sac Ca. Terminal sac stage of lung development (stage 4&5) Malformations DIGESTIVE SYSTEM Stenosis of gastrointestinal tract Atresia aniimperforate ani; failure of anal membrane to break down Oesophageal stenosis RESPIRATORY SYSTEM 1. Larygotracheal abnormalities Tracheal hypoplasia/stenosisabnormal narrowing of the trachea in part or entirely. Collapsed tracheatracheal lumen is partly occluded and the tracheal cartilages flattened. Tracheal atresia total lack of tracheal patency. Subglottic stenosismalformations of larynx 2. Pulmonary abnormalities. Accessory lungs an extra lung bud in abnormal site e.g. neck, abdomen. Pulmonary hypolasiadecreased lung development Pulmonary agenesis/aplasiaabsence of lung, very rare. Congenital pulmonary cystspart of bronchial tree loses connection with main bronchusendodermal secretions form cysts. 3. Respiratory distress syndromedifficulties in neonatal breathing difficultiesinability of alveolar epithelial cells to form enough surfactants. 4 .Neonatal maladjustment syndromeexample immotile cilia syndromeabnormal structure Summary Digestive system The gut tube is formed by folding of the splanchnopleure Divisions of gut tube into pharyngeal, foregut, midgut and hindgut regions. Each part of gut tube forms specific parts of the gastrointestinal tract, digestive glands and non-digestive organs. Morphogenesis of the stomach involves; --displacement of the stomach --differential growth and enlargement --reorientation. Development of the intestines involves elongation, herniation and rotation. Respiratory system. The pharyngeal and rostral foregut form the laryngo-trachral groove ventrally. The larynx develops cranially. The Trachael groove bifurcates into two tracheo-oesophageal grooves one on either side.The tracheal part develops into the respiratory tree by successive branching. Trachea bifurcates into 2 principal bronchi, then lobar and secondary bronchi. The branching form at different levels of bronchi down to alveolar sacs. References. 1. 2. 3. Gilbert, S., “Developmental Biology”. 7th Edition. Sinauer. Sunderland, Masachusetts.pp511-512. Carlson, B., “Patten’s Foundations of Embryology”. 6th. Edition. Mcgraw Hill. London.pp547-557. Noden, D.M., & de LaHunta, A., “The Embryology of Domestic Animals”. Pp292-305.