Development of digestive and respiratory systems

1. Development of digestive and respiratory systems M.A.Kai-Kai.

2. Learning Objectives UNDERSTANDING: • development of the gut tube from the splanchnopleure. • the diverticula of the gut tubepharyngeal, foregut, midgut and hindgut. • the derivatives of the diverticulalung 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

3. Formation Of The Gut Tube(1) • Folding of somatopleure and splanchnopleure of a flat 12 day dog embryobody 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.

4. 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)

5. The Intestinal Portal Tube

6. Differentiation Of Gut Tube Notochord MIDGUT FOREGUT PHARYNX Amnion Brain Amniotic cavity HINDGUT Pd stomach Cloacal plate Bladder D Liver Oral plate Heart Cr. Ca. Pericardial cavity Yolk sac V Median section through 18 days gestation of pig

7. Differentiation Of Gut Tube • Branching formpharyngeal, foregut, midgut and Hindgut regions. Each forms specific adult organs. • Pharyngealmost rostral forms the pharynx and oesophagus • Foregut forms oesophagus, stomach and cranial duodenum, the pancreatic and hepatic diverticula. • Midgut and hindgut form the intestines. Pancreatic diverticulum Foregut Stomach Mid gut Gallbladder Lungs Hind gut Hepatic diverticulum Yolk sac Pharyngeal Urachus Bladder Cloaca

8. Derivatives Of The Gut tube/Oesophagus 2 • Gut tube consists of three layers. --inner epithelium(1) derived from endoderm forms the different functional cells of the mucosa of the GI-tract. --the hepatocytes of the liver and secretory cells of pancreas. --the middle layer(2) of mesoderm forms the stroma, supporting cells and the striated and smooth muscle of the muscularis propria. --the outer layer(3) is mesoderm and visceral peritoneum forms the outer connective tissue 2 1 3 2 Epithelium 1 1 2 3 2 2 1 2 Muscle 3 Endoderm T.S. of oesophagus Mesoderm

9. Morphogenesis Of The Gut tube Morphogenesis of the gut involves processes of: • Elongation by mitosis and looping • Differential growth • Herniation of part of the gut into the umbilical stalk. • Rotation of several local regions of the gut. • Histogenesis and functional maturation.

10. Ca. Pharyngeal and Foregut region Pharynx (i).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 cervical,and thoracic and abdominal regions. • Failure to maintain growth rate results in a short oesophagus resulting in hiatal diaphragmatic hernia which is pocketing of stomach between pleuro-peritoneal membranes Bronchial bud Cr. Oesophagus Schematic diagram of ventral view of gut tube showing development of pharynx and oesophagus

11. D dorsal cranial Dorsal mesogastrium Morphogenesis Of The Foregut.The Monogastric Stomach: The Dog B Oesophagus ventral First rotation 90o counterclockwise Cranial-caudal along longitudinal axis Duodenum caudal Cystic diverticulum Stomach Hepatic diverticulum A Second rotation 90o counterclockwise on dorsoventral axis Ventral mesogastrium cranial C D caudal Completion of rotation Stomach lies transverse Ventral Mesogastrium/ Lesser omentum Pylorus Fundus Duodenum Differential growth, large fundus, narrow pylorus E Dorsal mesogastrium/fold of peritoneum from body wall forms greater omentum

12. Morphogenesis Of The Intestinal Loop D Ca Cr V • Long intestinal loop herniates into the coelomic cavity of the umbilical cord. • Abdominal cavity expands to accommodate the intestine the midgut returns to the body cavity. • Sequence of withdrawal of the loop determines final position of the intestines. • Cranial limb returns first and forms the small intestines • Caudal limb follows and forms part of the small intestine and the large intestines Midgut (Small intestines) Amniotic cavity Foregut Chorion Amnion Pharynx Notochord (Large intestines) Brain Yolk sac Heart Herniated loop

13. 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 Dorsalaorta Peritoneum (contains allantoic connection)

14. Morphogenesis Of The Foregut-hindgut • 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 forms a diverticulum; the caecum. • Hindgut forms distal colon,rectum and cloaca. • Intestinal loop enlongates, and rotates twice(360o) clockwise around cranial mesenteric artery.

15. Ca. Development Of The Respiratory Diverticulum A Foregut (A).The L-T groove forms on ventral floor, at level of 4th pharyngeal arch Tracheo-oesophageal groove Laryngo-tracheal Grove(L-T) B Pharynx Oesophagus (B). L-T gives rise to larynx and trachea Larynx D Ca. Cr Trachea V Pharynx Pharynx C Tracheo-oesophageal septum Cr. Trachea ( C ). Bifurcation of lung bud , forms about 14 bifurcations Bronchial bud Bronchial bud Oesophagus Oesophagus A and B, lateral view C, ventral view

16. C Cr. Ca. RIGHT Ventral Views of branching of trachea into principal bronchi and lobar bronchi LEFT Pharynx Trachea Principal bronchi Parietalpleura Pleural cavity Pleuroperitoneal canal Visceral pleura Principal bronchi branch into lobar bronchi Peritoneal cavity Endoderm Trachea D Respiratory epithelium, glands of trachea,bronchi, larynx and lungs Principal bronchi Parietal pleura Mesoderm Cartilage,muscle,blood vessels and connective tissues of trachea bronchi,larynx and lungs lobar bronchi Viscera pleura

17. Cr. Ca. LEFT RIGHT Cranial part of cranial lobe Trachea Species differences in lobes of lungs Minor differences Right lung has four lobes in except the horse cranial, middle,accessory and caudal lobes Left lung has three lobes Cranial lobe with cranial and caudal parts and caudal lobes B Caudal part of cranial lobe Caudallobe Accessorylobe Canine lungs Terminal bronchioles Mesodem C Alveolar cells Terminal sac Terminal sac stage of lung development

18. Malformation of Respiratory System 1. Larygotracheal abnormalities • Tracheal hypoplasia/stenosisabnormal narrowing of the trachea in part or entirely. • Collapsed tracheatracheal lumen is partly occluded and the tracheal cartilages flattened. • Tracheal atresia total lack of tracheal patency. • Subglottic stenosismalformations of larynx • Tracheoesophageal fistula 2. Pulmonary abnormalities. • Accessory lungs an extra lung bud in abnormal site e.g. neck, abdomen. • Pulmonary hypolasiadecreased lung development • Pulmonary agenesis/aplasiaabsence of lung, very rare. • Congenital pulmonary cystspart of bronchial tree loses connection with main bronchusendodermal secretions form cysts. 3. Respiratory distress syndromedifficulties in neonatal breathing difficultiesinability of alveolar epithelial cells to form enough surfactants. 4 . Neonatal maladjustment syndromeexample immotile cilia syndromeabnormal structure

19. Summary Digestive system The gut tube is formed by folding of the splanchnopleure • The gut tube is divisible into the pharyngeal, foregut, midgut and hindgut regions. Each part of the gut tube forms specific parts of the gastrointestinal tract and digestive glands. • Morphogenesis of the stomach involvesdisplacement of the stomach, differential growth and enlargement and reorientation. • Development of the intestines involves elongation, herniation and rotation. Respiratory system • Pulmonary morphogenesislaryngotrachealgroovetracheooesophagealridgestracheoesophagealseptumlungbudlaryngotrachealtubetrachea. • Regional specification established early in development by expression of Hox genes along cranial-caudal axis. • Growth factors regulate anatomical and functional properties.

20. References. • 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.