Development of digestive and Development of digestive and respiratory systemsrespiratory systems

M.A.Kai-Kai.M.A.Kai-Kai.

Learning Objectives

UNDERSTANDING:UNDERSTANDING: development of the development of the gut tubegut tube from the splanchnopleure. from the splanchnopleure.the the diverticula diverticula of the gut tubeof the gut tubepharyngeal, foregut, midgut pharyngeal, foregut, midgut and hindgut.and hindgut.the derivatives of the diverticulathe derivatives of the diverticulalung buds, thymus, lung buds, thymus, gastrointestinal tract, liver and pancreas.gastrointestinal tract, liver and pancreas.morphogenesismorphogenesis of the stomach and intestines by of the stomach and intestines by

----rotationsrotations and and positional positional shifts that result in the definitive shifts that result in the definitive positions of the positions of the GI-tract.GI-tract.Morphogenesis of the Morphogenesis of the respiratoryrespiratory system system the the laryngotracheal groove, the lung bud, the laryngotracheal laryngotracheal groove, the lung bud, the laryngotracheal tube, branching of the bronchitube, branching of the bronchi

Formation Of The Gut Tube(1)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)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 TubeThe Intestinal Portal Tube

HeartPericardialcavity

Oral plate

AmnionAmniotic cavity

Brain

Notochord

Yolk sac

Liver

FOREGUTMIDGUT

HINDGUT

PHARYNX

Differentiation Of Gut TubeDifferentiation Of Gut Tube

D

V

Ca.Cr.

Pd

Median section through 18 days gestation of pig

Bladder

Cloacal plate

stomach

Lung bud

Derivatives Of The Gut tube/OesophagusDerivatives Of The Gut tube/Oesophagus Gut tube consists ofGut tube consists of three three layerslayers..

----inner epithelium(1)inner epithelium(1) derived from derived from endoderm forms the different endoderm forms the different functional cells of the mucosa of functional cells of the mucosa of the GI-tract.the GI-tract.

--the hepatocytes of the liver and --the hepatocytes of the liver and secretory cells of pancreas.secretory cells of pancreas.

--the--the middle layer(2)middle layer(2) of of mesoderm forms the stroma, mesoderm forms the stroma, supporting cells and the striated supporting cells and the striated and smooth muscle.and smooth muscle.

--the--the outer layer(3) outer layer(3) is is mesoderm and visceral mesoderm and visceral peritoneum forms the outer peritoneum forms the outer connective tissueconnective tissue

1

2

2

3

3

3Splanchnic mesoderm Submucosal and muscular layers Endoderm

Epithelial surface

T.S of oesophagus

Morphogenesis Of The Gut tubeMorphogenesis Of The Gut tube

DevelopmentDevelopment of the gut involves processes of: of the gut involves processes of:ElongationElongation by rapid differential mitosis and enlargement.,by rapid differential mitosis and enlargement.,Herniation Herniation of part of the gut into the umbilical stalk.of part of the gut into the umbilical stalk.RotationRotation of several local regions of the gut.of several local regions of the gut.HistogenesisHistogenesis and functionaland functional maturation.maturation.

Pharyngeal and Foregut regionPharyngeal and Foregut regionPharynx and oesophagusPharynx and oesophagus. . The short The short rostralrostral tip of the tip of the pharyngealpharyngeal region region form the pharynx form the pharynx The caudal part of The caudal part of pharyngealpharyngeal region and rostral region and rostral foregut forms the foregut forms the oesophagusoesophagus..Oesophagus elongates to match growth of Oesophagus elongates to match growth of cervical,and thoracic and abdominal regions.cervical,and thoracic and abdominal regions.Failure to maintain growth rate results in Failure to maintain growth rate results in

a a short oesophagusshort oesophagus resulting in resulting in hiatalhiatal diaphragmatic herniadiaphragmatic hernia pocketing of stomach pocketing of stomach between pleuro-peritoneal membranesbetween pleuro-peritoneal membranes

Bronchialbud

Oesophagus

Pharynx

Schematic diagram of ventral view of gut tube showing development

of pharynx and oesophagus

Ca.

Cr.

Morphogenesis Of The Foregut.The Monogastric Stomach: The Dog

Dorsal mesogastrium

Ventral mesogastrium

Oesophagus

Stomach

DuodenumCystic diverticulum/gallbladder

Hepatic diverticulum/liverAPylorus

Duodenum

Ventral Mesogastrium/Lesser omentum

Dorsal mesogastrium/fold of peritoneum form body wall forms greater omentum

D B

(i) A. Lateral view of the gut tube. The embryonic stomach is suspended dorsally and ventrally The embryonic stomach is suspended dorsally and ventrally by the dorsal and ventral mesogastrium, a derivative of the splanchnopleure.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 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 omental bursa.Ventral mesogastrium forms the lesser omentum and connects the liver to the lesser curvature. lesser curvature.

Oesophagus

Cranial

Caudal

Cr. Ca.

Morphogenesis Of The Foregut-hindgutMorphogenesis Of The Foregut-hindgut

Derivatives and development of Derivatives and development of the intestines in carnivoresthe intestines in carnivores

The distalThe distal foregutforegut-->develops into cranial -->develops into cranial duodenum, liver, and duodenum, liver, and pancreas.pancreas.TheThe midgutmidgut---> caudal-> caudal duodenum, jejunum. ileum, duodenum, jejunum. ileum, caecum, colon (ascending).caecum, colon (ascending).TheThe hindguthindgut--->colon ->colon (transverse, descending), (transverse, descending), cloaca.cloaca.TheThe cloacacloaca---> rectum, -> rectum, bladder, urogenital sinusbladder, urogenital sinus (contains allantoic connection)

stomach

Dorsal aortaPeritoneum

Morphogenesis Of Morphogenesis Of The Foregut-hindgutThe Foregut-hindgut

Mitosis and growth of foregut and growth of foregut forms theforms the intestinal loop.Gut tube is suspended by is suspended by dorsal mesentery through dorsal mesentery through whichwhich passes the passes the cranial mesenteric artery(CMA).artery(CMA).CMA acts as acts as axis for looping for looping of the intestines.of the intestines.Caudal limb develops alimb develops a diverticulum,,thethe caecum.Hindgut forms distal colon,rectum and cloaca.Intestinal loop enlongates, and rotates twice(360o) clockwise around cranial mesenteric artery.

Morphogenesis Of The Intestinal LoopMorphogenesis Of The Intestinal Loop

Sequence of withdrawal of loopdetermines final position of the intestines. Cranial limb returns first and forms the small intestinesCaudal limb follows and forms part of the small intestine and the large intestines

CrCa

D

V

Chorion

Notochord

Brain

Heart

Amnion Amniotic cavity MidgutForegut

Pharynx

Yolk sacHerniated loop

(Small intestines)

(Large intestines)

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.

Diaphragm

Stomach

Dorsalmesogastrium

Ventralmesogastrium

CysticDiverticulum/gall bladder

Dorsal pancreaticdiverticulum

HepaticDiverticulum/liver

Ventral pancreaticdiverticulum

Duodenum

Blood vessels

Oesophagus

Diaphragm

Development 0f pancreas, liver and gall bladder

A

B

C

Development Of The Respiratory Diverticulum

Laryngo-trachealGrove(L-T)

Tracheo-oesophagealgroove

Foregut

Pharynx

Larynx

Oesophagus

Trachea

Trachea

Pharynx

Tracheo-oesophagealseptum

(A).The L-T groove forms on ventral floor, at level of

4th pharyngeal arch

A and B, lateral viewC, ventral view

(B). L-T gives rise to larynx and trachea

( C ). Bifurcation of lung

bud , forms about 14 bifurcations

D

V

Cr Ca.

Cr.

Ca.

Bronchialbud

Oesophagus

Pharynx

RIGHT LEFT

Pharynx

Trachea

Parietal pleura

Pleural cavity

Pleuroperitonealcanal

Principalbronchi

Visceralpleura

Trachea

Principalbronchi

lobarbronchi

Parietalpleura

Viscerapleura

C

D

Ventral Views of branching of trachea into principal

bronchi and lobar bronchi

Cr.

Ca.Endoderm

Respiratory epithelium,glands of trachea,bronchi,

larynx and lungsMesoderm

Cartilage,muscle,blood vessels and connective

tissues of tracheabronchi,larynx and lungs

LEFT RIGHT

TracheaCranial lobe

Caudal lobe

Accessory lobeCanine lungs

Alveolar cells

Mesoderm

Terminal sac

Terminalbronchioles

Terminal sac stage of lung development (stage 4&5)

B

C

Cr.

Ca.

Middle lobe

Species differences in lobes of lungs

Minor differencesRight lung has four lobes in

Most speciescranial, middle,accessory

and caudal lobesLeft lung has three lobes

cranial(2parts) and caudal lobes

(dorsal view)

MalformationsMalformationsDIGESTIVE SYSTEMDIGESTIVE SYSTEM Stenosis of gastrointestinal tractStenosis of gastrointestinal tract Atresia aniAtresia aniimperforate ani; failure of anal membrane to break downimperforate ani; failure of anal membrane to break down Oesophageal stenosisOesophageal stenosisRESPIRATORY SYSTEMRESPIRATORY SYSTEM1. Larygotracheal abnormalities Tracheal hypoplasia/stenosisTracheal hypoplasia/stenosisabnormal narrowing of the trachea in part or abnormal narrowing of the trachea in part or

entirely.entirely. Collapsed tracheatracheal lumen is partly occluded and the tracheal cartilages

flattened. Tracheal atresia total lack of tracheal patency. Subglottic stenosismalformations of larynx2. 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

SummarySummaryDigestive systemDigestive systemThe gut tube is formed by folding of the splanchnopleureThe gut tube is formed by folding of the splanchnopleureDivisions of gut tube into pharyngeal, foregut, midgut and hindgut Divisions of gut tube into pharyngeal, foregut, midgut and hindgut regions.regions.Each part of gut tube forms specific parts of the gastrointestinal tract, Each part of gut tube forms specific parts of the gastrointestinal tract, digestive glands and non-digestive organs.digestive glands and non-digestive organs.Morphogenesis of the stomach involves;Morphogenesis of the stomach involves;--displacement of the stomach--displacement of the stomach--differential growth and enlargement--differential growth and enlargement--reorientation.--reorientation.Development of the intestines involves elongation, herniation and Development of the intestines involves elongation, herniation and rotation.rotation.Respiratory system.Respiratory system.The pharyngeal and rostral foregut form the The pharyngeal and rostral foregut form the laryngo-trachrallaryngo-trachral groove groove ventrally. ventrally. The larynx develops cranially.The larynx develops cranially.The Trachael groove bifurcates into two tracheo-oesophageal grooves The Trachael groove bifurcates into two tracheo-oesophageal grooves one on either side.The tracheal part develops into the respiratory tree by one on either side.The tracheal part develops into the respiratory tree by successive branching. Trachea bifurcates into 2 principal bronchi, then successive branching. Trachea bifurcates into 2 principal bronchi, then lobar and secondary bronchi. The branching form at different levels of lobar and secondary bronchi. The branching form at different levels of bronchi down to alveolar sacs.bronchi down to alveolar sacs.

References.References.

1.1. Gilbert, S., “Developmental Biology”. 7Gilbert, S., “Developmental Biology”. 7 thth Edition. Edition. Sinauer. Sunderland, Masachusetts.pp511-512.Sinauer. Sunderland, Masachusetts.pp511-512.

2.2. Carlson, B., “Patten’s Foundations of Carlson, B., “Patten’s Foundations of Embryology”. 6Embryology”. 6thth. Edition. Mcgraw Hill. . Edition. Mcgraw Hill. London.pp547-557.London.pp547-557.

3.3. Noden, D.M., & de LaHunta, A., “The Noden, D.M., & de LaHunta, A., “The Embryology of Domestic Animals”. Pp292-305.Embryology of Domestic Animals”. Pp292-305.