Development of digestive and respiratory systems
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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 tube pharyngeal , foregut, midgut and hindgut.

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Development of digestive and respiratory systems

Development of digestive and respiratory systems

M.A.Kai-Kai.


Learning objectives

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


Formation of the gut tube 1

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.


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 tube

The Intestinal Portal Tube


Development of digestive and respiratory systems

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


Differentiation of gut tube

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


Derivatives of the gut tube oesophagus

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


Morphogenesis of the gut tube

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.


Pharyngeal and foregut region

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


Morphogenesis of the foregut the monogastric stomach the dog

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


Morphogenesis of the intestinal loop

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


Morphogenesis of the foregut hindgut

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)


Morphogenesis of the foregut hindgut1

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.


Development of digestive and respiratory systems

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


Development of digestive and respiratory systems

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


Development of digestive and respiratory systems

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


Malformation of respiratory system

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


Summary

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.


References

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.


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