Organogenesis Of The Gastrointestinal Tract.

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.
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)
•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)
•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 aniimperforate ani; failure of anal membrane to break down

Oesophageal stenosis
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
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
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.
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