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
D
Liver
Heart
Pericardial
cavity
Yolk sac
Median section through 18 days gestation of pig
Ca.
Cr.
V
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
Hepatic
diverticulum Yolk sac
Pharyngeal
Urachus
Bladder
Cloaca
Hind
gut
Derivatives Of The Gut tube/Oesophagus
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
2
1
3
2
Epithelium
1
3
2
1
2
2
1
2
Muscle
3
Endoderm
Mesoderm
T.S. of oesophagus
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
(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
Cr.
cervical,and thoracic and abdominal regions.
•Failure to maintain growth rate results in
Ca.
a short oesophagus resulting in hiatal
diaphragmatic hernia which is pocketing
of stomach between pleuro-peritoneal
membranes
Pharynx
Bronchial
bud
Oesophagus
Schematic diagram of ventral view
of gut tube showing development
of pharynx and oesophagus
dorsal
D
Dorsal mesogastrium
B
Oesophagus
cranial
ventral
First rotation 90o counterclockwise
Cranial-caudal along longitudinal axis
Duodenum
Stomach
caudal
Cystic diverticulum
Hepatic diverticulum
A
Second rotation 90o
counterclockwise on dorsoventral axis
Ventral mesogastrium
cranial
C
D
caudal
Completion of rotation
Stomach lies transverse
Fundus
Ventral
Pylorus Mesogastrium/
Lesser omentum
Morphogenesis Of The Foregut.
The Monogastric Stomach: The Dog
Duodenum
E
Differential growth, large fundus, narrow pylorus
Dorsal mesogastrium/fold of peritoneum from body wall forms
greater omentum
Morphogenesis Of The Intestinal Loop
D
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
(SmallAmnion
intestines)
Amniotic cavity
position of the intestines.
Pharynx
• Cranial limb returns first and
forms the small intestines
• Caudal limb follows and
forms part of the small
intestine and the large
intestines
Ca
•
(Large intestines)
Brain
Heart
Cr
V
Foregut
Midgut
Chorion
Notochord
Yolk sac
Herniated loop
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 forms 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
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)
A
Foregut
Tracheo-oesophageal
groove
B
Pharynx
(B). L-T gives rise to larynx
and trachea
Oesophagus
Larynx
D
Trachea
V
Pharynx
Tracheo-oesophageal
septum
( C ).
Bifurcation of lung
bud , forms about 14
bifurcations
Ca.
Cr
C
Cr.
Trachea
Ca.
Bronchial
bud
Oesophagus
A and B, lateral view
C, ventral view
C
RIGHT
Ventral Views of branching of
trachea into principal
bronchi and lobar bronchi
LEFT
Pharynx
Trachea
Parietal pleura
Principal
bronchi
Pleural cavity
Pleuroperitoneal
canal
Principal bronchi branch into
lobar bronchi
Visceral
pleura
Peritoneal
cavity
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
Trachea
RIGHT
Cranial part of
cranial lobe
Species differences in lobes of lungs
B
Caudal part of
cranial lobe
Caudal lobe
Accessory lobe
Canine lungs
Terminal
bronchioles
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
Mesodem
C
Alveolar cells
Cr.
Terminal sac
Ca.
Terminal sac stage of lung development
Malformation of Respiratory System
1.





2.




3.
4.
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
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.
Respiratory distress syndromedifficulties in neonatal breathing
difficultiesinability of alveolar epithelial cells to form enough surfactants.
Neonatal maladjustment syndromeexample immotile cilia
syndromeabnormal structure
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laryngotracheal
groovetracheooesophageal ridgestracheoesophageal septumlung
budlaryngotracheal tubetrachea.
Regional specification established early in development by
expression of Hox genes along cranial-caudal axis.
Growth factors regulate anatomical and functional properties.
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.