1. Development of digestive and respiratory systems
M.A.Kai-Kai.
I am least happy about this lecture. There seems to be far too much detail on the stomach and intestinal regions at the expense of respiratory, liver and pancreas

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
Make proper learning outcomes
Allantois as a diverticulum?
Surely not species differences in the pancreatic ducts!!

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.
Not clear to me that this diagram is showing what you want it to show. No sign of folds or enclosure of endoderm. I have covered the basic body folding (caudal, rostral, body sides ) in the membranogenesis lecture. We should stick to the same diagrams

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)
I don’t find this very helpful - especially ‘umbilicus forming ‘ when the aperture is so open. The dorsal view tells us nothing

5. The Intestinal Portal Tube
Dorsal view not useful

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

7. 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.
--the outer layer(3) is mesoderm and visceral peritoneum forms the outer connective tissue 2 2 1 3
T.S of oesophagus
Splanchnic mesoderm
Submucosal and muscular layers 3 3
Endoderm
Epithelial surface

8. 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.

9. 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 cervical,and thoracic and abdominal regions.
Failure to maintain growth rate results in
a short oesophagus resulting in hiatal diaphragmatic hernia pocketing of stomach between pleuro-peritoneal membranes
Bronchial
bud
Cr.
Ca.
Oesophagus
Schematic diagram of ventral view
of gut tube showing development
of pharynx and oesophagus

10. Morphogenesis Of The Foregut. The Monogastric Stomach: The DogB
Dorsal mesogastrium/fold of peritoneum form
body wall
forms greater omentum
Dorsal mesogastrium
Oesophagus
Oesophagus
Ventral
Mesogastrium/
Lesser omentum
Caudal
Cr.
Ca.
Cranial
Duodenum
Cystic diverticulum/
gallbladder
Stomach
Duodenum
Pylorus
Hepatic diverticulum/liver A
Ventral mesogastrium
Morphogenesis Of The Foregut. The Monogastric Stomach: The Dog
(i) A. Lateral 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.

11. 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
Dorsal aorta
Peritoneum
(contains allantoic connection)

12. 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 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

13. Morphogenesis Of The Intestinal LoopD
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. Ca Cr V
Sequence of withdrawal of 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
(Small intestines)
Amniotic cavity
Foregut
Midgut
Amnion
Chorion
Pharynx
Notochord
(Large intestines)
Brain
Yolk sac
Heart
Herniated loop

14. Development 0f pancreas, liver and gall bladder
Dorsal pancreatic
diverticulum
Stomach
Dorsal
mesogastrium
Oesophagus
Duodenum
Diaphragm
Ventral pancreatic
diverticulum
Hepatic
Diverticulum/
liver
Ventral
mesogastrium
Diaphragm
Blood vessels
Cystic
Diverticulum/gall bladder

15. Development Of The Respiratory Diverticulum
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
(B). L-T gives rise to larynx and trachea
Pharynx
Oesophagus
Larynx D Cr
Ca.
Trachea V
( C ).
Bifurcation of lung bud , forms about 14 bifurcations
Pharynx
Pharynx C
Tracheo-oesophageal
septum
Cr.
Trachea
Ca.
Bronchial
bud
Oesophagus
A and B, lateral view
C, ventral view

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

17. Species differences in lobes of lungs
LEFT
RIGHT
(dorsal view)
Cranial lobe
Trachea
Species differences in lobes of lungs
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 B
Middle lobe
Caudal lobe
Accessory lobe
Canine lungs
Terminal
bronchioles
Mesoderm C
Alveolar cells
Cr.
Ca.
Terminal sac
Terminal sac stage of lung development (stage 4&5)

18. Malformations DIGESTIVE SYSTEM Stenosis of gastrointestinal tract
Atresia aniimperforate ani; failure of anal membrane to break down
Oesophageal stenosis
RESPIRATORY SYSTEM
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
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
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.

20. References.
Gilbert, S., “Developmental Biology”. 7th Edition. Sinauer. Sunderland, Masachusetts.pp
Carlson, B., “Patten’s Foundations of Embryology”. 6th. Edition. Mcgraw Hill. London.pp
Noden, D.M., & de LaHunta, A., “The Embryology of Domestic Animals”. Pp