1. Embryology Digestive and Respiratory Systems
ANHB 2212 – Week 8
Avinash Bharadwaj

2. The Primitive Gut Septum transversum*
Yolk Sac
Yolk Sac
Septum transversum
Note gut tube – foregut, midgut and hindgut
Communication between midgut and yolk sac

3. The Definitive Gut
Endodermal gut tube  lining epithelium and glands only!
Connective tissue and muscle is mesodermal.
Some features shown schematically!
Diaphragm
Abdominal foregut
Ventral and dorsal mesogastrium
Developing liver
Midgut
Elongates substantially
Vitellointestinal duct
Hindgut
Arteries from dorsal aorta

4. Further… Ventral mesogastrium Arteries Lesser omentum
Falciform ligament
Arteries
Coeliac
Foregut
Superior mesenteric
Midgut
Inferior mesenteric
Hindgut
Lesser
omentum
Liver C
Falciform
Ligament SM IM

5. Abdominal Foregut Abdominal part of oesophagus Stomach
Ventral border – lesser curvature (attachment – lesser omentum)
Dorsal border – greater curvature (attachment – dorsal mesogastrium)
Proximal half of duodenum V D

6. The Midgut “Loop” Superior mesenteric artery
Cranial (“Prearterial” ) limb (segment)
Vitellointestinal duct
“Postarterial” (caudal) limb
Caecum (Caecal “bud”)
Part of colon
Cranial
Caudal
V-I
duct
Caecum *
The coeliac and the inferior mesenteric arteries
are omitted for clarity

7. Rotation – Midgut Also note hindgut derivatives A C V-I-D C : caecum
A : appendix
V-I-D : vitellointestinal duct
Rotation – Midgut
Also note hindgut derivatives

8. Anal Canal Separation from common cloaca Partly ectodermal
“Proctodeum”
Anal membrane
Implications
Blood supply, venous drainage, nerves

9. Vitellointestinal Duct
Normally disappears
Persistence – Ileal (Meckel’s) diverticulum
Possibilities – ectopic mucosa (epithelium)
Proximity to the appendix
Partial persistence

10. Stomach and Lesser Sac Mesogastria Divisions
Dorsal – splenic connections
Ventral – hepatic connections
Gastric borders
Liver
Spleen
L.O. F L R
Lesser Sac

11. Peritoneal Cavity
Lesser
sac TC SI GS
TMc C
V-I-D A

12. Greater Omentum Lesser sac TC SI GS TMc Peritoneal layers
(mesothelium)
Connective tissue X P D

13. Pancreas, Liver, Gall Bladder
Two “buds”
Differential duodenal growth
Fusion
Biliary tree stays with ventral duct
Hepatic and cystic parts  liver and gall bladder
Liver – massive proliferation V D
Blood supply :
Liver and gall bladder – largely coeliac, S-m frequent
Pancreas – always double

14. Examples of Anomalies
Hollow organs grow by proliferation of lining cells
Recanalisation by cell death essential
Failure of recanalisation  atresia, stenosis
Oesophageal, duodenal, biliary
Anomalies of rotation
Pancreatic anomalies
Others
Imperforate anus
Pyloric stenosis (hypertrophic)

15. Respiratory System Offshoot of the digestive tube
Arises from the upper foregut
Single endodermal diverticulum
Ventral to the foregut
Branching H L F M

16. Coelom, Pleura, Lobes Separation of pleural cavity Note relationshipsPt
Separation of pleural cavity
Note relationships
Phrenic nerve…
Lobes – right and left lungs

17. Lung – Histogenesis Pseudoglandular – embryonic period
Canalicular : 16 – 26 weeks
Terminal sac phase : 7m
Lung development determines the viability of a premature baby

18. Tracheo-oesophageal anomalies
Atresia – stenosis – fistula combinations.