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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

Tracheo-oesophageal anomalies Atresia – stenosis – fistula combinations.