DEVELOPMENT OF GASTROINTESTINAL SYSTEM

Lecture by Prof. Ansari

(for MBBS students)

01/12/2008, Monday, 1.30—2.30pm

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OBJECTIVES

• Salivary glands development.

• Esophagus / stomach / small intestine development.

• Large intestine / anal canal development.

• Liver / gall bladder / pancreas and spleen development.

• Rotation of midgut.

• Congenital anomalies of GIT.

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Salivary glands

• The parotid gland is an ectodermal in origin.• It arises as a diverticulum arising from the oral

cavity, stomodeum.• It expands around the ear and forms the parotid

glands.• The submandibular and sublingual glands are

endodermal in origin.• Originating from the endoderm of the pharynx.

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The primitive gut tube

• The dorsal part of yolk sac will give rise to the primitive gut tube.

• The upper part of the primitive gut tube is derived from the pharyngeal pouches.

• The lower part of the anal canal is derived from the proctodeum.

• The liver, gall bladder and pancreas develops from the epithelium of the fore gut.

• The primitive gut is having foregut/midgut and hind gut parts.

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The arteries of the primitive gut

• The fore gut segment is supplied by the foregut artery, coeliac artery.

• All the derivatives of fore gut are supplied by the branches from the coeliac artery.

• The midgut artery is the superior mesentric artery, all the derivatives of midgut are supplied by branches of superior mesentric artery.

• The hindgut artery is the inferior mesentric artery, which supplies all the derivatives of hindgut.

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Arteries of the gut

• Coeliac artery

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Stomach development• There is a rapid growth of dorsal wall of stomach in comparison with the

ventral wall.

• The foregut is attached to the anterior and posterior wall of the abdomen, by means of ventral meso-gastrium and dorsal meso-gastrium.

• The differential growth of the walls of stomach will result in the formation of greater curvature and lesser curvature.

• The attached dorsal mesogastrium gets detached from the posterior abdominal wall and forms the greater omentum.

• The ventral mesogastrium forms the lesser omentum, liver develops in the ventral mesogastrium, the leftover part of ventral mesogastrium forms the falciform ligament of the liver.

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The mucosal wall is endodermal where as the muscular wall is derived from the visceral layer of splanchnopleuric

mesoderm

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Dorsal mesogastrium

• The spleen develops in the dorsal mesogastrium.

• Spleen is a mesodermal aggregation in colonies growing in the dorsal mesogastrium.

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Ventral mesogastrium

• Liver develops in the septum transversum and ventral mesogastrium.

• Liver bud arises from the junction of foregut and midgut, as hepatic diverticulum.

• It is endodermal in origin.• The connective tissues and sinusoids

develop from the mesoderm of septum transversum.

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Liver and gall bladder development

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The hepatic bud is endodermal.

• The hepatic bud grows into a bilobular structure, the smaller bud doesnot grow and remains as cystic bud and forms gall bladder.

• The larger bud grows into the septum transversum and proliferates and form hepatic cords.

• The sinusoids and ligaments are developing from the ventral mesogastrium and septum transversum.

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Development of pancreas

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Dorsal and ventral pancreatic buds

• The pancreas develops from the endoderm of the foregut.

• There are two pancreatic buds growing from dorsal and ventral wall of foregut.

• The dorsal and ventral pancreatic buds.

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Rotation of midgut

• Due to rotation of midgut, the dorsal and ventral pancreatic buds also rotates and over laps and form the adult pancreas.

• If the rotation occurs in reverse, the annular pancreas forms a ring around the duodenum.

• The axis of rotation of mid gut is around the superior mesentric artery.

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Annular pancreas

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The head of adult pancreas

• Is the remains of the ventral pancreatic bud, after rotation.

• The dorsal pancreatic bud forms the neck, body and tail of pancreas.

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The derivatives of hind gut

• The transverse colon distal third, descending colon, sigmoid colon, rectum and anal canal upper part all develops from hind gut.

• The lower part of anal canal develops from the proctodeum, it is an ectodermal anal pit.

• After rupture of the cloacal membrane, the ectodermal anal canal becomes continuous with the endodermal anal canal.

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Congenital anomalies of digestive system

• Esophageal atresia– abnormal division of the tracheoesophageal septum.

• Congenital hypertrophic pyloric stenosis– overgrowth of the longitudinal muscles of pylorus.

• Annular pancreas.• Ileal diverticulum/Meckel’s diverticulum– it

is due to the persistence of vitellointestinal duct.

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Mal rotation of midgut.

• Sub hepatic caecum and appendix.

• Hirschsprung’s disease—mega colon.

• Imperforate anus.• Situs inversus.

IMPERFORATE ANUS

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Situs inversus

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Review

• Parotid gland=ectoderm

• Submandibular/sublingual glands=endoderm.

• Esophagus/stomach/duodenum= foregut

• Duodenum/ileum/jejunum=midgut

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Caecum/appendix/ascending colon/proximal 2/3rd of transverse colon=midgut

• Distal 1/3rd of transverse colon/descending colon/sigmoid colon/rectum & anal canal=hindgut

• Lower part of anal canal=proctodeum(ectoderm)

• Liver/gall bladder/pancreas= fore gut

• Spleen=mesoderm