Development of digestive system

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Development of GIT

• Foregut Development

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Introduction

• Origin
• Endoderm of gut (except mouth and lower half of
  anal canal which are ectodermal) ? mucosa its
  glands.
• Splachnic secondary mesoderm ? smooth muscles and
  connective tissue.

• GIT is formed from the incorporation of the
  dorsal part of yolk sac into the embryo due to
  head, tail and lateral folds.

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Development of the primitive gut tube

• It extents from the oral membrane to the cloacal
  membrane.
• It is divided into
• 1-Foregut from pharynx to the middle of 2nd
  part of duodenum.
• 2-Midgut from lower half of 2nd part of
  duodenum to the junction between medial 2/3
  lateral 1/3 of transverse colon.
• 3-Hindgut the remaining part of large intestine.

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Derivatives of the gut
Foregut Midgut Hindgut
Pharynx Oesophagus Stomach 1st and half of 2nd parts of duodenum Liver and gall bladder Pancreas Respiratory system Half of 2nd , 3rd and 4th parts of duodenum Jujenum Ileum Appendix Caecum Ascending colon Right colic flexure Right 2/3 of transverse colon. Left 1/3 of transverse colon. Left colic flexure. Descending colon. Segmoid colon. Rectum. Upper ½ of anal canal. Primitive urogenital sinus derivatives.
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Development of the oesophagus

• Development
• At 4 weeks old a respiratory diverticulum
  appears at the ventral wall of the foregut.
• The trachea develops from its ventral border. The
  esophagus develops from its posterior part. They
  are comunicating then a tracheaoesophageal
  septum develops between them.

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1- Endoderm of foregut -----?mucosa its
glands.2- Splanchynic secondary mesoderm
---?submucosa musculosa.3- Mesenchyme of
branchial arches ?striated muscles of upper 1/3
of oesophagus.
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• The oesophagus is first short then
  elongates.Epithelium of oesophagus proliferates,
  obliterating the lumen then recanalization
  occurs.

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Congenital anomalies of Esophagus

• 1. Short oesophagus
• Due to failure of elongation . It is
  associated with thoracic stomach.
• 2.Tracheo-oesophageal fistula
• Due to non separation between trachea and
  oesophagus ? milk in lungs? pneumonia.
• ? air in stomach ?
  respiratory distress.
• 3. Oesophageal atresia
• Due to failure of recanalization.
• 4. Oesophageal stenosis
• Due to incomplete recanalization.

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Development of the Stomach

• Appears as a fusiform dilation of the foregut (4
  week).
• It rotates 90 degrees clockwise around a
  longitudinal axis so
• - left side becomes the anterior surface and the
  right side becomes the posterior surface.
• - left vagus becomes anterior gastric nerve
  right vagus becomes posterior gastric nerve.

Figure is from Langmans Embryology
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• Later, the appearance and position change due to
  differential growth and change in surrounding
  organs as follows.
• 1-The left margin grows faster than the right
  resulting in the formation of the greater and
  lesser curvatures.
• 2- The pyloric end moves to the right and the
  cardiac end moves to the left due to development
  of the liver (the stomach becomes oblique).

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Congenital anomalies of the stomach

1. Thoracic stomach associated with short
   oesophagus.
2. Congenital pyloric stenosis due to hypertrophy
   of circular muscles in the pyloric region ?
   projectile vomiting of the infant after feeding.
3. Hourglass stomach.
4. Transposition of stomach ( may be associated with
   situs inversus).

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Congenital anomalies of the duodenum

• 1- Duodenal atresia
• due to non canalization.
• 2- Duodenal stenosis
• due to partial canalization.
• 3- Congenital intestinal obstruction due to
  traction of Treitz ligament on the duodenojejunal
  junction.
• 4- Duplication of the duodenum due to abnormal
  recanalization.

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Development of the liver

• Hepatic bud develops from the ventral border of
  duodenum (foregut).
• It divides into pars hepatica and pars cystica.
• Pars cystica undergoes canalization and gives
  gall bladder and cystic duct.

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• Pars hepatica divides into right and left
  branches which arrange in solid cords. These
  cords invade septum transversum giving liver
  cells and epithelial lining of bile canaliculi,
  hepatic ducts and common hepatic duct.
• Septum transversum gives the liver capsule,
  forms the stroma, the falciform ligament, lesser
  omentum and the blood forming or hematopoietic
  tissue (Kupffer cells) of the liver.

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• Congenital anomalies
• 1- Increased lobulation of liver.
• 2- Absence of gall bladder and cystic duct It is
  due to failure of development of pars cystica.
• 3- Double gall bladder and cystic duct It is due
  to development of two separate gall bladders
  connected by a single cystic duct or by separate
  ducts.
• 4- Atresia of common bile duct It is due to
  failure of canalization of biliary passage and
  associated with jaundice after birth.
• 5- Atresia of gall bladder.
• 6- Congenital choledochal cyst It is a dilated
  part of common bile duct due to weakness of the
  wall of this part.

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Development of the Pancreas

• The pancreas develops from dorsal and ventral
  pancreatic buds that arise from the endoderm of
  the duodenum.
• The dorsal pancreatic bud grows more rapidly
  than the ventral and soon extends dorsally behind
  the duodenum.

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• The duodenum grows and rotates to the right
  (clockwise) and carries the ventral pancreatic
  bud dorsally where it fuses with the dorsal bud
  during the seventh week.
• The dorsal bud forms the body and tail of the
  pancreas.
• Ventral bud forms the uncinate process and most
  of the head of the pancreas.

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• The main pancreatic duct is formed by union of
  distal part of the duct of the dorsal bud with
  the duct of the ventral bud and the communication
  in between.
• - The accessory pancreatic duct is formed from
  the proximal part of the duct of the dorsal bud.
• - Each solid duct gives branches (ductules) which
  gives solid cell masses connected to the duct
  system (acini) and solid cell masses without
  connection to duct system (Islets of Langerhans).
• - The connective tissue of the gland develops
  from the splanchnic mesoderm.
• - By the fifth month, insulin secretion begins.

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Congenital anomalies

• 1- Annular pancreas
• The part of the ventral pancreatic bud rotates
  towards the left in front of the duodenum.
• Hence, the pancreatic tissue surrounds the
• duodenum, it obstructs the duodenum.

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• 2- Accessory or ectopic pancreatic tissue
• It lies frequently in the mucosa of the stomach
  and Meckels diverticulum.
• 3- Absence of dorsal or ventral pancreas.
  
• 3- Separate ducts.

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Thank You
Prof. Dr. Shawky Tayel