Development of the Alimentary Canal and associated Secondary Organs Flashcards
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The embryo folds in both the longitudinal (cranio-caudal/sagittal) and the transverse (lateral) planes/axes. State the effect of embryonic folding on the yolk sac.
State the derivatives of the endoderm in the alimentary canal.
(a) Epithelial lining of the gut wall
(b) Exocrine glands: both intrinsic (e.g. gastric glands, Brunnerβs glands etc.) and extrinsic (e.g. biliary system, liver, pancreas)
State the derivatives of splanchnic mesoderm in the alimentary canal.
(a) Connective tissue elements of the gut
(b) Smooth musculature of the gut wall [muscularis mucosa and muscularis externa]
(c) Mesentery
State the derivatives of the neural crest cells in the alimentary canal.
[They migrate and invade the developing gut tube.]
They give rise to the enteric nervous plexus of the gut wall. [Myenteric nerve plexus and the submucosal nerve plexus.]
[Diagram]
The primordial gut has three parts: foregut, midgut and hindgut. State the derivatives of the foregut.
Gut components: pharynx, esophagus, stomach, duodenum [proximal part only]
Extrinsic glands: liver, pancreas and biliary tree
[also the lower respiratory systemβ¦]
The primordial gut has three parts: foregut, midgut and hindgut. State the small gut and large gut derivatives of the midgut.
Small gut: distal part of duodenum, jejunum, ileum
Large gut: caecum, appendix, ascending colon, transverse colon [right 1/2 to 2/3]
The primordial gut thas three parts: foregut, midgut and hindgut. State the derivatives of the hindgut.
right part of the transverse colon, descending colon, sigmoid colon, rectum, anal canal [Diagram]
Name the artery of the:
(a) Foregut
(b) Midgut
(c) Hindgut
(a) Celiac artery
(b) Superior mesenteric artery
(c) Inferior mesenteric artery
[Image 1]
Further notes:
The regions where these three arteries anastomose represent the regions which have dual origin in terms of the gut segments e.g. the duodenum and transverse colon.
Summarize the steps in the development of the esophagus.
[Hints: it is tied to the development of the lower respiratory tractβ¦]
β The respiratory diverticulum forms from the ventral aspect of the foregut.
β The foregut undergoes septation to separate the esophagus and the trachea.
β Elongation takes place.
β The esophagus enters the solid stage of development. [This is due to high rate of proliferation of endodermal cells, hence obliteration of the lumen. This is a universal process in the development of all tubular structures lined by endoderm.]
β Recanalization takes place.
[Diagram]
Name A to E: [Image].
A: esophageal atresia without tracheoesophageal fistula
B: esophageal atresia with proximal tracheoesophageal fistula
C: esophageal atresia with distal tracheoesophageal fistula
D: esophageal tresia with proximal and distal tracheoesophageal fistula
E: tracheoesophageal fistula without esophageal atresia
Further notes:
π Clinical presentations of A: 1. frothing at the mouth, 2. vomiting of breast milk, 3. inability to advance a nasogastric tube
π Type B presents similarly to A with choking.
π Type C presents similarly to A with distension of the abdomen due to entry of gases.
π Type E is diagnosed late.
Name two embryological defects caused by inadequate recanalization of the esophagus.
Summarize the steps in the development of the stomach.
β It begins as a fusiform dilatation in the distal parts of the foregut.
β Its posterior border grows faster than its anterior border, leading for curvature formation.
β The developing stomach then undergoes rotation in the vertical axis and in the anteroposterior axis.
[Diagram]
Discuss the rotation of the stomach in the vertical axis and state the consequences of this rotation.
β Rotation in the vertical axis occurs 90Β° in the clockwise direction [if viewed anteriorly].
β This results in the greater curvature facing the left side, and the lesser curvature facing the right.
β The left vagus nerve becomes the anterior vagal trunk and the right vagus nerve becomes the posterior vagal trunk.
β Ventral mesogastrium moves to the left, dorsal mesogastrium moves to the right.