Development of GI tract

Question 1

Germ layers

Answer 1

ECTODERM; forms epidermis, epithelium of nasal and oral cavities, the NS and sense organs
MESODERM; forms muscle and connective tissue, bone, parts of circulatory, urinary and genital systems
ENDODERM; forms mucosal epithelium and glands of respiratory and digestive systems

Question 2

Teeth development

Answer 2

• ectoderm; epithelium of oral cavity
• 1st indication of teeth= thickening of epithelium down surrounded by mesenchyme
• These swellings represent enamel organ
• Bud invaginates and dental papilla is formed
• Surrounded by odontoblasts

Question 3

How does the GI tract development begin?

Answer 3

• Starts as a single tube of endoderm
• Then alimentary tract and its glands

Question 4

Foregut development

Answer 4

• Stomach comes from a dilation of the foregut between the oesophagus and the SI
• Primitive dorsal and ventral mesentery attached (mesogastrium)
• Stomach development needs; displacement, reorientation and differential enlargement

Question 5

Simple stomach development

Answer 5

• Tube becomes convex dorsally
• Rotates 90 degrees left
• Then rotates anti-clockwise around dorso-ventral axis
• Liver growth pushes cranial end of stomach left
• Increases growth on left cranial provides fundus region
• Endoderm forms epithelium lining

Question 6

Complex stomach development

Answer 6

• Rumen develops as an expansion of the fundus
• Reticulum develops as a caudoventral pocket of the rumen
• Omasum develops as a bulge along the greater curve
• Abomasum develops from rest of the stomach

Question 7

Liver development

Answer 7

• Originates from endoderm as a hepatic diverticulum
• Divides into cranial and caudal branch
• Cranial branch forms glandular tissue, bile duct and hepatic ducts
• Caudal branch forms the gallbladder and cystic duct

Question 8

Pancreas development

Answer 8

• Arises from the same portion of the foregut as the liver; 2x endodermal diverticulum
• One is dorsal, second is ventral
• Islet tissue forms by budding from the ducts

Question 9

What endodermal derivatives are produced by the foregut section of the primitive gut?

Answer 9

• Oesophagus
• Stomach
• Duodenum (cranial)
• Liver
  -Pancreas
• Gallbladder

Question 10

What endodermal derivatives are produced by the midgut section of the primitive gut?

Answer 10

• Duodenum (caudal)
• Jejunum
• Caecum
• Ascending colon
• Transverse colon (1st 2/3)

Question 11

Development of the intestinal loop

Answer 11

• From where the yolk sack is attached
• midgut forms an elongated loop that herniates through umbilical cord
• Loop rotates clockwise 360 degrees
• Caudal limb of the loop becomes a diverticulum; the future caecum

Question 12

What endodermal derivatives are produced by the hindgut section of the primitive gut?

Answer 12

• Transverse colon
• Descending colon
• Cloaca
• Rectum