Development Flashcards
Foregut area
Anything in the digestive tract before the middle of the duodenum
Midgut area
Distal 1/2 of duodenum to last 1/3 of transverse colon
Hindgut area
Distal 1/3 of transverse colon to last 1/3 of anal canal
Lateral folding of the embryo
2D structure of 3 layers (ectoderm, mesoderm and endoderm) forms a cylinder
The ectoderm and mesoderm fold laterally and ventrally which closes off the endoderm forming a separated gut tube structure
The endoderm forms the epithelial lining of the tube
The mesoderm gives rise to the supporting structures and smooth muscle
The outer mesenchymal ayer gives rise to the outer tissue layer
The space in between the mesoderm is the body cavity
Longitudinal folding
3D structure bends over to form the foetal position
At about 17 days the opening of the gut tube closes like a purse string, dividing into foregut and hindgut. The midgut remains open to the yolk sac
Further folding causes communication with yolk sac to get smaller and the 3 gut regions become more refined
2 membranes closing off the tube
Oropharyngeal membrane at the cranial end
Anal membrane at the caudal end
Key embryonic event at week 4
Oropharyngeal membrane ruptures
Key embryonic event at week 8
Anal membrane ruptures
Lumen of the gut tube
Initially the gut tube is patent. As epithelium proliferates the lumen of the gut tube is plugged up. During week 8, recanalisation occurs
The foregut receives blood from:
The coeliac trunk
The midgut receives blood from:
The superior mesenteric artery
The hindgut receives blood from:
The inferior mesenteric artery
Tracheoesophageal fistula/atresia
Fistula: connection
Atresia: blockage
Both occur as a result of incomplete partitioning
Congenital hiatal hernia
Short oesophagus
Displaces stomach cranially and herniates into thorax through oesophageal hiatus
Dilation and rotation of stomach
Gut tube starts to dilate and continues through the rotations
Rotation of tube on long axis 90° clockwise. Anterior mesogastrium moves to the right and posterior mesogastrium moves to the left.
Then, rotation of tube on coronal axis 90° clockwise. Right boundary becomes superior (lesser curvature) and left boundary becomes inferior (greater curvature)
Formation of greater omentum
As dorsal mesogastrium is dragged round by rotation of stomach it hangs down under the weight of gravity. Both sides of the hanging fold fuse together making a 4 layered peritoneal structure, the greater omentum.
Congenital hypertrophic pyloric stenosis
Marked thickening of the muscular wall of the pylorus, blocking exit of the stomach into the duodenum
Hepatic diverticulum
Outgrowth of the duodenum at week 4 of development forming the liver and biliary apparatus
Pancreas development
Develops between both layers of mesogastrium
Ventral and dorsal bud: eventually anastamose forming a pancreatic duct
Midgut herniation
Normal process where loop migrates through into umbilical cord. Eventually this herniation retracts and the loop returns to the abdominal cavity
Abnormal midgut rotations
Non-rotation Twisting Reversed rotation Sub-hepatic caecum and appendix (failure to descend) Internal hernia Midgut volvulus (obstructs duodenum)
Umbilical herniation or fistula
Failure of umbilical cord to close properly. Gut herniates through weak region in the body wall
Meckels diverticulum
Ileal diverticulum
Remnant of the vitelline duct
Cloaca
Expanded distal part of hindgut divided into dorsal and ventral parts
Mesenchymal urorectal septum
As septum grows it separates rectum from urogenital sinus
Rectum/anal canal
Boundary between outer ectoderm and inner endoderm
Inferior mesenteric artery supplies upper 2/3
Anocutaneous line
Portion of the anal canal where the lymphatics change. Below this line superficial inguinal nodes are found
Hirschsprungs disease
Segment of colon is dilated due to absence of ANS ganglion cells in distal gut wall
Peristalsis failure in aganglionic part means the colon can’t relax which prevents movement of intestinal contents
Imperforated anus
Failure of anal membrane to perforate
Rectal atresia
Anal canal and rectum are separated
Fistulas may present which can connect intestine to urethra, bladder or vagina
