Development of the Gut Flashcards
What are the foregut structures?
Distal oesophagus to proximal half of (technically starts in mouth, but diff blood supply)
What are the midgut structures?
Distal half of duodenum to proximal two thirds of transverse colon.
What are the hindgut structures?
Distal third of the transverse colon to proximal two thirds of anal canal.
What do the epiblast ans hypobast become?
Epiblast-ectoderm
hypoblast- endoderm
(mesoderm in between)
What happens during lateral/transverse folding?
Ectoderm and mesoderm migrate laterally and ventrally.
This pinches of the endoderm to form the primitve gut tube.
The endoderm becomes the epithelial lining
The mesoderm will become smooth muscle
What is happening in longitudinal folding?
- The cranial and caudal ends of the embryo are moving towards each other.
- The folding causes the yolk sac and gut tube contact to become smaller, causing defined areas, i.e foregut midgut and hindgut.
- The midgut is still in contact with the yolk sac
What are the extremities of the tube and when do they rupture?
Cranial end- oropharyngeal membrane- ruptures Wk 4
Caudal end- anal membrane- ruptures Wk 8
What are the arterial supplies to the different regions of the gut? What spinal level are they at?
Foregut- Celiac trunk, T12
Midgut- Superior mesenteric artery, L1 ( contacts with yolk sac)
Hindgut- Inferior mesenteric artery, L3
How does the oesophagus form?
- Initially, in contact with respiratory diverticulum.
- This pinches off, to make lung buds (ventral) and oesophagus (dorsal).
- Rapidly elongates.
What congenital abnormality is associated with failed oesophagus development?
-Tracheoesophageal fistula/atresia.
Incomplete partitioning causes blockage of oesophagus and a connection between trachea and oesophagus.
-Congenital Hiatal Hernia
Short oesophagus means stomach is more cranial, causing herniation into the thorax.
What are the 3 stages of stomach development?
Stage 1- gut tube dilates
Stage 2- dilation continues; stomach roates ~90 dgerees clockwise on its long axis; ant mesogastirum moves right, post. mesogastrium moves left.
Stage 3- Dilation; Rotation on coronal axis ~90 degrees; right boundary becomes lesser curvature (sup), left boundary becomes greater curvature (inf).
How is the greater omentum formed?
Dorsal mesogastrium is dragged by stomach rotation.
GO hangs with weight of gravity
The hanging folds fuse together (with transverse colon peritoneum) (TRY VISUALISE)
What is a congenital abnormality associated with the stomach?
Congenital hypertrophic pyloric stenosis.
Thickening on muscle in the pylrous region, causing no bilious vomitting.
When does the hepatic diverticulum form and what does it split into?
How does the bile duct end up dorsal?
Wk 4
Will form the liver and biliary apparatus.
The bile duct which is attached to the ventral duodenum, will move dorsally as the duodenum rotates.
Where does the pancreas develop?
In both layers of mesogastrium, with the larger of the two buds in the dorsal mesogastrium.
How do the pancreatic buds fuse and what happens with the pancreatic duct?
When the duodenum roates, the ventrak bud is carried around and fuses with the dorsal bud.
The pancreatic duct is made up of the ventral duct and the distal portion of the dorsal duct.
How does the midgut develop? What do the caecum and appendix do?
The cranial and caudal ends of the midgut (named in relation to position around superior mesenteric artery) HERNIATE into the yolk sac and ROTATE 270 degrees.
This causes the herniation to retract.
The caecum and appendix rotate towards the lower abdomen.
What congenital malformations are associated with midgut development?
- Rotation problems ( no rotation. mixed rotation)
- Umbilical herniation where umbilical cord doesnt close properly, so gut herniates.
- Mickels diverticulum, remnant of yolk stalk.
What is the cloaca and how is divided?
expanded distal part of the hindgut, and is separated into dorsal and ventral parts by the urorectal septum. Grows out to separate hindgut from urogenital sinus.
What is the rectum/anal canal divide?
The inner endoderm and outer ectoderm.
What are congenital malformations of the hindgut?
- Megacolon (Hirschprungs) where a lack of ANS innervation of part of the colon means it can not distend. Causes dilation of colon as no innervation means no peristalsis.
- Imperforated anus, anal membrane does not perforate.
- Rectal atresia where no anal canal forms. fistulas can occurs connecting large intestine to bladder/urethra/ vagina.
