3 - Development of the Gut Flashcards
What do I need to know?
- Define fore/mid/hindgut
- Structures that originate from fore/mid/hindgut
- Describe the development of the gut
- Explain the major congenitial anomalities associated with the development of the gut
What is an example of structures that began as intraperitoneal and have become retroperitoneal?
Parts of the small and large intestines
Arterial supply to fore/mid/hindgut?
Foregut = Celiac Artery Midgut = Superior Mesenteric Artery Hindgut = Inferior Mesenteric Artery
A ligament refers to …
2 layers of peritoneum that connect 2 organs or an organ to the body wall
Mesenchyme?
Non-specialised embryonic stem cells
Hypoblast becomes …
Epiblast becomes …
Endoderm
Ectoderm
How does embryo development occur?
Longitudinal and lateral folding
How do the ectoderm and mesoderm fold?
Laterally and ventrally
> They then meet centrally closing off the endoderm to from a separate gut-tube structure
What do each of the layers end up forming?
Endo - epithelial lining of the tube
Meso - supporting structures and smooth muscle/musculature of the gut tube
Ecto - outer tissue layer
Space in between the mesoderm layers - body cavity/greater sac
What causes the folding?
The ectoderm (and mesoderm) cells proliferate much faster outwards than the endoderm so it wraps AROUND and down
What happens to the yolk sac?
The mesoderm pinches in the yolk sac to form a separate gut tube (endoderm > mucus membrane)
Longitudinal Folding?
- draws the opening of the gut tube to the yolk sac closed (like a purse string)
- divides the anterior gut tube and posteiror gut tube (fore and hindgut) while the midgut remains open to the yolk sac
- further longitudinal folding means the communication with the yolk sac gets smaller and the regions become more refined
Membranes at cranial and caudal ends?
Oropharyngeal membrane from the ectoderm of the stomodeum
Anal membrane from the ectoderm of the anal pit
Describe what happens to the lumen of the gut tube during development
Initially patent. As the epithelium proliferates it plugs up the lumen of the gut tube. At week 8 by the end of the embryonic period recanalization occurs, it loses patency and re-opens
Gut supply to foregut?
Celiac Trunk
Gut supply to midgut?
Superior Mesenteric Artery (also continues into the yolk sac)
Gut supply to hindgut?
Inferior Mesenteric artery
How does knowing the arterial supply help with knowing the ANS and lymphatics?
ANS follows the arterial supply and deep lymphatics follow the arteries
Describe the development of the oesophagus
- is immediately caudal to the pharynx
- partitions/divides from the trachea (ventral)/respiratory diverticulum
- initially short but rapidly elongates
- also plugs and recananalizes
What is a diverticulum?
A usually abnormal sac or pouch formed at a weak point in the wall
What are 2 types of oesophagus congenital malformations?
- Tracheoesophageal Fistual/Artesia
2. Congenital Hiatal Hernia
What is a tracheoesophageal fistula?
Where there is a CONNECTION between the trachea and oesophagus when they should be partitioned. Is common as they originate from the same tissue.
What is a tracheoesophageal artesia?
Where there is a BLOCKAGE/the oesophagus ends in a blind ended pouch. It results commonly in a child refluxing milk (not chyme/gastric contents as hasn’t gotten past the oesophagus
What causes both an tracheoesopheal artesia and fistua?
Incomplete partitioning
What is congenital hiatal hernia?
It is when a child is born with a short oesophagus. This displaces the stomach cranially and it will herniate through the oesophageal hiatus of the diaphragm and into the thorax. Occurs when elongation doesn’t occur
Stage 1 of stomach development?
The gut tube starts to dilate
Step 2 of stomach development?
- dilation continues
- the tube rotates on its long axis 90 degrees clockwise (spins)
- ventral mesogastrium moves RIGHT
- dorsal mesogastrium moves LEFT
Describe the mesogastrium of the foregut
Is attached both ventrally and dorsally to the body wall by mesentery - dorsal/ventral mesogastrium
Does the ventral mesogastrium move left or right?
RIGHT
… boundary becomes superior and the … curvature
Right/ventral boundary becomes superior and becomes the lesser curvature medially
The … side of the stomach moves inferior and becomes the … curvature
Dorsal
Greater curvature laterally
How is the greater omentum formed?
- dorsal mesogastrium is dragged round by rotation of stomach and begins to hang down under gravity and reflects back onto itself
- the 2 folds fuse as well as with the transverse colon mesentery forming the GASTROCOLIC ligament
how many layers is the greater omentum?
4 layers of peritoneum
What is 1 congenital malformation of the stomach?
Congenital Hypertrophic Pyloric Stenosis
Congenital Hypertrophic Pyloric Stenosis?
- Is a marked thickness of the muscular wall of the pylorus
- can result in spasming at the end of the stomach
- blocks exit into 1st part of the duodenum
- results in non-billius vomitting (no bile)
- can occur in adults due to chronic peptic ulcers > inflammation > swelling > stenosis in pyloris
How does the liver and biliary tree arise?
As a ventral outgrowth called the hepatic diverticulum
Large, cranial division of the hepatic diverticulum …
Liver
Smaller caudal division of the hepatic diverticulum
Biliary aparatus
Bile?
Fat emulsifer
How do the glandular areas of the gut begin?
As diverticulum/blind ended out pouches
Where do the liver and gall bladder develop?
IN the ventral mesogastrium i.e. between 2 layers of peritoneum
Describe the positioning of the bile duct as it develops.
The bile duct begins attached to the ventral duodenum. As the duodenum grows and ROTATES, the bile duct position becomes DORSAL
Where does the pancreas develop?
Between both layers of mesogastrium
The pancreas is the … part of the foregut
CAUDAL
What duct is the main duct of the pancreas and why?
The duct from the ventral bud/head of the pancreas through to the bile duct and into the duodenum in order for pancreatic and bile juices to be released together
The ventral pancreatic bud begins anteriorly on the hepatic diverticulum and then rotates around and fuses with the dorsal bud where their ducts anastomose
What is the accessory duct?
The duct directly from the body/dorsal of the pancreas through to the duodenum. (9% accessory duct remains, may regress or not be present)
What is the pancreatic duct?
Fusion of the dorsal and ventral ducts at the body/head of the pancreas
Ligaments of the foregut
- what ligaments does the ventral mesogastrium go to form?
- faciform ligament between the body wall and liver
- lesser omentum between the liver and stomach/doudenum
Ligaments of the foregut
- what ligaments does the dorsal mesogastrium go on to form?
- gastrosplenic ligament and splenorenal ligament
is the spleen a foregut structure?
NO it is lymphatic. Does develop in the dorsal mesogastrium (meso not endoderm)
What is the movement of the midgut during development?
270 degrees counter clockwise
> caecum moves from upper right quadrant under liver to lower right
