Lecture 5- Embryology of gut development 2 Flashcards
midgut starts at
the midpoint of the second part of the duodenum- where the common bile duct and majkor bile duct enter the duodenum
the midgut consists of
- Remainder of the duodenum, jejunum, ileum, cecum, ascending colon, 2/3 along transverse colon
- Large bowl part of the midgut rights to the right and the small bow part to the left
midgut development starts at
During the 6th week of development the intestinal loop begins to elongate rapidly, this is because liver is developing in abdominal cavity at the same time- meaning there isn’t enough room for both to develop
- Therefore the intestinal loop herniates out into the umbilical cord to create space
- Axis= superior mesenteric artery (SMA)
midgut development- roations of the inestinal loop is known as
physiological herniation
outline physiological hernation
- cranial portion develops into future small intestin
- cranial portion elongates further forming loops of the small bowl
- following this the intestinal loop undergoes a 90 degree anticlockwise rotation
- this means at this point the small intestine lies on the right and the large intestine lies on the left hand side
- we then undergo a further 2 90 degrees anticlockwise rotations
- this leaves the small intestine on the left and the large intestine on the right hand side
- Now a cecum (dilated portion at the start of the large intestine) bulge appears
how do the earlier folds affect the large intestine?
- large intestine lies to the right and superior to the small intestine. The cecum also descends (right iliac fossa)
Physiological herniation (summary)
- Week 6 intestinal loop herniates into umbilical cord to create space in the abdomen
- By the 10th week intestinal loop returns to the abdominal cavity
midgut development problem
- malrotation
- reversed rotation
- omphalocele
- gastroschisis
- partially patent vitelline duct
- recanilisation failure
malrotation
midgut development problem
- If we only have 1 x90 degrees rotation
- Left sided colon
reversed rotation
midgut development problem
- 1 x 90 degrees rotation clockwise
- Transverse colon behind the SI
omphalocele
midgut development problem
- When the herniation fails to return to the abdominal cavity in week 10
- Herniated contents still remain within the umbilical cord
- Midgut structures still covered with peroneal covering
- Not exposed to amniotic fluid
- Mortality is high due to other developmental abnormalities
gastroshisis
midgut development problem
- Failure of abdominal wall to form anteriorly due to incomplete lateral folding
- Defect in abdominal wall through which abdominal viscera can permeate
- Not covered in peritoneum
- Exposed to amniotic fluid
- Negatively effects gut development
- May not fit in abdominal cavity
- Fewer developmental defect than omphalocele so mortality rate lower
partially patent vitelline duct
midgut development problem
- Usually the vitelline duct should regress after week 7
- However if it doesn’t then we can be left with a range of abnormalities
- Vitelline cyst
- Vitelline fistula (complete vitelline duct connects the gut to the umbilicus- can get faecal discharge from belly button)
-
Meckel’s diverticulum (most common)
- A bit like an appendix
- 2% of population
- Located 2 feet proximal to ileo-caecal valve
- Detected in under 2s
- A bit like an appendix
2:1 ration M:
Vitelline duct is the
connection between the midgut and the developing yolk sac
Recanalization failure
midgut development disorders
- period of rapid cell division
- can be partial or unsuccessful (mostly affects duodenum
The hindgut consists of the
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- Distal 1/3 transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Superior anal canal
- Bladder epithelia
what happens to the urorecttal septum during the 4th to 7th week
- descends caudally, separates the cloaca into an anterior urogenital and a posterior anorectal space
- urogenital space is a wedge of mesoderm that continues to descend until we have completely separated urogenital and anorectal spaces
ectoderm covers where the anus is going to be- what is this called
proctodaeum- we see a depression
anul membrane rupture
- When the anal membrane ruptures this bit of the cloacal membrane, we get ectoderm invaginating into the distal anus- junction of ectoderm (stratified squamous) and endoderm (columnar) - pectinate line
pectinate line
The white line represents that junction where the anus is non-keratiniserd and keratinised
characteristics of above The pectinate line
Different characteristics of the gut above and below the pectinate line
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- Above
- Vague pain
- Stretch
- Chemical injury
- Gut blood supply
- Vague pain
characteristics of below The pectinate line
Different characteristics of the gut above and below the pectinate line
- Below (somatic derived pain reception)
- Localised pain
- Systemic blood supply
hindgut abnormalities
- imperforate anus
- anorectal agenesis
- fistulae
4.
Imperforate anus
hindgut abnormality
Failure of the anal membrane to rupture
Anorectal agenesis
hindgut abnormality
- Problems with blood supply to hindgut
- Anus doesn’t form (bigger problem that imperforate anus
fistulae
Hindgut abnormality
- Abnormalities during development can cause fistulae occurring between the rectal and anal section and either the bladder or vagina
- Fistulae- Abnormal connection between two hollow epithelial lined cavities
