Lecture 5- Embryology of gut development 2

Question 1

midgut starts at

Answer 1

the midpoint of the second part of the duodenum- where the common bile duct and majkor bile duct enter the duodenum

Question 2

the midgut consists of

Answer 2

• 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

Question 3

midgut development starts at

Answer 3

During the 6^th 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)

Question 4

midgut development- roations of the inestinal loop is known as

Answer 4

physiological herniation

Question 5

outline physiological hernation

Answer 5

1. cranial portion develops into future small intestin
2. cranial portion elongates further forming loops of the small bowl
3. 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
4. Now a cecum (dilated portion at the start of the large intestine) bulge appears

Question 6

how do the earlier folds affect the large intestine?

Answer 6

• large intestine lies to the right and superior to the small intestine. The cecum also descends (right iliac fossa)

Question 7

Physiological herniation (summary)

Answer 7

• Week 6 intestinal loop herniates into umbilical cord to create space in the abdomen
• By the 10^th week intestinal loop returns to the abdominal cavity

Question 8

midgut development problem

Answer 8

1. malrotation
2. reversed rotation
3. omphalocele
4. gastroschisis
5. partially patent vitelline duct
6. recanilisation failure

Question 9

malrotation

Answer 9

midgut development problem

• If we only have 1 x90 degrees rotation
• Left sided colon

Question 11

reversed rotation

Answer 11

midgut development problem

• 1 x 90 degrees rotation clockwise
• Transverse colon behind the SI

Question 12

omphalocele

Answer 12

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

Question 13

gastroshisis

Answer 13

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

Question 14

partially patent vitelline duct

Answer 14

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

2:1 ration M:

Question 15

Vitelline duct is the

Answer 15

connection between the midgut and the developing yolk sac

Question 17

Recanalization failure

Answer 17

midgut development disorders

• period of rapid cell division
• can be partial or unsuccessful (mostly affects duodenum

Question 19

The hindgut consists of the

*

Answer 19

• Distal 1/3 transverse colon
• Descending colon
• Sigmoid colon
• Rectum
• Superior anal canal
• Bladder epithelia

Question 20

what happens to the urorecttal septum during the 4th to 7th week

Answer 20

• 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

Question 21

ectoderm covers where the anus is going to be- what is this called

Answer 21

proctodaeum- we see a depression

Question 22

anul membrane rupture

Answer 22

• 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

Question 23

pectinate line

Answer 23

The white line represents that junction where the anus is non-keratiniserd and keratinised

Question 24

characteristics of above The pectinate line

Different characteristics of the gut above and below the pectinate line

*

Answer 24

• Above
  
  • Vague pain
    
    • Stretch
    • Chemical injury
  • Gut blood supply

Question 25

characteristics of below The pectinate line

Different characteristics of the gut above and below the pectinate line

Answer 25

• Below (somatic derived pain reception)
  
  • Localised pain
  • Systemic blood supply

Question 26

hindgut abnormalities

Answer 26

1. imperforate anus
2. anorectal agenesis
3. fistulae
   4.

Question 27

Imperforate anus

Answer 27

hindgut abnormality

Failure of the anal membrane to rupture

Question 28

Anorectal agenesis

Answer 28

hindgut abnormality

• Problems with blood supply to hindgut
• Anus doesn’t form (bigger problem that imperforate anus

Question 29

fistulae

Answer 29

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