Flashcards in Development Of Midgut And Hindgut Deck (54)
What structures does the midgut give rise to?
Prox two thirds of transverse colon
How does the midgut start to develop?
Begins as a short tube, elongates enormously until it has run out of space
It then forms a primary intestinal loop
PICTURESGive features of the primary intestinal loop
The superior mesentric artery is its axis
It is connected to the yolk sac by the vitelline duct
Has cranial and caudal limbs
Why does physiological herniation occur?
Primary intestinal loop grows so rapidly at he same time as the liver. The abdominal cavity is too small to accommodate them so intestines herniate into umbilical cord
In which week does the physiological herniation occur?
PICTURE What happens in the first 90* turn?
The distal part of the gut tube is left and the proximal part is right
PICTURE What happens after the first 90* turn?
The distal part develops a bulge which will become the caecum/caecum bud
The proximal part becomes convoluted
PICTURE How does the midgut return to the abdominal cavity?
Proximal part returns first, passing under the distal part, making the second rotation
The distal limb then returns, making another rotation
What happens in the descent of the cecal bud?
Temporarily lies in the upper right quadrant, just beneath the liver
Descends down the right hand side of the abdominal cavity into the right iliac fossa
It develops a narrow diverticulum - the appendix
Derivatives of the proximal limb of the midgut?
Distal duodenum, jejunum, proximal ileum
Derivatives of the caudal/distal limb of the midgut?
Distal ileum, cecum, appendix, ascending colon, proximal two thirds of the transverse colon
What happens if there is incomplete rotation of the midgut?
When the midgut makes only one 90* rotation, colon and cecum are the first to return causing a left sided colon
What happens if there is reverse rotation?
Midgut makes a rotation clockwise
Transverse colon passes posterior to the duodenum
What is a vitelline cyst?
Caused by persistence of the vitelline duct in the middle but both ends form fibrous strands
A cyst forms in the middle portion
What is a vitelline fistula?
When the whole vitelline duct remains patent over the entire length, forming a direct communication between the umbilicus and intestinal tract.
What is a Meckel's diverticulum?
When a small portion of the vitelline duct persists, forming an outpocketing of the ileum
When can problems arise in a Meckel's diverticulum?
If it contains heterotopic pancreatic tissue or gastric mucosa
Can cause ulceration, bleeding, perforation
Give the rule of twos about the Meckel's diverticulum
2% of population
2ft from ileocoecal valve
2 inches long
Detected in under 2s
When a Meckel's diverticulum becomes inflamed, what is the main differential diagnosis?
What incomplete recanalisation lead to?
Atresia of the tube affected - lumen is obliterated
Stenosis of the tube - lumen is narrowed
What can contribute to the incomplete recanalisation?
Impairment of blood supply to that part of the tube
Where can incomplete recanalisation occur?
Duodenum (most common)
What is pyloric stenosis?
Hypertrophy of the circular muscle in the region of the pyloric sphincter NOT A RECANALISATION FAILURE
Clinical presentation of pyloric stenosis?
Projectile vomiting in infants
What can 'vascular accidents' be caused by?
Body wall defect
Clinical presentation of gastroschisis?
Protrusion of abdominal contenders through the body wall directly into the amniotic cavity.
Occurs lateral to umbilicus
Viscera are not covered by peritoneum or amnion
Clinical presentation of an omphalocoele/examphalos?
Persistence of physiological herniation
Covering of amnion
What has the worst survival rate? Omphalocoele or gastroschisis?
Why is omphalocoele different to an umbilical hernia?
In an omphalocoele, there is no covering of skin or subcutaneous tissue, just a covering of amnion
What does the hind gut give rise to?
Distal third of the transverse colon
Superior part of anal canal
Epithelium of urinary bladder
What divides the anal canal and what does this indicate?
The pectinate line
Histologically distinct inferior and superior parts
Differences in arterial and venous supply, lymphatic drainage and innervation
What is the cloaca and what is it covered by?
The part where the hindgut ends
Covered by the cloacal membrane
What divides the cloaca and into what?
A wedge of mesoderm called the urorectal septum
Divided into the urogenital sinus anteriorly and anorectal canal posteriorly
What is the blood supply above and below the pectinate line?
Above - inferior mesentric artery
Below - pudendal artery
What is the epithelium above and below the pectinate line?
Above - simple columnar
Below - stratified squamous
Lymph drainage above and below the pectinate line?
Above - internal iliac nodes
Below - superficial inguinal nodes
Innervation above and below the pectinate line?
Above - S2, 3, 4 pelvic parasympathetic nerves
Below - S2, 3, 4 pudendal nerve
What sensation can be felt above and below the pectinate line?
Above - stretch only
Below - temperature, touch, pain
Is visceral pain well or poorly localised?
What is imperforate anus?
Failure of the anal membrane to rupture
What other hindgut defects see there?
Anal canal or anorectal agenesis
Hindgut fistulae (between anal canal and bladder)
Which ligament connects the spleen and the stomach?
What structures does the dorsal mesentery become?
Mesentery proper of the ileum and jejunum
Which structures does the ventral mesentery become?
Lesser omentum from foregut to liver
Falciform ligament from liver to ventral body wall
Blood supply of the midgut?
Superior mesentric artery and vein
Innervation of the midgut?
Parasympathetic - vagus nerve
Sympathetic - superior mesenteric ganglion and plexus
Blood supply of the hind gut?
Inferior mesenteric artery and vein
Innervation of the hindgut?
Parasympathetic - pelvic - S2, 3, 4
Sympathetic - inferior mesenteric ganglion and plexus
Give a timeline in weeks of gut development
3. Tubular gut begins to form
4. Primordium of liver, pancreas, and trachea. Buccopharyngeal membrane ruptures
5. Expansion and early rotation of the stomach. Primary intestinal loop appears. Caecum and bile duct
6. Liver growth. Herniation of intestinal loop. Appendix. Urorectal septum appears
7. Pancreatic buds fuse. Cloacal partitioning complete. Rupture o cloacal membrane
8. Anti-clockwise rotation of intestinal loop. Recanalisation
10. Return of herniated loop
What does the endoderm of the gut tube give rise to? (Below are just a few structures)
What do you get if there is failure of the ceacal bud to descend?
Sub hepatic caecum
What is the allantois?
Structure that serves as a respiratory and waste storage organ for embryos.
Extends from ventral region of urogenital sinus to umbilicus.
What does a remnant of the allantois become in adult life?
A distal portion of the allantois called the urachus becomes a fibrous cord and forms the median umbilical ligament.