3.1 Development Of The Gut 3 + 4 Flashcards
Wha does the midgut give rise to?
- Small intestine, including most of duodenum
- Caecum & appendix
- Ascending colon
- Proximal 2/3 transverse colon
How is the primary intestinal loop formed?
The midgut elongated enormously and runs out of space.
Makes a loop with the superior mesenteric artery as its axis.
When does physiological herniation occur?
6th week
Why does physiological herniation occur?
Rapid growth and elongation of the primary intestinal loop
Rapid growth of liver
Abdominal cavity is too small to accommodate both
Intestines herniate into the umbilical cord.
Briefly describe the rotation of the midgut
Midgut has a cranial and caudal end with the SMA as the axis
Goes through 3 counter clockwise 90 degree rotations
Caudal derivates end up lying to the right of cranial derivates
Transverse colon lies above the duodenum
What are common developmental defects associated with the midgut?
Malrotation Reversed rotation Remnants of yolk sac Meckel’s diverticulum Recanalisation Atresia’s and stenoses Pyloric stenosis
What occurs in malrotation of the midgut?
Midgut loop only makes one 90 degree rotation
Results in a left sided colon
What occurs in reversed rotation of the midgut?
- Midgut loop makes one 90° rotation clockwise
* Transverse colon passes posterior to the duodenum
What are developmental problems associated with rotation of the midgut?
Reversed rotation
Malrotation
What abnormalities can occur as a result of a persistent vitelline duct?
Vitelline cyst
Vitelline fistula
Meckel’s diverticula
What is a vitelline fistula?
Direct communication between the umbilicus & intestinal tract
What is the rule of 2s of meckel’s diverticulum?
2% of population
2 feet from ileocaecal valve
Usually detected in under 2s
2:1 ratio male:female
What happens if recanalisation of the gut lumen is partially or wholly unsuccessful?
Atresia - lumen obliterated
stenosis - lumen narrowed
Where do problems with recanalisation usually occur?
Duodenum
What is pyloric stenosis?
hypertrophy of the circular muscle in the region of the pyloric sphincter
In who is pyloric stenosis usually seen?
In infants
What are the characteristic symptoms of pyloric stenosis?
Projectile vomiting
Dysphagia
What are common defects of the anterior abdominal wall?
Gastroschisis
Omphalocele
What is gastroschisis?
- Failure of closure of the abdominal wall during lateral folding of the embryo
- Leaves gut tube & derivatives outside the body cavity
What is omphalocele?
a.k.a. exomphalos
Persistence of physiological herniation, midgut structures remain in umbilical cord. Herniation occurs through the umbilical ring
What structures derive from the hind gut?
- Distal 1/3 transverse colon
- Descending colon
- Rectum
- Superior part of anal canal
- Epithelium of urinary bladder
What divides the superior and inferior parts of the anal canal?
Pectinate line
How does the superior anal canal differ from the inferior anal canal?
Arterial supply, venous drainage, lymphatic drainage, innervation, epithelium type
Describe the structure and neuromuscular supply of epithelium above the pectinate line?
inferior mesenteric artery
S2 S3 S4 pelvic parasympathetics - vague pain due to stretch
Columnar epithelium
Lymph drainage via the internal iliac nodes
- derived from endoderm
Describe the structure and neuromuscular supply of epithelium below the pectinate line?
Pudendal artery
S2 S3 S4 pudendal nerve - localised pain, sensitive to Temperature and touch
Stratified squamous epithelium
Lymphatic drainage via the superficial inguinal nodes
- derived from ectoderm
What abnormalities can occur with development of the hind gut?
Imperforate anus - Failure of anal membrane to rupture
Anal / anorectal agenesis
Hindgut fistulae
What structures of the midgut and hindgut maintain their mesenteries?
Jejunum Ileum Appendix Transverse colon Sigmoid colon
What structures of the midgut and hind gut become secondary retroperitoneal?
Duodenum
Ascending colon
Descending colon
Rectum (no peritoneal covering in distal 1/3)
When does the intestinal loop return to the abdominal cavity after physiological herniation?
10th week
How does omphalocoele vary from umbilical herniation?
Differs from umbilical hernia because hernias have covering of skin and subcutaneous tissue, omphalocoele only have peritoneal covering. In Omphalocoeles the process of gut development isnt complete, it has in umbilical hernias.
Why is mortality high in patients with omphalocoele?
As generally have other sever developmental defects associated with omphalocoele
Name a lateral folding defect
Gastroschisis
Why might the herniated gut contents not fit in abdominal cavity in gastroschisis?
Herniated gut contents not covered in peritoneum and is therefore exposed to the amniotic fluid during development. This exposure negatively affects gut development and causes growth of gut tissue. Abdominal cavity has not developed to be large enough to fit in the expanded herniated contents.
Why is mortality in gastroschisis lower than in omphalocoele?
As gastroschisis has fewer other associated developmental defects the omphalocoele
What is a meckels diverticulum?
An outpouching of the midgut due to incomplete obliteration of the vitelline duct.
Describe the structure of the hindgut in early embryology? (4th week)
Blind ended structure called the cloaca. Covered by the cloacal membrane
What is the role of the urorectal septum?
Descends during the 4th to 7th week to divide the cloaca into the urogenital sinus and anoretal canal
When does the primitive anus form?
In the 7th week the cloacal membrane ruptures, opening the Andre tail canal to the amniotic fluid
What is the urorectal septum?
A wedge of mesoderm that descends to cleave the cloaca
What is the proctodeum?
An embryological structure. Layer of ectoderm that covers the depression where the anus is going to be.
What is the junction of the anus between the stratified squamous epithelium and the columnar epithelium called?
The pectinate line
What is the white line?
The junction distal to the pectinate line that marks the change from non-keratinised stratified squamous above to keratinised stratified squamous below
What developmental hindgut abnormalities can occur?
Imperforate anus
Anorectal agenesis
Fistulae
