GI development pt 2 Flashcards
What does the midgut give rise to?
o Small intestine, including most of the duodenum (post bile duct entry)
o Caecum and appendix
o Ascending colon
o Proximal 2/3rds of the transverse colon
How is the primary intestinal loop formed?
As a result of the rapid elongation of the midgut and the large size of the developing liver
Describe the midgut loop - What are its two parts, what is its axis and where does it connect?
- Cranial and caudal limbs
- Superior mesenteric artery at ais
- Connected to vitelline duct
What does the cranial limb of the midgut loop become?
Distal duodenum
Jejunum
Proximal ileum
What does the caudal limb become?
Distal Ileum Cecum Appendix Ascending Colon Proximal 2/3 transverse colon
What process occurs to make room for developing midgut?
Physiological herniation
What is physiological herniation?
Intestines herniate into the proximal umbilical cord
What is rotation of the midgut?
Midgut rotates in a counterclockwise direction until we get the shape of the normal Gi. 270* counterclockwise rotation
In what order do parts of the midgut return to the abdominal cavity?
Cranial limb return first, moving to left hand side
Cecal bud returns last
What happens to the cecal bud once it has returned to the abdomen
Descends, moving caecum to right lower quadrant
Give two types of malrotation
Incomplete rotation
Reversed rotation
What does malrotation result in?
Gut hypermobility and volvulus
What is incomplete rotation?
Midgut makes only one 90* rotation
Results in left sided colon
What is reversed rotation?
Midgut makes one 90* rotation clockwise
Transverse colon passes posterior to the duodenum
What is a volvulus?
A bowel obstruction where a loop of bowel abnormally twists in on itself
More likely with hypermobile (malrotates) guts
What can volvulus lead to/
Strangulation and herniation
What does the hind gut give rise to?
o Distal 1/3 Transverse Colon o Descending colon o Rectum o Superior part of anal canal o Epithelium of the urinary bladder
What is the cloaca?
The end of the hind gut
What is the cloaca separated from the outside world by?
Cloacal membrane
What happens at 6 weeks to the cloaca?
Partioning by the urorectal septum
What does partioning by the urorectal septum create in the cloaca?
Urogenital sinus
Anorectal sinus
What are the two parts of the anal canal derived from?
Superior derived from hindgut
Inferior from ectoderm
What is the line at which the two parts of the anal canal separate?
Pectinate line
What is the Blood Supply Innervation Epithelia Lymph Drainage above the pectinate line
Blood Supply - IMA
Innervation - S2-S4 PS
Epithelia - Columnar
Lymph Drainage - Internal iliac nodes
What is the Blood Supply Innervation Epithelia Lymph Drainage below the Pectinate line
Blood Supply - Pudendal A
Innervation - S2-S4 Pudendal nerve
Epithelia - Stratified squamous (non K)
Lymph Drainage - Superficial inguinal nodes
What is the only sensation possible aboe pectinate line?
Stretch
What is the sensation possible below pectinate line and why?
Temperature, touch and pain due to somatic innervation from pudendal nerve
What is the white line?
A portion of ectodermal anal canal which separates Non-K Strat squamous from K Strat Squamous
What is meckel’s diverticulum?
Ileal diverticulum. Cul-de-sack as the result of failure of closure of vitelline duct
What is the rule of 2’s for meckel’s diverticulum? (6)
o 2% of the population affected o 2 feet from the ileocecal valve o 2 inches long o Usually detected in under 2’s Can be asymptomatic o 2:1 Male:Female - 2 types of tissue, gastric or pancreatic
What is a vitelline cyst?
Vitelline duct frorm fibrous strands at either end
What is a vitelline fistula?
Direct communication between the umbilicus and intestinal tract. This results in faecal matter coming out of the umbilicus.
What is atresia and stenosis of intestines?
Complete loss or narrowing of lumen
Give two reasons for lumen atresia
Unsuccesful recanalisation
Vascular accidents due to a loss of blood supply and dead gut
Where does most atresia occur?
Duodenum
Where is loss of blood supply causing atresia most common?
Duodenum, but not the most common cause >Jejunum = Ileum > Colon
What is most common cause of atresia in upper duodenum?
Failure of recanalisation
What is most common cause of atresia in lower duodenum?
Vascular accident (malrotation and volvulus)
What is pyloric stenosis?
Narrowing of pyloric sphincter resulting in projecile vomiting
Give two defects of abdominal wall
Gastroschisis
Omphalocoele
What is gastrochisis?
Failure of closure of abdominal wall during embryo folding leaving gut tube and its derivatives outside the body
NO COVERING
What is omphaocoele?
Persisence of physiological herniation
Umbilical cord covered by reflection of the amnion
COVERING PRESENT
Give three hindgut abnormalities
Imperforate anus - Failure of anal membrane rupture
Anal agenesis - Failure of development
Hindgut fistula - Abnormal connection to bladder
What five structures retain their mesentery?
o Jejunum o Ileum o Appendix o Transverse colon o Sigmoid colon
What four structures have fused mesenteries?
o Duodenum
o Ascending colon
o Descending colon
o Rectum (no peritoneal covering in distal 1/3)
