Development Of The Gut 3,4 Flashcards
What are 4 things the Midgut gives rise to?
- Small Intestine, including most of duodenum
- Caecum and appendix
- Ascending colon
- Proximal 2/3 of Trasverse Colon
What is the Primary Intestinal Loop?
How is it connected to the Yolk Sac?
What are its 2 ends?
- An enormous elongation of the midgut that has ran out of space, so makes a loop around the Superior Mesenteric Artery
- By Vitelline Duct
- Has a Cranial and Caudal limb
In week 6, what happens to the Primary Intestinal Loop?
What else happens?
Elongates very rapidly and herniates into Umbilical cord
Liver also grows rapidly (abdominal cavity too small for both so intestine herniates)
What happens to the Primary Intestinal Loop once it has formed?
- Cranial end (Small Intestine) elongates
- Loop undergoes 3 90 degree clockwise rotations
- Small intestine finishes on the left and large intestine on the right
What happens to the Cecum between rotations 2 and 3?
Descends from its original position, where the liver would be
What should have happened to the intestinal loop by week 10?
Should have returned to abdominal cavity
Reversed rotation is a developmental problem associated with the Rotation of the Primary Intestinal Loop.
Describe it
What do we end up with?
- Midgut loop makes 1 90 degree Anti-Clockwise rotation instead of 3 clockwise ones
- Transverse colon ends up posterior to duodenum
What is an Omphalocoele?
This is when the rotated midgut loop fails to return to abdominal cavity by week 10 (Still remain in umbilical cord)
What are 2 Anterior Ab Wall defects of the Midgut
- Omphalocoele
- Gastroschisis
Malrotation is a developmental problem associated with the Rotation of the Primary Intestinal Loop.
Describe it
What do we end up with
- This is when only 1 (as opposed to 3) 90 degree rotation is made
- Left sided colon
Describe Gastroschisis (sometimes confused with Omphalocoele)
- Failure of the abdominal wall to close during lateral folding of the embryo
- Leaves gut tube and derivatives outside body cavity
Compare the;
- Mortality rate
- Quality of gut development
in Omphalocoele and Gastroschisis
Omphalocoele:
- Higher (More associated developmental abnormalities)
- Semi normal (Not exposed to amniotic fluid)
Gastroschisis:
- Lower
- Negatively affected, as herniated contents not covered in peritoneum
The Vitelline Duct is the connection between midgut and yolk sac, and should regress by week 7.
What are 3 possible abnormalities when it remains?
- Vitelline Cyst
- Vitelline Fistula
- Meckel’s Diverticulum
Describe a Vitelline Cyst
Describe a Vitelline Fistula
Cyst:
- Patent middle section of previous Vitelline Duct
Fistula:
- Vitelline Fistula remains completely intact, connecting midgut and umbilicus (Fetal matter can exit here)
Describe a Meckel’s Diverticulum (most common Vitelline duct abnormality)
- Essentially another appendix, but off of the small intestine
With reference to Meckel’s Diverticulum, what is the Rule of 2s?
- 2% of population
- 2 feet proxima to ileo-caecal valve
- Usually detected in under 2s
- 2:1 ratio male: female (more common in males)
In some gut structures, cell growth becomes so rapid that the lumen is partially/ completely closed off.
What process occurs to restore the lumen?
What can partial/ complete failure of the process lead to?
- Recanalisation occurs
- Partial failure-> Stenosis (Lumen narrowed, mostly in duodenum)
- Complete failure-> Atresia (Lumen obliterated/ no lumen)
Describe Pyloric Stenosis
Describe its incidence
What is it characterised by?
- Hypertrophy of circular muscle in region of pyloric sphincter (NOT a recanalisation failure)
- Common stomach abnormality in infants
- Projectile vomiting, caused by narrowing of exit from stomach
What are 5 things the Hindgut gives rise to?
- Distal 1/3 of transverse Colon
- Descending colon
- rectum
- superior part of anal canal
- epithelium of urinary bladder
Describe how the Cloca is separated into Urogenital and Ana structures in week 4-7
Urorectal Septum (wedge of mesoderm) descends, dividing Cloaca into an anterior Urogenital Sinus and posterior Anorectal canal
In Week 7, what happens to the Cloacal membrane?
Ruptures, opening anorectal canal to amniotic fluid
What is the Proctodeum
The ectoderm covering a depression where the anus is going to be
Describe the development of the anal canal
- When anal membrane rutures the cloacal membrane, some Proctodeum enters the anal canal
- Hence the anal canal is split into Superior( Deeper) and Inferior parts
What is the Pectinate/ dentate line?
An imaginary line between the histologically distinct Superior and Inferior parts of the anal canal
(These parts have a different arterial supply, innervation, venous and lymphatic drainage)
