Development of GIT Midgut and Hindgut Structure Flashcards
What are the derivatives of the midgut?
Lower half of duodenum
Jejunum
Ileum
Cecum
Appendix
Ascending colon
Proximal 2/3 of transverse colon
What are the derivatives of the hindgut?
Distal 1/3 of transverse colon
Descending colon
Sigmoid colon
Rectum
Upper 2/3 of anal canal
What is the embryological origin of the upper 2/3 and lower 1/3 of the anal canal?
Upper 2/3: Endoderm (hindgut)
Lower 1/3: Ectoderm (proctodeum)
What is the significance of the pectinate (dentate) line?
Marks the junction between the superior (endodermal) and inferior (ectodermal) anal canal, differing in:
Epithelium
Blood supply
Venous/lymphatic drainage
Nerve supply
What causes Hirschsprung’s disease (aganglionic megacolon)?
Absence of parasympathetic ganglion cells in the colon wall (myenteric plexus), leading to stenosis and proximal dilation.
What are the clinical features of Congenital Hypertrophic Pyloric Stenosis (CHPS)?
Projectile vomiting (non-bilious)
Palpable pyloric “tumor”
Visible peristalsis
Hypochloremic alkalosis
More common in firstborn males
What is Meckel’s diverticulum, and what is its rule of 2’s?
Definition: A remnant of the vitelline duct in the ileum.
Rule of 2’s:
2% of population
2 feet from ileocecal valve
2 inches long
2% symptomatic
2 types of ectopic tissue (gastric/pancreatic)
What is the difference between omphalocele and gastroschisis?
Omphalocele: Herniated midgut covered by amnion, umbilical cord at apex.
Gastroschisis: Intestines protrude through a full-thickness abdominal wall defect, no sac, normal umbilical cord.
What is the role of the urorectal septum in hindgut development?
Divides the cloaca into:
Ventral: Urogenital sinus
Dorsal: Anorectal canal
Fusion with cloacal membrane forms the perineal body.
What are the arterial supplies to the superior and inferior anal canal?
Superior: Superior rectal artery (from inferior mesenteric artery)
Inferior: Inferior rectal artery (from internal iliac artery)
What is malrotation of the midgut, and what complication can it cause?
Definition: Abnormal rotation of midgut loop during development.
Complication: Midgut volvulus (twisting leading to obstruction/ischemia).
What is imperforate anus, and what embryological defect causes it?
Definition: Absence or narrowing of the anal opening.
Cause: Failure of urorectal septum to divide cloaca or proctodeum to canalize.
What is the physiological midgut hernia, and when does it occur?
Temporary herniation of the midgut loop into the umbilical cord during the 6th week due to rapid elongation and limited abdominal space.
Resolution: Returns to the abdomen by the 10th week after rotating 270° counterclockwise.
What structures form at the apex of the midgut loop during development?
Vitelline duct (narrow remnant of yolk sac)
Cecal diverticulum (swelling that becomes the cecum and appendix).
What is the difference between the cranial (pre-arterial) and caudal (post-arterial) limbs of the midgut loop?
Cranial limb: Develops into distal duodenum, jejunum, and part of ileum.
Caudal limb: Forms distal ileum, cecum, appendix, ascending colon, and proximal transverse colon.
What is a subhepatic cecum, and why does it occur?
Definition: Cecum positioned near the right liver lobe after midgut rotation.
Cause: Due to the additional 180° counterclockwise rotation during abdominal re-entry.
What are the ligaments derived from the ventral mesentery of the stomach?
Lesser omentum (liver to stomach).
Falciform ligament (liver to anterior abdominal wall).
What are the ligaments derived from the dorsal mesentery of the stomach?
Gastrosplenic ligament (stomach to spleen).
Lienorenal (splenorenal) ligament (spleen to posterior body wall near the kidney).
What is the greater omentum, and how does it form?
Definition: A double-layered “apron” of peritoneum hanging over the intestines.
Development: Forms from dorsal mesogastrium, later fuses and encapsulates the lesser sac.
What is the cloacal membrane, and how does it partition?
A transient bilayer (endoderm + ectoderm) separating the cloaca from the proctodeum.
Partitioning: Urorectal septum divides it into:
Urogenital membrane (anterior).
Anal membrane (posterior), which later ruptures to form the anus.
What is a rectourethral/rectovaginal fistula, and what causes it?
Definition: Abnormal connection between rectum and urethra/vagina.
Cause: Incomplete division of the cloaca by the urorectal septum.
What is meconium, and what does its delayed passage suggest?
Definition: Sterile, sticky first stool of neonates (bile, amniotic fluid, cells).
Delayed passage (>48h): Suggests Hirschsprung’s disease or intestinal obstruction.
What is the difference between omphalocele and congenital umbilical hernia?
Omphalocele: Herniated organs covered by amnion (failure of midgut return).
Umbilical hernia: Protrusion through linea alba, covered by skin/subcutaneous tissue (post-return herniation).
What is the blood supply to the hindgut derivatives?
Inferior mesenteric artery (supplies distal transverse colon to upper anal canal).
Superior rectal artery (terminal branch for rectum/upper anal canal).
