Development of GI

Question 1

name the yolk sac endoderm derivatives

Answer 1

• epithelial lining and glands

Question 2

name the splanchnic mesoderm derivatives

Answer 2

• smooth muscle and connective tissue

Question 3

name the derivatives of the foregut

Answer 3

• pharynx and its derivatives
• lower respiratory tract
• esophagus
• stomach
• liver
• billary apparatus
• pancreas
• duodenum up to the major duodenal papilla

Question 4

which artery supplies the foregut structures

Answer 4

• celiac artery
  
  • also supplies the spleen (not part of foregut dev.)

Question 5

name the derivatives of the midgut

Answer 5

• duodenum distal to the major duodenal papilla
• jejunum & ileum
• cecum and appendix
• ascending colon
• right 2/3 of transverse colon

Question 6

which artery supplies the midgut structures?

Answer 6

• superior mesenteric

Question 7

name the derivatives of the hindgut

Answer 7

• left 1/3 of transverse colon
• descending colon
• sigmoid colon
• rectum
• anal canal up to the pectinate line
• urinary bladder and most of urethra

Question 8

what artery supplies the hindgut structures

Answer 8

• inferior mesenteric artery

Question 9

describe congenital hypertrophic pyloric stenosis

Answer 9

• hypertrophy of muscles in the pyloric region -> narrowing (stenosis) of the lumen of pyloric canal
• stomach becomes distended and its contents are expelled with force aka projective vomiting (no bile though)

Question 10

Answer 10

1. lesser curvature
2. greater curvature
3. region of the pyloric sphincter (pyloric sphincter stenosis seen here)
4. 1st part of duodenum
5. 2nd part of duodenum

Question 11

describe duodenal stenosis vs duodenal atresia

Answer 11

• duodenal stenosis: partial occlusion of lumen due to incomplete recanalization; leads to vomiting which is usually bile stained (if stenosis is distal to bile duct opening)
• duodenal atresia: complete occlusion of lumen (failure to recanalize), and leads to vomiting immediately after birth

Question 12

Answer 12

• “double bubble” sign of duodenal atresia
  
  • ​2 bubbles for air in stomach and duodenum

Question 13

describe the relationship between the duodenum and the pancreas

Answer 13

• the main pancreatic duct traverses the length of the gland to join the common bile duct at the hepatopancreatic ampulla. Together they drain into the duodenum at the major duodenal papilla

Question 14

describe an annular pancreas

Answer 14

• due to bifid ventral pancreatic bud
  
  • ring of pancreas encircles the 2nd part of duodenum and causes obstruction

Question 15

the spleen is derived from ______ between the layers of ______

Answer 15

the spleen is derived from mesenchymal cells between the layers of dorsal mesogastrium

Question 16

contrast nonrotation of the midgut vs reversed rotation

Answer 16

• nonrotation: caudal limb returns first -> small intestine lies to the right; generally asymptomatic
• reversed rotation: midgut loop rotates clockwise direction. Duodenum lies anterior to the transverse colon & posterior to the superior mesenteric artery

Question 17

describe a subhepatic cecum & appendix

Answer 17

• cecum gets adherent to the liver/doesn’t descend to the iliac fossa
  
  • may cause difficulty in diagnosis of appendicitis

Question 18

describe mixed rotation and volvulus

Answer 18

• cecum lies inferior the pylorus and is fixed to the posterior abdominal wall by peritoneal bands
  
  • may cause duodenal obstruction (failure of midgut loop to complete the final 90 degree rotation)

Question 19

describe an omphalocele

Answer 19

• herniation or protrusion of abdominal contents into the base of the umbilical cord
• embryological defect: persistence of the abdominal herniation
• in contrast to umbiliac hernia, it is covered by peritoneum

Question 20

describe an umbilical hernia

Answer 20

• embryological defect: incomplete closure of the umbilical ring
• clinical presentation: soft swelling covered by skin
  
  • protrudes during crying, coughing and straining and can be easily reduced through the fibrous ring at the umbilicus
  • consists of omentum and small portions of the small intestines

Question 21

describe gastroschisis

Answer 21

• anomaly is due to incomplete closure of lateral folds
• due to defect near the median plane of the abdominal wall
• viscera protrudes into the amniotic cavity

Question 22

describe Meckel’s diverticulum

Answer 22

• a fingerlike projection from the ileum, representing retention of the embryonic intestinal stalk

Question 23

describe anal stenosis

Answer 23

• narrowed anal canal
• the urorecetal septum deviates slightly in a dorsal direction as it grows to fuse with the cloacal membrane, which results in a narrowed anal canal and membrane

Question 24

describe an imperforate anus

Answer 24

• failure of the anal membrane to perforate

Question 25

describe anorectal agenesis

Answer 25

• the most common anorectal anomaly
• due to incomplete separation of cloaca by urorectal septum
• there may be a fistula to:
  
  • the bladder: rectovesical fistula
  • the vagina: rectovaginal fistula
  • the urethra: rectourethral fistula

Question 26

describe rectal atresia

Answer 26

• the anal canal and rectum are present but there is no communication between them
• may be due to:
  
  • abnormal recanalization
  • defective blood supply

Question 27

describe Hirschsprung Disease aka congenital megacolon

Answer 27

• absence of autonomic ganglia in the myenteric plexus of the narrowed segment
  
  • caused by faulty migration of neural crest cells
• most common cause of neonatal intestinal obstruction
• aganglionic segment = no peristalsis

Question 28

Answer 28

barium swallow; can see dilatation in part of the colon = Hirschsprung disease