Development

Question 1

Oropharyngeal membrane

Answer 1

• everything anterior to this is supplied sensory fibers by trigeminal
• everything posterior to this is supplied sensory fibers by the glossopharyngeal

Question 2

Cloacal membrane

Answer 2

caudal end of digestive tract (proctodeum and anal pit)

Question 3

Lining of digestive tract and related glands

Answer 3

develop from ENDODERM –> except stomodeum and proctodeum (ectoderm)

Question 4

Skeletal muscle of pharynx and upper esophagus

Answer 4

derived from branchial arch mesoderm (4th and 6th)

Question 5

Smooth muscle and CT of GI tract

Answer 5

splanchnic mesoderm

Question 6

Nervous component

Answer 6

neural crest cells
Vagus –> parasympathetics (left colic flexure)
Pelvic splanchnics –> parasympathetics (remaining)

Question 7

Postganglionic parasympathetic nerve cell bodies?

Answer 7

located near the organs of innervation

Question 8

Sympathetic cell bodies?

Answer 8

located in the ganglia (celiac, superior, inferior mesenteric nerve plexuses)

Question 9

Esophageal atresia

Answer 9

defective tracheoesophageal septum (leads to polyhydramnios)

Question 10

Foregut

Answer 10

celiac artery and vagus nerve

Question 11

Midgut

Answer 11

superior mesenteric artery and vagus nerve

Question 12

Hindgut

Answer 12

inferior mesenteric artery and pelvic splanchnics (S2-4)

Question 13

Dorsal mesentery

Answer 13

suspends distal esophagus, stomach, and proximal duodenum from dorsal wall

Question 14

Ventral mesentery

Answer 14

• derived from transverse septum
• connects distal esophagus, stomach, and proximal duodenum to ventral wall
• encloses liver and forms visceral peritoneum
• forms lesser omentum (between stomach and duodenum)
• forms falciform ligament

Question 15

Development of distal esophagus, stomach, and duodenum

Answer 15

90 degree rotation of stomach occurs to bring greater curvature to left and lesser curvature to right
- because of rotation, L vagus supplies ventral surface of stomach and R vagus supplies dorsal surface of stomach

Question 16

Omental bursa

Answer 16

forms behind stomach and dorsal mesentery folds upon rotation
- dorsal mesentery and transverse mesocolon form gastrocolic ligament

Question 17

Spleen

Answer 17

develops in dorsal mesentery and is of mesodermal origin

• rotation also forms gastrosplenic and splenorenal ligaments
• serves as site of hematopoietic cell development during fetal life

Question 18

Pyloric stenosis

Answer 18

results from hypertrophy of circular layer of stomach smooth muscle and pyloric outlet –> narrowing of canal
- non-bilious vomitting

Question 19

Intestinal atresia

Answer 19

occurs due to failure of recanalization of intestine (usually in distal 1/3 of duodenum)
- vomitus is bilious

Question 20

Liver

Answer 20

occupies large portion of ventral mesentery

- endoderm of foregut (buds) grow into ventral mesentery and transverse septum

Question 21

Hepatic diverticulum

Answer 21

gives rise to hepatic cells and bile ducts draining into liver

• transverse septum gives rise to fibrous capsule
• gallbladder, cystic duct, and ventral pancreas develop from this

Question 22

Pancreas

Answer 22

develops from ventral (from hepatic diverticulum) and dorsal buds (endoderm)

• duct of dorsal bud fuses with ventral to form pancreas
• duct of dorsal bud usually degenerates and ventral duct is definitive pancreatic duct

Question 23

Omphaloenteric yolk stalk

Answer 23

attached at apex of midgut loop, remains if present in adult may form ileal diverticulum (Meckel)

Question 24

Herniation and Rotation of GI Tract

Answer 24

at 6/7 week, gut herniates into umbilical cord and returns by 10/11 weeks with rotation occuring
- superior mesenteric artery supplies midgut and serves as pivot point for rotation –> Cecum goes to lower right quadrant when colon returns

Question 25

Ileal Diverticulum (Meckel)

Answer 25

persistence of proximal part of yolk stalk | - can be a blind pouch, fibrous cord, fistula, volvulus, extopic stomach tissue or pancreatic tissue

Question 26

Omphalocele

Answer 26

failure of intestinal loops to return from umbilical cord --> herniation covered by amnion

Question 27

Gastroschisis

Answer 27

ventral abdominal wall fails to close --> GI contents not covered by amnion

Question 28

Congential umbilical hernia

Answer 28

ventral ab walls fail to close --> covered by skin

Question 29

Non-rotation of midgut

Answer 29

results when caudal limb returns to abdomen first --> small intestine of R and large intestine on L

Question 30

Cloacal membrane

Answer 30

ectoderm and endoderm --> separates cloaca from proctodeum

Question 31

Urorectal septum

Answer 31

grows and divides cloaca into urogenital sinus and rectum/anal canal - perineal body forms where septum approaches cloacal membrane

Question 32

Vasculature of anal canal

Answer 32

upper 2/3 --> hindgut (inferior mesenteric) | lower 1/3 --> proctodeum (inferior rectal and internal pudendal)

Question 33

Pectinate line

Answer 33

indicates site of anal membrane and where endoderm become continuous with ectoderm

Question 34

Lymphatics of anal canal

Answer 34

hindgut drainage --> inferior mesenteric nodes | proctodeum --> superficial inguinal nodes

Question 35

Congential megacolon

Answer 35

absence of parasympathetic ganglia in wall of colon due to failure of neural crest cells to migrate --> no peristalsis --> distal ileum

Question 36

Imperforate anus

Answer 36

persistence of cloacal membrane to atresia of anal canal

Question 37

Hindgut fistula

Answer 37

Rectovaginal --> hindgut to vagina Rectourethral --> hindgut to urethra Rectovesical --> hindgut to bladder - ALL occur because of incomplete division of cloaca by urorectal septum