GI Tract Flashcards
What does the GI tract include?
mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus, liver, gallblader, and pancreas
What makes up the small intestine?
duodenum, illeum, joujenum
The gut tube is created by ____ ____ in week 4
body folding
what is the gut tube lined with?
endoderm and splanchnic lateral plate mesoderm (splanchnopleure)
Parietal cells of the somatic lateral plate mesoderm become mesothelial and form the
parietal layer of the peritoneal, pleural, and pericardial cavities
Epithelium of the gut and the parenchyma of glands associated with the digestive tract are derived from…
endoderm
Muscular walls of the digestive tract and connective tissues are derived from…
visceral mesoderm
connective tissue of digestive tract
lamina propria, muscularis mucosae, submucosa, muscularis externa, adventitia, and/or serosa
Foregut stretches from
oropharyngeal membrane to liver outgrowth
Midgut stretches from
liver outgrowth to junction of right 2/3 and left 1/3 transverse colon
Hindgut stretches from
left 1/3 transverse colon to cloacal membrane
Foregut blood supply
celiac artery
foregut adult derivatives
pharynx, respiratory system, esophagus, stomach, proximal half of duodenum, liver, biliary apparatus, and pancreas
midgut blood supply
superior mesenteric artery
Hindgut blood supply
inferior mesenteric artery
Anterior 2/3 of oral cavity derived from
stomodeum
Posterior 1/3 of oral cavity derived from
foregut
anterior 2/3 and posterior 1/3 of oral cavity are separated by
oropharyngeal membrane
Respiratory diverticulum - timeline and formation
4 weeks - forms on ventral wall of foregut
Tracheoesophageal septum
partitions the diverticulum into respiratory primordium and esophagus
Tracheoesophageal folds
come together to form the tracheoesophageal septum
Esophageal atresia & tracheoesophageal fistula
results if the tracheoesophageal septum is deviated posteriorly. This causes incomplete separation of the esophagus from the laryngotracheal tube and results in a concurrent tracheoesophageal fistula.
Esophageal atresias can happen… (2 ways)
spontaneous or mechanical. Spontaneous - genetic abnormality, mechanical - they were pressing up against each other
Symptoms of esophageal atresia and tracheoesophageal fistula
maternal polyhydramnios (EA), absence/small stomach bubble on prenatal ultrasound (EA); copius, fine, white frothy bubbles of mucus in the mouth and nose (EA); coughing, choking
Congenital esophageal stenosis
narrowing of the esophageal lumen, most frequent in the distal third of esophagus….
What causes congenital esophageal stenosis
incomplete esophageal recanalization….
Development of the stomach
dilation in the foregut by 4th week, dorsal part grows faster than ventral part. Stomach rotates 90 degrees clockwise.
Rotation of stomach
left - ventral; right - dorsal. Cranial region moves left and inferior, caudal region moves right and superior.
Congenital hypertrophic pyloric stenosis
More common in males, thickening of the smooth muscle in the pylorus that narrows the region. Food is unable to pass into the duodenum. Symptoms include projectile vomiting, weight loss, hunger
Stomach is attached to the dorsal and ventral body wall by a….
dorsal and ventral mesogastrium respectively. Disproportionate growth and rotation alter the position of these mesenteries.
Hepatic diverticulum (liver bud)
forms liver and hepatic duct
cystic diverticulum
forms gallblader and cystic duct
The stalk connecting hepatic and cystic ducts to the duodenum becomes the
bile duct
The liver grows
ventrally into the ventral mesentary
Ventral pancreatic bud forms
main pancreatic duct, uncinate process and inferior portion of head of the pancreas
Dorsal pancreatic bud forms
superior head of pancreas, body and tail of pancreas, accessory pancreatic duct
The proximal portion of duodenum to bile duct is derived from
foregut
Distal portions of duodenum to bile duct is derived from
midgut
Duodenal stenosis
incomplete recanalization of duodenum
duodenal atresia
no recanalization
symptoms of duodenal stenosis
variable - recurrent vomiting, gastroesophageal reflux, peptic ulceration
symptoms of duodenal atresia
maternal polyhydramnios, bile containing vomitus, distended stomach
Adult derivatives of midgut
distal duodenum, jejenum, ileum, yolk stalk, cecum w/ appendix, ascending colon, and proximal 2/3 transverse colon
Cranial (cephalic) portion of midgut adult derivatives
jejunum, proximal ileum
Caudal portion of midgut adult derivatives
distal ileum, cecum, appendix, ascending colon, proximal 2/3 transverse colon
Physiologic umbilical hernia
midgut goes outside of your body (because body is too small) to finish development
Rotation of the midgut
6 weeks - midgut herniates into umbilical cord (rotates 90 degrees counter clockwise)
10 weeks - midgut returns to abdominal cavity (rotates 180 degrees counter clockwise)
Total rotation of midgut
270 degrees counter clockwise around axis formed by superior mesenteric artery
Initially, cecum lies below
right lobe of liver but descents into right iliac fossa
appendix forms during
descent of cecum
Malrotation of midgut can cause
volvulus - can cause obstructions and necrosis
What is nonrotation or malrotation of midgut assoc with
abnormal mesenteric attachment
Omphalocoel
failure of midgut to return to abdominal cavity, herniated intestines are enclosed in umbilical cord and covered with amnion.
Gastroschisis
protrusion of viscera directly into amniotic cavity, occurs lateral to the umbilicus (often found on the right), due to abnormal closure of body wall. viscera is NOT covered by amnion.
Ileal (Meckel’s) Diveriticulum
Congenital anomaly in 1-2% of population. Caused by incomplete obliteration of vitelline duct (yolk stalk). Diverticulum usually appears as a fingerlike pouch protruding from the ileum. Sometimes attached to umbilicus. Can form vitelline cyst and vitelline fistula.
Adult derivatives of hindgut
forms 1/3 transverse colon, descending colon, sigmoid colon, rectum, proximal 2/3 of anal canal
Cloaca
terminal end of hindgut. Partitioned into urogenital sinus and rectum.
Cloacal membrane made of
surface ectoderm and hindgut endoderm
what is the cloacal membrane partitioned into
urogenital membrane and anal membrane
What is the distal 1/3 of anal canal made of
surface ectoderm of anal membrane
pectinate line
demarcates junction between columnar epithelium and stratified squamous epithelium
Urorectal fistula with imperforate anus
Imperforate anus: anal membrane fails to break down
Urorectal fistula: incomplete partitioning of the hindgut
Hirschsprung’s disease aka aganglionic megacolon
absence of parasympathetic ganglia in gut wall, caused by failure of neural crest to migrate to walls of intestines, thus causes an absence of peristalsis in affected regions
Dorsal and ventral mesenteries
portions of the gut are suspended from the body wall by mesenteries - bilayer of peritoneum that enclose the organ and connect it to the body wall
Dorsal mesentery becomes (BIG hITTER becomes most of GI)
greater omentum, mesentery of small intestine, mesoappendix, transverse mesocolon, sigmoid mesocolon
ventral mesentery becomes
Omental bursa
lesser sack, behind stomach
SAD PUCKER - retroperitoneal structures
Suprarenal glands
Aorta and IVC
Duodenum
Pancreas
Ureters
Colon
Kidneys
Esophagus
Rectum
Intrapertioneal viscera structures
