Gastrointestinal Tract Development Quiz

Gastrointestinal Embryology

• The gastrointestinal (GI) tract develops from the endoderm
• Many abdominal organs bud off from the GI tract (e.g. liver, pancreas, trachea)
• Mesoderm forms the surrounding structures of the GI tract (e.g., GI tract connective tissue, muscles, peritoneum, spleen)
• Day 12: Mesoderm formation
• Day 23: Amniotic sac enlargement
• The foregut, midgut, and hindgut are divisions of the GI tract
• Foregut: mouth to ampulla of Vater
• Midgut: ampulla of Vater to transverse colon
• Hindgut: transverse colon to rectum
• The mesentery suspends abdominal organs from the cavity walls
• Intraperitoneal organs are enclosed by the mesentery
• Retroperitoneal organs are covered by peritoneum only on the anterior wall and lie against the posterior abdominal wall
• Dorsal mesentery moves away from the posterior wall during development
• Ventral mesentery exists only at the bottom of the esophagus, stomach and upper duodenum
• In adults, the ventral mesentery becomes lesser omentum and falciform ligament
• Mesogastrium, mesoduodenum, mesocolon are parts of the mesentery
• Greater omentum hangs from the greater curvature of the stomach and covers the intestines
• Lesser omentum is between the stomach and liver and formed from the ventral mesentery
• Lung buds originate from the foregut
• Tracheoesophageal septum divides the respiratory diverticulum into separate trachea and esophagus
• Abnormal septum development may result in esophageal atresia
• Esophageal atresia (closed esophagus) occurs when the septum deviates posteriorly
• Types of esophageal atresia; EA with TEF (most common), Pure EA, H-Type
• Characteristics of esophageal atresia may include esophageal does not connect to stomach, polyhydramnios, drooling, choking, vomiting, no passing of NG tube into stomach and fistula esophagus → trachea
• Treatment for esophageal atresia is surgical repair
• Midgut herniation occurs in the 6th week of development
• In the 6th week, the abdominal cavity is too small to accommodate the growing intestines
• The intestines temporarily herniate through the umbilical cord during development
• A persistence of normal herniation is omphalocele
• omphalocele= Intestines covered by membrane outside body
• Liver does not hernia if lateral embryonic folds fail, which may contribute to the liver in omphalocele
• Omphalocele key features include covering by peritoneum and through the umbilical cord
• Many genetic defects are associated with omphalocele (e.g., Trisomy 21, Down syndrome; Trisomy 18, Edwards syndrome; Trisomy 13)
• Other conditions associated with omphalocele include congenital heart defects, orofacial clefts, and neural tube defects
• Gastroschisis is extrusion of bowel through abdominal wall
• The exact mechanism for gastroschisis is unclear, however it is likely incomplete closure of the abdominal wall
• Gastroschisis is usually on the right side of the umbilical cord
• Gastroschisis is not covered by the peritoneum
• Poor GI function, atresia, stenosis are often associated with gastroschisis
• If GI function is restored, prognosis is good
• Rarely associated with Down's syndrome or other congenital disease
• Abnormalities at Abdominal Wall Defect can include omphalocele which has an umbilical defect, is covered by membrane and usually has normal bowel function, and gastroschisis which has a paraumbilical defect, is not covered by membrane, and usually has poor bowel function
• During physiologic herniation bowel rotates around the SMA
• Malrotation can lead to obstruction if cecum is positioned in the mid-upper abdomen
• Peritoneal tissue = Ladd bands
• Duodenal obstruction=common with malrotation
• Volvulus is small bowel twisting around the SMA
• This can cause vascular compromise, ischemia, vomiting, sepsis, abdominal distention, blood in the stool
• Treatment of malrotation is surgical intervention
• Vitelline duct pathology occurs in early development during which the midgut is open to the yolk sac.
• By week 5, the connection with the yolk sac narrows, which are also known as the yolk stalk, vitelline duct, and omphalomesenteric duct
• Persistent vitelline duct may lead to congenital anomalies
• Mecel's diverticulum is the most common vitelline duct anomaly, which presents as cysts or polyps
• A ''true diverticulum'' contains all layers of the bowel, mucosa, submucosa, muscular layer
• Most diverticula only contain mucosa/submucosa
• Often a small defect/hole in the the muscular layer of a diverticulum
• Ectopic gastric tissue is sometimes in a Meckel's diverticulum
• Typically no symptoms in Meckel's diverticulum but in some cases, it can result in symptoms like abdominal pain, potential cause of obstruction or diverticulitis, and bleeding
• Rule of 2’s are 2% of population, Male-to-female 2:1; Within 2 feet from ileocecal valve and Usually 2 inches in size
• Other vitelline anomalies can include cysts, cavity behind umbilicus and persistent duct which can result in intestinal discharge from umbilicus
• Atresia is closed/absent opening, Stenosis is a narrowing/obstruction; Duodenum is the most common location for these disorders
• Failure of recanalization in early development may result in duodenal occlusion due to endodermal proliferation of epithelium
• The double bubble sign is commonly seen with duodenal atresia
• Jejunal-Ileal-Colonic Atresia results from vascular disruption resulting in ischemic necrosis of the intestine
• The necrotic tissue is resorbed resulting in blind ends of the bowel via arterial ligation
• The bowel distal to the blind end may be curled ("Apple peel atresia")
• The pylorus is connection to the stomach and duodenum.
• Pyloric stenosis = hypertrophy of pylorus
• Often occurs in newborns (few weeks old) and more common in males
• The spleen originates from dorsal mesodermal tissue in a part of the stomach
• Blood supply is similar to the stomach (celiac trunk)
• The spleen is on the left side as a result of stomach rotation
• Gastrosplenic(gastrolienal) ligament carries short gastric, left gastroepiploic vessels
• The GI tract is comprised of many organs, including the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus, with corresponding regions of the GI tract
• Abdominal CT scans are diagnostic images of the abdomen, which includes the liver, spleen, and gallbladder, and the GI tract
• Intraperitoneal organs include stomach, appendix, liver, spleen, duodenum, jejunum, ileum, transverse colon, sigmoid colon and part of rectum and Tail of pancreas
• Retroperitoneal organs include aorta, IVC, kidneys, small intestine: 2nd/3rd portions duodenum and colon: ascending/descending, part of rectum and Pancreas: Head, body
• Retroperitoneal bleeding is often complication of surgical procedures
• The peritoneal cavity is divided into greater and lesser sacs
• The greater sac encompasses entire width of abdomen from diaphragm to pelvic floor
• The lesser sac is behind liver, stomach and lesser omentum
• In addition to the greater and lesser sacs, there is an epiploic foramen that connects the two sacs
• The dentate or anocutaneous line is a part of the anal canal
• The superior rectal artery is a branch of the inferior mesenteric artery
• Venous drainage of superior rectal vein → inferior mesenteric vein → portal system
• Lymph drainage of superior rectal vein → internal iliac nodes
• Visceral innervation is present above the pectinate line; no pain
• Internal hemorrhoids, adenocarcinoma; are common disorders above the pectinate line; rare form of anal cancer
• Hindgut and ectoderm meet to form anus; absence of anal opening = imperforate anus; commonly associated with GU malformations (e.g., renal agenesis, bladder exstrophy)
• The celiac trunk supplies organs of the foregut including the esophagus, stomach, liver, gallbladder, spleen, part of the duodenum, and pancreas
• The superior mesenteric artery (SMA) supplies the midgut from the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and first two-thirds of the transverse colon
• The inferior mesenteric artery (IMA) supplies the hindgut from the last one-third of transverse colon to descending, sigmoid, and part of the rectum
• The liver receives blood from the portal vein (about 80%) and the hepatic artery (about 20%)
• Hepatic veins carry processed blood away from the liver, and the bile duct carries the bile produced by the liver away
• Liver zones include zone I (periportal), Zone II (mid zone), Zone III (centrilobular).
• Zone I is affected by viral hepatitis first, whereas ZOne III is the furthest from the blood supply and most vulnerable to ischemia
• Fatty accumulation in Alcoholic Liver Disease usually begins in zone III
• High concentration P450 enzymes in hepatocytes of liver zone III
• The pancreas is an exocrine organ that produces secretions that aid in digestion (fluid: bicarb, water, electrolytes) and digestive enzymes
• Two buds from foregut (dorsal and ventral) form the pancreas.
• Ventral bud contributes to head, uncinate process and Main pancreatic duct
• Dorsal bud contributes to rest of pancreas including head, body, tail and accessory duct
• The pancreas is secondarily retroperitoneal, and it initially forms intraperitoneal and then fuses to the posterior wall, becoming retroperitoneal
• Annular pancreas is a congenital anomaly
• Ventral bud pieces remain separate (accessory dorsal duct) leading to pancreas divisum
• Three major salivary glands including parotid, submandibular, and sublingual glands, throughout the mouth
• Saliva is mostly water, mucin, glycoproteins; lubricates food and binds bacteria; IgA, lysozymes, lactoferrin
• Salivary fluid is produced by acinar cells and modified by ductal cells
• Initial fluid in saliva is isotonic (similar to plasma), but ductal cells remove Na, Cl and secrete K, HCO3-
• Saliva becomes hypotonic as a result of the above process
• Composition of saliva varies with flow rate, and closer to isotonic with plasma at higher flow rates
• Aldosterone ↑ Na absorption and ↑ K secretion which acts on salivary glands similar to kidneys
• Saliva is regulated by both sympathetic and parasympathetic systems, not gastrointestinal hormones
• Sympathetic effect is smaller than parasympathetic effect
• Muscarinic receptors (M1 and M3) are important for increase saliva production
• Muscarinic antagonists can cause dry mouth
• Pilocarpine used in Sjogren's syndrome increases saliva production
• Sialolithiasis (salivary duct stones) is an obstruction of salivary flow leading to pain and swelling of the salivary glands
• Sialadenitis = inflammation of the salivary gland
• Usually secondary to obstructing stone.
• Mumps is a viral infection of the parotid glands.
• Swollen parotid glands are a key feature; often bilateral
• Salivary tumors present in the parotid gland , most are benign; mobile (not invading nerves) and painless.
• Pleomorphic adenoma; benign mixed tumor=Most common salivary gland tumor
• Risk factors for Pleomorphic adenoma include prior radiation
• Warthin tumors= Second most common salivary tumor; located in the parotid gland. Smoking is a key risk factor.
• Key histological finding is cysts filled with fluid surrounded by lymphoid infiltrate
• Mucoepidermoid carcinomas are most common malignant salivary tumors, sometimes invade facial nerve, and may cause pain.
• It is characterized with squamous, mucous and hybrid cells
• Hernias are protrusion of organ through the cavity wall.
• Common in inguinal canal, esophagus, or umbilicus
• Femoral vessels include nerve, artery, and vein that run lateral to medial; venous to penis
• Femoral sheath = tunnel between femoral artery/vein and femoral ring
• Hemorrhoids are engorged veins in rectum, occur in portal hypertension.
• Umbilicus contains paraumbilical vein
• Esophageal varices result from dilated submucosal veins, commonly occurring in portal hypertension.
• Mallory-Weiss Syndrome = damage to esophageal mucosa at GE junction causing painful hematemesis
• Boerhaave syndrome = transmural rupture of esophagus, due to severe chronic vomiting or retching
• Esophageal webs, are growths or folds of tissue obstructing food passage
• Schatzki ring = most common cause of dysphagia to solids; in the squamocolumnar junction
• Plummer-Vinson Syndrome=triad of conditions; iron deficiency anemia; beefy red tongue and esophageal web. Common in middle-aged, white women
• Zenker's diverticulum= uncommon disease of the hypopharynx in Killian's triangle
• Usually result from chronic swallowing issues.
• Viral hepatitis= Hep A,B,C,D,E which are very high AST/ALT (>1000), Hyperbilirubinemia and Jaundice, and may have hypoglycemia, abnormal PT/PTT, low albumin. Diagnosed with viral antibody test
• Autoimmune Hepatitis= autoinflammatory disease of liver; more common in women in 40s/50s.
• Symptoms may range from asymptomatic acute liver disease → cirrhosis.
• Anti-nuclear antibodies and/or Anti-smooth muscle antibodies typical
• Treatment is steroid and immunosuppressants
• Tylenol overdose =Acetaminophen, Paracetamol, APAP = high AST/ALT (1000s)
• Treatment = Activated charcoal may prevent absorption, N-acetylcysteine is treatment of choice
• Shock/Ischemic Hepatitis= diffuse liver injury from hypoperfusion
• Symptoms may include abdominal pain, markedly elevated AST/ALT, and is usually self-limited.
• Zone 3 necrosis is typically seen in pathology
• Cirrhosis is irreversible end-stage liver disease with many underlying causes = Viral Hep. B, C, Chronic alcohol use and non-alcoholic fatty liver disease (NAFLD)
• Cirrhosis is characterized by shrunken liver, liver tissue replaces fibrosis, smoother liver surface replaced by nodules
• Hyperammonemia, jaundice, hypoalbuminemia, coagulopathy, and elevated estrogen are clinical features in cirrhosis
• Treatment for hyperammonemia may include low protein diet or Lactulose which neutralizes gastric acid
• Portal hypertension is high pressure in portal vein due to cirrhosis, and blood flows portal vein → liver → hepatic vein.
• Venous collaterals= high portal pressure opens connections between portal/systemic vessels.
• Small bowel, Rectum, and Esophagus are common locations. These veins will engorge (swell) due to portal hypertension
• The symptoms of hypersplenism are the result of increased spleen engorgement which leads to low portal HTN and low platelets counts. This is a rare cause of portal hypertension
• Portal vein thrombosis is a rare cause of portal hypertension which may result in gastric varices and bleeding.
• Ascites is accumulation of fluid in the peritoneal cavity due to liver disease and portal hypertension which may not be present if portal hypertension is absent
• Serum Ascites Albumin Gradient (SAAG) >1.1g/dl if high pressure driving fluid into peritoneum = portal hypertension, SAAG <1.1 g/dL if serum and ascitic albumin levels are similar = malignancy (leaky vasculature).
• Ascites treatment options are Sodium restriction and diuretics (Spironolactone being the drug of choice) and Large volume paracentesis
• TIPS is a Transjugular Intrahepatic Portosystemic Shunt = creates a channel in the liver to connect portal vein to hepatic vein; treatment for portal hypertension
• SBP (Spontaneous Bacterial Peritonitis)= Ascitic fluid infection; Usually E. Coli and Klebsiella
• Treatment for SBP = 3rd generation cephalosporin (cefotaxime)
• MELD Score is used to estimate 3-month mortality of liver disease. Factors measured include bilirubin level, creatinine level and INR
• Child-Pugh is a classification that estimates risk/survival of liver disease; factors measured include encephalopathy, ascites, bilirubin, albumin and PT levels.
• Gold standard for diagnosing cirrhosis = Liver biopsy; it is rarely required if there is sufficient history to clearly diagnose the disorder.
• Stellate cells are perisinusoidal cells that store retinoids, which become activated in liver disease and secrete TG-B. Proliferate to produce fibrous tissue which is a major contributor to cirrhois
• Hepatocellular carcinoma is most common primary liver tumor and is associated with chronic liver disease (Hepatitis B, C), alcoholic cirrhosis, Wilson’s disease, hemochromatosis, and alpha 1 anti-trypsin
• Aspergillus = fungus that produces aflatoxin, which is a risk factor in hepatocellular carcinomas
• Most colon cancers are adenocarcinomas.
• Early colon cancer (noninvasive cancer) results in approximately 95% 5-year survival. Advanced cases have a 15% 5-year survival rate.
• Colon cancers from right sided and left sided locations may result in different symptoms and causes
• A colon polyp is a growth of tissue that protrudes into the lumen of the colon that may be pre-cancerous
• Types of colon polyps include hyperplastic, adenomatous, juvenile, and others, with varied risk factors and characteristics
• Risk factors in colon cancer include age > 50 years; smoking and diabetes and chronic pancreatitis
• HNPCC= Hereditary Non-Polyposis Colorectal Cancer; Inherited mutation of DNA mismatch repair enzymes that leads to colon cancer via microsatellite instability
• HNPCC= Risk is usually 80%, with the majority of these cancers starting without a pre-existing adenoma
• Frequently leads to right sided tumors and increased risk of endometrial cancer
• Cyclooxygenase-2 (COX-2): Has increased expression in colon cancer cells, and is commonly in left-sided cancers (more common)
• Rationale for aspirin therapy; may reduce risk of colorectal cancer 20-40%. BUT, increases bleeding/ulcer risk. No clinical trial evidence supports its use in prevention
• DCC gene is a tumor suppressor gene (chromosome 18q) and frequently mutated in advanced colorectal cancers
• FAP = Familial Adenomatous Polyposis; Autosomal dominant disorder; germline mutation in APC gene (chromosome 5q)
• FAP variants include; Gardner's syndrome- polyposis plus multiple extracolonic manifestations (benign bone growths, skin cysts, connective tissue growths, etc.); Turcot syndrome- polyposis plus brain tumors (mostly medulloblastomas and gliomas)
• Dermatitis herpetiformis = skin condition associated with celiac disease; has herpes-like lesions from IgA deposition in dermal papillae
• Typically resolves with a gluten-free diet
• Tropical sprue = malabsorption due to unknown infectious agents; presents in tropics; Celiac is typically in duodenum, while tropical affects entire small bowel; Folate/B12 deficiency is common
• Whipple's disease: infection with Tropheryma whipplei; involves the small intestine, joints, brain, and heart
• 4 cardinal features = diarrhea (malabsorption of fats and sugars), abdominal pain, weight loss, and joint pains
• Diagnosis = biopsies of small intestines; PAS-positive
• Lactose intolerance is due to the insufficient lactase enzyme in the small intestine to break down lactose into monosaccharides (galactose and glucose). Secondary causes= mucosal injury/bacterial overgrowth/viral infections, and distal location. Symptoms of lactose intolerance is bloating, abdominal pain, and diarrhea after lactose-containing foods
• Pancreatic insufficiency = results when there's a loss of pancreatic lipase and colipase secondary to cystic fibrosis or chronic pancreatitis which results in fat malabsorption, steatorrhea and deficiencies of fat soluble vitamins, and diabetes
• Acute pancreatitis=acute inflammation of pancreas characterized by pain, nausea, vomiting, and spread of necrosis/hemorrhage
• Rare findings = periumbilical or flank hemorrage; often in patients with rupturing ectopic pregnancy
• Pathophysiology: blocked flow of enzymes, and activation of trypsin→ activates other enzymes→ autodigestion of pancreas
• Diagnosis of acute pancreatitis is elevated serum pancreatic enzyme levels ; amylase and lipase are typically elevated and lipase is more specific in diagnosis
• Diagnostic imaging for acute pancreatitis includes ultrasound and CT scans.
• Common causes (often without recurrence except for alcohol and cystic fibrosis) = gallstones that result in abdominal symptoms and Obstruction of common bile duct from stones which leads to acute pancreatitis
• Common treatment = NPO, IV fluids, and pain control
• SIRS (Systemic Inflammatory Response Syndrome)= Clinical syndrome of dysregulated inflammation; possible complications from multiple causes (e.g., trauma, pancreatitis and sepsis)
• Ranson's criteria is a method to assess pancreatitis using scoring system of physical exam findings at admission and 48 hours
• Complications of acute pancreatitis = DIC (Disseminated Intravascular Coagulation- diffuse activation of clotting factors), ARDS (Acute lung injury), pseudocyst, fat necrosis, abscess, hypocalcemia, multiorgan failure
• (All) Duodenal ulcers can lead to upper GI bleeding which cause hematemesis or melena(dark stools).