Flashcards for USMLE Step 1 Gastrointestinal 2023

Flashcards for USMLE Step 1 Gastrointestinal 2023 Foregut - ANS-Pharynx to duodenum Midgut - ANS-Duodenum to proximal 2/3 of transverse colon Hindgut - ANS-Distal 1/3 of transverse colon to anal canal above pectinate line Abnormal Rostral Fold Closure - ANS-Developmental defect of anterior abdominal wall that leads to STERNAL DEFECTS Abnormal Lateral Fold Closure - ANS-Developmental defect of anterior abdominal wall that leads to OMPHALOCELE, GASTROSCHISIS Abnormal Caudal Fold Closure - ANS-Developmental defect of anterior abdominal wall that leads to BLADDER EXSTROPHY Duodenal atresia - ANS-Failure to recanalize [Trisomy 21] Jejunal, Ileal, Colonic atresia - ANS-Due to vascular accident [Apple Peel Atresia] Midgut development - ANS-1. 6th week = Midgut herniates through umbilical ring 2. 10th week = Returns to abdominal cavity + ROTATES around SUPERIOR MESENTERIC ARTERY [SMA] Malrotation of midgut leads to - ANS-Omphalocele, intestinal atresia or stenosis, Volvulus Gastroschisis - ANS-Extrusion of abdominal contents through abdominal folds, not covered by peritoneum Omphalocele - ANS-Persistence of herniation of abdominal contents into umbilical cord, sealed by peritoneum Esophageal atresia with distal tracheoesophageal fistula - ANS-1. Esophageal atresia [EA] with distal tracheoesophageal fistula [TEF] = MOST COMMON [85%] Clinical Manifestations: 1. Drooling 2. Choking 3. Vomiting w/ first feeding TEF Allows air into stomach [Visible on CXR] CYANOSIS SECONDARY TO LARYNGOSPASM [To avoid reflux-related aspiration] Clinical Test: FAilure to pass nasogastric tube into stomach H-Type Pure Tracheoesophageal fistula - ANS-Fistula resembles the letter H Pure Esophageal atresia - ANS-CXR shows gasless abdomen Congenital Pyloric Stenosis - ANS-Hypertrophy of pylorus causes obstruction Palpable "OLIVE MASS" in epigastric region NONBILIOUS PROJECTILE VOMITING at 2-6 weeks old Occurs in 1/600 live births, more often in FIRST BORN MALES LAb Findings: 1. Hypokalemia 2. Hypochloremia 3. Metabolic alkalosis [Secondary to vomiting of gastric acid and subsequent volume contraction] Treatment: Surgical incision [Pyloromyotomy] Pancreas - ANS-Derived from foregut VENTRAL PANCREATIC BUDS contribute to UNCINATE PROCESS and MAIN PANCREATIC DUCT DORSAL PANCREATIC BUD alone forms body, tail, isthmus, and accessory pancreatic duct BOTH VENTRAL and DORSAL buds contribute to PANCREATIC HEAD Annular Pancreas - ANS-VENTRAL pancreatic duct abnormally encircles 2nd part of duodenum Forms a ring of pancreatic tissue that may cause duodenal narrowing Pancreas Divisum - ANS-VENTRAL and DORSAL parts fail to fuse at 8 weeks Common anomaly Mostly asymptomatic May cause chronic abdominal pain and/or pancreatitis Spleen - ANS-Arises in mesentery of stomach [MESODERMAL] Supplied by FOREGUT [CELIAC ARTERY] Retroperitoneal Structures - ANS-Include GI structures that lack mesentery and non-GI structures Injuries to retroperitoneal structures can cause BLOOD OR GAS ACCUMULATION in retroperitoneal space SAD PUCKER: 1. Suprarenal [Adrenal] Glands 2. Aorta and IVC 3. Duodenum [2nd-4th parts] 4. Pancreas [Except tail] 5. Ureters 6. Colon [Descending and Ascending] 7. Kidneys 8. Esophagus [Thoracic portion] 9. Rectum [Partially] Falciform Ligament - ANS-Connects: Liver to anterior abdominal wall Structures Contained: Ligamentum teres hepatis [Derived from fetal UMBILICAL VEIN] DERIVATIVE OF VENTRAL MESENTERY Hepatoduodenal Ligament - ANS-Connects: Liver to duodenum Structures Contained: Portal triad 1. Hepatic artery 2. Portal vein 3. Common bile duct Notes: Pringle maneuver = Ligament may be compressed between thumb and index finger placed in omental foramen to control bleeding Borders the omentum foramen which connects the greater and lesser sacs Gastrohepatic Ligament - ANS-Connects: Liver to lesser portion of stomach Structures Contained: Gastric arteries Notes: Separates greater and lesser sacs on right May be cut during surgery to access the less sac Gastrocolic Ligament - ANS-Connects: Greater curvature and transverse colon Structures Contained: Gastroepiploic vessels Notes: Part of greater omentum Gastrosplenic Ligament - ANS-Connects: Greater curvature and spleen Structures Contained: Short gastrics, left gastroepiploic vessels Notes: Separates greater and lesser sacs on left Splenorenal Ligament - ANS-Connects: Spleen to posterior abdominal wall Structures Contained: Splenic artery and vein, tail of pancreas Notes: Separates greater and lesser sacs on left Layers of the Gut Wall Inside to Out - ANS-MSMS 1. Mucosa = Epithelium, lamina propria, muscularis mucosa 2. Submucosa = Submucosal nervous plexus [Meissner], Secretes Fluid 3. Muscularis Externa = Includes myenteric plexus [Auerbach], Motility 4. Seroa [When Intraperitoneal], Adventitia [When Retroperitoneal] Frequencies of basal electric rhythm - ANS-Stomach: 3 waves/min Duodenum: 12 waves/min Ileum: 8-9 waves/min Esophagus histology - ANS-Nonkeratinized Stratified Squamous epithelium Gastric Glands Histology - ANS-Gastric Glands Duodenum Histology - ANS-Villi and microvilli ↑ Absorptive surface BRUNNER GLANDS = HCO3 secreting glands of submucosa CRYPTS of LIEBERKUHN Jejunum Histology - ANS-Plicae circulares and CRYPTS OF LIEBERKUHN Ileum Histology - ANS-Peyer's patches [Lymphoid aggregates in lamina propria, submucosa] Plicae circulares [Proximal ileum] Crypts of lieberkuhn Colon Histology - ANS-Crypts of Lieberkuhn but NO VILLI, Abundant goblet cells Abdominal Aorta and its branches - ANS-Arteries supplying GI structures run anteriorly Arteries supplying non-GI structure run laterally T12: Celiac Trunk L1: Superior Mesenteric Artery, Left renal artery L3: Inferior Mesenteric Artery L4: BiFOURcation of abdominal aorta Superior Mesenteric Artery Syndrome - ANS-Occurs then transverse portion [3rd part] of duodenum is trapped between SMA and aorta CAUSES INTESTINAL OBSTRUCTION GI Blood Supply and Innervation: Foregut - ANS-Artery: Celiac Parasympathetic Innervation: Vagus Vertebral Level: T12/L1 Structures Supplied: 1. Pharynx [Vagus nerve only] 2. Lower esophagus [Celiac artery only] 3. Duodenum 4. Liver CONTINUES...