Carlos Shared "19 Gastrointestinal" - 137 Picmonics
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19 Gastrointestinal
Normal gastrointestinal embryology
- Foregut—esophagus to upper duodenum.
- Midgut—lower duodenum to proximal 2/3 of transverse colon.
- Hindgut—distal 1/3 of transverse colon to anal canal above pectinate line.
- Embryonic Overview
- Arterial blood to the gut tube is supplied by the abdominal aorta. The gut tube is composed by the foregut, with blood supply from the celiac artery, Midgut, supplied by the Superior Mesenteric Artery, and Hindgut, supplied by the Inferior Mesenteric
- Midgut development
- 6th week—physiologic midgut herniates through umbilical ring since the fetus cannot yet accomodate the size of the midgut
- Midgut herniation is divided into Cranial Limb and Caudal Limb
- 10th week—the abdominal cavity enlarges and midgut is able to return to it. As the midgut does this, it rotates 270° counterclockwise around superior mesenteric artery (SMA).
- The Caudal (distal) part will develop a buldge that will become the cecum and the Cranial (proximal) part will become convoluted
- The Cranial limb will return first
- Caudal limb returns last
- Anterior look of final result of Midgut rotation
Ventral wall defects and hernias
- Failure of Rostral fold closure—sternal defects (ectopia cordis)
- Failure of Lateral fold closure—omphalocele, gastroschisis
- Failure of Caudal fold closure—bladder exstrophy
- Gastroschisis
- Extrusion of abdominal contents through abdominal folds (typically right of umbilicus); not covered by peritoneum or amnion.
- Omphalocele
- Persistent herniation of abdominal contents into umbilical cord, sealed by peritoneum
- Congenital umbilical hernia
- Incomplete closure of umbilical ring. Many close spontaneously.
Tracheoesophageal Fistula (TEF)
- Cause
- Esophageal Atresia
- Ends in Blind Pouch
- Assessment
- Coughing
- Choking
- Cyanosis
- Drooling
- Considerations
- NPO
- Surgical Emergency
- Aspiration Pneumonia
2 mins
Intestinal Atresia and Biliary Atresia
- All intestinal atresias present with bilious vomiting and abdominal distension within first 1–2 days of life.
- Duodenal atresia
- Failure to recanalize
- Associated with “double bubble” (dilated stomach, proximal duodenum) on x-ray.
- Associated with Down syndrome
- Polyhydramnios
- Jejunal and ileal atresia
- Disruption of mesenteric vessels leads to ischemic necrosis, causing segmental resorption (bowel discontinuity or “apple peel”).
- X-ray may show “triple bubble” (dilated stomach, duodenum, proximal jejunum) and gasless colon.
- Associated with cystic fibrosis and gastroschisis.
- May be caused by tobacco smoking or use of vasoconstrictive drugs (eg, cocaine) during pregnancy.
- BILIARY ATRESIA
- Failure to form or early destruction of extrahepatic biliary tree
- Leads to biliary obstruction within the first 3 months of life
- Presents with jaundice and progresses to cirrhosis
- Increased Conjugated Bilirubin (CB) causes Jaundice.
- Pale stool, dark urine, firm hepatomegaly.
Hypertrophic Pyloric Stenosis (HPS) Assessment
- Mechanism
- Hypertrophied Pylorus
- Risk Factor
- Macrolide Use
- Assessment
- 3-6 Weeks of Age
- Projectile Vomiting After Feeding
- No Pain or Discomfort
- Weight Loss
- Dehydration
- Hungry Baby
- Olive Mass
2 mins
Pancreas and spleen embryology
- Pancreas
- Derived from foregut
- Ventral pancreatic buds contribute to uncinate process and main pancreatic duct. The dorsal pancreatic bud alone becomes the body, tail, isthmus, and accessory pancreatic duct. Both the ventral and dorsal buds contribute to pancreatic head.
- Annular pancreas - ventral pancreatic bud abnormally encircles 2nd part of duodenum; forms a ring of pancreatic tissue that may cause duodenal narrowing and vomiting.
- Pancreas divisum - ventral and dorsal parts fail to fuse at 8 weeks. Common anomaly; mostly asymptomatic, but may cause chronic abdominal pain and/or pancreatitis.
- Spleen
- Arises in mesentery of stomach (hence is mesodermal) but has foregut supply (celiac trunk gives rise to splenic artery).
Retroperitoneal structures
- Retroperitoneal structures include GI structures that lack a mesentery and non-GI structures.
- Injuries to retroperitoneal structures can cause blood or gas accumulation in retroperitoneal space.
- SAD PUCKER:
- Suprarenal (adrenal) glands
- Aorta and IVC
- Duodenum (2nd through 4th parts)
- Pancreas (except tail)
- Ureters
- Colon (descending and ascending)
- Kidneys
- Esophagus (thoracic portion)
- Rectum (partially)
Important gastrointestinal ligaments
- Falciform
- Liver to anterior abdominal wall
- Ligamentum teres hepatis (derivative of fetal umbilical vein)
- Derivative of ventral mesentery
- Hepatoduodenal
- Liver to duodenum
- Portal triad: proper hepatic artery, portal vein, common bile duct
- Pringle maneuver—ligament may be compressed between thumb and index finger placed in omental foramen to control bleeding
- Borders the omental foramen, which connects the greater and lesser sacs
- Part of lesser omentum
- Gastrohepatic
- Liver to lesser curvature of stomach
- Gastric arteries
- Separates greater and lesser sacs on the right
- May be cut during surgery to access lesser sac
- Part of lesser omentum
- Gastrocolic (not shown)
- Greater curvature and transverse colon
- Gastroepiploic arteries
- Part of greater omentum
- Gastrosplenic
- Greater curvature and spleen
- Short gastrics, left gastroepiploic vessels
- Separates greater and lesser sacs on the left
- Part of greater omentum
- Splenorenal
- Spleen to posterior abdominal wall
- Splenic artery and vein, tail of pancreas
Digestive tract anatomy
- Layers of gut wall (inside to outside—MSMS):
- Mucosa—epithelium, lamina propria, muscularis mucosa
- Submucosa—includes Submucosal nerve plexus (Meissner), Secretes fluid
- Muscularis externa—includes Myenteric nerve plexus (Auerbach), Motility
- Serosa (when intraperitoneal), adventitia (when retroperitoneal)
- Ulcers
- Ulcers can extend into submucosa, inner or outer muscular layer.
- erosions
- Erosions are in the mucosa only
Frequencies of basal electric rhythm (slow waves)
- Frequencies of basal electric rhythm (slow waves) determines rate of contractions
- Stomach—3 waves/min
- Duodenum—12 waves/min
- Ileum—8–9 waves/min
Digestive tract histology
- Esophagus
- Nonkeratinized stratified squamous epithelium
- Stomach
- Gastric glands.
- Duodenum
- Villi and microvilli increase absorptive surface.
- Brunner glands (HCO3 −-secreting cells of submucosa) and crypts of Lieberkühn (contain stem cells that replace enterocytes/goblet cells and Paneth cells that secrete defensins, lysozyme, and TNF)
- Jejunum
- Plicae circulares (also present in distal duodenum) and crypts of Lieberkühn
- Ileum
- Peyer patches (lymphoid aggregates in lamina propria, submucosa), plicae circulares (proximal ileum), and crypts of Lieberkühn.
- Largest number of goblet cells in the small intestine.
- Colon
- Crypts of Lieberkühn but no villi; abundant goblet cells.
Abdominal aorta and branches/GI blood supply and innervation
- Arteries supplying GI structures branch anteriorly. Arteries supplying non-GI structures branch laterally and posteriorly.
- Gastrointestinal blood supply and innervation
- Foregut is supplied by the Celiac Artery and innervated by the Vagus. At the level of T12/L1. Consist of Pharynx (vagus nerve only) and lower esophagus (celiac artery only) to proximal duodenum; liver, gallbladder, pancreas, spleen (mesoderm)
- Midgut is supplied by the SMA and innervated by Vagus. Located at L1. Consists of Distal duodenum to proximal 2/3 of transverse colon.
- Hindgut is supplied by the IMA. Innervated by the Pelvic nerve. Located at L3. Consists of Distal 1/3 of transverse colon to upper portion of rectum
Superior mesenteric artery syndrome
- Characterized by intermittent intestinal obstruction symptoms (primarily postprandial pain) when transverse (third) portion of duodenum is compressed between SMA and aorta.
- Typically occurs in conditions associated with diminished mesenteric fat (eg, low body weight/malnutrition).
Celiac trunk
- Branches of celiac trunk: common hepatic, splenic, and left gastric. These constitute the main blood supply of the stomach.
- Strong anastomoses exist between:
- Left and right gastroepiploics
- Left and right gastrics
Posterior duodenal ulcers vs Anterior duodenal ulcers
- Posterior duodenal ulcers penetrate gastroduodenal artery causing hemorrhage.
- Anterior duodenal ulcers perforate into the anterior abdominal cavity, potentially leading to pneumoperitoneum.
- May see free air under diaphragm with referred pain to the shoulder via irritation of phrenic nerve
Portosystemic anastomoses
- 1
- SITE OF ANASTOMOSIS: Esophagus
- CLINICAL SIGN: Esophageal varices
- PORTAL ↔ SYSTEMIC: Left gastric ↔ azygos
- 2
- SITE OF ANASTOMOSIS: Umbilicus
- CLINICAL SIGN: Caput medusae
- PORTAL ↔ SYSTEMIC: Paraumbilical ↔ small epigastric veins of the anterior abdominal wall.
- 3
- SITE OF ANASTOMOSIS: Rectum
- CLINICAL SIGN: Anorectal varices
- PORTAL ↔ SYSTEMIC: Superior rectal ↔ middle and inferior rectal
- 4
- Treatment with a transjugular intrahepatic portosystemic shunt (TIPS) between the portal vein and hepatic vein relieves portal hypertension by shunting blood to the systemic circulation, bypassing the liver.
- Can precipitate hepatic encephalopathy
Gastric varices
- Can cause Upper GI Bleeding and death
- Can also be due to splenic vein thrombosis, pancreatitis, pancreatic cancer and abdominal tumor
- Melena
- Short gastric ↔ splenic vein
- Only occurs in the fundus of the stomach
Pectinate (dentate) line
- Formed where endoderm (hindgut) meets ectoderm.
- Above pectinate line
- Internal hemorrhoids, adenocarcinoma.
- Arterial supply from superior rectal artery (branch of IMA).
- Venous drainage: superior rectal vein → inferior mesenteric vein → splenic vein → portal vein.
- Internal hemorrhoids receive visceral innervation and are therefore not painful.
- Lymphatic drainage to internal iliac lymph nodes.
- Below pectinate line
- External hemorrhoids, anal fissures, squamous cell carcinoma.
- Arterial supply from inferior rectal artery (branch of internal pudendal artery).
- Venous drainage: inferior rectal vein → internal pudendal vein → internal iliac vein → common iliac vein → IVC.
- External hemorrhoids receive somatic innervation (inferior rectal branch of pudendal nerve) and are therefore painful if thrombosed.
- Lymphatic drainage to superficial inguinal nodes.
Anal fissure
- Tear in the anal mucosa below the Pectinate line.
- Pain while Pooping
- Blood on toilet Paper
- Located Posteriorly because this area is Poorly Perfused
- Associated with lowfiber diets and constipation.
Liver tissue architecture
- Apical surface of hepatocytes faces bile canaliculi. Basolateral surface faces sinusoids. Sinusoids drain to the central vein, which then turns into the hepatic vein
- Kupffer cells, which are specialized macrophages, form the lining of these sinusoids (black arrows in picture ; 2 yellow arrows show hepatic venule).
- Hepatic stellate (Ito) cells in space of Disse store vitamin A (when quiescent) and produce extracellular matrix (when activated).
- Zone I—periportal zone:
- Affected 1st by viral hepatitis
- Ingested toxins (eg, cocaine)
- Zone II—intermediate zone
- Yellow fever
- Zone III—pericentral vein (centrilobular) zone
- Affected 1st by ischemia
- Contains cytochrome P-450 system
- Most sensitive to metabolic toxins
- Site of alcoholic hepatitis
