Carlos Shared "19 Gastrointestinal" - 135 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
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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.
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Tracheoesophageal Fistula (TEF)
Cause
Esophageal Atresia
Ends in Blind Pouch
Assessment
Coughing
Choking
Cyanosis
Drooling
Considerations
NPO
Surgical Emergency
Aspiration Pneumonia
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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”).
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.
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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
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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).
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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)
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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
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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
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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
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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.
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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
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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).
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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
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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
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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
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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
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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.
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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.
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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
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