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Gastrointestinal - Embryology and Anatomy Flashcards

1
Q

GI embryology

  • Foregut
  • Midgut
  • Hindgut
  • Developmental defects of anterior abdominal wall due to failure of:
    • Rostral fold closure
    • Lateral fold closure
    • Caudal fold closure
A
  • Foregut
    • Pharynx to duodenum.
  • Midgut
    • Duodenum to proximal 2/3 of transverse colon.
  • Hindgut
    • Distal 1/3 of transverse colon to anal canal above pectinate line.
  • Developmental defects of anterior abdominal wall due to failure of:
    • Rostral fold closure: sternal defects
    • Lateral fold closure: omphalocele, gastroschisis
    • Caudal fold closure: bladder exstrophy
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2
Q

GI embryology

  • Pathology
  • Duodenal atresia
  • Jejunal, ileal, colonic atresia
  • Midgut development
  • Gastroschisis
  • Omphalocele
A
  • Pathology
    • Malrotation of midgut, omphalocele, intestinal atresia or stenosis, volvulus.
  • Duodenal atresia
    • Failure to recanalize (trisomy 21).
  • Jejunal, ileal, colonic atresia
    • Due to vascular accident (apple peel atresia).
  • Midgut development
    • 6th week—midgut herniates through umbilical ring
    • 10th week—returns to abdominal cavity + rotates around SMA
  • Gastroschisis
    • Extrusion of abdominal contents through abdominal folds
    • Not covered by peritoneum.
  • Omphalocele**
    • ​Persistence of herniation of abdominal contents into umbilical cord, sealed by peritoneum [A].
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3
Q

Tracheoesophageal anomalies

  • Most common
  • Clinical test
  • H-type vs. pure
A
  • Esophageal atresia (EA) with distal tracheoesophageal fistula (TEF) is the most common (85%).
    • Results in drooling, choking, and vomiting with first feeding.
    • TEF allows air to enter stomach (visible on CXR).
    • Cyanosis is 2° to laryngospasm (to avoid reflux-related aspiration).
  • Clinical test
    • Failure to pass nasogastric tube into stomach.
  • H-type vs. pure
    • In H-type it is a fistula alone.
    • In pure atresia (isolated) EA the CXR shows gasless abdomen.
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4
Q

Congenital pyloric stenosis

A
  • Hypertrophy of the pylorus causes obstruction.
  • Occurs in 1/600 live births, more often in firstborn males.
  • Palpable “olive” mass in epigastric region and nonbilious projectile vomiting at ≈2–6 weeks old.
  • Treatment is surgical incision.
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5
Q

Pancreas and spleen embryology

  • Pancreas
  • Annular pancreas
  • Pancreas divisum
  • Spleen
A
  • Pancreas
    • Derived from foregut.
    • Ventral pancreatic buds contribute to the pancreatic head and main pancreatic duct.
    • The uncinate process is formed by the ventral bud alone.
    • The dorsal pancreatic bud becomes everything else (body, tail, isthmus, and accessory pancreatic duct).
  • Annular pancreas
    • Ventral pancreatic bud abnormally encircles 2nd part of duodenum
    • Forms a ring of pancreatic tissue that may cause duodenal narrowing.
  • Pancreas divisum
    • Ventral and dorsal parts fail to fuse at 8 weeks.
  • Spleen
    • Arises in mesentery of stomach (hence is mesodermal) but is supplied by foregut (celiac artery).
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6
Q

Retroperitoneal structures

  • Retroperitoneal structures
  • Injuries to retroperitoneal structures
A
  • Retroperitoneal structures include GI structures that lack a mesentery and non-GI structures.
    • A DUCK PEAR
    • Adrenal glands (suprarenal)
    • Duodenum (2nd through 4th parts)
    • Ureters
    • Colon (asecnding & descending)
    • Kidneys
    • Pancreas (except tail)
    • Esophagus (lower 2/3)
    • Aorta and IVC
    • Rectum (partially)
  • Injuries to retroperitoneal structures can cause blood or gas accumulation in retroperitoneal space.
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7
Q

Falciform ligament

  • Connects…
  • Structures contained
  • Notes
A
  • Connects…
    • Liver to anterior abdominal wall
  • Structures contained
    • Ligamentum teres hepatis (derivative of fetal umbilical vein)
  • Notes
    • Derivative of ventral mesentery
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8
Q

Hepatoduodenal ligament

  • Connects…
  • Structures contained
  • Notes
A
  • Connects…
    • Liver to duodenum
  • Structures contained
    • Portal triad: proper hepatic artery, portal vein, common bile duct
  • Notes
    • 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
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9
Q

Gastrohepatic ligament

  • Connects…
  • Structures contained
  • Notes
A
  • Connects…
    • Liver to lesser curvature of stomach
  • Structures contained
    • Gastric arteries
  • Notes
    • Separates greater and lesser sacs on the right
    • May be cut during surgery to access lesser sac
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10
Q

Gastrocolic ligament

  • Connects…
  • Structures contained
  • Notes
A
  • Connects…
    • Greater curvature and transverse colon
  • Structures contained
    • Gastroepiploic arteries
  • Notes
    • Part of greater omentum
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11
Q

Gastrosplenic ligament

  • Connects…
  • Structures contained
  • Notes
A
  • Connects…
    • Greater curvature and spleen
  • Structures contained
    • Short gastrics, left gastroepiploic vessels
  • Notes
    • Separates greater and lesser sacs on the left
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12
Q

Splenorenal ligament

  • Connects…
  • Structures contained
A
  • Connects…
    • Spleen to posterior abdominal wall
  • Structures contained
    • Splenic artery and vein, tail of pancreas
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13
Q

Digestive tract anatomy

  • Layers of gut wall
  • Ulcers vs. erosions
  • Frequencies of basal electric rhythm
    • Stomach
    • Duodenum
    • Ileum
A
  • Layers of gut wall (inside to outside—MSMS):
    • ƒƒMucosa—epithelium (absorption), lamina propria (support), muscularis mucosa (motility)
    • Submucosa—includes Submucosal nerve plexus (Meissner)
    • ƒƒMuscularis externa—includes Myenteric nerve plexus (Auerbach)
    • Serosa (when intraperitoneal)/adventitia (when retroperitoneal)
  • Ulcers vs. erosions
    • Ulcers can extend into submucosa, inner or outer muscular layer.
    • Erosions are in the mucosa only.
  • Frequencies of basal electric rhythm (slow waves):
    • Stomach—3 waves/min
    • ƒƒDuodenum—12 waves/min
    • Ileum—8–9 waves/min
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14
Q

Digestive tract histology

  • Esophagus
  • Stomach
  • Duodenum
  • Jejunum
  • Ileum
  • Colon
A
  • Esophagus
    • Nonkeratinized stratified squamous epithelium.
  • Stomach
    • Gastric glands.
  • Duodenum
    • Villi and microvilli increase absorptive surface.
    • Brunner glands (submucosa) and crypts of Lieberkühn.
  • Jejunum
    • Plicae circulares and crypts of Lieberkühn.
  • Ileum
    • Peyer patches (lamina propria, submucosa), plicae circulares (proximal ileum), and crypts of Lieberkühn.
    • Largest number of goblet cells in the small intestine.
  • Colon
    • Colon has crypts of Lieberkühn but no villi.
    • Numerous goblet cells.
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15
Q

Abdominal aorta and branches

  • Arteries supplying…
    • GI structures branch…
    • Non-GI structures branch…
  • Superior mesenteric artery (SMA) syndrome
A
  • Arteries supplying…
    • GI structures branch anteriorly.
    • Non-GI structures branch laterally.
  • Superior mesenteric artery (SMA) syndrome
    • Occurs when the transverse portion (third segment) of the duodenum is entrapped between SMA and aorta, causing intestinal obstruction.
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16
Q

GI blood supply and innervation for the following embryonic gut regions

  • For each
    • Artery
    • Parasympathetic innervation
    • Vertebral level
    • Structures supplied
  • Foregut
  • Midgut
  • Hindgut
A
  • Foregut
    • Artery: Celiac
    • Parasympathetic innervation: Vagus
    • Vertebral level: T12/L1
    • Structures supplied: Pharynx to proximal duodenum, liver, gallbladder, pancreas, spleen (mesoderm)
  • Midgut
    • Artery: SMA
    • Parasympathetic innervation: Vagus
    • Vertebral level: L1
    • Structures supplied: Distal duodenum to proximal 2/3 of transverse colon
  • Hindgut
    • Artery: IMA
    • Parasympathetic innervation: Pelvic
    • Vertebral level: L3
    • Structures supplied: Distal 1/3 of transverse colon to upper portion of rectum
      • Splenic flexure is a watershed region
17
Q

Celiac trunk

  • Branches of celiac trunk
  • Short gastrics
  • Strong anastomoses exist between:
A
  • Branches of celiac trunk:
    • Common hepatic, splenic, left gastric.
    • These constitute the main blood supply of the stomach.
  • Short gastrics
    • Have poor anastomoses if splenic artery is blocked.
  • Strong anastomoses exist between:
    • Left and right gastroepiploics
    • Left and right gastrics
18
Q

Collateral arterial circulation:
If branches off of the abdominal aorta are blocked, these arterial anastomoses (origin) compensate

A
  • Superior epigastric (internal thoracic/mammary) ↔ inferior epigastric (external iliac)
  • Superior pancreaticoduodenal (celiac trunk) ↔ inferior pancreaticoduodenal (SMA)
  • ƒƒMiddle colic (SMA) ↔ left colic (IMA)
  • Superior rectal (IMA) ↔ middle and inferior rectal (internal iliac)
19
Q

Portosystemic anastomoses

  • Varices commonly seen with portal hypertension
  • Treatment of portal hypertension
A
  • Varices commonly seen with portal hypertension
    • Varices of gut, butt, and caput (medusae)
    • Esophagus [1]
    • Umbilicus [2]
    • Rectum [3]
  • Treatment of portal hypertension [4]
    • Treatment with a transjugular intrahepatic portosystemic shunt (TIPS) between the portal vein and hepatic vein percutaneously relieves portal hypertension by shunting blood to the systemic circulation.
20
Q

Portosystemic anastomoses

  • For each site of anastomosis
    • Clinical sign
    • Portal ↔ systemic
  • Esophagus
  • Umbilicus
  • Rectum
A
  • Esophagus [1]
    • Clinical sign: Esophageal varices
    • Portal ↔ systemic: Left gastric ↔ esophageal
  • Umbilicus [2]
    • Clinical sign: Caput medusae
    • Portal ↔ systemic: Paraumbilical ↔ small epigastric veins of the anterior abdominal wall.
  • Rectum [3]
    • Clinical sign: Anorectal varices (not internal hemorrhoids)
    • Portal ↔ systemic: Superior rectal ↔ middle and inferior rectal
21
Q

Pectinate (dentate) line

  • Formed…
  • Above vs. below the pectinate line
    • Conditions
    • Arterial supply
    • Venous drainage
    • Innervation
    • Lymphatic drainage
  • Anal fissure
A
  • Formed where endoderm (hindgut) meets ectoderm.
  • Above vs. below the pectinate line
    • Conditions
      • Above: Internal hemorrhoids, adenocarcinoma
      • Below: External hemorrhoids, anal fissures, squamous cell carcinoma
    • Arterial supply
      • Above: Superior rectal artery (branch of IMA)
      • Below: Inferior rectal artery (branch of internal pudendal artery)
    • Venous drainage
      • Above: Superior rectal vein –>Ž inferior mesenteric vein –>Ž portal system
      • Below: Inferior rectal vein –>Ž internal pudendal veinŽ –> internal iliac vein –> IVC
    • Innervation
      • Above: Internal hemorrhoids receive visceral innervation and are therefore not painful
      • Below: External hemorrhoids receive somatic innervation (inferior rectal branch of pudendal nerve) and are therefore painful
    • Lymphatic drainage
      • Above: To deep nodes
      • Below: To superficial inguinal nodes
  • Anal fissure
    • Tear in the anal mucosa below the Pectinate line.
    • Pain while Pooping
    • Blood on “toilet” Paper.
    • Located Posteriorly since this area is Poorly Perfused.
22
Q

Liver anatomy

  • Apical vs. basolateral surface
  • Zone I
  • Zone II
  • Zone III
A
  • Apical vs. basolateral surface
    • Apical surface of hepatocytes faces bile canaliculi.
    • Basolateral surface faces sinusoids.
  • Zone I: periportal zone
    • Affected 1st by viral hepatitis
    • Ingested toxins (e.g., cocaine)
  • Zone II: intermediate zone
  • Zone III: pericentral vein (centrilobular) zone
    • Affected 1st by ischemia
    • Contains cytochrome P-450 system
    • ƒƒMost sensitive to metabolic toxins
    • Site of alcoholic hepatitis
23
Q

Biliary structures

  • Gallstones
  • Tumors
A
  • Gallstones that reach the common channel at ampulla of Vater can block both the bile and pancreatic ducts.
  • Tumors that arise in the head of the pancreas (near the duodenum) can cause obstruction of the common bile duct.
24
Q

Femoral region

  • Organization
  • Femoral triangle
  • Femoral sheath
A
  • Organization
    • Lateral to medial: Nerve-Artery-Vein-Empty space-Lymphatics.
    • You go from lateral to medial to find your NAVEL.
  • Femoral triangle
    • Contains femoral nerve, artery, vein.
    • Venous near the penis.
  • Femoral sheath
    • Fascial tube 3–4 cm below inguinal ligament.
    • Contains femoral artery, vein, and canal (deep inguinal lymph nodes) but not femoral nerve.
25
Q

Inguinal canal (343)

26
Q

Hernias

  • Definition
  • Hesselbach triangle
  • Direct vs. indirect hernia
A
  • Definition
    • A protrusion of peritoneum through an opening, usually a site of weakness.
  • Hesselbach triangle
    • Inferior epigastric vessels
    • Lateral border of rectus abdominis
    • Inguinal ligament
  • Direct vs. indirect hernia
    • MDs don’t LIe
    • Medial to inferior epigastric artery = Direct hernia.
    • Lateral to inferior epigastric artery = Indirect hernia.
27
Q

Diaphragmatic hernia

  • Definition
  • Sliding hiatal hernia
  • Paraesophageal hernia
A
  • Definition
    • Abdominal structures enter the thorax
    • May occur in infants as a result of defective development of pleuroperitoneal membrane.
    • Most commonly a hiatal hernia, in which stomach herniates upward through the esophageal hiatus of the diaphragm.
  • Sliding hiatal hernia
    • Most common.
    • Gastroesophageal junction is displaced upward
    • “Hourglass stomach.”
  • Paraesophageal hernia
    • Gastroesophageal junction is normal.
    • Fundus protrudes into the thorax.
28
Q

Indirect inguinal hernia

A
  • Goes through the internal (deep) inguinal ring, external (superficial) inguinal ring, and into the scrotum.
    • Enters internal inguinal ring lateral to inferior epigastric artery.
  • Occurs in infants owing to failure of processus vaginalis to close (can form hydrocele).
    • Much more common in males.
  • An indirect inguinal hernia follows the path of descent of the testes.
    • Covered by all 3 layers of spermatic fascia.
29
Q

Direct inguinal hernia

A
  • Protrudes through the inguinal (Hesselbach) triangle.
    • Bulges directly through abdominal wall medial to inferior epigastric artery.
    • Goes through the external (superficial) inguinal ring only.
    • Covered by external spermatic fascia.
  • Usually in older men.
30
Q

Femoral hernia

A
  • Protrudes below inguinal ligament through femoral canal below and lateral to pubic tubercle.
  • More common in females.
  • Leading cause of bowel incarceration.

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