Updated: 4/3/2018

GI Embryology

Topic
Review Topic
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Questions
7
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Evidence
5
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Overview
  • Developmental derivatives
    • foregut (supplied by celiac trunk) → pharynx to duodenum
    • midgut (supplied by the superior mesentric artery) → duodenum to transverse colon
    • hindgut (supplied by the inferior mesentric artery)→ distal transverse colon to rectum
  • GI embryologic timeline
    • week 6
      • midgut herniates through umbilical ring
    • week 10-11
      • rotates 270 degrees counterclockwise around SMA as it returns to the abdominal cavity 
        • abnormal rotation and fixation of the midgut during early fetal life may result in obstruction and volvulus (which may lead to intestinal ischemia) 
Pathology
  • Anterior abdominal wall defects due to failure of
    • rostral fold 
      • sternal defects result 
    • lateral fold 
      • omphalocele 
        • abdominal contents (stomach, liver, intestines, etc.) protrude through umbilical cord and persist outside of the body but covered by peritoneum
        • associated with trisomy 13 and 18
      • gastoschisis 
        • failure of lateral body folds to fuse, resulting in extrusion of intestines through umbilical ring but not covered by peritoneum
    • caudal fold 
      • bladder extrophy is the protrusion of the anterior bladder through the lower abdominal wall
  • Duodenal atresia
    • due to failure to recanalize lumen of intestines 
    • associated with trisomy 21
    • "double bubble" sign
    • NOTE: atresia is occlusion of the lumen of the intestines and stenosis is narrowing of the lumen
  • Jejunal, ileal, and colonic atresia
    • due to vascular accident ("apple peel/corkscrew" atresia 
    • segment of bowel wrapped around a remnant of mesentary
  • Congenital pyloric stenosis  
    • hypertrophy of muscalaris externa causing the pylorus lumen to narrow 
      • palpable "olive" mass in epigastric region
      • food obstructs in pyloric region
      • nonbilious and projectile vomiting at about 2 weeks of age
    • treatment: surgery
    • incidence: 1/600; mainly first born males
  • Pancreas divisum- failed fusion of the ventral and dorsal pancreatic buds

 

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Questions (7)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
Calculator

(M1.EB.26) A 2-week-old boy has developed bilious vomiting. He was born via cesarean section at term. On physical exam, his pulse is 140, blood pressure is 80/50 mmHg, and respirations are 40/min. His abdomen appears distended and appears diffusely tender to palpation. Abdominal imaging is obtained (Figures A). Which of the following describes the mechanism that caused this child's disorder? Review Topic

QID: 101048
FIGURES:
1

Ischemia-reperfusion injury in premature neonate

11%

(1/9)

2

Telescoping segment of bowel

11%

(1/9)

3

Abnormal rotation of the midgut

56%

(5/9)

4

Hypertrophy of the pylorus

11%

(1/9)

5

Partial absence of ganglion cells in large intestine

11%

(1/9)

M1

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PREFERRED RESPONSE 3
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(M1.EB.4707) A 1-month-old boy is brought to the emergency department by his parents for recent episodes of non-bilious projectile vomiting and refusal to eat. The boy had no problem with passing meconium or eating at birth; he only started having these episodes at 3 weeks old. Further history reveals that the patient is a first born male and that the boy’s mother was treated with erythromycin for an infection late in the third trimester. Physical exam reveals a palpable mass in the epigastrum. Which of the following mechanisms is likely responsible for this patient’s disorder? Review Topic

QID: 108429
1

Defect of lumen recanalization

12%

(25/211)

2

Hypertrophy of smooth muscle

64%

(135/211)

3

Intestinal vascular accident

3%

(6/211)

4

Neural crest cell migration failure

10%

(22/211)

5

Pancreatic fusion abnormality

8%

(17/211)

M1

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PREFERRED RESPONSE 2

(M1.EB.17) A 1-week-old male is brought by his mother to their pediatrician's office with complaints of a 3 day history of feeding intolerance and frequent bilious vomiting. An upper GI contrast radiograph is obtained (Figure A) and shows obstruction of the 3rd part of the duodenum with displacement of the duodenojejunal junction to the right of midline. Which of the following mechanisms is responsible for this infant's condition? Review Topic

QID: 101911
FIGURES:
1

Failure to recanalize the lumen of the duodenum

27%

(3/11)

2

Hypertrophy of the muscularis externa at the pylorus

27%

(3/11)

3

Failed fusion of lateral body folds

0%

(0/11)

4

Intestinal malrotation

27%

(3/11)

5

Failed fusion of the dorsal and ventral pancreatic buds

9%

(1/11)

M1

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PREFERRED RESPONSE 4
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