Pediatric Surgery: Anatomy & Physiology

Anatomy

Fetal Circulation

  • Ductus Arteriosus
    • Left Pulmonary Artery to Descending Aorta
    • Bypass Lungs
    • Prostaglandin E1 Keeps Open
  • Ductus Venosum
    • Portal Vein to IVC
    • Bypass Liver
  • Umbilical Arteries (x2)
    • From Internal Iliac Artery
    • To Placenta
  • Umbilical Vein (x1)
    • From Placenta
    • To Portal Vein/IVC

Fetal Circulation 1

Anatomic Remnants

  • Vitelline (Omphalomesenteric) Duct – Fully Obliterates
    • Yolk Sac to Midgut
  • Allantois/Urachus – Median Umbilical Fold
    • Bladder to Umbilical Cord
    • Urachus is the Fibrous Remnant
  • Umbilical Arteries – Medial Umbilical Folds
  • Umbilical Veins – Falciform Ligament
  • Lateral Umbilical Folds Contain Epigastric Vessels (Remain Patent)

Umbilical Ligaments 2

Gut Embryology

  • Foregut
    • GI Tract: Esophagus to Proximal Duodenum (To Ampulla of Vater)
    • Organs: Liver, Gallbladder, Bile Ducts, Pancreas & Lungs
    • Arterial Supply: Celiac Artery
    • Hepatic Portal Drainage: Splenic Vein
  • Midgut
    • GI Tract: Distal Duodenum to Distal 1/3 Transverse Colon
    • Arterial Supply: Superior Mesenteric Artery
    • Hepatic Portal Drainage: Superior Mesenteric Vein
    • Rotates 270 Degrees Counterclockwise
  • Hindgut
    • GI Tract: Distal 1/3 Transverse Colon to Anal Canal
    • Arterial Supply: Inferior Mesenteric Artery
    • Hepatic Portal Drainage: Inferior Mesenteric Vein

Classic “En-Bloc Rotation” Model of Gut Morphogenesis: Midgut Herniates and Rotates 90-Degrees (B1), Forms Loops (B2), & Slides Back into the Abdomen (B3). The Midgut Then Rotates an Additional 180-Degrees to its Final Position (C). 3

Branchial Apparatus Embryologic Derivatives

  • Pharyngeal Clefts:
    • First: External Acoustic Meatus
    • Second-Third-Fourth: Cervical Sinus
  • Pharyngeal Pouches:
    • First: Middle Ear & Eustachian Tube
    • Second: Palatine Tonsil
    • Third: Thymus & Inferior Parathyroid
    • Fourth: Superior Parathyroid & C Cells of Thyroid
  • Pharyngeal Arches:
    • Form Bones, Muscles, Arteries & Multiple Cranial Nerves

Branchial Apparatus 4

Physiologic Differences

Pediatric Vital Signs

Age HR Systolic BP RR
Newborn 120-160 50-70 30-50
1-12 Months (Infant) 80-140 70-100 20-30
1-3 Years (Toddler) 80-130 80-110 20-30
3-5 Years 80-120 80-110 20-30
6-13 Years 70-110 80-120 20-30
≥ 14 Years 55-90 90-120 12-20

Respiratory Physiologic Differences

  • Higher Respiratory Rate
  • Obligate Nose Breathers (Cannot Breathe Through Mouth)

Cardiovascular Physiologic Differences

  • Higher Heart Rate
  • Lower Blood Pressure
    • Hypotension Definition: < 70 mmHg + (2 x Age in Years)
  • Compensation:
    • Better Early Compensation
    • Rapidly Decompensate
    • Cardiac Output Compensation is Maintained by Increased Heart Rate (Stroke Volume Minimally Changed)

Renal Physiologic Differences

  • Impaired Renal Function (GFR < Half of Adults)
  • Obligatory Diuresis & Salt Excretion
  • Impaired Hormone Sensitivity

Gastrointestinal Physiologic Differences

  • Decreased Capacity to Conjugate Bilirubin

General Physiologic Differences

  • Larger Surface Area:Mass Ratio (Up to 3x) – High Risk for Hypothermia

General Considerations

Pediatric Immunity

  • IgG: Crosses Placenta
  • IgA: Secreted in Breast Milk

Most Common Pediatric Malignancies

  • Peds Malignancy: Leukemia (ALL)
  • Solid Tumor: CNS Tumors
  • Abdominal Tumor < 2 Yr & Overall: Neuroblastoma
  • Abdominal Tumor > 2 Yr: Nephroblastoma (Wilms)
  • Lung Tumor: Carcinoid
  • Larynx Tumor: Laryngeal Papillomatosis

References

  1. Gray H. Anatomy of the Human Body (1918). Public Domain.
  2. Dmcmdissa. Wikimedia Commons. (License: CC BY-SA-4.0)
  3. Soffers JH, Hikspoors JP, Mekonen HK, Koehler SE, Lamers WH. The growth pattern of the human intestine and its mesentery. BMC Dev Biol. 2015 Aug 22;15:31. (License: CC BY-4.0)
  4. Austanfell L. Wikimedia Commons. (License: CC BY-SA-3.0)