Updated: 5/1/2020

Germ Layer Derivatives

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 germ layers 
 
Ectoderm
  • Surface ectoderm
    • adenohypophysis 
    • lens of the eye
    • sensory organs 
      • ear
      • olfactory epithelium
    • epithelial linings
      • oral cavity
      • lower anal canal
      • external auditory meatus
    • epidermis, hair, and nails
    • mammary, sweat, and salivary glands
  •  Neuroectoderm - CNS and brain 
    • brain - all neurons within brain and spinal cord/CNS
      • neurohypophysis
      • oligodendrocytes
      • astrocytes
      • ependymal cells
      • pineal gland
    • retina
  • Neural Crest - PNS and nearby non-neural structures
    • ANS
    • enteric nervous system 
    • ganglia (dorsal root, cranial, and autonomic)
    • cranial nerves
    • celiac ganglion
    • melanocytes  
    • chromaffin cells of adrenal medulla
    • enterochromaffin cells
    • Schwann cells
    • pia and arachnoid
    • bones of the skull
    • odontoblasts
    • aorticopulmonary septum
Endoderm
  • Epithelium lining of 
    • respiratory: trachea, bronchi, and lungs
    • urinary: urinary bladder, female urethra, and majority of male urethra
    • GI tract
    • biliary system
    • lower 2/3 of vagina
    • middle ear cavity and auditory tube
  • Liver
  • Parathyroid
  • Thyroid follicular cells
  • Thymus 
  • Pancreas
  • Parafollicular (C) cells of thyroid
Mesoderm
  • Muscle (smooth, cardiac, and skeletal)
  • Dermis and subcutaneous layers of skin
  • Bone, cartilage, and connective tissue
  • Dura mater
  • Serous linings of body cavities
    • peritoneum
  • Spleen
  • Cardiovascular structures
  • Lymphatics
  • Laryngeal cartilage
  • Blood: RBCs, WBCs, Kupffer cells, and microglia
  • Urogenital structures
    • male: testes, epididymis, ductus deferens, seminal vesicle, and ejaculatory duct
    • female: ovaries, uterus, uterine tubes, and upper 1/3 of vagina
  • Kidneys
  • Adrenal cortex
Defects
  • Types of errors
    • malformation vs. deformation 
      • malformation is intrinsic embryological disruption during the embryonic period
      • deformation is extrinsic disruption, occurs after embryonic period
    • agenesis vs. hypoplasia vs. aplasia
      • agenesis = organ is absent because of absent primordial tissue
        • e.g., renal agenesis - failure of one or both kidneys to develop
      • hypoplasia = organ develops incompletely with remnant primordial tissue
        • e.g., microorchidism in Klinefelter syndrome
      • aplasia = organ absent but primordial tissue present
        • e.g., thymic aplasia in DiGeorge syndrome
  • Craniopharyngioma
    • benign Rathke's pouch tumor containing cholesterol crystals and calcifications, tends to compress the optic chiasm 
  • Mesodermal defects VACTERL 
    • Vertebral defects: usually small hypoplastic vertebrae or hemivertebrae, only half of the bone is formed
    • Anal atresia/imperforate anus 
    • Cardiac defects: ventricular septal defect, atrial septal defect, and Tetralogy of Fallot
    • Tracheo-Esophageal fistula
    • Renal defects: incomplete formation of one or both kidneys
    • Limb defects: absent or displaced thumbs, polydactyly, and syndactyly
 

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(M1.EB.15.28) A 52-year-old woman sees you in her office with a complaint of new-onset headaches over the past few weeks. On exam, you find a 2 x 2 cm dark, irregularly shaped, pigmented lesion on her back. She is concerned because her father recently passed away from skin cancer. What tissue type most directly gives rise to the lesion this patient is experiencing? Tested Concept

QID: 101046
1

Ectoderm

20%

(17/86)

2

Neuroectoderm

13%

(11/86)

3

Mesoderm

1%

(1/86)

4

Neural crest cells

64%

(55/86)

5

Endoderm

0%

(0/86)

M 1 D

Select Answer to see Preferred Response

(M1.EB.15.28) A 75-year-old patient presents to the dermatologist with a 4 cm brown lesion on the right cheek (Figure A). The patient states that the lesion has been there for years but just recently began to change in appearance. She has noticed cracking and oozing from the lesion over the past few months. Which cell line most directly gives rise to the pathologic cell in this patient? Tested Concept

QID: 101922
FIGURES:
1

Notochord

0%

(0/200)

2

Endoderm

0%

(0/200)

3

Neural crest cells

81%

(162/200)

4

Mesoderm

2%

(4/200)

5

Ectoderm

16%

(32/200)

M 1 D

Select Answer to see Preferred Response

(M1.EB.14.63) Twenty-four hours after birth, a male newborn has not passed meconium. The newborn's abdomen is distended and he has had two episodes of bilious vomiting. Based on findings during physical exam of the patient (Figure A), for which other abnormalities should this patient also be evaluated? Tested Concept

QID: 106457
FIGURES:
1

Vision defects

3%

(4/157)

2

Hearing defects

4%

(7/157)

3

Arteriovenous malformation

26%

(41/157)

4

Urogenital tract anomalies

65%

(102/157)

5

Bleeding disorder

1%

(2/157)

M 2 E

Select Answer to see Preferred Response

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Evidence (14)
VIDEOS (2)
Topic COMMENTS (12)
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