Материал: Kaplan USMLE-1 (2013) - Anatomy

Chapter 4 • Embryonic Period (Weeks 3-8)

Table 11-4-1. Germ Layer Derivatives

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Section II • Early Embryology

ChapterSummary

•The critical events ofthe third week are gastrulation and early development ofthe nervous and cardiovascular systems. Gastrulation is the process which establishes 3 primary germ layers that derive from epiblast: ectoderm, mesoderm, and endoderm. Gastrulation begins with the development of the primitive streak and node. The adult derivatives of ectoderm, mesoderm, and endoderm are given in Table 11-4-1.

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VERTEBRAL COLUMN

Embryology

During week 4, sclerotome cells ofthe somites (mesoderm) migrate medially to surround the spinal cord and notochord. After proliferation ofthe caudal portion ofthe sclerotomes, the vertebrae are formed, each consisting ofthe caudal part of one sclerotome and the cephalic part ofthe next.

Vertebrae

The vertebral column is the central component ofthe axial skeleton which func­ tions in muscle attachments, movements, and articulations ofthe head and trunk.

•The vertebrae provide a flexible support system that transfers the weight of the body to the lower limbs and also provides protection for the spinal cord.

•The vertebral column (Figure III- 1-1) is composed of 32-33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, and the fused 5 sacral, and 3-4 coccy­ geal), intervertebral disks, synovial articulations (zygapophyseal joints) and ligaments.

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