BASIC EMBRYONIC BODY PLAN

I. Ectoderm

60- hourchick

embryo15x

60 X

Neural crest development

Neural crest again

Mesoderm

1. Neural tube 3. somite 5. yolk sac 7. aorta2. Amniotic cavity 4. nephrogenic cord 6. notochord 8.

embryonic coelom

Development of the Heart Splanchnic mesoderm : an area of the

endoderm induces development of the cardiogenic mesoderm ; BMP, FGF

Heart and great vessels form from bilaterally paired tubes that fuse in the midline beneath the foregut to produce a single tube

See p. 118, Figure 6-15 Layers of the single tube:

endocardial lining “cardiac jelly” Myocardium Epicardium

The straight tubular heart Endocardial tubes fuse one tube

Common cardinal veins flow into R and L sinus venosus

Sinus venosus leads to atrium Atrium leads to ventricle Outflow tract = truncus arteriosus

D-loop-- S-shape

See p. 117, Figure 6-14.

Blood and Blood Vessels Blood islands form in mesodermal wall of

yolk sac ( note: extraembryonic ) Blood islands contain hemangioblasts Inducer may be signaling molecule Indian

hedgehog Central part of blood islands

hemocytoblasts Peripheral cells endothelial cells lining the

vessels.

Development of the Endoderm See Figure 6-20, p. 122 Three divisions: Foregut, Midgut, Hindgut FGF-4 influences devel. of the hindgut Hox genes + retinoic acid regulates

regional development along the digestive tract

1) Flat intraembryonic sheet of endoderm 2) Lateral body folds form that sheet into

a tubular structure 3) Head and Tail folds form foregut,

hindgut

Hox genes determine the form, number, and evolution of repeating parts, such as the number and type of vertebrae in animals with

backbones. In the developing chick (left), the Hoxc-6 gene controls the pattern of the seven thoracic vertebrae (highlighted in purple),

all of which develop ribs. In the garter snake (right), the region controlled by the Hoxc-6 gene (purple) is expanded dramatically

forward to the head and rearward to the cloaca.