24 hr

[24-HR CHICK] STRUCTURE -

DESCRIPTION

Peripheral region

margin of growth

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zone junction

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germ wall

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Area opaca vasculosa

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Area opaca vitellina

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FATE

WHOLE MOUNT Area Opaca of the chick blastodisc surrounding the area pellucida & in direct contact with the yolk 3 ZONES: Peripheral zone cells have proliferated over the yolk without becoming adherent to it Intermediate region cells cut free from the yolk and are added to the area pellucida Inner zone Cells originated from the zone junction, thus containg yolk granules 2 REGIONS:

Inner region of the area opaca Thickenings of the splanchnic mesoderm form blood sinus Outer region of the ares opaca Lacks any blood islands or blood vessels AREA PELLUCIDA Central region of the blastodisc where primitive streak forms Lies directly over the subgerminal cavity epiblast – outer layer → ectoderm & mesoderm will differentiate - hypoblast – inner layer -

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Primitive streak Primitive groove Primitive ridges Primitive pit Hensen’s node Syn: primitive knot

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Proamnion

Neural folds Neural groove Head fold Notochord Foregut

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longitudinal cleft formed on surface of amniote blastodiscby a convergence of cell gastrulation starts as epiblast ells central furrow of the thickening margins of the primitive streak flanking the primitive groove on either side an indented region of the blastoderm at the anterior end of primitive streak thickened area at the anterior end of the primitive steak cells invaginate to form notochord homologous to dorsal lip of blastopore ( amphibian) anterior to the developing avian embryo surrounding the heart contains only endoderm & ectoderm margins of neural plate that are about to fuse at the mid-dorsal region of the developing embryo a median longitudinal groove formed by rolling up of the neural plate folded region of the blastoderm dark crescentic line: marks the boundary of the head longitudinal band of cells from the caudal region of neural folds to hensen’s node between foregut and neural plate 1st part of the digestive tract with definitive floor endodermal cells, dome-shaped structure inside the head

Invaded with mesoderm Incorporated with amnion

[24-HR CHICK] Anterior intestinal portal Mesenchyme of the head

mesoderm

Somite Unsegmented mesoderm

Head ectoderm Anterior neuropore Prechordal plate Oral plate Syn: oropharyngeal membrane Subcephalic pocket Somatopleure

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beneath the neural plate opening of the foregut continues with the lateral walls of the foregut

Loose network of cells Occupies space between ectoderm of the head and foregut Anterior border of mesoderm - faintline extending across the area pellucida - level of anterior end of notochord Thickened splanchnic mesoderm formed by delamination of lateral plate mesoderm - three or four pairs of somite lying immediately to the neural folds - Undivided region of the mesoderm - posterior to the somites Transverse section Sec. thru the pharyngeal membrane - layer of cuboidal cells enclosing the head - temporary external opening of the neurocoel

Becomes part of the yolk stalk

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mass of choramesoderm cells located anterior to the notochord will form head mesenchyme Where the floor of the foregut is in contact with neural ectoderm

Cavity formed beneath the embryonic head as the head develops Membrane composed of ectoderm and somatic mesoderm

Splanchnopleu re

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Consists of splanchnic mesoderm and endoderm

Coelom

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Subgerminal cavity

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Body cavity formed when somatic mesoderm and mesoderm separates Space beneath hypoblast

Neural tube

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Neural crest

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Amnio-cardiac vesicle

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Heart, part of circulatory system

Break open to form mouth

Forms part of body wall Chorion and amnion Forms part of body wall Allantois and yolk sac

midgut

Sec thru anterior intestinal portal

Midgut

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Tube of tissue formed by thickening and rolling up at neural plate during embryonic neurulation Group of cells found t the edges of neural plate Above the neural tube after its formation Proximal wall of the semi-cardiac vesicle by thickened splanchnic mesoderm Dorsal wall composed of somatopleure Sec thru midgut Floorless region of the gut Posterior to anterior intestinal portal Sec thru somite

Brain and spinal cord Ganglia, pigment cells, part of gill arches Heart amnion

[24-HR CHICK] somites Intermediate mesoderm Lateral plate mesoderm Syn: hypomere Nephrotome

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Arise from dorsal mesoderm Adjacent to somite

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Lateral to intermediate mesoderm Distal to nephrotome

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Stalk-like connection between somites and lateral plate mesoderm Forms the pronephros and mesenchyme

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kidney Delaminate to form splanchnic and somatic pronephros mesonephros metanephros