Organogenesis of chick

• Area Opaca


  Peripheral region of chick blastodisc surrounding Area Pellucida and direct contact with the yolk
• Area Opaca


  • 3 zones: 1. peripheral zone, margin of growth, where the cells prolifereataed over the yolk without being adherent to it, 2. zone junction, intermediate region where cells separate from the yolk and belonging to A.P., 3. inner zone, the germ wall, from the zone junction that is why there is the presence of yolk granules
• Area Opaca Vasculosa


  Inner region of Area Opaca, thickenings of the splanchnic mesoderm forming blood islands
• Area Opaca Vitellina


  Outer region of Area Opaca, no blood islands/vessels
• Area Pellucida


  Central region of blastodisc where primitive streak forms. Lies directly over the subgerminal cavity. Outer Layer: Epiblast (later differentiates into the ectoderm and mesoderm) and Inner Layer: Hypoblast
• Primitive Streak


  Longitudinal cleft formed by the convergence of cells. Gastrulation begins as the epiblast cells migrates towards and into the streak
• Primitive Groove


  Central furrow
• Primitive Ridges


  Margins on both sides of the streak
• Primitive Pit


  Indented region of the blastoderm at the anterior end of the Primitive Streak
• Hensen's Node/Primitive Knot


  Thickened area at the anterior end of the Primitive Streak, where the cells form the notochord
• Proamnion


  • Region anterior of embryo, contains only endoderm and ectoderm, later invaded with mesoderm and incorporated into the amnion
• Neural Folds


  • Margins of the Neural Plate that are about to fuse at the mid dorsal region of the embryo
• Neural Groove


  • Median longitudinal groove which is formed by the rolling up of the neural plate
• Head Fold


  • Folded region of the blastoderm, dark crescentic line and boundary of the head of the embryo
• Notochord


  • Longitudinal band of cells extending caudal from the region of the neural folds to the primitive knot
• Foregut


  • First part of the digestive tract, dome shaped, and with a flooring composed of endodermal cells
• Anterior Intestinal Portal


  • Opening of the foregut, appears like a prominent arched line beneath the neural folds, moves posteriorly as gut elongates and becomes part of the yolk stalk
• Mesenchyme of the Head


  • Loose network of cells that occupies beneath the foregut and ectoderm of the head
• Anterior Border of the Mesoderm


  • Faint line extending across the area pellucida at the level of the anterior end of the notochord
• Thickened Splanchnic Mesoderm


  • Darker line of each the lateral border of the ALP, formed by the delamination of the lateral plate mesoderm, later forms the heart, part of the circulatory systems, and many other structures
• Somites


  • Apparent division of the dorsal mesoderm into 3-4 pairs of somites lying immediately lateral to the neural folds
• Unsegmented Mesoderm


  • Undivided region of the mesoderm posterior to the somites
• Head Ectoderm


  • Layer of cuboidal cells enclosing the head
• Anterior Neuropore


  • Temporary external opening of the neurocoel
• Prechordal Plate


  • Mass of chordamesodermal cells anterior the notochord and forms the head mesenchyme
• Oral Plate/Oropharyngeal Membrane


  • Region where the floor of the foregut is in contact with the neural ectoderm of the head, will later break open and forms the mouth
• Subcephalic Pocket


  • Cavity formed beneath the embryonic head as head fold develops
• Somatopleure


  • Membrane composed of ectoderm and somatic mesoderm, will form part of the body wall as well as the chorion and amnion
• Splanchnopleure


  • Cellular layer consisting of the splanchnic mesoderm and endoderm, will later form part of the body wall, yolk sac, and allantois
• Coelom


  • Body cavity formed when the somatic mesoderm and the mesoderm separates from one another
• Subgerminal Cavity


  • Space beneath the hypoblast within the A.P. and will give rise to the midgut
• Neural Tube


  • Tube of tissue formed by the thickening and rolling up of the N.P. during neurulation and will later form the brain and spinal cord
• Neural Crest


  • Group of the cells at the edges of the neural plate and lying above the N.T., will later migrate throughout the embryo forming the ganglia, pigment cells, parts of the gill arches, and etc.
• Amnio-Cardiac Vesicle


  • Region of coelom that gives rise to the amnion and heart, thickened splanchnic mesoderm making up the proximal wall is the forerunner of the heart, dorsal wall composed of somatopleure forms the amnion
• Midgut


  • Floorless region of the gut posterior to the AIP
• Nephrotome/Intermediate Mesoderm/Mesomere/Nephromere


  • Stalk-like connection between the somites and lateral plate mesoderm which anteriorly forms the pronephros and posteriorly forms mesenchyme and later develops into the mesonephros and metanephros
• Hypomere


  • Region of the mesoderm distal to he nephrotome, subdivided into two layers, somatic and the splanchnic mesoderm
• Hensen's Node/Primitive Streak


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• Primitive Pit


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• Primitive Groove


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