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The face and neck development of the human embryo refers to the development of the structures from the third to eighth week that give rise to the future head and neck.They consist of three layers, the ectoderm, mesoderm and endoderm, which form the mesenchyme (derived form the lateral plate mesoderm and paraxial mesoderm), neural crest and neural placodes (from the ectoderm). [1]
At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. Human embryology is the study of this development during the first eight weeks after fertilization.
The third pouch possesses dorsal and ventral wings. Derivatives of the dorsal wings include the inferior parathyroid glands, while the ventral wings fuse to form the cytoreticular cells of the thymus.
Only a comparatively small part of the head at term is represented by the face. The rest of the head is composed of the firm skull, which is made up of two frontal, two parietal, and two temporal bones, along with the upper portion of the occipital bone and the wings of the sphenoid. These bones are separated by membranous spaces, or sutures.
The embryo becomes embedded in the endometrium in a process called implantation. In most successful pregnancies, the embryo implants 8 to 10 days after ovulation. [7] The embryo, the extra-embryonic membranes, and the placenta are collectively referred to as a conceptus, or the "products of conception".
The embryo measures 4 mm (1 ⁄ 8 in) in length and begins to curve into a C shape. The heart bulges, further develops, and begins to beat in a regular rhythm. Septum primum appears. [1] Pharyngeal arches, grooves which will form structures of the face and neck, form. The neural tube closes. The ears begin to form as otic pits. Arm buds and a ...
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