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Genetics of Endocrine Disorders and Diabetes Mellitus
Published in George H. Gass, Harold M. Kaplan, Handbook of Endocrinology, 2020
Bess Adkins Marshall, Abby Solomon Hollander
Kallmann syndrome is characterized by anosmia and hypogonadotropic hypogonadism. Familial Kallmann syndrome can be transmitted in an X-linked, autosomal recessive, or autosomal dominant fashion.1–6 The X-linked form of the syndrome is the most common, and the gene responsible for this form of the syndrome has been identified. The gene appears to be necessary for proper migration of the cells of the olfactory placode.
Prenatal Development of the Facial Skeleton
Published in D. Dixon Andrew, A.N. Hoyte David, Ronning Olli, Fundamentals of Craniofacial Growth, 2017
At about 5 weeks, the future nasal region is marked by two thickenings of the ectoderm, one on each side, at the inferolateral part of the frontnasal prominence. These are the nasal or olfactory placodes. Each placode becomes bordered by enlarging lateral and medial nasal elevations that are continuous above the placode but separated below by the nasal groove (Figure 4.1). With continued proliferation of mesenchyme around each nasal groove, the placodes “sink in” to form the nasal pits, the precursors of the anterior nasal apertures or nares (Waterman and Meller, 1973). Differential growth of surrounding mesenchyme converts each pit into a deeper nasal sac that is separated from the stomatodeum only by a thin floor, the oronasal membrane, which is composed of two layers derived from the surface ectoderm. The oronasal membrane becomes further attenuated and soon ruptures, so that the primitive nasal and mouth cavities become continuous by the beginning of the 7th week (20 mm CRL), cutting off a median segment of the frontonasal swelling that lies between the two primitive nares. This small wedge of ectodermal-covered mesenchyme extends backwards as the primary palate from the deep aspect of the formative upper lip.
Oral cavity
Published in Paul Ong, Rachel Skittrall, Gastrointestinal Nursing, 2017
By the end of the fourth week of gestation the frontonasal prominence forms thickenings of ectodermal tissue or nasal placodes on each side of the developing face. Each nasal placode is divided into the larger medial and smaller lateral nasal processes. The nasal processes surround a small opening called a nasal pit (Figure 2.3b). The nasal pit gradually enlarges into a nasal sac, lined with a thick epithelium of olfactory tissue into which sensory nerves develop to allow the sensation of smell. The sac is separated from the oral cavity by an oral nasal membrane.
The Development, Growth, and Regeneration of the Crystalline Lens: A Review
Published in Current Eye Research, 2020
The embryological development of the eye in mammals begins with the formation of the optic pit as a result of the evagination of the ventral forebrain/prechordal mesenchyme (Figure 1).5 The optic pits enlarge to form the optic vesicles and in parallel the overlying surface ectoderm thickens to form the lens placode.58 The lens placode thickens towards the presumptive neural retina of the optic vesicle and both primordial tissues invaginate such that the presumptive neural retina and retinal pigmented epithelium form the optic cup and the folded surface ectoderm forms the lens pit. The lens vesicle forms from the closing of the lens pit and detachment from the surface ectoderm, the lens vesicle matures into the lens and the now closed surface ectoderm differentiates into the cornea.58
Congenital Spinal Lipomatous Malformations. Part 1. Spinal Lipomas, Lipomyeloceles, and Lipomyelomeningoceles
Published in Fetal and Pediatric Pathology, 2020
When spinal cord attachment occurs with a congenital spinal lipomatous malformation, the involved cord in these closed dysraphic lesions has been termed the neural placode. This operational definition is meant to distinguish damaged cord in congenital spinal lipomatous malformation cases from the myelomeningocele placode, which is a term used in open spinal dysraphism, as described above, to denote the principal feature of a myelomeningocele [19]. For spinal lipomas, although spinal cord attachment is a notable feature when it occurs, the presence of this neural placode is not the major feature of these malformations. The fibrolipomatous tissue rather than any spinal cord association is the diagnostic finding of congenital spinal lipomatous malformations.
Lack of FOXE3 coding mutation in a case of congenital aphakia
Published in Ophthalmic Genetics, 2018
Yusuke Sano, Yusuke Matsukane, Akihisa Watanabe, Ko-hei Sonoda, Hiroyuki Kondo
The cells of the crystalline lens originate from the surface ectoderm (4,7). The area of the surface ectoderm designated as the lens placode invaginates toward the optic vesicle, so that it becomes the lens pit (4,7). The lens pit separates from the surface ectoderm then close to form the lens vesicle, the primitive crystalline lens (4,7). Congenital primary aphakia is due to the failure in forming the lens placode that can also lead to various other ocular defects including microphthalmia, sclerocornea, absence of iris or ciliary body, dysgenesis of trabecular meshwork, cataracts, Peters’ anomaly, iris coloboma, and optic disc coloboma (1,2).