Skin, embryonic

In laboratory tests, appHcation of DMAC to the skin of pregnant rats has caused fetal deaths when the dosages were close to the lethal dose level for the mother. Embryonal malformations have been observed at dose levels 20% of the lethal dose and higher. However, when male and female rats were exposed to mean DMAC concentrations of 31,101, and 291 ppm for 6 h per day over several weeks, no reproductive effects were observed (6). 

The central cleavage of P-carotene 1 is most likely the major pathway by which mammals produce the required retinoids il), in particular, retinal 2, which is essential for vision and is subsequently oxidized to retinoic acid 3 and reduced to retinol 4. An alternative excentric cleavage of 1 has been reported involving scission of the double bond at C7-C8 producing P-8 -apocarotenal 5 (2a,2b) which is subsequently oxidized to 2 (Fig. 1) (2c). The significance of carotene metabolites such as 2, 3 and 4 to embryonic development and other vital processes such as skin and membrane protection is a major concern of medicinal chemistry. 

Most cancers in humans can be divided into three groups according to age (i) embryonic tumours (neuroblastoma, Wilms tumour) (ii) tumours found mainly in the young (leukaemias, bone, testis) and (iii) tumours that appear frequently in middle and old age (prostate, colon, skin, bladder and breast). 

The growth of tissue (or, more precisely, the number of cells) is actually regulated by apoptosis. In addition, apoptosis allows the elimination of unwanted or superfluous cells—e.g., during embryonic development or in the immune system. The contraction of the uterus after birth is also based on apoptosis. Diseased cells are also eliminated by apoptosis—e.g., tumor cells, virus-infected cells, and cells with irreparably damaged DNA. An everyday example of this is the peeling of the skin after sunburn. 

The principal pigment of human skin, hair, and eyes is melanin, which is synthesized in specialized cells, the melanocytes. They lie between the epidermis (outer layer) and the dermis (inner layer) as shown in Box 8-F. Melanocytes originate from embryonic nervous tissue and migrate into the skin by the third month of fetal life. They retain the highly branched morphology of neurons. Persons of different races all have the same numbers of melanocytes but the numbers and sizes of the pigmented melanosomes (Box 8-F) vary as does the content and chemical composition of the melanin.a d Melanosomes not only are found in the dendrites of the melanocytes but are transferred from them into adjacent epithelial cells.6 1... 

Glycosaminoglycan synthesis, in culture, using fibroblasts from human skin,97,98 human normal and hypertrophic scar,99 and embryonic chick... 

Perlish, and J. D. Termine, Decorin interacts with fibrillar collagen of embryonic and adult human skin. /. Struct. Biol., 106(1991)82-90. 

Gallicano, G. I., Bauer, C., and Fuchs, E. (2001). Rescuing desmoplakin function in extra-embryonic ectoderm reveals the importance of this protein in embryonic heart, neuroepithelium, skin and vasculature. Development 128, 929-941. 

The ECM that surrounds cells also contains variable levels of HA. It is composed predominantly of structural proteins such as collagen and elastin, as well as proteoglycans, and a number of glycoproteins. The HA content is greatest in embryonic ECM, and in tissues undergoing rapid turnover and repair. The basal lamina or basement membrane that separates dermis and epidermis is also considered an ECM structure. The basal lamina contains HA, though the precise structural position is not known. Loss of basement membrane HA in the skin of diabetic patients correlates with skin stiffness.50... 

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