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When fetal kidneys begin to function around week 16, fetal urine also contributes to the fluid. [1] In earlier times, it was believed that the amniotic fluid was composed entirely of excreted fetal urine. The fluid is absorbed through the fetal tissue and skin. [2] After 22 to 25 week of pregnancy, keratinization of an embryo's
Keratinization begins in the stratum spinosum, [5] although the actual keratinocytes begin in the stratum basale. [4] They have large pale-staining nuclei as they are active in synthesizing fibrillar proteins, known as cytokeratin, which build up within the cells aggregating together forming tonofibrils. The tonofibrils go on to form the ...
Keratinization is part of the physical barrier formation (cornification), in which the keratinocytes produce more and more keratin and undergo terminal differentiation. The fully cornified keratinocytes that form the outermost layer are constantly shed off and replaced by new cells.
Microscopy of keratin filaments inside cells. Keratin (/ ˈ k ɛr ə t ɪ n / [1] [2]) is one of a family of structural fibrous proteins also known as scleroproteins.It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, and the outer layer of skin in vertebrates.
The embryonic disc begins flat and round, but eventually elongates to have a wider cephalic part and narrow-shaped caudal end. [10] At the beginning, the primitive line extends in cephalic direction and 18 days after fertilization returns caudally until it disappears.
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In human pregnancy, prenatal development is also called antenatal development. The development of the human embryo follows fertilization, and continues as fetal development. By the end of the tenth week of gestational age, the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where ...
The vagina itself does not contain mucous glands. [ 29 ] [ 30 ] Though mucus is not produced by the vaginal epithelium, mucus originates from the cervix. [ 8 ] The cervical mucus that is located inside the vagina can be used to assess fertility in ovulating women. [ 29 ]