These studies were undertaken to evaluate the morphological development of the epidermis, hair, sebaceous gland, eccrine sweat gland and basement membrane in the´ skin of the Korean fetuses.
Nineteen fetuses, 4 to 28 weeks of age, ranging in size from 4 to 230mm crown-rump length, obtained from healthy Korean mothers, were used in these studies and histological observation was done in the different fetal weeks and in tl.a various parts of the body such as face, perioral, scalp, axilla, abdomen, palm and sole.
The results are as follows:
1) At 4-5 weeks of fetal age, the epidermis consists of a single layer of undifferentiated cells and by the 6th week it becomes two-layered; the periderm and the stratum germinativum.
At 12-13 weeks, the germinative layer proliferates in a centrifugal direction to form a stratum intermedium and also proliferates in a centripetal direction, giving rise to clusters of cells that grow into the subjacent dermis, to form pre-hair germs and eccrine sweat gland germs.
Keratohyaline granules first make an appearance at 20th week and the stratum granulosum appears at 28 weeks of fetal life.
From 20th week onward the periderm gradually disappears and is replaced by a stratum corneum at 28 weeks.
These morphological development are dyschronous in the different parts of the: body; the epidermis of the scalp and face is relatively more differentiated than that of the axilla and abdomen in´ the same fetal wed
2) The first pre-hair germs make an appearance at 1213 weeks in the perioralregion. From the 14th week, the developing hair germs are observed in the scalp, per ioral, axilla and abdomen.
At 22~23 weeks, well formed hairs appear in the scalp, axilla, and abdomen. The developmental process of hair is more rapid in the scalp and face than that_ in the axilla and abdomen.
3) The anlagen of sebaceous glands appear at the 16th week, and they are differentiated partially into sebaceous gland cells.
So the first anlagen of sebaceous glands may be supposed to appear at about 15 weeks because no anlagen of glands are observed at 14 weeks.
By the 20th week, most cells in the center part of sebaceous gland anlagen are-nearly all differentiated into sebaceous gland cells.
4) The first anlagen of eccrine sweat glands appear at 12~13 weeks in the palm and sole.
At 20 weeks, coiled portion of eccrine glands are observed, and intraepidermal duct makes an appearance at 22~23 weeks.
At 28 weeks, secretory cells appear and intraepidermal duct and lumen of glands. are more clearly observed than those in the previous fetal life.
5) Well defined basement membrane at the dermo-epidermal junction begins to appear as a continuous, homogenous PAS positive band from 16th week, and thereafter no significant changes are observed.
|