耳鼻咽喉科展望
Online ISSN : 1883-6429
Print ISSN : 0386-9687
ISSN-L : 0386-9687
ヒト胎児中耳腔の発生について
妊娠16週より妊娠36週の観察標本より
清水 佐和道
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ジャーナル フリー

1987 年 30 巻 2 号 p. 155-192

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The present study was carried out using sequential frontal and sagital sections of temporal bones from 100 sides of human fetuses between 16 th and 36 th week of pregnancy.
From the findings obtained, it was indicated that the process of genesis for the portion from the middle tympanic cavity to the antrum is different from that for the mastoid cells.
In the growth of the portion from the middle tympanum to the antrum, which consists of a single sinus, a process different from that for the mastoid cells with complicated morphological characteristics is involoved. Namely, in the portion to the antrum the organ development as a cavity progress with fetal mesenchyma contained before entering of the epithelium from the auditory tube, and this process is characterized with enlargement of the cavity chiefly by absorption of existing bone rather than by active bone metabolism and bone formation.
Moreover, as the genesis of middle ear in humans, the morphological formation of the otic capsule is completed until the middle phase of pregnancy.
As the morphology of the middle ear cavity near it, there are mesotympanum, epitympanum and antrum.
The growth process for the portion from the mesotympanum to the antrum is greatly affected by the morphology of the area around the oticcapsule which is situated whithin it. In the formation of the portion from the tympanum to the antrum, passive formation of pneumatic space in the predetermined portion through absorption of bone of the otic capsule and its surroundings is involoved.
This is less affected by acquited changes even at the later stage of fetal development as compared to the mastoid cells with immatured growth.
The genesis of the mastoid cells is considered to be determined by the following three elements.:
1) outward glowth of the temporal bone it self, 2) expansion of the existing pneumatic space due to bone metabolism within the temporal cells, and 3) the resulting advance of the epithelium into the pneumatic space associated with it. Formation of the cells progresses through the harmonous combination of each of these elements. When this harmony is broken, inhibition of the pneumatization occurs.
Namely, the formation of the mastoid cells is characterized by the growth pattern dependent on active and rapid bone metabolism, in which each of these factors are involved. However, the above described three factors do not always show the essential harmonious growth. It appears that inhibition of the mastoid cells occurs when this harmony is broken. As an example, we observed in an experiment in pigs performed at our labonatory that inflammatory changes of the respiratory epithelium gave influences on subepithelial bone metabolism to inhibit growth and cause depressed pneumatization.

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