京都大学 大学院医学研究科 人間健康科学系専攻 病理学研究室（形態形成医療科学）

比較解剖学的研究で哺乳類の気管支樹の基本モデルとして提案されている左右の気管支の対称性が、ヒトの胎児の気管支樹に当てはまるかどうかを検討しました。 ヒト成人の気管支分岐構造の原型が胎児期に形成され、維持されることを実証しました。 すべての肺葉気管支、B6、B8、B9、および B10 の亜分節気管支の形態および分岐位置は、遺伝的に決定される可能性があります。 一方、B10 の亜分節気管支以降の末梢枝では個々の胚間に共通の構造は見つからず、この領域での枝形成は遺伝的要因よりも環境的要因により影響されることが示唆されました。

Fujii S, Muranaka T, Matsubayashi J, Yamada S, Yoneyama A, Takakuwa T. Bronchial tree of the human embryo: Examination based on a mammalian model. J Anatomy 2023, in press http://doi.org/10.1111/joa.13946 .

The symmetry of right and left bronchi, proposed in a previous comparative anatomical study as the basic model of the mammalian bronchial tree, was examined to determine if it applied to the embryonic human bronchial tree. Imaging data of 41 human embryo specimens at Carnegie stage (CS) 16–23 (equivalent to 6–8 weeks after fertilization) belonging to the Kyoto collection were obtained using phase-contrast X-ray computed tomography. Three-dimensional bronchial trees were then reconstructed from these images. Bronchi branching from both main bronchi were labeled as dorsal, ventral, medial, or lateral systems based on the branching position with numbering starting cranially. The length from the tracheal bifurcation to the branching point of the labeled bronchus was measured, and the right-to-left ratio of the same labeled bronchus in both lungs was calculated. In both lungs, the human embryonic bronchial tree showed symmetry with an alternating pattern of dorsal and lateral systems up to segmental bronchus B9 as the basic shape, with a more peripheral variation. This pattern is similar to that described in adult human lungs. Bronchial length increased with the CS in all labeled bronchi, whereas the right-to-left ratio was constant at approximately 1.0. The data demonstrated that the prototype of the human adult bronchial branching structure is formed and maintained in the embryonic stage. The morphology and branching position of all lobar bronchi and B6, B8, B9, and the subsegmental bronchus of B10 may be genetically determined. On the other hand, no common structures between individual embryos were found in the peripheral branches after the subsegmental bronchus of B10, suggesting that branch formation in this region is influenced more by environmental factors than genetic factors.

福井さんの修士論文がJ Anatomyに受諾されました。ヒト胎児期初期の左房の形成を肺静脈のとりこみと左心耳の形成を中心に解析しました。

Fukui N, Toru KanahashiT, MatsubayashiJ, ImaiH, YoneyamaA, OtaniH, YamadaS, Takakuwa T. Morphogenesis of the pulmonary vein and left atrial appendage in human embryos and early fetuses. J Anatomy 2023, in press, https://doi.org/10.1111/joa.13941

Abstract

The left atrium wall has several origins, including the body, appendage, septum, atrial–ventricular canal, posterior wall, and venous component. Here, we describe the morphogenesis of left atrium based on high-resolution imaging (phase-contrast X-ray computed tomography and magnetic resonance imaging). Twenty-three human embryos and 19 fetuses were selected for this study. Three-dimensional cardiac images were reconstructed, and the pulmonary veins and left atrium, including the left atrial appendage, were evaluated morphologically and quantitatively. The positions of the pericardial reflections were used as landmarks for the border of the pericardial cavity. The common pulmonary vein was observed in three specimens at Carnegie stage 17–18. The pericardium was detected at the four pulmonary veins (left superior, left inferior, right superior, and right inferior pulmonary veins) at one specimen at Carnegie stage 18 and all larger specimens, except the four samples. Our results suggest that the position of the pericardial reflections was determined at two pulmonary veins (right and left pulmonary vein) and four pulmonary veins almost simultaneously when the dorsal mesocardial connection between the embryo and heart regressed. The magnetic resonance images and reconstructed heart cavity images confirmed that the left atrium folds were present at the junction between the body and venous component. Three-dimensional reconstruction showed that the four pulmonary veins entered the dorsal left atrium tangentially from the lateral to the medial direction. More specifically, the right pulmonary veins entered at a greater angle than the left pulmonary veins. The distance between the superior and inferior pulmonary veins was shorter than that between the left and right pulmonary veins. Three-dimensional reconstruction showed that the venous component increased proportionally with growth. No noticeable differences to discriminate between the right and left parts of the venous component emerged, while the junction between the venous component and body gradually became inconspicuous but was still recognizable by the end of the observed early fetal period. The left superior pulmonary vein had the smallest cross-sectional area and most flattened shape, whereas the other three were similar in area and shape. The left atrial appendage had a large volume in the center and extended to the periphery as a lobe-like structure. The left atrial appendage orifice increased in the area and tended to become flatter with growth. The whole left atrium volume^(1/3) increased almost proportionally with growth, parallel to the whole heart volume. This study provided a three-dimensional and quantitative description of the developmental process of left atrium, comprising the venous component and left atrial appendage formation, from the late embryonic to the early fetal stages.

22年度卒業式が行われました。久しぶりの対面での開催でした。

おめでとうございます