[Radiation effects on pregnant women, fetuses, and children].

We conducted a review of literature related to radiation effects on pregnant women, fetuses, and children from the perspective of epidemiology, pathology, and radiobiology. During 8-25 weeks post-conception the central nervous system is particularly sensitive to radiation. Fetal doses in excess of 100 mGy can result in some reduction of IQ (intelligence quotient). Fetal doses in the range of 1000 mGy can lead to severe mental retardation and microcephaly, particularly during 8-15 weeks and to a lesser extent 16-25 weeks after conception. Recent studies of cancers and chromosome aberrations indicated less radiosensitivity in prenatally exposed A-bomb survivors compared with postnatally exposed survivors, for which we provide possible hypotheses as an explanation.

Formal genesis of the outflow tracts of the heart revisited: previous works in the light of recent observations.

The formal genesis of the great arteries continues to be controversial due to the lack of consensus of septation of the developing outflow tract. In order to make it clear how the great arteries are generated, we have re-examined our previous papers which emphasized the formation of the aorta and pulmonary trunk, concept of the aorticopulmonary septum, formation of the leaflets of semilunar valves, morphogenesis of the crista supraventricularis, programmed cell death and rotation of the outflow tract. In the present paper, we compare outcomes gained from the re-examination of our previous papers with prevalent interpretations of the arterial trunk. We obtained conclusions as follows: (i) The elongation of the fourth and sixth aortic arch arteries, which sprout from the wall of the aortic sac at the expense of the distal truncus, contributes to the formation of the aorta and pulmonary trunk; (ii) Smooth muscle cells of the tunica media of the arterial trunks do not arise from the transformation of the myocardial cells of the truncus wall (not 'arterialization'); (iii) Truncus swellings are divided into two parts: distal and proximal. The former contributes to the separation of the orifices of arterial trunks ('aorticopulmonary septum'). The latter contributes to the formation of the leaflets of the semilunar valves of the aorta and pulmonary trunk; (iv) The origin of the myocardial cells of the crista supraventricularis is a wall of the conus originated from secondary/anterior heart fields; and (v) There has been no acceptable proof that rotation and counterclockwise rotation are involved.