RESUMEN
Larvae of priapulids are characterized by radial symmetry evident from both external and internal characters of the introvert and lorica. The bilaterality appears as a result of a combination of several radial symmetries: pentaradial symmetry of the teeth, octaradial symmetry of the primary scalids, 25-radial symmetry of scalids, biradial symmetry of the neck, and biradial and decaradial symmetry of the trunk. Internal radiality is exhibited by musculature and the circumpharyngeal nerve ring. Internal bilaterality is evident from the position of the ventral nerve cord and excretory elements. Externally, the bilaterality is determined by the position of the anal tubulus and two shortened midventral rows of scalids bordering the ventral nerve cord. The lorical elements define the biradial symmetry that is missing in adult priapulids. The radial symmetry of larvae is a secondary appearance considered an evolutionary adaptation to a lifestyle within the three-dimensional environment of the benthic sediment.
Asunto(s)
Equinodermos/anatomía & histología , Animales , Equinodermos/embriología , LarvaRESUMEN
Priapulids possess a radial symmetry that is remarkably reflected in both external morphology and internal anatomy. It results in the appearance of 25-radial (a number divisible by five) symmetry summarized as a combination of nonaradial, octaradial, and octaradial (9+8+8) symmetries of scalids. The radial symmetry is a secondary appearance considered as an evolutionary adaptation to a lifestyle within the three-dimensional environment of bottom sediment. The eight anteriormost, or primary, scalids retain their particular position because of their innervation directly from the circumpharyngeal brain. As a result of a combination of the octaradial symmetry of primary scalids, pentaradial symmetry of teeth, and the 25-radial symmetry of scalids, the initial bilateral symmetry remains characterized by the single sagittal plane.
Asunto(s)
Equinodermos/anatomía & histología , AnimalesAsunto(s)
Bloqueo Cardíaco/terapia , Marcapaso Artificial , Adulto , Femenino , Bloqueo Cardíaco/psicología , Humanos , Calidad de VidaRESUMEN
BACKGROUND: This study aimed to investigate a possible association between low birth weight (LBW) and other perinatal major characteristics and the risk of a child having accessory pathways of conduction tissue and cardiac arrhythmia later in life. METHODS: Thirty-one children aged 1-15 years (12 boys, 19 girls), in whom the persistence of accessory pathways of conduction tissue in the heart and inducible reciprocating supraventricular tachycardia were confirmed by means of programmable transoesophageal pacing, constituted the study group. None of them exhibited signs of either inborn or acquired heart disease causing arrhythmia, and their parents and siblings did not suffer cardiac arrhythmias. The control group was formed of 62 apparently healthy children (two controls for each case) matched to cases for sex, age, date and place of birth. Information on infant perinatal and maternal characteristics was collected retrospectively. RESULTS: High risk of arrhythmia in children was associated with LBW (< 2500 g): odds ratio was equal to 14.6 (95% CI: 1.7-127.9; P = 0.015), and it remained after adjustment had been made for major potential confounders. In addition, children with arrhythmia were more often born with retarded intrauterine growth (birth weight < 10 percentile), preterm (< 37 weeks of gestation), of higher birth order, and had lower Apgar scores at 1 and 5 min. Their mothers more often had diagnosed gynaecological diseases. CONCLUSIONS: Antenatal stress leading to LBW may be associated with atypical development and maturation of cardiac conduction system and increased risk of cardiac arrhythmias later in life.
Asunto(s)
Arritmias Cardíacas/epidemiología , Recién Nacido de Bajo Peso , Adolescente , Arritmias Cardíacas/diagnóstico , Arritmias Cardíacas/etiología , Estudios de Casos y Controles , Niño , Preescolar , Intervalos de Confianza , Femenino , Sistema de Conducción Cardíaco/anomalías , Humanos , Lactante , Recién Nacido , Masculino , Oportunidad Relativa , Factores de Riesgo , Federación de Rusia/epidemiología , Estadísticas no ParamétricasRESUMEN
Introverts of Priapulus caudatus and P. tuberculatospinosus bear 25 rows of scalids, as well as 8 spines and scattered papillae in the region the circumoral lip. These, as well as the first ring of pharyngeal teeth in P. tuberculatospinosus, are sensory organs. Although superficially they differ between species, they are all characterized by apical and/or subapical openings which are located on tiny cuticular tubules. All sensory organs contain cilia bearing bipolar receptor cells. The 8 sensory spines situated between the circumoral area and the beginning of the scalids are ultrastructurally similar to the scalids. The introvert and pharyngeal body walls, and associated muscles are described. © 1994 Wiley-Liss, Inc.