Desarrollo del Aparato Digestivo / Digestive System Development

El aparato digestivo deriva del endodermo y el mesodermo, que forman su epitelio y la musculatura lisa respectivamente. Al igual que en el resto de los sistemas, existe un interacción epitelio-mesenquimática mediada por moléculas como Hedgehog, BMP y FoxF1 que determinan el crecimiento intestinal en sus ejes principales. Los genes Hox, junto con el resto de las moléculas, participan en la regionalización del sistema digestivo. En sus inicios lo denominaremos intestino primitivo, formado por un tubo endodérmico que deriva del saco vitelino; dividiéndose en intestino anterior, medio y posterior. En esta revisión veremos cómo estos 3 segmentos darán origen a las diferentes estructuras del sistema digestivo en los vertebrados.

The digestive system is derived from the endoderm and mesoderm, which form its epithelium and smooth muscle, respectively. As in the other systems, there is an epithelial-mesenchymal interactions mediated by molecules such as Hedgehog, BMP and FoxF1, determining intestinal growth in the main axes. The Hox genes, together the rest of the molecules, involved in the regionalization of the digestive system. In the beginning we call it primitive gut, consisting of a tube derived of endodermal yolk sac, divided into foregut, midgut and hindgut. In this review we will see how these 3 segments give rise to different structures of the digestive system in vertebrates.

Development beyond the gastrula stage and digestive organogenesis in the apple-snail Pomacea canaliculata (Architaenioglossa, Ampullariidae)

Development of Pomacea canaliculata from the gastrula stage until the first day after hatching is described. Trochophore embryos are developed after gastrulation, showing the prototroch as a crown of ciliated orange-brownish cells. However, no true veliger embryos are formed, since the prototroch does not fully develop into a velum. Afterward, the connection between the fore- and midgut is permeated and the midgut becomes full of the pink-reddish albumen, which is stored into a central archenteron's lake, from where it is accumulated into the large cells forming the midgut wall ("giant cells"). Electron microscopy of giant cells in late embryos showed that albumen is engulfed by large endocytic vesicles formed between the irregular microvilli at the top of these cells. By the end of intracapsular development, giant cells become gradually replaced by two new epithelial cell types which are similar to those found in the adult midgut gland: the pre-columnar and the pre-pyramidal cells. Pre-columnar cells have inconspicuous basal nuclei and are crowned by stereocilia, between which small endocytic vesicles are formed. Pre-pyramidal cells have large nuclei with 2-3 nucleoli and show a striking development of the rough endoplasmic reticulum. The genesis of the three cell lineages (giant, pre-columnar and pre-pyramidal cells) is hypothetically attributed to epithelial streaks that occur at both sides of the midgut since early stages of development.

Differential densities of nitric oxide synthesizing nerves in the sphincteric and non-sphincteric smooth muscles of human gut during fetal development

Nitric oxide (NO) is involved in the inhibitory neurotransmission in the sphincter and non-sphincteric smooth muscles. However, the relative contribution of nitric oxid synthesizing innervation to these functionally diverse parts of the gut, particularly during development, is unknown. Gastrointestinal sphincters and adjoining non-sphincteric bowel segments were obtained by nicotinamide adenine deoxinucleotide ages between 12 and 23 weeks. NO synthesizing nerves were examined by nicotinamide adenine deoxinucleotide phosphate (NADPH) diaphorase histochemistry. The densities of NADPH positive nerves in the smooth muscle were quantified using a computerized image analyzing system on randon section. The NO synthesizing nerve density in intestinal smooth muscles decreased during fetal development as a results of increased interspacing between myenteric ganglia and a disproportionately larger increase in smooth muscle area than neuronal area. Similarly, the nerve densities were lower in sphincteric regions than adjoining non-sphincteric regions at the same gestational ages. There is a relative reduction of the density of NO synthesizing nerves in intestinal smooth muscle particularly in sphincteric regions during development. These findings may have relevance to the occurence of congenital dysmotility disordere of the sphincteric regions

Malformaciones del tubo digestivo / Malformation of the digestive system

Se examinaron 124.324 recién nacidos consecutivos en la Maternidad del Hospital Clínico de la Universidad de Chile en busca de malformaciones congénitas, como parte del Estudio Colaborativo Latinoamericano de Malformaciones Congénitas (ECLAMC). Se encontraron 149 niños con alguna malformación del tubo digestivo, lo que representa una prevalencia al nacimento del 11,9 por 10000 nacidos vivos. La incidencia de cada malformación fue similar que en la muestra total del ECLAMC, salvo en hernia diafragmática (2,56/1,28 por 10.000 respectivamente; p> 0,01). Los factores de riesgo para tener un hijo malformado (enfermedades agudas y crónicas maternas del primer trimestre del embarazo, metrorragia, agentes físicos como exposición a radiaciones ionizantes, ademas de escolaridad de los padres, presentación fetal, tipo de parto, edad de la madre, número de abortos previos, edad gestacional y peso de nacimiento) fueron significativamente mas frecuentes entre los antecedentes de los recién nacidos malformados que en sus controles, pero no se tomaron medidas para evitar sesgos de recuerdo e información