function abrirPag(valor){

var url = valor;

xmlRequest.onreadystatechange = mudancaEstado;
xmlRequest.open("GET",url,true);
xmlRequest.send(null);
if (xmlRequest.readyState == 1) {document.getElementById("conteudo_mostrar").innerHTML = "<img src='loader.gif'>";
}
return url;
}
function mudancaEstado(){
if (xmlRequest.readyState == 4){
document.getElementById("conteudo_mostrar").innerHTML = xmlRequest.responseText;
}
}