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 = "<p aligh='center'><br/><img src='imagens/loading.gif'><br/>Loading...<br><br><br><br></p>";
}
return url;
}

function mudancaEstado(){
if (xmlRequest.readyState == 4){
document.getElementById("conteudo_mostrar").innerHTML = xmlRequest.responseText;
}
}