从2D阵列传输密钥以填充1D阵列

PHP has plenty of useful functions and Im wondering if Im overlooking one that has already been built.

Lets say you have an array such as:

$first_array = array("Name"=>"Angela", "Age"=>24);

and you wanted to grab the keys from the first array to create a second array (which could then be pushed into a third array). So you need to create:

$second_array = array("Name", "Age");

Is there a way to achieve this result without this loop?:

foreach($first_array as $k=>$v){
    array_push($second_array, $k);
}