Dear Dhanjit,
The core understanding between the 2 dept is lacking even in professionals, the HR is all about the Human values and related things ,whereas Admin means all of it , not one aspect as human resources, this is because all office related like the Cafeteria ,Housekeeping,vendors , all things needed for the offices functionally & Academically are taken care of by Admin , where HR is a part of it.
The Org can differ from places & its so its functionality, where they may be bound to look into the 2 depts together, so noramlly people & enterpreneurs do not think much on these things , as a result , it is widely looked after & known as one dept.
But not necessarily all follow the same, There are org's, who have kept diff heads for these 2 depts.
Now this will help you tailor make results as per your queries.
MMD-