Laravel eloquent querying with multiple relationships

I have four tables which is departments, users, items, items_inventories

The relationship is like this:

A user has a assigned department. An item has a assigned department. item_inventories has many items.

Structure:

users
->id
->name
->password
->access_type (department_id)

departments
->id
->name

items
->id
->name
->department_id

items_inventories
->id
->item_id
->qty

My models:

class Item extends Model
{
    public function department()
    {
        return $this->hasOne('App\Http\Models\Department', "id", "department_id");
    }
}


class ItemsInventory extends Model
{
    public function item()
    {
        return $this->hasOne('App\Http\Models\Item', "id", "item_id");
    }
}

In my items_inventories how do I query all items that belongs to a specific department? Since items has already a relationship to departments, How do I query like: select all items in items_inventories where item department_id is equal to 3?

My goal is, I have a user who is logged in, and I can access the assigned department to him/her via access_type (department_id) when my page loads, I want to list only items in the items_inventories that is assigned to his/her department. I already checked: https://laravel.com/docs/5.4/eloquent-relationships#relationship-methods-vs-dynamic-properties but can't seem to find something that matches my requirement. Thanks

via Yassi