PMA: There are two ways to pay back a mortgage. These are called Interest only or repayment mortgages.
With an interest-only mortgage, your monthly payment does not chip away at your actual debt - it just covers the cost of borrowing the money, so it's your responsibility to ensure you have enough funds to repay the balance at the end of the mortgage term.
Repayment mortgages mean that as well as covering the interest, you're paying off the original debt too, meaning if you make all of your monthly repayments, you'll owe nothing at the end of your term. So, with a repayment mortgage, there is no need to put aside more money in a separate account.