Giving up the ghost

I'd like to know the meaning of the highlighted part of this sentence:

At the time he set up his clinic his father had grown into an old man and retired from his post at the kerosene dealer's depot at which he had worked for forty years, and his mother died soon after, giving up the ghost with a sigh that sounded positively happy, for it was her own son who ministered to her in her last illness and who sat pressing her feet at the last moment -such a son as few women had borne .

I know its a bit long

Thanks!!