With regards to a site hosting on a web host, it will have a registration done at an Internet registrar with an entry on their DNS servers, subsequently on the web hosts DNS, the address where the site is hosted will be listed.
You have to remove at least the web host from this equation since in the case of hosting from home, the role of the web host is taken by your home PC and role of the web host DNS functionality is taken over by the dynamic DNS Company you hire.
This is achieved through a program installed on your PC and by keeping a watch on the IP address you are using to connect to the Internet (which may change every time you reconnect to the ISP).
By doing this, they know the IP you are currently on and this will enable them to direct any user who may be coming to visit your website to you.