I've been reading about gastro intestinal problems. The esophagus, mouth, teeth, tongue...their purpose is for eating.
It seems to me that they are necessary for animals. But, we aren't stupid animals.
All of the above could be replaced by introducing baby food right directly into the stomach. I could have done it with the plastic tube I ran down to my stomach.
It also seems to me that if you knew what the head needed from the blood, you could keep a head alive by supplying it externally. I'd be surprised if someone hasn't that done that yet.