Why can’t your body heal an amputation, such as the loss of a finger, the same way it can heal a cut?

For a limb to regenerate, you need bone, muscle, blood vessels and nerves. There are adult stem cells, a kind of undifferentiated cell that can become specialized, that regenerate muscle, but they don't seem to activate.

the major parts of the digestive system:

salivary glands.

pharynx.

esophagus.

stomach.

small intestine.

large intestine.

rectum.

accessory digestive organs: liver, gallbladder, pancreas.