Consumption and Eucharist

I eat bread, swallow it. The digestive system then actively absorbs the material into the body. The quantity and qualities (accidents) of the bread now become part of my body. There is an exchange of substances from bread to my person.Does the substance of the bread continue to exist only in memory?
A person receives the Eucharist. The active principle is not the digestive system. The human body is united to the glorified Body of Christ under the appearance of bread and wine. The individual body of the person, including the digestive system, undergoes a unitive participation or transformation? Does the active Substance of the Divine through the Eucharist transform the substance of the person, or elevate the ontological condition of the person through the contact of individual body and the Eucharistic body of Christ?

I remember either hearing or reading once that the substance (Christ’s body, blood, soul, and divinity) disappears once you swallow the Eucharist. You have already received the grace from it so it doesn’t really matter that it disappears. Of course, I could be wrong.

I cannot remember the source who said in so many words to paraphrase that once the host dissolves from digestion the presence is not there anymore for the time being.
The other Sacraments like Baptism and Confirmation somehow leave an indeliable mark. Christ designates or sanctifies water and oil as the matter informed by the official performing them. The words spoken activate the communication of grace channeled through the matter, which contact the body to penetrate through to the soul. This is an instrumental effect of Christ’s power; whereas in the Eucharist, the reception is the very substance of Christ in his glorified body and soul united with divinity. There has to be an ontological difference beyond comphrension for me.

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