“This is preposterous. Jesus lived about 33 years—actually, perhaps, 40. A human being’s body contains all new material every seven years, they say. So the material that was once Jesus equals almost six entire bodies. What happened to all the material that was once constitutive of Jesus’ body? It’s incorruptible, you say. So where is it?”
As I said before, the incorruption of Christ’s body and blood is miraculous. Therefore, knowing how, where, why, etc. are not essential. While Christ’s body was mortal, and fully human, it was different from our bodies in that it never was corrupted by Adamic sin. I think it is reasonable to believe that it underwent no corruption whatsoever. Perhaps an incorruptible body does not need to constantly replenish dying cells. I do not know.
1 Corinthians 15:35-38
But someone will say, “How are the dead raised up? And with what body do they come?” Foolish one, what you sow is not made alive unless it dies. And what you sow, you do not sow that body that shall be, but mere grain—perhaps wheat or some other grain. But God gives it a body as He pleases, and to each seed its own body.
You believe in transubstantiation. Have you ever asked yourself how tons of bread and wine could be transformed into Christ’s physical body and blood?
I believe that those who are in Christ are joined to Christ in a spiritual union by God’s Spirit. And some day this unity will come to a fruition as our bodies are transformed into incorruptible and immortal bodies as His is now. How God will accomplish this is a great mystery. In some form and fashion we are already joined to Him as parts of His body. But what God is doing in this regard will not be complete until the resurrection.
The corruption of sin resides in our mortal bodies now. This is true even for believers. However, part of God’s plan of redemption involves the redemption of our bodies. The salvation process requires an exchange — my corruption for His incorruption, my sin for His righteousness, my mortality for His immortality.
It is my opinion that the references to Christ’s incorruptible human nature applies to His entire mortal existence. The scripture says His blood was not a corruptible thing, and God would not allow His body to go through corruption.
There is a sense in which the Eucharist is NOT "Christ's physical body and blood." Christ's physical body and blood are physically present in heaven--wherever that may be, physically. It is inaccurate to say that Christ's body and blood are "physically" present in the Eucharist. It IS accurate to say that Christ's real body and real blood, which are physical things, are present in the Eucharist.
"Transubstantiation" means exactly what the words of Jesus (This is my body/blood...) mean: that THIS, that I am holding in my hand, IS (not "represents," not "suggests," not "reminds you of...") my body/blood. The Catholic Church teaches "transubstantiation" because only the concept of "transubstantiation" preserves the clear meaning of the words Jesus spoke when he instituted the sacrament. All contrary doctrines on the Eucharist explain away the words of Jesus.
"Transubstantiation" means that the whole substance of the bread and wine are changed into the whole substance of the Body and Blood of Christ. This is not a physical process or a natural event. It is entirely miraculous. Not one physical atom, proton, neutron, or electron is disturbed by the event of transubstantiation. Thus, absolutely nothing regarding the physical characteristics or appearances of the bread and wine are changed. But the Body and Blood of the Risen Christ are now present, really and substantially, and the bread and wine no longer exist, but only their appearances--their "accidents."
For example: Suppose Jesus, physically present in heaven, weighs 180 lbs. If one ton of bread is consecrated, Jesus does not suddenly weigh one ton. Rather: In the whole one ton of bread, the 180-lb. Jesus is really and substantially present. If a piece of the "bread" weighing 3 grams is broken off, the 180-lb. Body of Jesus is present, really and substantially, in that piece of "bread." And Jesus is present with all HIS accidents: His height, weight, brown hair, etc. HIS accidents are not visible to us, of course, just as his very body is not visible to us.
Similarly, if 1,000 gallons of wine are consecrated, Jesus does not suddenly have 1,000 gallons of blood. Rather, the normal quantity of blood in an adult male (since Jesus is Risen, i.e., alive) is now present, really and substantially, in the whole 1,000 gallons of "wine" and in any portion of it, no matter how large or small.
Wikipedia has excellent articles on this. The first link is to the most thorough article on "transubstantiation." The others treat it in other contexts, such as the Mass and Eucharistic devotion.
https://en.wikipedia.org/wiki/Transubstantiation
https://en.wikipedia.org/wiki/Eucharist_in_the_Catholic_Church#Transubstantiation
https://en.wikipedia.org/wiki/Real_presence_of_Christ_in_the_Eucharist#Catholic:_Transubstantiation
Thomas Aquinas's treatment of the Eucharist in the Summa Theologica:
http://www.newadvent.org/summa/4.htm
You can scroll down on the page to these links, or use them from here:
http://www.newadvent.org/summa/4073.htm
http://www.newadvent.org/summa/4074.htm
http://www.newadvent.org/summa/4075.htm
http://www.newadvent.org/summa/4076.htm
http://www.newadvent.org/summa/4077.htm
http://www.newadvent.org/summa/4078.htm
http://www.newadvent.org/summa/4079.htm
http://www.newadvent.org/summa/4080.htm
http://www.newadvent.org/summa/4081.htm
http://www.newadvent.org/summa/4082.htm
http://www.newadvent.org/summa/4083.htm