"They were saddened, and one by one they said to him, 'Surely you don't mean me?'" NIV translation
The reaction of the apostles was interesting as each one wondered if the person in question was him. Each of these men had spent about three years with Jesus being taught about the kingdom of God and yet they each understood that it could be them. They understood that we all have the capacity to betray Jesus in our hearts and it is only through Him that we can remain faithful. You can almost feel the sadness that would have been in that room as they each asked and waited for the answer.
"'It is one of the Twelve,' he replied, 'one who dips bread into the bowl with me. The Son of Man will go just as it is written about him. But woe to that man who betrays the Son of Man! It would be better for him if he had not been born.'" NIV translation
Jesus explains that it will happen just as the scriptures predicted. Even so, He explains that there will be consequences for the one that betrays Him. It would have been better to never live than to suffer the eternal consequences of denying Jesus. The same thing applies to those that hear the gospel and yet refuse to accept that Jesus is the Son of God and our only hope.
"While they were eating, Jesus took bread, and when he had given thanks, he broke it and gave it to his disciples, saying, 'Take it; this is my body.'" NIV translation
They continued with the Passover meal as Jesus explained what it truly meant. When He identified Himself with the bread, Jesus was making a clear statement of the fact that it would only be His sacrifice that would sustain them. Bread was a major part of the daily food that sustained them physically and He was extending that to the fact that He would also sustain them spiritually.
"Then he took a cup, and when he had given thanks, he gave it to them, and they all drank from it. 'This is my blood of the covenant, which is poured out for many,' he said to them." NIV translation
Jesus explained that the drink was a picture of His blood and the fact that all contracts (covenants) required the shedding of blood.