In Macbeth, how do Macbeth's reactions and conflicts in Act V affect our understanding of his character as the tragic hero?

By the conclusion of the play, Macbeth has evolved into a murderous tyrant with much innocent blood on his hands. He is despised by his own people who have risen up against him, supported by foreign allies. Had Macbeth always been so despicable, there could have been nothing heroic in his character, but this was not the case. In the beginning of the play, Macbeth had been a loyal and courageous general. Before Macbeth's death, Shakespeare gives us a final glimpse of him as he had been in order to emphasize the tragedy of his fall and destruction.

In Act V Macbeth wavers between fear and confidence. Surrounded and outnumbered, he calls for his armor, vowing "I'll fight, till from my bones my flesh be hacked." Yet he still feels security in the witches' final prophecy:

They have tied me to a stake; I cannot fly,

But bearlike I must fight the course. What's he

That was not born of woman? Such a one

Am I to fear, or none.

When he finally meets Macduff in battle, Macbeth's former heroic character is revealed briefly. Having slaughtered Macduff's entire household, he does not wish to kill Macduff himself. When he learns that the witches' prophecy won't protect him (Macduff was not born of a woman), Macbeth chooses to fight rather than surrender: 

I will not yield,

To kiss the ground before young Malcom's feet, And to be baited with the rabble's curse.

Though Birnam Wood be come to Dunsinane,

And thou opposed, being of no woman born,

Yet I will try the last. Before my body

I throw my warlike shield. Lay on, Macduff;

And damned be him that first cries "Hold, enough!"

Thus, in our last glimpse of Macbeth, he acts with courage and honor, which emphasizes the tragedy of his downfall and destruction.