Lady macbeth reads her husband’s letter then asks the following: “make thick my blood, / stop up th’ access and passage to remorse”-- what is she asking?

This is from Act 1 Scene 5, so we're pretty early in the play. This is Lady Macbeth's famous "unsex me here" speech, which is where she sort of calls on the spirits to quiet her feminine, maternal instincts to be empathetic and emotional (super sexist, I know). So she asks the spirits to fill her "with direst cruelty" so that she'll be able to help Macbeth kill Duncan and take the crown. That's what she means by "Make thick my blood." It's like, "please spirits, take away my ability to feel guilty about all the murderous shenanigans I'm about to throw down."