In a large bowl, whisk together flour, baking powder, baking soda and salt. Set aside.
In another large bowl, beat butter (or margarine) until smooth. Add sugar and beat for 2 to 3 minutes until fluffy. Beat in eggs, one at a time, beating well after each addition. Add lemon juice, lemon zest and vanilla and beat until combined. Beat in flour in three additions, alternating with buttermilk. Beat for 2 minutes. Fold in blueberries. Spoon into prepared pan.
Bake at 350F for 50 minutes or until a toothpick inserted in center of cake comes out clean. Cool on a wire rack for 20 minutes. Run a sharp knife around edges of the pan. Turn out and cool completely.
Glaze: in a small bowl, mix together confectioners' sugar, lemon juice and corn syrup until smooth. Drizzle over top of cake and let it roll down the sides.