The following appears in the abstract of Garabed Eknoyan, The Kidneys in the Bible: What Happened?
The abstract is available at http://jasn.asnjournals.org/content/16/12/3464.full.
“The kidneys are mentioned… sometimes in direct connection with the heart, as the site of emotions and intellect. Some of the attributes principally assigned to one of these two organs are at times credited to the other. Thus, whereas the heart is the organ considered to be the site of wisdom and the governing center of rational processes, it is a function that is attributed also to the kidneys, as in, “I will bless the Lord, who has given me counsel; my reins also instruct me in the night seasons” (Psalms 16:7). The Midrash on Genesis (Genesis Rabbah 61:1) tells that the illiterate Abraham was taught the law by his kidneys and then developed the recognition of God from within himself (13,38). Conversely, whereas the kidneys are considered the site of affections, as in the verses of joy, “Yea my reins shall rejoice, when thy lips speak right things” (Prov. 23:16), and of faithfulness, “And righteousness shall be the girdle of his loins, and faithfulness the girdle of his reins” (Isa. 11:5), they seem to share their position as the site of affections with the heart as in the following verse of grief: “Thus my heart was grieved, and I was pricked in my reins” (Psalms 73:21). No other internal organs of the body are mentioned in parallel in the Bible as often as are the heart and the kidneys.
Garabed Eknoyan, “The Kidneys in the Bible: What Happened?” Journal of the American Society of Nephrology. 2005 16: 3464-3471.