Stem cells are undifferentiated cells that could develop to perform a variety of tasks. One type of stem cell is the embrionic stem cell. There are also adult stem cells. To use embrionic stem cell you need to have fertilized embrios. These can be donated to research. The use of the embrionic stem cells is controversial for this reason.
The kidneys make two main hormones, vitamin D and erythropoietin. Vitamin D is essential for a number of different functions in the body. Most of the vitamin D that is in the blood is inactive and it is modified by the kidney and other tissues to activate it.
