Complex sentence: A mast cell (also known as a mastocyte or a labrocyte) is derived from the myeloid stem cell and a part of the immune system that contains many granules rich in histamine and heparin.
Split into simpler sentences: A mast cell (also known as a mastocyte or a labrocyte) is derived from the myeloid stem cell. It is a part of the immune system and contains many granules rich in histamine and heparin.