Microsome is another name for the smooth endoplasmic reticulum (ER). It is the site of steroid synthesis in steroid-secreting cells. Cells secreting steroid hormones like the testis and the ovaries are rich in smooth ER. It is also the site of detoxification of drugs and poisons in other cells, specially, liver cells. In skeletal and cardiac muscle, the smooth ER is called the sarcoplasmic reticulum. It stores Ca2+ in high concentration and plays an important role in muscle contraction.