In the cellular world “ER” does not mean “emergency room”. Rather, it means “endoplasmic reticulum,” and there are two kinds of them: smooth ER and rough ER.
Our story for the day is about the “smooth ER.” The other kind will be the subject of another post.
Liver cells, steroid hormone-secreting cells, and muscle cells especially abound with smooth ER. In these cells the smooth ER performs different functions.
In liver cells, the smooth ER performs two major functions: detoxification and glucose metabolism especially conversion of glycogen to glucose. People who regularly use drugs have liver cells with very extensive smooth ER. The enzymes of the smooth ER convert the drugs into water soluble compounds that can then be easily eliminated from the body. The detoxifying effect is the reason why drug users need higher and higher doses of drugs.
In steroid hormone-secreting cells, the smooth ER is involved in the synthesis of steroid hormones like estrogen, testosterone and progesterone. While in muscle cells, they serve as depot for Calcium ions.
Changes in Calcium ion levels inside cells is an important signal for activities like muscle contraction and exocytosis. It is thus important to keep low the levels of Calcium ions in the cytoplasm.
In muscle cells, the smooth ER has a special name - “sarcoplasmic reticulum”.