The SR takes up the calcium ions from the cytoplasm and releases them when the muscle cell is triggered by a nervous stimulus, resulting in muscle contraction. Regulation of calcium concentration: In muscle cells, a specialized SER called the sarcoplasmic reticulum (SR) is responsible for the storage and regulation of calcium ions that are required to trigger the coordinated contractions of the muscle cells. These enzymes act by adding a hydroxyl group to drug molecules, making them more soluble and easier to flush from the body.ģ. Drug detoxification: A specialized group of enzymes, cytochrome P450s present on the smooth endoplasmic reticulum membrane, help detoxify drugs and poisons, especially in liver cells. They also play a vital role as a structural element of the cell.Ģ. The lipids thus synthesized form a major portion of the lipid bilayer of the cell membrane. Different types of lipids formed by SER are phospholipids, ceramides, sterols, and steroids. The enzymes present in these sites are activated by signals from outside and inside the cell. MCS are the areas where membranes of SER make close contact with other cytoplasmic organelles, such as mitochondria, Golgi apparatus, lysosomes, peroxisomes, and plasma membrane, and allow the transfer of substances. Lipid synthesis: The smooth endoplasmic reticulum is the primary site for lipid synthesis, especially at its membrane contact sites (MCS). Let us discuss these functions of SER in details:ġ.
Some other functions of SER would include regulation of calcium concentration in the muscle cells, and carbohydrate metabolism in liver and kidneys. For instance, in some endocrine glands it synthesizes lipids, whereas in liver it helps in the detoxification or removal of several drugs from the body. The function of the SER may vary, depending on the cell type.
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