Smooth Endoplasmic Reticulum Structure
Smooth Endoplasmic Reticulum is the endoplasmic reticulum with smooth appearance. It is also called Agranular reticulum and because it is formed by many interconnected tubules, it is also named as Tubular Endoplasmic Reticulum. This type of Endoplasmic reticulum is devoid of ribosomes and constitute a small part of the total ER. The agranular reticulum functions mainly in the synthesis of lipid substances and for other processes of the cells promoted by intrareticular enzymes.
In striated (skeletal and cardiac) muscle, the Smooth endoplasmic reticulum is called the sarcoplasmic reticulum and helps to stores calcium ions in high concentration and plays an important role in muscle contraction. Most cells have very little smooth ER but it is a prominent feature of cells processing lipids.
Smooth Endoplasmic Reticulum Function
- Smooth ER is responsible for further processing of proteins synthesized in rough ER.
- It is also responsible for synthesis of lipids, especially that of membrane phospholipids (necessary for membrane formation).
- The agranular endoplasmic reticulum (smooth ER) is also the site of steroid synthesis in steroid-secreting cells and the site of detoxification processes in other cells.
Function of Smooth Endoplasmic Reticulum in the Synthesis of non-protein substance
Smooth endoplasmic reticulum is responsible for synthesis of non-protein substances such as cholesterol and steroid. This type of endoplasmic reticulum is abundant in cells that are involved in the synthesis of lipids, phospholipids, lipoprotein substances, steroid hormones, sebum, etc. In most of the other cells, smooth endoplasmic reticulum is less extensive than the rough endoplasmic reticulum.
The Role of Smooth Endoplasmic Reticulum in cellular metabolism
Outer surface of smooth endoplasmic reticulum contains many enzymes which are involved in various metabolic processes of the cell.
Function of Smooth Endoplasmic Reticulum in the Storage and metabolism of calcium
Smooth endoplasmic reticulum is the major site of storage and metabolism of calcium. In skeletal muscle fibers, it releases calcium which is necessary to trigger the muscle contraction.
Function of Smooth Endoplasmic Reticulum in catabolism and detoxification
Smooth endoplasmic reticulum is also concerned with catabolism and detoxification of toxic substances like some drugs and carcinogens (cancer-producing substances) in the liver.