Smooth Endoplasmic Reticulum: Definition, Characteristics And Functions
The endoplasmic reticulum is an organ of the cell made up of membranes connected to each other. These membranes are continuous with those of the center of the cell, the cell nucleus.
There are two types of endoplasmic reticulum: one, called rough, whose membranes form flattened cisterns and with spherical structures called ribosomes, and the other called smooth, which is organized with membranes forming tubules without these ribosomes.
In this article let’s talk about the smooth endoplasmic reticulum and what its parts and functions are.
This cellular organelle consists of a set of tubular and membranous structures that are connected to each other, which continue in the cisternae of its counterpart, the rough endoplasmic reticulum.
The smooth endoplasmic reticulum It differs from its rough counterpart in that it does not have ribosomes attached to its membranes It is for this reason that it is called smooth. Due to this lack of ribosomes, the proteins present in this organelle have their origin in the rough endoplasmic reticulum.
This organelle It performs very necessary functions for the survival of the cell and the organism in which it is found participating in the synthesis of lipids, detoxification of alcohol and other harmful substances, regulates blood glucose levels and also serves as a reserve of essential minerals such as calcium.
Features
This organelle performs a few important functions for the cell and for the proper maintenance of the organism.
In the smooth endoplasmic reticulum most of the fats that make up the cell membranes are synthesized such as cholesterol and glycerophospholipids.
It should be noted that more than synthesis, what is carried out in this organelle is the assembly of lipids, whose raw material comes from other organelles. For example, to make glycerophospholipids, the smooth endoplasmic reticulum requires fatty acids, which come from the cytosol, that is, the internal environment of the cell.
The transport of these lipids to the membranes they will constitute can be carried out using vesicles or transport proteins.
One of the substances that are synthesized in the smooth endoplasmic reticulum is cholesterol This substance acquires great importance since it is the component of the double lipid layer of the cell. This substance is transported from this organelle to the plasma wall by soluble protein transporters.
In the smooth endoplasmic reticulum, in addition to cholesterol to form cell membranes, triacylglycerols are formed, lipids very present in adipose cells, which store fat for thermal insulation and as a nutritional reserve.
Also It is involved in the synthesis of some hormones such as steroid hormones, bile acids and the lipid part of lipoproteins.
2. Detoxification
Detoxification is understood as the process in which substances, such as drugs and metabolites produced in the reactions that take place within the body, are transformed into water-soluble compounds that is, they can dissolve in water and be excreted through urine.
This process is possible thanks to the presence of oxygenase enzymes, which are located in the membranes of this organelle, such as the cytochrome P450 family of proteins. This family of enzymes is of great importance in drug metabolism.
Detoxification takes place mainly in liver cells, which are called hepatocytes. These cells are characterized by having a highly developed smooth endoplasmic reticulum.
Notably The absence of ribosomes in this type of reticulum allows a greater surface area for enzymatic action in proportion to the size of the reticle.
3. Glucose-6-phosphate dephosphorylation
Glucose is a sugar that is stored in the form of glycogen, mostly in the liver. For this reason, this organ is responsible for introducing sugar into the bloodstream, through two hormones that are responsible for regulating this process: glucagon and insulin
Glycogen, when broken down, forms glucose-6-phosphate. This substance cannot leave the cell, because it is unable to cross the membranes.
Through the action of glucose-6-phosphatase, an enzyme, glucose-6-phosphate is degraded, forming glucose which can be carried into the blood.
4. Intracellular calcium reserve
The smooth endoplasmic reticulum It is responsible for collecting and storing calcium that is floating in the cytosol This collection of this element is carried out through the action of calcium pumps found in the reticulum membrane.
The calcium found inside this organelle can be expelled to the outside en masse if the necessary signal is given to do so, whether it originates inside or outside the cell.
This process takes place primarily in muscle cells where the smooth endoplasmic reticulum is called sarcoplasmic reticulum.
If a motor neuron, that is, a neuron involved in muscle movement, receives a nerve impulse, the reticulum causes acetylcholine to be released at the neuromuscular plate. This acetylcholine binds to the receptors of the muscle cell, causing the membrane to deporalize.
When depolarization occurs, calcium ions that were stored in the sarcoplasmic reticulum are released and end up in the cytosol. Thus, through this process, muscle contraction ordered by the nervous system occurs.
When the nerve impulse stops being sent, calcium ions stop being released into the cytosol and the one that has been previously released is actively collected into the sarcoplasmic reticulum.
