Exocytosis is the reverse of endocytosis. This article gives you a brief explanation of these processes and also compares the two.
The cells inside an organism’s body perform actions like secreting chemicals, releasing energy, expelling wastes, etc. For these functions, body cells carry out the processes of exocytosis and endocytosis. Let’s understand the two in detail and also find the differences between them.
In this process, a cell expels molecules and other contents that are too large to pass through the cell membrane structure. This discharge is accompanied by the fusion of the vesicular membrane and the plasma membrane. This process is carried out in three ways that separately involve the molecular constituents like endosomes, lysosomes, exosomes, neurotransmitters, etc.
Inside the cell, constituents like water, chemicals, and ions are surrounded by the vesicles, which may draw out these molecules. The vesicles are small sacs that are enclosed in membranes, and they can surround a specific type of molecule and swallow it. These vesicles travel towards the cell membrane, and get attached to it. After this action, the molecules are then pushed/forced out of the cellular membrane. Common examples of exocytosis include secretion of pancreatic digestive enzymes, repairing wounds of the plasma membrane, discharge of neurotransmitter from presynaptic neurons, secretion of antibodies and peptide hormones, functions involving antigens during immunity body responses, etc.
In this process, the body cells ingest various molecules such as proteins, polar molecules, and other substances, through their hydrophobic plasma membrane. This process is carried out by many eukaryotic cells to ingest food particles by surrounding them, and in this case, the plasma membrane is extended outwards. The basic mechanism of both the processes of exocytosis and endocytosis, is more or less the same. Vesicles are the structures used for the transportation of molecules. They are also used for storage and transportation of food. Also, many bacteria and pathogens may enter the body by this process. These structures may have a completely different internal composition as compared to that of the body cells.
Endocytosis is of three types: phagocytosis, pinocytosis, and receptor-mediated endocytosis. In case of phagocytosis, the cell takes in a bacterium or a food particle. In pinocytosis, the cell ingests a liquid material. In the last type, specific molecules like low-density lipoproteins (LDL) are transported towards the cell interior. The ingested molecules travel to the binding sites of specific receptors, which are present on the plasma membrane. The interior part of the receptor proteins gets embedded in this membrane. In the pit area, the membrane’s interior is coated by a protein called clathrin. The coated pit deepens and seals off in the form of a coated vesicle, when there are plenty of molecules in it. These vesicles are carried into the cell along with the molecules. Main examples of endocytosis are transportation of food, entry of bacteria and pathogens in the body, functions involving various proteins, etc.
|It results is expelling molecules outside the cell.||It helps to ingest molecules towards the cell interior.|
|This process leads to the destruction of vesicles.||This process leads to creation of vesicles.|
|There is a discharge of enzymes, hormones, proteins, and glucose. All these constituents are used for the functioning of other body parts.||By this process, nutrients, food particles, and proteins are received by the body cells. Apart from this, some bacteria and pathogens can also gain entry into the body through this process.|
|Example 1: Neurotransmitters released from the neuron cells.||Example 1: The body cells engulf pathogens and destroy them.|
|Example 2: In case of an infection, the cells communicate among themselves, and strengthen the immune system of the body by the process of exocytosis.||Example 2: Endocytosis is used in case of cell migration and adhesion related functions.|
|This process helps in expelling wastes from the body.||This process serves as a signal receptor.|
Thus, the processes of exocytosis and endocytosis are opposite, as well as complementary to each other. These mechanisms are very important for the existence and functioning of the body cells.