Endocytosis and exocytosis are active transport processes that facilitate nutrient absorption and waste secretion at a cellular level. While both require energy to transport ions and molecules, they are completely different mechanisms that play equally important roles in the body.
Summary Table
| Endocytosis | Exocytosis |
| A process where the cell membrane either engulfs the substance or creates a pathway for dissolved nutrients to enter the cell | A process where the vesicles fuse with the plasma membrane to draw out large molecules from the cell |
| Two main types are phagocytosis and pinocytosis | Three main types are regulated (Ca2+ triggered non-constitutive), constitutive exocytosis, and active transport via lysosomes |
| Forms internal vesicles such as phagosomes | Forms secretory vesicles |
| Aids in cell migration, cell adhesion, nutrient ingestion, and pathogen entry | Aids in waste excretion, hormone and enzyme release, and in the communication of defense methods against a particular disease |
Definitions
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Endocytosis is a process where macromolecules and other large substances are actively transported into the cell without passing through the cell membrane.
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Exocytosis is a type of bulk transport that fuses vesicles into the plasma membrane to excrete large particles and substances outside the cell.
Endocytosis vs Exocytosis
Although they both function to maintain homeostasis in the body, there is a major difference between endocytosis and exocytosis.
Mechanism
Some macromolecules are not capable of passing through the cell membrane because of their large size, making active transport processes such as endocytosis and exocytosis critical in the ingestion and excretion of these substances. Endocytosis allows macromolecules to enter the cell by the use of the cell membrane and an endocytic vesicle. During endocytosis, the cell membrane either engulfs the substance or creates a pathway for dissolved nutrients to enter the cell. The endocytic vesicle, which is a membrane-bound sac, then moves and transports the substance into the cytosol.
Exocytosis, by contrast, is responsible for expelling macromolecules from the cell without passing through the cell membrane. During excretion, the vesicles fuse with the plasma membrane to draw out large molecules. Vesicles have the ability to surround a molecule, swallow it and transport it outside the cell. Once these vesicles attach to the membrane, the molecules are consequently forced out of the cell.
Types
There are two main kinds of endocytosis: phagocytosis and pinocytosis. Phagocytosis, which is a process where the cell “eats,” is a type of active transport system where the plasma membrane folds over the solid substance and completely encloses it, creating a phagocytic vesicle. Once the cell membrane engulfs the macromolecule, the vesicle moves the substance into the cytosol. Pinocytosis, on the other hand, enables the cell to “drink” liquid substances. During pinocytosis, the cell membrane folds inward to create a pathway or a channel for dissolved substances to enter the cell.
Exocytosis also exists in different forms. The three main types of exocytosis are regulated (Ca2+ triggered non-constitutive), constitutive exocytosis and active transport with the help of lysosomes. Also known as the late stage of neurotransmitter and protein secretion, regulated exocytosis mostly occurs in secretory cells. It is an active transport system induced by a stimulus, such as an increase in the calcium in the cells. Once stimulated, the plasma membrane fuses with specialized secretory granules or vesicles to excrete intracellular waste. Constitutive exocytosis, by contrast, is common among all cells. During this process, membrane lipids and proteins are transported to the surface of the cell to facilitate waste excretion. The third type of exocytosis involves the fusion of lysosomes, which contain enzymes that can break down waste materials, and vesicles. Once the digested substances are enclosed in the lysosomes, they are carried and expelled to the extracellular matrix.
Vesicles
Endocytosis and exocytosis form different vesicles that serve as the entry and exit point of large substances. During endocytosis, internal vesicles such as phagosomes are developed. Phagosomes are membrane-bound vesicles that store phagocytized substances. Exocytosis, on the other hand, gives way to the formation of secretory vesicles.
Functions
Aside from serving as a transport system for nutrients, endocytosis also aids in cell migration, cell adhesion, and the entry of pathogen. Exocytosis, by contrast, mainly functions by excreting intracellular waste, releasing hormones and enzymes in different body parts, and communicating defense methods against a particular disease.