At the cellular level, your body is a very busy place. Your cells create energy, secrete chemicals, expel waste, and many, many other functions. Two key functions in which your cells engage are exocytosis and endocytosis.

The definitions of exocytosis and endocytosis are as follows:
Exocytosis ‘“ the process by which a cell expels molecules and other objects that are too large to pass through the cellular membrane
Endocytosis ‘“ the process by which a cell takes in molecules and other objects that are too large to pass through the cellular membrane

The basic mechanism by which a cell performs exocytosis or endocytosis is much the same. Both make use of vesicles for their molecular transport. Vesicles are small, membrane-enclosed sacs that move around a cell. They are generally used for storage and transport. Because they are entirely enclosed by a membrane, inside they can have a completely different composition than that of their cell.

How are vesicles used for exocytosis and endocytosis?
Exocytosis ‘“ Waste or other chemicals inside the cells are surrounded by the vesicle. Sometimes the vesicle is able to draw the molecule through its membrane. Other times it surrounds the molecule and ‘swallows’ it. Then the vesicle moves to the edge of the cell and tethers itself to the cellular membrane. It then pushes its molecular cargo out through the cellular membrane.
Endocytosis ‘“ The cell engulfs molecules or proteins near the surface of the cellular membrane. It can swallow large molecules, small bits of protein, or create receptor pockets to which specific types of molecules are attracted. Once the molecule is surrounded by the cellular membrane, the area is pinched off to create a vesicle inside the cell that holds the molecule.

One might say that endocytosis creates vesicles and exocytosis uses and can potentially destroy vesicles.

Exocytosis is used for the following purposes:

• Release enzymes, hormones, proteins, and glucose to be used in other parts of the body
• Neurotransmitters (in the case of neurons)
• Communicate defense measures against a disease
• Expel cellular waste

Endocytosis is used for the following purposes:

• Receive nutrients
• Entry of pathogens
• Cell migration and adhesion
• Signal receptors

Summary:
1. Endocytosis brings molecules into a cell while exocytosis takes molecules out of a cell.
2. Both processes use vesicles for molecular transport.
3. Endocytosis creates vesicles while exocytosis can destroy them.
4. The primary function of endocytosis is getting nutrients and the primary function of exocytosis is expelling waste.

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