Exocytosis and endocytosis

The exocytosis is intracellular transport material outwardly; while endocytosis consists of the transfer of particles and substances into the cell. An essential economy for the cell to relate to its environment and survive.

ExocytosisEndocitosis
DefinitionCellular mechanism to release or export content to the extracellular medium.Cellular mechanism to trap substances from the extracellular environment.
ProcessIntracellular vesicles fuse with the plasma membrane.The plasma membrane envelops and surrounds the substance.
Types and examplesConstitutive or regulated secretory pathway

Example: endocrine cells release hormones by exocytosis

Phagocytosis (solid material) and pinocytosis (fluid material)

Example: white blood cell ingesting bacteria.

Definition of exocytosis

Exocytosis, which from the Greek means “outside the receptacle,” is a durable, energy-consuming process during which a cell directs the contents of its secretory vesicles out of the cells or extracellular space . This mechanism occurs through the fusion of the membrane of the vesicular organelle with the cytoplasmic membrane, expelling the material to the outside.

In some way it is the reverse process of endocytosis, since here the material is expelled from the same cell, which naturally maintains relationships with its environment. It is from the Golgi apparatus where vesicles destined to fuse with the plasma membrane are formed.

Secretion can be constitutive or regulated. In the first case, the vesicles fuse with the plasma membranes continuously; it is the way in which the cell eliminates waste. The second case, on the contrary, requires some special signal inside the cell that tells it to exonerate the products inside the vesicles.

The last route is very normal in cells specialized in releasing products: good examples are neurons and their neurotransmitters or endocrine cells that disperse hormones, those chemical messengers that are so important to the body.

Definition of endocytosis

Endocytosis, as opposed to exocytosis, refers to a key mechanism by which cells introduce large molecules, small cells, and extracellular particles . These are encompassed in an invagination of the eukaryotic plasma membrane. The result is the formation of a vesicle that ends up detaching from the membrane, forming the cytosol, the site where most of the intracellular fluid is found.

What is the purpose of such a mechanism? They regulate the composition of the lipids and proteins of the plasma membrane, they determine how cells interact with the environment, which is why they constitute a fundamental role for cell physiology and homeostasis (exchange with the outside).

This process that allows cells to incorporate nutrients, such as vitamins, cholesterol and iron, will vary depending on the size and consistency of the material to be ingested. Therefore, on the one hand we have phagocytosis and on the other pinocytosis.

Phagocytosis

Phagocytosis is an endocytosis of large , solid particles , a cell, in common use, eating. Unicellular organisms such as amoebae use this mechanism to feed.

In the case of higher and multicellular organisms, we have phagocytes of office. They are white blood cells or leukocytes and macrophages, cells that are responsible for defending the body against invading agents, such as bacteria, viruses and parasites.

The vesicle of phagocytosis is called a phagosome. The latter fuse with lysosomes, which are the intracellular organelles involved in material digestion.

Pinocytosis

Pinocytosis is another type of endocytosis, but here we do not have large solid particles, but molecules dissolved in a fluid . If in phagocytosis the cell eats, in pinocytosis it is drinking (engulfing a soluble molecule).

In this way, material is captured from the extracellular space by invagination of the same plasma membrane. This happens with detachment into the cell of a vesicle that contains liquid, with possible dissolved molecules or somewhat solid particles in suspension.

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