Difference Between Phagocytosis and Pinocytosis

The key difference between phagocytosis and pinocytosis is that phagocytosis is a form of endocytosis which uptakes solids through the plasma membrane to the cell while pinocytosis is another form of endocytosis which uptakes fluids including solutes and small molecules through the plasma membrane to the cell.

Endocytosis is a mechanism by which cells intake macromolecules and other suspended particles including cell parts, macromolecular aggregates, and foreign particles into the cell. Exocytosis is the opposite mechanism of endocytosis by which cells exclude substances from the cells. Exocytosis takes place mainly in secretory cells. There are two types of endocytosis based on the nature of the particles that are taken into living cells. They are phagocytosis and pinocytosis. The mechanism used in both processes is the same. They form vesicles surrounding the materials in order to take them inside. Both processes are active processes. Hence, you can observe mitochondria near the surfaces where these processes occur.

CONTENTS

1. Overview and Key Difference
2. What is Phagocytosis 
3. What is Pinocytosis
4. Similarities Between Phagocytosis and Pinocytosis
5. Side by Side Comparison – Phagocytosis vs Pinocytosis in Tabular Form
6. Summary

What is Phagocytosis?

Phagocytosis, also called cell eating, is the intake of solid particles larger than about 0.5µm in diameter through endocytosis. In this case, plasma membrane fuses forward and surrounds the particles near the cell surface to form phagocytic vesicles called phagosomes. Then lysosomes come and fuse with these phagosomes and release their digestive enzymes to digest the content in phagosomes.

Phagocytosis is a process by which most protozoa including amoeba engulf and digest their prey.  In higher animals, neutrophils and macrophages of the immune system utilize this process to defend against foreign bodies such as bacteria, virus, dust particles, dead cells, cellular parts, and other waste matter.

What is Pinocytosis?

Pinocytosis is the active intake of droplets of extracellular fluid along with small particles. Because of the nature of the material involved in pinocytosis, it is a form of cell drinking. It helps to intake important solutes such as insulin and lipoproteins in concentrated form.

Additionally, ions, sugars, and amino acids also enter the cell by this method. In this case, first extracellular fluid with minute particles adheres to specific receptors located on the cell membrane. Then, the plasma membrane of that particular area invaginates and surrounds the particles to form membrane-bounded vesicles called pinosomes. The pinosomes then move into the cytoplasm, and the content is released.  Pinocytosis can be seen very often in the cells that line the blood capillaries.

What are the Similarities Between Phagocytosis and Pinocytosis?

• Phagocytosis and pinocytosis are two types of endocytosis.
• Both methods take in materials through the plasma membrane by forming vesicles.

What is the Difference Between Phagocytosis and Pinocytosis?

Phagocytosis is the intake of solid particles larger than about 0.5µm in diameter, whereas pinocytosis is the intake of droplets of extracellular fluid along with small particles. So, this is the key difference between phagocytosis and pinocytosis. Generally, phagocytosis is a mechanism for defensive purposes while pinocytosis is a mechanism to take in important materials into cells. Thus, this is the functional difference between phagocytosis and pinocytosis.

Moreover, phagocytosis forms vesicles called phagosomes, whereas pinocytosis forms vesicles called pinosomes. Also, unlike in pinocytosis, the involvement of lysosomes can be seen in phagocytosis. Hence, this is a significant difference between phagocytosis and pinocytosis. Cells uptake solid particles such as bacteria, dust, cellular parts, etc, by phagocytosis; hence, it is a type of cell eating. On the other hand, cells uptake fluids including ions, sugars, amino acids, small molecules, etc, into cells by pinocytosis; hence, it is a type of cell drinking. Therefore, this is an important difference between phagocytosis and pinocytosis. Besides, a further difference between phagocytosis and pinocytosis is that pinocytosis often occurs in the cell lining of blood capillaries, whereas phagocytosis is used by white blood cells such as neutrophils and macrophages, and protozoan.

Summary – Phagocytosis vs Pinocytosis

Phagocytosis and pinocytosis are two mechanisms by which cells uptake materials inside through the plasma membrane. The key difference between phagocytosis and pinocytosis lies in the materials taken inside. Phagocytosis uptakes solid materials while pinocytosis uptakes fluids including solutes. Furthermore, phagocytosis is a mechanism that helps in defense while pinocytosis is a mechanism for taking materials inside. Furthermore, at the end of the phagocytosis, exocytosis occurs; however, exocytosis does not occur in pinocytosis. Thus, this is the summary of the difference between phagocytosis and pinocytosis.

Reference:

1. “Pinocytosis.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 Nov. 2014, Available here.
2. “Phagocytosis.” Khan Academy, Available here.

Image Courtesy:

1. “Phagocytosis2” By GrahamColm at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. Pinocytosis” By Jacek FH – modified Image:Endocytosis types.svg, author Mariana Ruiz Villarreal LadyofHats (Public Domain) via Commons Wikimedia