Why is phagocytosis and pinocytosis important?

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.

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

Cells are the smallest unit of life. Both phagocytosis and pinocytosis are essential for a cell to survive. All organisms on this earth follow similar biochemical processes and out of them, endocytosis is the one that has two parts, phagocytosis and pinocytosis. 

Phagocytosis vs Pinocytosis

The main difference between Phagocytosis and pinocytosis is that phagocytosis is a process where small particles larger than 0.5 μm are ingested and eliminated by cell. A process where liquid is ingested by cell through small vesicles budded on plasma membrane is called pinocytosis.

Phagocytosis is a cellular process where a cell engulfs foreign particles such as viruses, dust, bacteria etc. with the help of pseudopodia also known as false feet. This is an active process which requires ATP for the activation. The process protects the body from many diseases from viruses, bacteria etc.

Pinocytosis is a cellular process where a cell absorbs nutrients from surrounding fluids.this is also an active process requiring ATP. The nutrients are taken up from the fluids outside the cell. The process plays a significant role in cell growth. The plasma membrane folds itself and absorbs the materials.

Comparison Table Between Phagocytosis and Pinocytosis

What is Phagocytosis?

Phagocytosis occurs when a cell destroys foreign pathogens such as bacteria, viruses etc. by engulfing them with the help of certain lytic enzymes.. Single-celled organisms such as amoeba also show similar process.

Phagocytic cells, i.e. macrophages and neutrophils in humans protects the body from various kinds of bacteria, viruses and foreign particles. Phagocytosis plays a vital role in human body.

Phagocytosis is an important part of the immune system carried out by phagocytic cells specialized to carry phagocytosis, i. e., neutrophils and macrophages. The immune system prevents the spread of infections and destroys the pathogens with the help of lymphocytes.

Phagocytosis is different from other types of endocytosis because it is very specific and relies on the cell’s ability to bind to the pathogen entered and engulf it. Phagocytosis occurs only when the particle comes in direct physical contact with the cell.

Several cells work for immune system including neutrophils, macrophages, dendritic cells, and B lymphocytes do phagocytosis continuously. The act of engulfing pathogenic particles makes immune system aware of the enemy and prepares it for the next time. Knowing the enemy allows immune system to specifically target similar particles circulating in the body and next time when they enter are killed before they start harming the body.

What is Pinocytosis?

Pinocytosis is the process by which a cell forms a special vesicle called Pinosome and ingests small particles present in extracellular fluid.

The term pinocytosis is derived from two Greek words: ‘pino’ means ‘to drink’ and ‘kytos’ means ‘cell.’ As a result, the term is an abbreviation for “cell drinking.”

 It entails the transport of extracellular fluids along with their content, which are small dissolved molecules. 

As a result, pinocytosis is classified as a type of endocytosis. Pinocytosis needs a significant amount of energy to function and the energy comes in the form of ATP. Therefore, it is a process that includes active transport. Certain ions or amino acids can initiate pinocytosis as the process is not substrate specific.

During this process, the cell drinks surrounding fluids along with the particles present in them. This process can also be called the Engulfing Extracellular Fluid process. Various ions and molecules activate the plasma membrane and start the process where the plasma membrane develops small cavities and absorbs the materials present in the fluids.

Being an active form of transport, it plays an important role in many cellular processes. Excretion of waste material and cleaning of kidneys include some of the important processes in human body.

Main Differences Between Phagocytosis and Pinocytosis

1. Phagocytosis is the process of ingestion of solid particles through the plasma membrane via lysosomes whereas Pinocytosis is the process of ingestion of small liquid particles through the plasma membrane via pinosomes.
2. Phagocytosis develops false feet called pseudopodia to engulf particles whereas in pinocytosis, engulfment occurs via invagination or infoldings.
3. Lysosomes have an important role in phagocytosis but no role in pinocytosis.
4. Phagocytosis has the protective role, i.e., to protect the body from foreign particles whereas pinocytosis absorbs important nutrients such as amino acids, sugars etc.
5. Phagocytosis is substrate specific and only allows certain materials to pass through plasma membrane but pinocytosis takes up all the surrounding liquid and is not substrate specific.

Conclusion

Both the processes, i.e. phagocytosis and pinocytosis are biochemical processes which play a very important role in a cell’s life. Cell being the basic unit of life has to undergo many processes in order to survive. Phagocytosis and pinocytosis, both are active processes requiring ATP and different vesicles to absorb and engulf food particles. In both the processes particles are absorbed but the main purpose is different. Phagocytosis where foreign particles are engulfed and pinocytosis where a cell absorbs nutrients. Even after having major differences, these processes are serving the same purpose and that is feeding the cell and in turn the whole body. Both of these are the processes included in endocytosis.

References

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