The main difference between pinocytosis and phagocytosis is that pinocytosis means cellular drinking whereas phagocytosis means cellular eating.
Pinocytosis vs. Phagocytosis
Pinocytosis is called cell drinking as the substances are in dissolved form and ready for cellular absorption. Phagocytosis is called cell eating as substances get broken down into simple substances with the help of enzymes for absorption. A process called engulfment is held in both Pinocytosis and Phagocytosis. In pinocytosis, infolding of the cell membrane occurs along with the extracellular fluid and the solute molecules dissolved in it. This process is called invagination. In phagocytosis, feet-like processes called pseudopodia are formed. These are extended around the molecule to be internalized and taken into the cell.
Pinocytosis is performed by all types of cell. It is generally responsible for the uptake of small molecules and solute molecules from the surroundings. Phagocytosis is performed by only phagocytic cells. It is concerned with the elimination of foreign pathogens and materials in higher animals. Pinocytic cells are not specific in the particles they invaginate whereas phagocytic cells are very specific in the molecules they engulf.
During pinocytosis, vesicles formed are of very small size about 0.5 to 5 µm in diameter and are called pinocytic vesicles and pinosomes. During phagocytosis, vesicles are formed from the engulfed particles and are called phagosomes. These phagosomes are more extensive than 0.75 µm in diameter. In pinocytosis, a small amount of energy is generated in the form of ATP whereas, in phagocytosis, a large amount of energy is given off. After pinocytosis, no exocytosis occurs whereas, after phagocytosis, foreign particles are eliminated by exocytosis.
What is Pinocytosis?
Christain de Due in 1963 gave the term endocytosis. Pinocytosis refers to the intake of substances through the plasma membrane by forming vesicles on the cell surface. Pinocytosis is the ingestion of small solute molecules by invagination into the cell. It occurs in all cells of multicellular organisms. Pinocytosis occurs through small narrow channels on the membrane. Plasma membrane surrounds the liquid molecules to pinch them off into the cell.
In the process of pinocytosis, small liquid molecules get engulfed by themselves by attaching on the surface of the plasma membrane. These small particles attach to the specific receptors located on the outer surface of the plasma membrane. Subsequently, plasma membrane forms the membrane-bounded vesicles called pinosomes which is an invaginated area encapsulating the particles. Pinosomes are formed by clathrin-coated pits. These pinosomes finally travel towards the cytoplasm and are released into the cell.
There are many examples of pinocytosis in cells. Cells take up hormones from the surrounding by pinocytosis. The epithelial cells of the ovum and intestine take up nutrients with the help of this process. Similarly, root hair cells in plants take water and solute molecules from the wet soil by this mechanism.
What is Phagocytosis?
Phagocytosis is a process in which a cell or any large particle is phagocytosed by another cell. This process is called the eating process. This occurs when another cell is stressed, old, damaged, cancerous or infected by virus or foreign. Cells engulf or eat large polar molecules, sugars and protein etc, through their hydrophobic cell membrane by the process of endocytosis. This is an energy-consuming process.
It is required by the cell to act several functions such as recycling of surface receptors, engulfing and degrading various pathogenic agents from the surrounding of cell and importing extracellular molecules into the cell. It is mostly present in the immune cells of the body. This process occurs through various receptors (immunoglobulin, mannose, ß-glucan, etc) hence regarded as a triggered process.
The plasma membrane of the cell surrounds and fuses with the molecules to be engulfed by forming pseudopodia, where phagocytic vesicles are formed called phagosomes. Food vacuole is created by the combination of the phagosomes and lysosomes of the cell. These phagosomes along with the lysosomes release digestive enzymes which help digest the phagosomes.
There are many examples of phagocytosis. For example certain protozoans (amoeba) engulf foreign food by phagocytosis. In the immune system of mammals, some foreign particles like pathogens are internalized by specialized phagocytic cells such as macrophages, neutrophils, etc. Phagocytosis can also be seen in Langerhans cells in the skin, the pigmented epithelium of the eye, Kupffer cells in the liver and microglia in the brain.
- Pinocytosis is a cell drinking whereas phagocytosis is cell eating.
- Pinocytosis has small vesicles whereas phagocytosis has large vesicles.
- Pinocytosis takes small molecules whereas phagocytosis engulfs large molecules.
- In pinocytosis, invagination happens whereas, in phagocytosis, pseudopodia form.
- In pinocytosis, energy is generated whereas, in phagocytosis, energy is taken off.
- In pinocytosis, the substance for ingested can be easily absorbed on the other hand in phagocytosis; particles must be broken down into simple substances for absorption.
It has concluded that both pinocytosis and phagocytosis are part of endocytosis. In pinocytosis, small solute molecules are taken for nutrition purpose whereas in phagocytosis large particles are eaten for defensive purpose.