Endocytosis is the process through which chemicals are absorbed by cells. Exocytosis is the opposite of endocytosis; it is the process through which chemicals are discharged from the cell.
In this article, we will look at the processes of endocytosis and exocytosis, as well as clinical disorders that might arise as a result of defects in these processes.
What exactly is endocytosis?
Endocytosis is the process by which cells take in things from their surroundings by enveloping them in a vesicle. Nutrients to nourish the cell or infections that immune cells engulf and kill are examples of these.
When a part of the cell membrane folds in on itself, it encircles extracellular fluid and different chemicals or bacteria. As a result, the vesicle separates and starts travelling within the cell.
Types of Endocytosis
Endocytosis is divided into two types: solid particle ingestion and solute-containing fluid ingestion. The swallowing of solid particles is referred to as phagocytosis, but the absorption of fluids containing solutes is referred to as pinocytosis.
1. Phagocytosis
Phagocytosis is also known as cell devouring in unicellular eukaryotes such as amoebas. Amoeba employs phagocytosis to consume food particles. Phagocytosis is the process by which specialised phagocytes in higher eukaryotes consume cell debris, bacteria, viruses, or even whole cells. Particles that bind to plasma membrane receptors initiate the process by forming pseudopodia that surround the particle.
2. Pinocytosis
Pinocytosis is a form of receptor-mediated endocytosis in which fluids and dissolved solutes are taken up by the cell. Clathrin-coated pits are areas of the plasma membrane that have a high concentration of receptors. In these places, the macromolecules to be taken up are bound to particular receptors. Pinocytosis is another term for cell sucking.
Functions of Endocytosis
- Taking in nutrients for cellular development, function, and repair: To function, cells require components such as proteins and lipids.
- Capturing pathogens or other unknown things that may pose a threat to the organism: When pathogens such as bacteria are recognised by the immune system, they are absorbed and eliminated by immune cells.
- Getting rid of old or damaged cells: When cells stop working correctly, they must be securely discarded to avoid causing damage to other cells. Endocytosis is the process through which these cells are destroyed.
What exactly is exocytosis?
Exocytosis is the process by which cells transport materials from inside the cell to the extracellular fluid. Exocytosis happens when a vesicle merges with the plasma membrane, releasing its contents outside the cell.
Types of Exocytosis
There are two types of secretory pathways involved in exocytosis: constitutive secretory pathways and regulated secretory pathways.
1. Pathway of Constitutive Secretion
Protein molecules that are not tagged with signal peptides are secreted via the intrinsic secretory pathway in the Golgi apparatus. Secretory vesicles store the cell’s secreted products. These vesicles are also known as dense-core vesicles because they feature a dense core. Cells emit tiny compounds like histamine as well as proteins like hormones and digestive enzymes. Secretory proteins are proteins that are meant to be secreted. These secretory proteins undergo post-translational alterations after being loaded into secretory vesicles, including the release of active compounds by proteolysis.
2. Regulated Secretory Pathway
Secretions can also be stimulated by extracellular signals. This regulated exocytosis is referred to as the controlled secretory pathway. Histamine is produced by mast cells after a soluble stimulant known as the ligand attaches to receptors on the cell’s surface. Histamine is responsible for sneezing, itching, and allergic responses. Neurotransmitters are also secreted via the regulated secretory pathway.
The function of Exocytosis
- Toxins or waste products must be removed from the cell’s inside: To sustain homeostasis, cells produce waste or poisons that must be eliminated. Cells, for example, create the waste products carbon dioxide and water during ATP synthesis in aerobic respiration. Exocytosis removes carbon dioxide and water from these cells.
- Facilitating cellular communication: Cells produce signalling molecules such as hormones and neurotransmitters to aid in cellular communication. They are distributed to other cells after being released from the cell via exocytosis.
- Facilitating cellular membrane development, repair, signalling, and migration: When cells absorb materials from outside the cell during endocytosis, they produce vesicles using lipids and proteins from the plasma membrane. When specific exocytotic vesicles merge with the cellular membrane, these resources are replenished.
Difference between Endocytosis and Exocytosis
| S.no | Endocytosis | Exocytosis |
| 1 | Endocytosis is the process by which chemicals from the external environment are taken up. | Exocytosis is involved in waste clearance and secretion of Golgi contents into the external environment. |
| 2 | Endocytosis is accomplished by both phagocytosis and pinocytosis. | Exocytosis takes place via both constitutive and controlled secretory routes. |
| 3 | Endocytosis involves the formation of an endocytic vesicle around a foreign material, which can be either solid or liquid. | The vesicle carrying the trash is fused with the plasma membrane during exocytosis to remove its contents. |
| 4 | Endocytosis results in the formation of internal vesicles similar to phagosomes. | Exocytosis results in the formation of secretory vesicles. |
| 5 | Endocytosis is demonstrated by phagocytes engulfing microorganisms. | Exocytosis is demonstrated by the release of hormones from the cell. |
Conclusion
Endocytosis is the process by which cells take in things from their surroundings by enveloping them in a vesicle, And Exocytosis is the process by which cells transport materials from inside the cell to the extracellular fluid. The active, bulk movement of products through the cell membrane is referred to as endocytosis and exocytosis. Endocytosis is the process by which cells take in things from their surroundings by enveloping them in a vesicle. Exocytosis is the process by which cells transport materials from inside the cell to the extracellular fluid. This regulated exocytosis is referred to as the controlled secretory pathway. They are distributed to other cells after being released from the cell via exocytosis. Exocytosis is involved in waste clearance and secretion of Golgi contents into the external environment.