10 Exocytosis Example: Explanations You Should Know

Exocytosis is the transport of larger molecules from the cytosol to the extracellular fluid by the expenditure of purinenergy in the form of ATP, so it’s active transport. Bulky materials are unable to diffuse passively through the cellular membrane due to their hydrophobicity. This process takes place through porosomes present in the plasma membrane. Exocytosis is mainly to excrete the waste products from the cell to the extracellular space. Exocytosis examples are discussed below:

  1. Transport of glucagon from the pancreas to the liver. It is processed there to facilitate absorption into the bloodstream.
  2. Transport of protein-filled vesicles from T cells to microbe-contaminated cells.
  3. Removal of carbon dioxide and water, which are waste products generated by aerobic respiration.
  4. Exocytosis facilitates the secretion of enzymes, antibodies, and peptide hormones from multiple cells.
  5. Recycling of receptors on the cell membrane
  6. Release of digestive enzymes by the pancreas.
  7. Exocytosis is involved in the formation of the cell wall in plants.
  8. Bacteria perform vascular exocytosis.
  9. Release of acetocholamine and transportation from the synaptic cleft.
  10. Macrophages are just like white blood cells and after the engulfing of pathogens, some unwanted residues are left inside the cell. These waste products can be eliminated through the process of exocytosis

Transportation of glucagon from the pancreas to the liver

Secretion of glucagon from α-cells of Islets of Langerhans regulates the release of glucose. The pancreas acts as both the exocrine and endocrine glands, releasing hormones like insulin, glucagon and somatostatin. Although these secretions are getting absorbed by cells and their target site receptors via the process of exocytosis.   

exocytosis example
Exocytosis through the plasma membrane
Image credit: Wikimedia commons

Transport of protein-filled vesicles from T cells to microbe-contaminated cells

In a viral septicity, after maturation, assembly, release and spread of virions from one cell to another, cells form extracellular vesicles to translocate these individuals from the inner region to extracellular space by adhering these vesicles to the plasma membrane and throw out the enveloped virions to an infected pathogen. And this process is taken place by exocytosis.

Exocytosis is involved in the formation of the cell wall in plants

In plants, secretory vesicles are ready to incorporate into the cell membrane and release their products outside the cell. Some polysaccharide precursors covered in exocytotic vesicles get deposited on the bi-layer membrane and result in increment girth and elongation of the cell. Lignin, which is harder than cellulose and strengthens wood tissue, is excreted by the woody plant via exocytosis and accumulates in the central lamella and cell wall.

Exocytosis is involved in the secretion of nectar from the gynoecium of the flowers to facilitate pollination. In many plants, oils are emitted through fragrant flowers, herbs, and spices. They can be purposely used for pollination and also as their defence mechanism like in mustard plant, secretory oil causes irritation in few animals thus preventing many herbivores from eating them.

Bacteria perform vascular exocytosis

Some prokaryotic eubacteria pinched off their periplasms as bacterial outer membrane vesicles (OMVs) and transmit microbial biochemical signals to eukaryotic host cells or other nearby microorganisms. Invasion of the protozoan pathogen Trypanosoma cruzi or adenovirus into host cells involves the use of lysosomal exocytosis.

Removal of carbon dioxide and water, which are waste products generated by aerobic respiration

In this example, during cellular respiration, the exchange of gases occurs through alveoli via haem proteins containing two isozymes termed Haem oxygenase-1 and Haem oxygenase2. They are the main hero of aerobic respiration whose activity depends upon the pressure gradient of different gases like oxygen, carbon dioxide, carbon monoxide, and nitrous oxide. And after the exchange of gases, cells are willing to excrete out some waste products and other by-products of the chemical reaction through the process of exocytosis. Binding affinity depends upon the pressure-concentration gradient.

Release of neurotransmitters and their transportation from the synaptic cleft

Neurotransmitters are transmitted by exocytosis. They are the chemical dialogues carried from nerve to nerve by synaptic vesicles. Synaptic vesicles are membrane sacs formed by endocytosis of the plasma membrane at presynaptic nerve endings. Vesicles filled with neurotransmitters then move towards the active zone of the plasma membrane. The influx of calcium ions creates action potentials across the membrane, allowing synaptic vesicles to fuse with the presynaptic membrane and deliver its contents to the extracellular space of neurons through exocytosis.

exocytosis example
Secretion of neurotransmitters by exocytosis
Image credit: Wikipedia

Exocytosis facilitates the secretion of enzymes, antibodies, and peptide hormones from multiple cells

Few cells produce antibodies and enzymes while some glands are there in the biological system for hormone production and these hormones should reach their target sites, they form the exocytotic vesicles to carry these materials from the source to sink via the cell membrane through exocytosis.

Regulation of receptors on cell membranes

Exocytosis plays an important role in the regulation of T cell receptor (TCR) signalling. The transport matrix is ​​involved in transporting TCRs and downstream signalling molecules to the cell surface. The formation of T-cell signalling molecules is initiated by the major histocompatibility complex (MHC) and facilitated by the exocytotic vesicles formed over the plasma membrane to transport the key molecules to the intracellular immunoreceptor consensus sites.

The formation of a structured interface among a T-cell and an antigen-presenting cell (APC), is termed the immunological synapse. Continuous delivery of TCRs to the immunological synapse is accompanied by continuous signalling T cell activation. As lytic granules are formed for transporting the signalling molecules, this is the type of lysosome-mediated exocytosis.

Release of digestive enzymes by the pancreas

Pancrease also releases some digestive enzymes through exocytosis as the exocytotic vesicle from where these enzymes are packed inside these vesicles and gets transported towards the plasma membrane and fuses up with integral proteins to exit the cell. Later, these vesicles move to the receptor site for further action and functioning. Through these chemical signals, cells can communicate with each other to maintain cells.

Conclusion

In my conclusion, exocytosis is the process to expel the cargo material from the inner side to the outer region of the cell. It also helps in the transportation of neurotransmitters, hormones, enzymes and other large molecules like protein bags, and polysaccharides from their source to their respective receptors.

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