Excretion vs Secretion: Difference and Comparison

Many biological processes take place inside a living organism. All these processes have different and specific role to play. These processes are vital for the survival of living organisms.

Scientists have researched a lot to understand many such processes, and two are excretion and secretion.

Key Takeaways

1. Excretion is the process of eliminating waste products from an organism’s body through urine, feces, sweat, or breath.
2. On the other hand, secretion is the process by which substances such as enzymes, hormones, or mucus are produced and released by cells or glands.
3. Excretion and secretion are vital for maintaining homeostasis, but their functions, mechanisms, and products differ.

Excretion vs Secretion

Excretion refers to releasing waste products from the body through urine, faeces, etc. Organs like kidneys and liver are responsible for the excretion process. Secretion is the release of substances like enzymes into the body to perform various functions, like breaking down food in the body.

Also, excretion is an external process, whereas secretion is an internal process.

Comparison Table

Parameter of Comparison	Excretion	Secretion
Type of materials released	In excretion, waste materials are released that cannot be used further.	In secretion, unwanted materials are released that can be used further.
Process type	It is a passive process.	It is an active process.
Materials released	The materials secreted in the body are hormones, enzymes, and saliva.	The materials which are secreted in the body are hormones, enzymes, and saliva.
Body parts involved	The parts involved in the process are: 1) Lungs 2) Skin 3) Tear ducts 4) Rectum	The parts which are involved in the process are: 1) Endocrine glands 2) Digestive glands 3) Salivary glands 4) Sliver 5) Pancreas 6) Gallbladder
Released Materials	The materials released are tears, sweat, and urine.	The materials released are saliva and hormones.

What is Excretion?

The cells in an organism’s body have to do some biochemical reactions to survive, and when these reactions occur, some by-products are formed. These by-products are lethal and toxic to the cell if they accumulate; therefore, in excretion, all these wastes are thrown out of the body.

In short, excretion is a process in which the waste products are thrown out of the body.

Excretion is also essential for many other things like Osmoregulation, and osmoregulation is essential because it provides a suitable environment for the cells to do the required reactions properly.

All organisms have different methods of secretion depending upon their species and type. Some examples of excretion in different organisms are:

1. Excretion in Unicellular Organisms: This process is simple in unicellular organisms. They mostly feed through the process of phagocytosis. During this process, the cell membrane gets folded inwards to create a food blister, and then this folded thing is taken into the cytoplasm of the cell, where digestive enzymes perform their task. After the food gets digested, the cyst’s remains, also known as waste, are removed by exocytosis.
2. Excretion in Animals:  The smallest and thinnest organisms excrete through their skin, which later diffuses away over time, and the other big animals have specialized organs and systems, especially for excretion.
3. Excretion in Plants: Just like animals, plants also undergo excretion. Small plants excrete wastes over their surfaces’ cells, whereas the larger vascular plants have a method of excretion in which the leaves play an important part.

The stoma, the series of openings in the leaves, lets oxygen (the waste product) out, bringing in fresh carbon dioxide the plants require.

What is Secretion?

Secretion is the process in which organisms actively move molecules manufactured within a cell to space outside of the cell. The substances secreted are functional proteins and many non-proteins, such as steroids.

Secreted substances are sometimes useful and sometimes useless for the body. Secretion occurs via many pathways depending on the cell type and the substance transported.

Some of the major secretory pathways are:

1. The ER-Golgi Pathway and Porosomes: In this type of pathway, the secretory products are first produced in the endoplasmic reticulum, which is then inserted into spherical containers like vesicles, known as transport vesicles, made up of lipid bilayer. These products then pass through the Golgi apparatus, where they are modified and then packaged into specialized secretory vesicles.
2. Membrane Transports: In some cases, the proteins in the cytosol move across the cell membrane through transporter proteins and not via exocytosis. In this case, the products are not packaged in vesicles but are transported individually by specialized proteins in the cell membrane.
3. Lysosomes: These are organelles that are generally thought to be important only for dehydration but in reality, they also play an important role in secretion. The lysosomal secretory pathway is frequently used in specialized cell types like pigment and blood stem cells.

Like secretory vesicles, lysosomes can also fuse with the cell membrane to release their contents, but a different kind of protein is used for the fusion process.

Main Differences Between Excretion and Secretion

1. In excretion, waste materials cannot be used further; in secretion, unwanted materials can be used further.
2. Excretion is a passive process, whereas secretion is an active process.
3. The materials excreted from the body are carbon dioxide, sweat, tears, faeces, and urine, whereas the materials secreted in the body are hormones, enzymes, and saliva.
4. The parts involved in the excretion are the lungs, skin, tear ducts, and rectum. In contrast, the parts involved in the secretion are the Endocrine glands, digestive glands, salivary glands, liver, pancreas, and gallbladder.
5. The materials released through excretion are tears, sweat, and urine, whereas those released through secretion are saliva and hormones.

References

1. http://search.ebscohost.com/login.aspx?direct=true&profile=ehost&scope=site&authtype=crawler&jrnl=21571716&AN=17656530&h=NRGnTXm57k6dyGteBMjUaPcmMG8EEar4FslkgywMFNNpB3wCVSgJsvMGih5Kgh5Yi7b7v5iuFaqMPwgKAAwX2g%3D%3D&crl=c
2. https://www.translationalres.com/article/0022-2143(64)90136-2/abstract