WHAT IS CELL EXCRETION? - ANATOMY AND PHYSIOLOGY - 2025

The excretion cell is the process by which cells expelled through the membrane, the substances that they no longer useful. Carbon dioxide, water, and ammonia are the waste substances that cells generally produce. However, according to the type of organism, there are additional substances such as tannins in the case of plants, for example.

The chemical reactions that take place during this process are known as metabolism. Cellular excretion allows organisms to regulate the amount of salts or any other substance that can negatively affect their functioning. It also helps maintain your water balance.

When the substance that expels the cell has some use for the organism, then we speak of cellular secretion.

How does cell excretion occur?

This process can be given by:

Osmosis

Osmose2-fr.png: PsYcHoTiKderivative work: Ortisa, via Wikimedia Commons

During this process, the water (or the waste liquid) passes through a semi-permeable membrane. The regulation or control of water and salt levels within cells is called osmoregulation.

It is also the way to control the osmotic pressure of the cell; that is, that the compounds within the cell are neither too dissolved nor too concentrated for transport by osmosis to occur.

Osmoregulation reveals its importance when these three conditions are analyzed:

• If the cytoplasm is hypertonic, which means that the concentration of dissolved substances is higher inside the cells than in their surroundings, then the water enters the cell by osmosis and could cause them to explode if the excess is not eliminated in time.
• If the cytoplasm is hypotonic, which is the opposite of the previous process (there is a higher concentration of dissolved substances in the extracellular environment), the water will tend to leave the cell and it could dehydrate and die, if it is not replaced.
• A cytoplasm is isotonic, on the other hand, it is one in which the dissolved substances are in the same concentration inside and outside the cell. So the inflow and outflow of water is regular, equivalent.

It is worth saying that the cytoplasm is the living and fundamental part of the cell. In it are the nucleus, vacuoles and other components of it.

Diffusion

Glucose facilitated diffusion transporter type 2 (GLUT2) changes its conformation by mobilizing the binding site for glucose from the outer side to the inner side of the membrane (transporter protein). By LadyofHats (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons.

It is the process of transporting the substances of the cells from the inside to the outside and vice versa, in order to equalize their magnitudes in terms of density, temperature, etc.

We can speak of simple diffusion when any place on the cell membrane serves for the substance to pass freely through it; Whereas if the participation of a protein in the process is required, to dilute the substance, we speak of a facilitated diffusion.

Dialysis

It is the process of separating substances of different density so that their transport through the cell membrane is possible.

These forms of cellular excretion require certain types of transport of the material to be discarded. According to the waste goes towards the interior or the exterior of the cell, it is spoken of:

Endocytosis

Source: Mariana Ruiz Villarreal derivative work: Gregor_0492

It occurs when a vacuole is formed with the material to be transported into the cell. There are three types: phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Exocytosis

In this case, it is a matter of transporting large particles to the outside of the cell through vesicles that fuse with the cell membrane and then open to the outside to expel the waste.

Exocytosis can be:

• Regulated

It occurs in cells specialized in secretion, where molecules are released that fulfill certain functions for the body or that affect the physiology of other cells regardless of how far or close they are within the body.

Examples of cells in which regulated exocytosis occurs are glandular cells, hormone-producing cells, and neurons.

• Constitutive

It consists of the release of molecules that will form part of the extracellular matrix or will serve to regenerate the cell membrane itself. It is a process that occurs in all cells on a constant basis.

The integration between the molecules of the membrane of the vesicles with the plasma membrane occurs simultaneously with the excretion of the vesicular content that will go to the blood, the interstitial fluid or certain cavities of the body such as the salivary glands.

Cellular excretion and uni and multicellular organisms

Bacteria

They are the unicellular organisms responsible for consuming, by endocytosis, those substances discarded by other living beings.

Yeasts

They secrete ethyl alcohol and carbon dioxide as part of alcoholic fermentation. They also secrete B-complex vitamins and a compound called ephedrine, used in many cases to treat asthma and some allergies.

Multicellular fungi

Their excretion process occurs by exocytosis, due to the lack of excretory tissues.

Certain aquatic unicellular organisms such as paramecium, developed contractile vacuoles to get rid of excess water.

What are the products of cellular excretion for?

As stated at the beginning of this text, waste substances are generally: carbon dioxide, water and ammonia; These substances are used by other organisms for certain vital processes such as:

Aerobic bacteria, algae, and protists secrete carbon dioxide and water, necessary for photosynthesis.

Anaerobic bacteria excrete lactic acid or acetic acid, useful in making yogurt and vinegar.

Yeasts secrete ethyl alcohol, necessary in the production of liqueurs. They also excrete vitamins (of the B complex), necessary for health care, as well as the antibiotics secreted by multicellular fungi.

Likewise, there are cells that transform this waste through chemical processes to obtain the energy they require to grow and self-regenerate dead tissues.

References

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3. The illustrated little Larousse (1999). Encyclopedic dictionary. Sixth edition. International coedition.
4. The science portal (2012). Excretion is a vital function. Recovered from: clasesdejuliocesar.blogspot.com.
5. Martínez Rubiano, Valeria (2017). Cell excretion. Recovered from: emaze.com.
6. Chemistry and biology (s / f). Excretion. Recovered from: quimicaybiologia.wixsite.com.