Excretion is the process by which metabolic waste is eliminated from the body. In vertebrates, it is primarily carried out by the lungs, kidneys and skin. The process contrasts with secretion, when the substance can have specific tasks after leaving the cell. Excretion is an important component in all forms of life. For example, in mammals, urine is excreted through the urethra, which is part of the excretory system. In unicellular organisms, waste is discarded directly through the surface of the cell.
What is the biological significance of excretion?
Every organism, from the smallest protist to the largest mammal, must get rid of the potentially harmful by-products of its life. This process in living beings is called elimination, which can be seen as encompassing all the various mechanisms by which life forms utilize or throw away waste, toxic substances and dead parts of the body. The nature of the process and the specialized structures designed for waste disposal vary greatly depending on the size and complexity of the body.
Terminology
The four terms are usually associated with waste disposal processes and are often used interchangeably, although not always correctly: excretion, secretion, excretion, and excretion.
Excretion is a general term referring to the separation and release of waste or toxic substances from the cells and tissues of a plant or animal.
Separation, development and elimination of certain products resulting from the cellular functions of multicellular organisms is called secretion. Although these substances may be an unnecessary product of the cell that produces them, they are often beneficial for other cells in the body. Examples of secretion are digestive enzymes produced by cells of the intestinal and pancreas tissue of vertebrates, hormones synthesized by specialized glandular cells of plants and animals, and sweat secreted by glandular cells in the skin of some mammals. Secretion implies that secreted chemicals are synthesized by specialized cells. They have functional value for the body. Therefore, the disposal of ordinary waste should not be considered secretory.
Isolation is the act of removing unsuitable or undigested material from a cell (both in the case of unicellular organisms and from the digestive tract of multicellular animals).
Disposal - This disposal broadly defines the mechanisms for waste disposal by living systems at all levels of complexity. The term may be used interchangeably with emphasis.
In cells
Cellular respiration is when several chemical reactions occur in the body. They are known as metabolism. These chemical reactions lead to the formation of wastes such as carbon dioxide, water, salts, urea and uric acid. Accumulation of these wastes above the level inside the body is harmful. Excretory organs remove them. Excretion is the process of removing metabolic waste from the body.
In plants
Green plants produce carbon dioxide and water as respiratory products. In green plants, carbon dioxide released during respiration is used during photosynthesis. Oxygen is a by-product generated during photosynthesis and exits through stomata, root cell walls, and other pathways. Plants can get rid of excess water by transpiration and gutting.
It has been shown that the leaf acts as an “excretophore” and, in addition to being the main organ of photosynthesis, is also used as a pathway for the excretion of toxic waste through diffusion. Other wastes emitted by some plants (resin, juices, latex, etc.) are displaced from the inside of the plant by hydrostatic pressure inside the plant and due to the absorbing forces of the plant cells. However, during the pre-decay phase, leaf metabolism is high. Plants also release some waste material into the soil around them. In this case, excretion is a passive process, since it does not need additional energy.
In aquatic animals
Aquatic animals usually release ammonia directly into the environment, as this compound has high solubility. In addition, there is enough water for dilution. In terrestrial animals, ammonia compounds turn into other nitrogenous materials, since the environment has less water and ammonia itself is toxic.
In birds
Excretion in birds occurs through nitrogenous waste of uric acid in the form of a paste. Although this process is metabolically more expensive, it allows more efficient water retention. In addition, it is easier to store in an egg. Many species of birds, especially sea birds, can also secrete salt through special nasal salt glands, physiological saline leaving the nostrils in the beak.
In insects
In insects, a system including the Malpighian tubules is used to isolate metabolic waste. Metabolic waste products diffuse or are actively transported into a tube that transfers waste to the intestines. Metabolic waste is then excreted along with feces.
In animals
In animals, the main excretory products are carbon dioxide, ammonia (in ammoniotelics), urea (urethothelics), uric acid (uricotheliins), guanine (in arachnids) and creatine. The liver and kidneys cleanse the blood of many substances (for example, by renal excretion), and the purified substances are then excreted from the body with urine and feces.
The loss of water through excretion when water molecules pass through a thin membrane that contains pores that are too large for the transfer of molecules is called osmosis, a process that occurs spontaneously and does not require energy. This process can be reversed by applying hydrostatic pressure to the solution.
The level of hydrostatic pressure at which there is no pure movement of water in any direction through the membrane is called the osmotic pressure of this particular solution; the higher the concentration of dissolved molecules, the greater the osmotic pressure and the greater the force required to remove water from the solution.