Main Difference
The main difference between Secretion and Excretion is that the Secretion is a controlled release of a substance by a cell or a tissue and Excretion is a elimination by an organism of the waste products that arise as a result of metabolic activity.
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Secretion
Secretion is the movement of material from one point to another, e.g. secreted chemical substance from a cell or gland. In contrast, excretion, is the removal of certain substances or waste products from a cell or organism. The classical mechanism of cell secretion is via secretory portals at the cell plasma membrane called porosomes. Porosomes are permanent cup-shaped lipoprotein structure at the cell plasma membrane, where secretory vesicles transiently dock and fuse to release intra-vesicular contents from the cell.
Secretion in bacterial species means the transport or translocation of effector molecules for example: proteins, enzymes or toxins (such as cholera toxin in pathogenic bacteria for example Vibrio cholerae) from across the interior (cytoplasm or cytosol) of a bacterial cell to its exterior. Secretion is a very important mechanism in bacterial functioning and operation in their natural surrounding environment for adaptation and survival.
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Excretion
Excretion is a process by which metabolic waste
is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell. Excretion is an essential process in all forms of life. For example, in mammals urine is expelled through the urethra, which is part of the excretory system. In unicellular organisms, waste products are discharged directly through the surface of the cell.
During life activities such as cellular respiration, several chemical reactions take place in the body. These are known as metabolism. These chemical reactions produce waste products such as carbon dioxide, water, salts, urea and uric acid. Accumulation of these wastes beyond a level inside the body is harmful to the body. The excretory organs remove these wastes. This process of removal of metabolic waste from the body is known as excretion.
Green plants produce carbon dioxide and water as respiratory products. In green plants, the carbon dioxide released during respiration gets utilized during photosynthesis. Oxygen is a by product generated during photosynthesis, and exits through stomata, root cell walls, and other routes. Plants can get rid of excess water by transpiration and guttation. It has been shown that the leaf acts as an ‘excretophore’ and, in addition to being a primary organ of photosynthesis, is also used as a method of excreting toxic wastes via diffusion. Other waste materials that are exuded by some plants — resin, saps, latex, etc. are forced from the interior of the plant by hydrostatic pressures inside the plant and by absorptive forces of plant cells. These latter processes do not need added energy, they act passively. However, during the pre-abscission phase, the metabolic levels of a leaf are high. Plants also excrete some waste substances into the soil around them.
In animals, the main excretory products are carbon dioxide, ammonia (in ammoniotelics), urea (in ureotelics), uric acid (in uricotelics), guanine (in Arachnida) and creatine. The liver and kidneys clear many substances from the blood (for example, in renal excretion), and the cleared substances are then excreted from the body in the urine and feces.
Aquatic animals usually excrete ammonia directly into the external environment, as this compound has high solubility and there is ample water available for dilution. In terrestrial animals ammonia-like compounds are converted into other nitrogenous materials as there is less water in the environment and ammonia itself is toxic.
Birds excrete their nitrogenous wastes as uric acid in the form of a paste. Although this process is metabolically more expensive, it allows more efficient water retention and it can be stored more easily in the egg. Many avian species, especially seabirds, can also excrete salt via specialized nasal salt glands, the saline solution leaving through nostrils in the beak.
In insects, a system involving Malpighian tubules is utilized to excrete metabolic waste. Metabolic waste diffuses or is actively transported into the tubule, which transports the wastes to the intestines. The metabolic waste is then released from the body along with fecal matter.
The excreted material may be called ejecta. In pathology the word ejecta is more commonly used.
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Secretion (noun)
any substance that is secreted by an organism
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Secretion (noun)
the act of secreting a substance, especially from a gland
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Excretion (noun)
The process of removing or excreting.
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Excretion (noun)
Something being excreted in that manner, especially urine or feces.
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Secretion (noun)
a process by which substances are produced and discharged from a cell, gland, or organ for a particular function in the organism or for excretion
“alcohol had a stimulatory effect on gastric acid secretion”
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Secretion (noun)
a substance discharged by secretion
“hormonal secretions”
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Excretion (noun)
(in living organisms and cells) the process of eliminating or expelling waste matter.
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Excretion (noun)
a product excreted by a living organism or cell
“bodily excretions”