Major Excretory Organs and Their Functions
The excretion definition in biology states that it is the process of expelling metabolic wastes from living organisms. All animals, including humans, consume food to survive. Afterwards, several biochemical reactions take place within the body.
During the process some toxic by-products form that are harmful. Hence, the bodies release those products through excretion.
Different animals use different organs to continue this process. For humans, the major excretory organs are liver, lungs, large intestine, kidneys and skin. Following is the list of each of these organs functioning in excretion.
Kidneys regulate urinary systems.
The large intestine removes solid wastes, resulting from the digestion of food.
The lungs breathe out carbon dioxide and water vapors.
The liver deaminates excess amino acids in the blood.
The skin releases salt and excess water through sweat.
To know more about what excretion is, read this piece.
Methods of Excretion
Each living being follows distinct modes of excretion. However, some significant types are mentioned below.
Ammonotelism – It is the procedure of removing ammonia. Several aquatic insects, amphibians and bony fishes show Ammonotelic nature. Since ammonia is easily soluble, a few diffusions across the body surface are enough to drive away this substance. However, in the case of fishes, the gill surface does the same, releasing ammonium ions. It comprises the most toxic excretion in animals.
Ureotelism – Several Ureotelic animals like mammals, marine fishes, terrestrial amphibians, etc. release Urea using this process. Due to metabolism, ammonia converts into Urea in the liver of these animals, which is finally mixed in blood. Following that, the kidneys filter the blood to eliminate the waste. However, some of the urea content can remain in the kidneys that later help in maintaining osmolarity. Moreover, the most crucial nitrogenous waste in humans is Urea which is released through urine.
Uricotelism – Some animals like birds, reptiles, insects, land snails, etc. eliminate nitrogenous wastes in the form of uric acid. This whole process takes place with a loss of minimum water. Uric acid is the least toxic among other excretions.
Aminotelism – This process occurs in some echinoderms and molluscs. Amino acids are excreted by it.
Guanotelism – Animals like Scorpio, spiders, etc. excrete guanine (uric acid) using this process. It is insoluble and non-toxic. This excretory substance comes out in solid forms. Most animals of arid areas adapt to this excretion.
Do it Yourself
1. Excretion in Amoeba occurs through
a. Diffusion
b. Infusion
c. Uricotelism
d. None of these
2. Which Vessel Transports Blood to Kidneys?
a. Renal vein
b. Renal arteries
c. Both a) and b)
d. Only b)
Answers: 1-a), 2-b)
Excretion in Human
The type of excretion in humans includes the urinary system. However, skin also helps in evaporating excess water and salt through sweat glands. The entire process of formation of urine takes place in the kidney. Every day the kidneys filter approximately 180L of blood.
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The urine formation takes place in three steps. They are Glomerular filtration, absorption and secretion. Urine contains substances like Urea, potassium, sodium, creatinine, chloride and other dissolved ions. Human excretory system is a vital topic when you have to study what excretion is.
DIY: Draw a table and write down the differences between excretion and secretion.
Some Examples of Excretions
Below are a few examples of excretion in different organisms.
Amoeba excretes through its body surface.
Molluscs use nephridia as an excretory organ.
The physiology of excretion in insects includes Malpighian tubules. For example, cockroaches, grasshoppers, etc.
A kidney is the main excretory organ of almost all vertebrates.
Flatworms excrete through protonephridia.
Question: What is excretion in plants? Elucidate with examples.
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Importance of Excretion in Living Organisms
Releases toxins from the body
Lessens anxiety and the stress levels
Regulates the body temperature
Regulates the blood pressure levels
Helps the organs perform all bodily functions in a proper manner
Improves the menstrual health in women
Relieves one from chronic constipation
How to Study for Excretion from Vedantu
Vedantu has pertinent study material on Excretion and all students who need to understand the topic can read the page that’s there. The page is in the name of Modes of Excretion - Methods, Organs with Functions and Examples
This page is an ideal guidebook and has relevant matters on Excretion. Students can go through this page and make notes. They can mark all the pointers that seem important to them and then revise those before a test on the subject.
FAQs on Modes of Excretion: Key Processes and Examples
1. What are the three main modes of excretion in animals based on the type of nitrogenous waste?
The three major modes of excretion are based on the primary nitrogenous waste product expelled by an organism. These are:
- Ammonotelism: The excretion of ammonia. This is common in aquatic organisms that have access to plenty of water to dilute this highly toxic waste.
- Ureotelism: The excretion of urea. This is found in mammals and amphibians, where toxic ammonia is converted into less toxic urea in the liver, which requires less water for removal.
- Uricotelism: The excretion of uric acid. This is typical of birds, reptiles, and insects, which need to conserve water. Uric acid is the least toxic and can be excreted as a semi-solid paste with minimal water loss.
2. What is excretion and why is this process important for living organisms?
Excretion is the biological process of eliminating harmful metabolic wastes from the body. It is a vital process because the accumulation of waste products like ammonia, urea, and uric acid can become toxic and disrupt the body's internal balance, a state known as homeostasis. Proper excretion helps regulate the concentration of water and salts, maintaining a stable internal environment essential for survival.
3. What is the primary difference between ureotelic and uricotelic organisms?
The primary difference lies in the main nitrogenous waste product they excrete. Ureotelic organisms, like humans and sharks, excrete urea, which is soluble in water and moderately toxic. In contrast, uricotelic organisms, like birds and lizards, excrete uric acid, which has very low toxicity and is nearly insoluble in water, allowing them to conserve water effectively by expelling it as a thick paste or pellet.
4. How do plants carry out the process of excretion?
Plants do not have a specialised excretory system like animals but use various methods to remove waste. They excrete gaseous wastes like CO₂ from respiration and O₂ from photosynthesis through stomata. Excess water is released via transpiration. Solid wastes are often stored in plant parts like leaves, bark, or fruits that are eventually shed from the plant. Some waste products are also secreted into the soil.
5. Which organs are involved in excretion in human beings?
While the kidneys are the primary excretory organs, several other accessory organs contribute to excretion in humans. The complete system includes:
- Kidneys: Filter blood to produce urine, removing urea, excess salts, and water.
- Lungs: Expel carbon dioxide, a gaseous waste product of cellular respiration.
- Skin: Removes a small amount of urea, salts, and excess water through sweat, though its main function is cooling.
- Liver: Converts highly toxic ammonia into less toxic urea through the Ornithine cycle, which is then sent to the kidneys.
6. Why have different animals evolved to excrete different types of nitrogenous wastes?
The evolution of different excretory products is primarily an adaptation to the availability of water in an animal's habitat. Ammonia is highly toxic and requires a large amount of water for its dilution and removal, making it suitable for aquatic animals. Urea is less toxic and requires less water, making it a good strategy for terrestrial animals with regular water access. Uric acid requires very little water and is ideal for animals in arid environments or for embryos inside shelled eggs where water is limited.
7. How does the liver function as an excretory organ if it doesn't directly remove waste from the body?
The liver plays a crucial, albeit indirect, role in excretion by detoxifying substances. Its most important excretory function is the urea cycle (or Ornithine cycle), where it converts highly toxic ammonia—a byproduct of protein metabolism—into urea. This less toxic compound is then safely transported through the blood to the kidneys, which filter it out into the urine. Therefore, the liver processes the waste, preparing it for removal by the kidneys.
8. What is the main excretory product in an earthworm?
An earthworm is primarily ureotelic, meaning its main nitrogenous waste is urea. However, when living in a water-rich environment, it can also excrete a significant amount of ammonia, exhibiting both ureotelism and ammonotelism depending on conditions. Excretion in earthworms is carried out by specialised coiled tubular structures called nephridia.
9. What would happen if an organism's excretory system failed?
If an organism's excretory system failed, toxic metabolic wastes such as urea and ammonia would accumulate in the blood, a condition known as uraemia. This would disrupt the body's pH and electrolyte balance, leading to the failure of other organ systems. Without medical intervention like dialysis to artificially filter the blood, this condition is fatal as it poisons the body from within.
