Modes of nitrogen excretion

Everyday we need to egest waste from our body in the form of poop the same we need to excrete some hormones, vitamins from our body as well, that goes in the form of urine. There is a difference between egestion and excretion. I have a different post for it, but today we are only going to talk about different modes of excretion.

Related article: Difference between excretion and egestion

What is excretion ?

As I said in the above paragraph that we need to remove certain waste from the body apart from just pooping that is known as the metabolic waste which needs to be excreted in order to maintain the composition of the body fluids and tissues.

Excretion means to eliminate or to remove these waste from your body which might also cause harm if not excreted. How are these waste products formed in the first place to be eliminated ? Well, these waste products are formed due to breakdown of glucose i.e. called as catabolism, amino acids, glycerol and fatty acids.

There are many wastes apart from acids like nitrogenous waste, inorganic salts, hormones and vitamins. Such wastes are known as non-volatile wastes. The organs that excrete such wastes is known as the excretory organ.

Modes of nitrogen excretion:

There are various modes by which nitrogenous waste can be excreted from the body. Here are the types of nitrogen excretion which takes please in living organisms.

1. Ammonotelism:

The excretory product which is in the form of ammonia is ammonotelism and the animals that excrete ammonia are known as ammonotelic animals. Ammonia is highly soluble in water that makes it highly toxic, hence it cannot be kept in the body for a longer time and needs to be excreted as it is formed.

To eliminate ammonia from the body a lot water is required i.e. about 300-500ml of water is needed to eliminate one gram of ammonia from the body. Due to the need of a lot of water you can see ammonotelism in aquatic invertebrates, bony fishes, tadpole larva of frog.

Ammonia is excreted through skin, gills and kidney. It is excreted by simple diffusion so its concentration in the body is kept low.

2. Ureotelism:

The excretory product which is in the form of urea is ureotelism and the animals that excrete urea are known as uricotelic animals. Examples of ureotelic animal are, terrestrial animals like frog, turtles, toads, mammals and marine fishes

As you know some animals can't excrete ammonia due to the need of high amount of water. This ammonia is converted to a less toxic form which is urea. Ammonia combines with carbon dioxide to form urea. It is formed in the liver by ornithine cycle

This does not require more water to be excreted so moderate amount of water is required i.e. 50ml of water for one gram of urea. Urea can be stored in the body for sometime before excretion and it also excreted at a lower rate. It is soluble in water and stored in a dissolved form called urine.

3. Uricotelism: 

You might now get confused between ureotelism and uricotelism but these both are different. Ureotelism is excretion of urea and uricotelism is excretion of uric acid which is less toxic, harmless and insoluble in water that means it can be stored for a longer time in he body. 

Uric acid is excreted by animals like land snails, reptiles, birds, terrestrial insects, lizards and snakes. As uric acid is insoluble in water it is very beneficial for the desert animals. In humans and other mammals, uric acid is formed by the breakdown of purine and pryrimidine nitrogen bases of nucleic acid. 

To synthesize uric acid from ammonia requires a lot of energy. It takes place in the liver by inosinic pathway. Uric acid is eliminated in the form of solid pallets or a thick paste which does not require a lot of water but a little amount of water is enough. About 10ml of water is required for one gram of uric acid. 

4. Aminotelism: 

The excretory product in the form of amino acid is aminotelism. Again, it will be difficult and confusing between ammonotelism and aminotelism but the trick here is that ammonotelism has two "m" whereas in aminotelism there is one "m" and amino instantly reminds you of amino acid.

Amino acid is excreted by certain invertebrates like some mollusces and some echinoderms and the animals that excrete amino acid are known as amnotelic animals.

5. Guanotelism:

The excretory product in the form of guanine is guanotelism. Guanine is excreted by spiders and the animals that excrete guanine are known as guanotelic animals. 

Why is it important to excrete nitrogenous wastes ?

There is not much to think about this but a very simple and easy reason that why should nitrogenous waste be excreted from the body. 

If you read the above paragraphs you would know that the by-products that is created during the metabolic activities can cause harm to the body tissues or maybe organs, that is why it has to be excreted out as soon as it is formed. 

Nitrogenous waste tends to form ammonia, but due to the need of high amount of water to excrete ammonia this is not possible in terrestrial animals like humans, birds, etc.. To excrete ammonia it has to be converted to a less toxic form which is either urea or uric acid. 

The more ammonia is stored in the body, the pH of the body fluids will start to rise damaging the surrounding tissues or organs.

Some other nitrogenous wastes:

Apart from the nitrogenous wastes mentioned above here are some other nitrogenous wastes you might need to know maybe for your general knowledge. The following are some other nitrogenous waste:

1. Creatine and creatinine:

Our muscle cells have molecules of creatine phosphate in it, which are highly energetic molecule that stores the bioenergy like ATP

It is excreted from the body through the urine but for that creatine has to be converted to creatinine first. 

2. Trim Ethylamine Oxide (TMO):

This type of nitrogenous waste is excreted by marine Teleost fishes which is the largest infraclass in the class of Actinopterygii. 

They excrete a large amount of trim ethylamine oxide as their nitrogen waste product. Some amount of this is also stored in their body for osmoregulation. 

3. Ornithuric acid:

This type of nitrogenous waste is excreted in small amounts by birds. Ornithuric acid is formed by combining benzoic acid with amino acid ornithine. 

4. Hippuric acid:

This a less toxic form of nitrogen waste which is formed by combining benzoic acid and glycine. 

5. Bilirubin and biliverdin:

These are the bile pigments which are formed in the liver by breakdown of haemoglobin of used RBC's which is excreted though bile. 

In jaundice, our skin gets yellow is due to the increase in the level of bilirubin in the blood. 

6. Allantoin:

Allantoin is formed by oxidation reaction of uric acid catalyzed by the enzyme uricase. Higher primates including man do not have the enzyme uricase. This type of nitrogen waste is excreted by the embryos of the amniotes. 

According to Google, "Amniotes are a clade of tetrapod vertebrates comprising he reptiles, birds and mammals". When the fetus is in it's early stage the excretory matter is stored in the form of allantois.

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