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Uncategorized June 13, 2023

A Simple Introduction To Homeostasis In Animals

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A Simple Introduction To Homeostasis In Animals. Homeostasis is the regulation and maintenance of the internal environment of the body with regard to the fluctuations of the external environment.

As the external environment constantly fluctuates, organisms need to regulate and maintain their internal environment in order for them to function properly. 

Homeostasis is maintained through osmoregulation, thermoregulation, and excretion. All these terms will be explained briefly later on.

But homeostasis differs in different organisms.

For animals it is different and for man it is different.

So right now, our main focus is homeostasis in animals.

What Is The Role Of Osmoregulation in Homeostasis – And Should You Even Care About It?

First of all, yes.

You should care about it because it plays a pretty important role in Homeostasis.

Now, what is osmoregulation exactly?

So first, let’s break down Osmo and Regulation.

Osmo = body fluid

Regulation = the process of being regulated

So why do organisms need osmoregulation you may ask?

Well, it is to regulate the concentration of solute (salts) and solvent (water), which can differ in different environments as not all environments are the same.

Organisms living in freshwater have different osmoregulatory adaptations compared to organisms living in marine water.

First, we will break down some terms for you. 

Hypertonic environment 

When the concentration of salts is extreme in the surrounding environment, the cells of the organisms shrink. For example- marine water environment.

Hypotonic environment

When the concentration of the solvent (water) is extreme in the surrounding environment, the cells of the organism swell. For example- The freshwater environment.

Isotonic environment

When the concentration of solvent and solutes are equal in the surrounding environment and there is no need for osmoregulation, the cells of organisms become turgid.

Now, there are two types of organisms.


Organisms that change the concentration of solutes and solvents according to that of the external environment and become isotonic to their surrounding are known as osmoconformers.

These include all marine invertebrates and some marine vertebrates. For example- hagfishes, sharks, and rays.


These are the organisms that maintain their internal concentration of solvents and solutes differently than their external environment. 

They’ll either be hypotonic or hypertonic to their environment.

This includes almost all freshwater animals and most marine vertebrates.

Now, as mentioned before, organisms have different osmoregulatory adaptations depending on their environment.

Freshwater animals

Freshwater animals are hypertonic to their outer environment.

These animals are constantly flooded with water and so they produce diluted urine in order to store salts as the concentration of salts is very little in freshwater.

Salts are also obtained from the food they eat.

Freshwater animals like amoeba and paramecium also have “contractile vacuoles” to excrete out as much as water they can.

Marine animals

These animals are hypotonic to their outer environment.

These animals drink large amounts of water to store as much water as they can and they produce concentrated urine in order to excrete out salts.

These organisms have developed “rectal glands” that remove salts from the digestive tract which are, eliminated from the body.

Most of the bony fishes of the marine environment are osmoregulators.

Terrestrial animals

The chitinous exoskeleton in arthropods and dead keratinized skin in vertebrates prevents the loss of water as the water is not available in high quantity and direct exposure to sun evaporates the water out of the body through sweating.

Desert animals are very much resistant and they can tolerate dehydration to a certain level. 

These animals feed upon the seeds of desert plants that contain a high amount of carbohydrates, which further breaks down in the stomach and produce water.

An example of a desert animal is the Kangaroo rat.

Role Of Thermoregulation

Thermoregulation means the regulation of temperature/heat.

As the temperature of the external environment constantly fluctuates, it is mandatory for organisms to regulate their internal environment.

Now, animals can be classified based on their ability to maintain their temperature.

Piokilotherms are animals that are unable to thermoregulate within narrow limits. 

Such as all invertebrates, fishes, amphibians, and reptiles.

Hoemeotherms are animals that are able to thermoregulate and maintain a constant body temperature.

Like mammals and birds.

Ectotherms are the ones that produce metabolic heat at low levels and are also exchanged quickly with the environment. 

Such as invertebrates, fishes, amphibians, and reptiles.

Endotherms are the ones who produce heat by heat production in muscle action, by the action of hormones that increase the metabolic rate.

Such as mammals and birds.

Thermoregulation In Animals

Most of animals have a fatty layer in order to survive in cold environments, like Polar Bears.

And some of animals produce sweat by panting, such as a Dog.

But not all animals are able to maintain the heat and thus, they have behavioral adaptations.

Like sometimes the birds will migrate when the weather is extremely cold.

Or some mammals hibernate during the cold weather.

For example ground squirrel.

Excretion In Animals

Excretion is also a form of homeostasis as it eliminates all the harmful substances from the body.

Removal of waste and toxic substances, especially nitrogenous substances is known as excretion.

And it is different for animals living in different environments.

Ammonia gas- Aquatic animals

Ammonia gas is excreted by aquatic animals as it is easily soluble in water and is not harmful when mixed in.

Ammonia gas is excreted out by the gills and skin of fishes.

Animals that excrete ammonia gas as their major excretion are known as Ammonotelic.

For example, most fishes, protozoans, coelenterates, and sponges.

Urea- Terrestrial animals

Most amphibians, mammals, and a few fishes excrete urea.

Urea is a thick bowel and most terrestrial animals excrete it out because almost all the water is reabsorbed.

Animals that excrete urea as their major nitrogenous waste are called Uretelic.

Uric acid- Egg-laying vertebrates

A Simple Introduction To Homeostasis In Animals. Uric acid is excreted by birds, reptiles, insects, and snails.

Again, most terrestrial organisms excrete this thick bowel paste as most water gets reabsorbed.

These animals are called Uricotelic.

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