Excretory Wastes in Animals

Introduction 

Organisms consume food for survival, development, and repair. Living creatures are essentially huge chemical laboratories. Hundreds of chemical interactions occur between diverse biomolecules in the bodies. Many of these interactions result in excretory products in animals. For example, photosynthesis is essentially a chemical process in plants. Such metabolic processes produce byproducts, which are removed through the excretion cycle.

Excretory Products of Animals

Excretion is the biochemical mechanism through which metabolic waste is removed from the body. Biomolecules, urea, serum creatinine, carbon dioxide, moisture, and ammonia are examples of excretory products.

Some molluscs and echinoderms expel waste from their bodies in the form of amino acids. Ammonia is the main excretory product of animals, and it is produced from the molecules in the food we consume. It is the most poisonous nitrogenous waste eliminated by most vertebrates and marine mammals by diffusion.

Urea is the nitrogen-containing waste excreted by mammals. It is less poisonous and has lower water solubility. Crocodiles excrete uric acid as nitrogenous waste.

In humans, this function is carried out by the kidneys, lungs, and skin. The following are the most common excretory system waste products:

• Ammonia
• CO2 (Carbon Dioxide)
• Urea
• Uric Acid
• Guanine
• Creatine

Types of Excretion

Below are the five types of excretion:

• Ammonotelism (excretion of ammonia)
• Ureotelism (excretion of urea) 
• Uricotelism (uric acid excretion)
• Aminotelism (excretion of amino acids)
• Guanotelism (excretion of guanine)

Ammonotelism

Ammonotelism refers to the process of removing ammonia from the body, and ammonotelic species are those that demonstrate this trait. This group includes most types of fish, parasitic organisms, echinoderms, poriferans, and invertebrates. Ammonia is present in the excreted wastewater of aquatic creatures in an attenuated form. It is extremely harmful to tissue growth.

Ureotelism

Urea is generated as a physiological waste product by most types of animals. These creatures are known as ureotelic. The ammonia generated in these organisms is transformed to urea in the hepatic system of mammals and discharged back into circulation.

The urea is filtered by the kidneys and removed from the body. However, some urea stays in the renal matrix for maintaining desired osmolarity. As living beings excrete urea via urine, they are ureotelic. Urea is less hazardous than ammonia.

Uricotelism

Uricotelic animals eliminate nitrogenous wastes as urinary pellets or paste. In uricotelism the water loss is less, and it is the least poisonous. As uric acid is insoluble in water, the faecal coliform bacteria form a pasty white mixture. Uricotelism is seen in a majority of reptiles, rodents, and insects.

Aminotelism

Many types of molluscs and marine invertebrates excrete nitrogenous waste in their feacal matter in the form of amino acids. This is known as aminotelism. 

Guanotelism

In spiders guanine is the metabolic waste of nucleotide metabolism. This trait can also be found in several reptiles, mammals and earthworms. As guanine is hydrophobic, therefore, it cannot be excreted with water.

The Major Organs that Excrete Waste

Ureter

A tiny tube emerges from each kidney and transports urine to the pelvic cavity.

Urinary Bladder

It is a sac-like structure where most urine is stored until micturition begins.

Urethra

It is a tube-like mechanism that stretches from the pelvic cavity and aids in the discharge of urine from the body.

Other Organs that Excrete Waste

In addition to the endocrine and exocrine organs listed above, living beings have other excretory organs as well. These are:

Skin

The skin is our body’s largest organ. Its key roles include temperature management, protection against hazardous infections, protection from sunlight and severe environmental circumstances, and support for the mechanical structure of bones and muscles.

Sweat and oil glands are found on the surface of the epidermis. Sweat glands produce sweat, a type of excretion containing NaCl, water, micronutrients, and glucose. Sebum is the discharge of the mucus membranes used to eliminate excess carbohydrates such as terpenoids and hydrocarbons.

Lungs

One of the major organs in the human body, the lungs allow gaseous exchange, in which oxygen is taken in, and carbon dioxide is expelled. As a result, lungs aid in the expulsion or elimination of carbon dioxide, a waste material for the body.

In addition to carbon dioxide, lungs expel water in the form of water vapour. The lungs expel around 18 litres of carbon dioxide per hour and 400 ml of water vapour each day.

The quantity of water expelled as vapour via the lungs is determined by the temperature of the surroundings and the state of the body. When the body’s energy levels are lower, the quantity of water condensate expelled is likewise lower.

The GI tract and the Intestines

Faeces, in addition to urine, are wastes excreted from the body. Faeces are solid waste passed by the body through the rectum. The stomach acid, particularly the intestines, is in charge of creating faeces. Additional fibre, sodium, carbohydrates, and minerals such as calcium and steel are excreted in the faeces.

Liver

The liver is essential for the synthesis and removal of urea. It reaches the kidneys, from where it is eliminated. Because RBCs are destroyed in the liver, it is regarded as regulation. RBC destruction, metabolised drug byproducts, and hormone metabolites are generated in the liver and emptied into the bile. Bile is subsequently transported to the intestines, where it is eliminated through faeces.

Salivary Glands

The primary task of salivary glands is to develop and release saliva naturally. Saliva is a fluid discharge containing enzymes that aid in the digestion of food as soon as it reaches the mouth cavity. In addition, salivary cysts are thought to play a role in the excretion of toxic metal ions such as emerging contaminants.

Conclusion

The majority of food is metabolised and used by the body to produce energy. The remaining amount is removed from the body through the stomach and digestive system in the form of faeces. This process, however, is not referred to as excretion. Rather, it is called egestion (also known as defeacation).