Excretory System
The process of removing the metabolic waste and excess water from the body is known as excretion. Each organ, but particularly the excretory system, plays a unique role in maintaining homeostasis.
Most of the products reaching the excretory system are metabolised and excreted by the body through sweat, urine, and faeces. The excretory system, also known as the urinary system, consists of kidneys, ureters, bladders, and urethra (Fig. 1.5). In addition to eliminating metabolic waste, the urinary system also regulates the pH of the blood, regulates levels of metabolites and ions such as sodium, potassium, and calcium, and regulates blood pressure and volume. Based on their evolutionary history, surroundings, and feeding and drinking habits, animals produce waste in various ways. These factors regulate water consumption in animals, and most metabolic waste must be dissolved in water before it can be expelled. The most significant by-product of food metabolism is ammonia, produced by the breakdown of proteins and is highly toxic to the body if stored. Thus, based on the amount of accessible water and the animal’s ability to store it, animals transform this ammonia into either urea or uric acid.
Fig. 1.5 Description of excretory system in animals. (Courtesy: BioRender)
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Fun Fact
If one kidney fails to function and is removed, the other kidney can increase in size by 50% within months to handle the entire task of filtration.
The end product of filtration in aquatic animals produces ammonia, expelled directly into the surrounding environment. In comparison, through the process of detoxification, terrestrial mammals convert ammonia-like compounds along with CO2 into urea in their livers. Birds excrete nitrogenous wastes in the form of uric acid.
Even though this process requires more energy, it allows less water to spare, and waste can be excreted as a paste. The kidneys begin by filtering out a large amount of fluid and compounds dissolved in the blood, then reabsorbing around 99% of it before excreting the remaining 1% in the form of urine. Thus, the majority of animals’ excretory systems are not exclusively dedicated to excretion but are also well suited for reabsorption. Further detailed description of kidney and its working force are mentioned in the respective chapter.There are numerous renal disorders in canines; one of the most devastating is chronic kidney disease (CKD). Previously, it was routine treatment with management practices like feeding renal diet, with mediations to prevent load on kidneys. Nevertheless, recently, with the knowledge of stem cells, researchers have bought up with adipose-derived stem cells (ADSCs) therapy. On conducting research, they could conclude that intravenous injection of ADSCs can improve the kidney recovery rate and functional capability in dogs suffering from CKD. In terms of animal welfare, stem cell therapy proved to be adequate to combat CKD.
Another field in nanoscience has the unlimited potential of overthrowing the present medication routines. Nanoscale and novel physiological engineering applications can answer the new dimensions of renal dialysis. Recently, many techniques like permeable selective membrane and nanoscale fabrication process have jumped into the market to treat dogs suffering from renal failure. Various electrokinetic methods for fluid treatment have emerged; for instance, the ion concentration polarisation (ICP) technique which is a part of an electroki- netic purification system acts as an artificial kidney. Through this, a peritoneal dialysis-based wearable artificial kidney device has been a device for end-stage renal disease dogs (ESRD). For dogs exposed to this technique, 10% of toxins were reduced by 3 h. By this, one can expect the wearable artificial kidney to advance more for quality ESRD dogs in the future.
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