Introduction
Ammonia, urea, uric acid, carbon dioxide, water, and ions such as sodium, potassium, chlorine, phosphate, sulfate, and others accumulate in animals either through metabolic activity or other mechanisms of overeating. These compounds must be removed entirely or in part. In this chapter, you’ll study the techniques that these chemicals use to get rid of them, focusing on common nitrogenous wastes. The main nitrogenous wastes emitted by mammals are ammonia, urea, and uric acid. The most harmful type, ammonia, necessitates a substantial amount of water for removal, whereas uric acid, which is the least hazardous, can be eliminated with minimal water loss. Excretory Products and their elimination are essential for living organisms to function properly.
What is an Elimination?
It is the process of an organism’s waste products being removed from its body. Waste products are undesirable and poisonous by-products that must be eliminated to maintain homeostasis and protect the organism from toxicity. Secretion is the discharge of a particularly synthesized product, whereas defecation eliminates undigested food residue from the alimentary canal. For instance, endocrine glands produce hormones, and salivary glands produce saliva.
The regulation of water content and salt concentration in an organism’s body is called osmoregulation. Homeostasis is preserving a stable internal environment despite changes in water content, solute concentrations, and the generation of hazardous waste metabolites.
Excretory Products and their Elimination Classification?
Excretory Products and their elimination classification include:
Ammonotelism is the process of excreting ammonia. Ammonotelic animals include bony fish, aquatic amphibians, and aquatic insects.
Because ammonia is so easily soluble, it is usually expelled as ammonium ions through diffusion across body surfaces or through gill surfaces (in fish). The kidneys do not remove it in any substantial way. For water conservation, terrestrial adaptation required the generation of less toxic nitrogenous wastes like urea and uric acid.
Ureotelism: Ureotelic animals are mammals, terrestrial amphibians, and marine fish that mostly excrete urea. The liver of these animals converts ammonia produced by metabolism into urea, which is then released into the bloodstream and filtered and expelled by the kidneys. Some of these animals’ kidney matrices may retain a little quantity of urea to maintain the desired osmolarity. Uric acid is excreted by reptiles, birds, land snails, and insects, the acid in the form of a pellet or pastes with the least amount of water loss. Animals with uricotelic characteristics are referred to as uricotelic.
EXCRETORY SYSTEM IN HUMANS
The excretory system in humans consists of two kidneys, one ureter, a urinary bladder, and a urethra. Kidneys are reddish-brown bean-shaped structures located near the dorsal inner wall of the abdominal cavity between the levels of the final thoracic and third lumbar vertebra. An adult human kidney averages 10-12cm in length, 5-7cm in width, and 2-3cm in thickness, with a weight of 120- 170g on average. The ureter, blood arteries, and nerves enter the kidney through a notch called the hilum, located in the center of the inner concave surface. The renal pelvis, a large funnel-shaped area with projections called calyces, is located within the hilum.
A strong capsule covers the outer layer of the kidney. There are two zones within the kidney: the outer cortex and the inner medulla.
FORMATION OF THE URINE
For Excretory products and their elimination, we must pass urine.
Urine is formed by three primary processes: glomerular filtration, reabsorption, and secretion. The nephron is a functional unit of kidney. The filtering of blood is the initial stage in the production of urine.
Glomerular filtration is the process of removing waste from the glomerulus. On the whole, The kidneys filter around 1100-1200 cc of blood every minute. Each heart ventricle pumps out approximately one-fifth of the blood 24 hours a minute. The glomerular capillary blood pressure causes blood filtration across three layers, namely the endothelium of glomerular blood vessels. Bowman’s capsule epithelial cells known as podocytes are structured in such a way as to leave certain minute spaces known as Slit holes or filtering slits. These filters sift blood so finely. There are membranes in which practically all of the plasma’s contents, except the plasma’s constituents, are contained. Proteins travel through the Bowman’s capsule lumen.
TUBULES AND THEIR FUNCTION
- PCT (Proximal Convoluted Tubule): Simple cuboidal cells line the PCT
Brush border epithelium, which enhances the reabsorption surface area. Almost all basic nutrients are present, as are 70-80% of the electrolytes. This segment re-absorbs both salt and water. PCT also aids in the maintenance of health. bodily fluids’ pH and ionic equilibrium through selective release by introducing hydrogen ions, ammonia, and potassium ions into the filtrate HCO3- absorption is a process in which HCO3- is absorbed into it.
In the ascending limb of Henle’s Loop, resorption is at a minimum. On the other hand, this region is critical to the preservation of high water levels. This function allows production of urine that is far more concentrated than blood, limiting the amount of water needed as intake for survival.
The ascending limb is made impervious to water but passively allows active or passive electrolyte transfer. As a result, it becomes less concentrated as the concentrated filtrate rises. Electrolytes travel through the medullary fluid, diluting the fluid. Conditional reabsorption of Na+ in the Distal Convoluted Tubule (DCT). Reabsorption is also possible with DCT of HCO3- and selective hydrogen and potassium ion secretion NH3 to keep the blood’s pH and sodium-potassium balance in check.
THE FILTRATE CONCENTRATION MECHANISM
For Excretory products and their elimination, Mammals can create highly concentrated urine. The Henle’s loop and the vasa recta are important in this. The filtrate flow in Henle’s loop’s two limbs is in opposite directions, forming a counter current. Blood flows in a counter-current pattern through the two limbs of the vasa recta. The proximity of the Henle’s loop and the vasa recta and the countercurrent between them aid in maintaining a rising osmolarity towards the inner medullary interstitium. NaCl and urea are the main causes of this gradient. The ascending limb transports NaCl.
The ascending section of the vasa recta returns NaCl to the interstitium. Small amounts of urea enter the ascending limb of Henle’s loop’s thin segment, which is then carried back to the interstitium by the collecting tubule. The counter-current mechanism is the above-described transport of chemicals assisted by the particular arrangement of Henle’s loop and vasa recta.
Conclusion
The lungs, liver, and skin, in addition to the kidneys, aid in the disposal of excretory wastes. CO2 is removed in enormous volumes by our lungs., 200mL (per minute), and large amounts of water every day. The largest organ is the liver. Our body’s bile-containing compounds, such as bilirubin, are secreted by this gland. Biliverdin, cholesterol, steroid hormones that have been destroyed, vitamins, and medications are all examples. The majority of these chemicals eventually pass through the digestive system with the waste material.
Sweat and sebaceous glands in the skin can remove some chemical substances as a result of their secretions. Sweat is a liquid that is produced by the sweat glands. Glands are a watery fluid containing sodium chloride, urea, and lactic acid.
Though sweat’s main purpose is to keep you cool, it also has other functions. It not only has a positive effect on the body’s surface, but it also aids in the removal of some of the body’s toxins.