At first glance, the excretory system appears to be a simple four-part organ system, but it is more complicated than this suggests. The kidneys, ureters, bladder, and urethra make up the excretory system. This system is responsible for removing waste via urine and maintaining proper chemical balances in the body. Waste gets filtered out from the blood through the kidneys, which convert it to urine and excrete it via the urethra.
For a body to be healthy and functional, internal systems must maintain physical and chemical homeostasis or a stable state of equilibrium. The excretory system is responsible for the chemical homeostasis of blood and waste. It filters the blood by maintaining the correct levels of water and dissolved substances. Required water and blood components recirculate through the body, while metabolic waste is filtered and passes through the urinary system.
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Similar to homeostasis, the excretory system also maintains osmoregulation, the management of water and salt concentrations. While homeostasis is a broader sense of balance in physiological systems, osmotic balance is important for distributing the correct levels of salt and water across the membranes of the body by ensuring appropriate levels of absorption. Neither homeostasis nor osmoregulation occurs independently, and the excretory system manages both to some degree; the kidneys perform the heavy lifting.
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The kidneys are among the most important and complex organs within the body. Simply put, the kidneys filter waste and extra water from the blood to create urine. During this process, the body maintains a healthy balance of salt, minerals, and water by removing excess acid. The kidneys are responsible for managing the balance of calcium, phosphorus, potassium, and sodium – all of which are necessary for the function of muscles and nerves.
The kidneys require advanced filtration units to maintain homeostasis and osmotic balance. Millions of nephrons help the organ achieve this. The glomerulus and a tubule make up nephrons. The glomerulus is the filter portion of the nephron, and the tubule is the mechanism for returning required substances to the blood and sending waste to the ureters.
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The kidneys have a highly advanced plumbing system. Not only is blood processed in one direction, but every tubule within a nephron must also differentiate between waste and a variety of minerals. It requires a plumbing system that recirculates some substances through absorption and also creates filtrate -- waste extracted from the blood. The filtrate is sent to tubules for additional filtration before undergoing molecular diffusion.
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The excretory system has many levels of filtration, including molecular diffusion through a concentration gradient that reabsorbs remaining water and generates highly concentrated urea. The loop of Henle, named after Friedrich Henle, makes hypertonic (highly salty) urea after it has extracted remaining water and salts that the body needs. After the filtrate passes through the loop of Henle, it is finally converted into urine as the kidneys complete the filtration process and absorb all of the water and minerals needed to maintain osmotic balance. Urine is now ready to complete its passage through the excretory system.
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Since the excretory system is constantly filtering blood throughout the day, the bladder is continually receiving urine, which is stored there until the body sends a signal to the brain reporting the bladder is full. A healthy adult can store around 16 ounces of urine in the bladder for up to five hours; hydrated adults will urinate between six and eight times each day.
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While the excretory system is highly complex, it cannot maintain homeostasis and osmotic balance alone. It must rely on other systems and organs to ensure proper functionality, including working with the digestive and respiratory systems, and organs such as the heart, liver, lungs, and skin. All of these play significant roles in maintaining a healthy balance in the body.
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Much like other systems in the body, diet and exercise play a key role in maintaining a healthy excretory system. Staying hydrated can reduce the amount of waste the kidneys must filter and help maintain osmotic balance. Exercise keeps these systems healthy and functioning correctly by increasing muscle strength. Perspiring also helps balance sodium levels in the body.
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The excretory system can provide warning signs of kidney stones and infections. Listening to the body is a good way to ensure continued health, and a few common signs are simple to monitor. The color of urine is a good indication of hydration. Symptoms such as burning or pain while urinating and an intense urge to urinate can indicate a urinary tract infection. Cloudy or smelly urine and an inability to fully empty the bladder can indicate kidney stones.
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