The excretory system – structure, functions, diseases. How is urine produced?

Every day we deliver nutrients to the body, which are then digested and processed by our body. Over time, the body begins to separate helpful and dangerous particles obtained from the food you eat. The excretory system plays a role in this process. It consists of organs that remove waste products and toxins from the body. In humans, this includes removing urea from the bloodstream and other waste produced by the body. Removal of urea occurs in the kidneys while solid waste is excreted from the large intestine. The proper functioning of the excretory system is crucial to our health as the build-up of toxic substances can be dangerous.

What is the excretory system?

The excretory system is designed to remove waste products from our body. The excretory system consists mainly of the kidneys and the bladder. The former filter urea and other waste products from the blood, which are then added to the urine in the bladder. Other organs, such as the liver, are also important, as they process the toxins but bring their waste back into the blood, so we need the kidneys to filter the blood so that no toxic substances accumulate in it.

In addition, the excretory system is also crucial in maintaining internal homeostasis. It is worth adding here that individual components of the excretory system can be influenced by other body systems, such as the muscular and skeletal systems (e.g. the kidneys secrete a hormone that instructs the bones to produce more red blood cells).

Malfunctioning of the excretory system can lead to dangerous consequences. The accumulation of urea in the blood can lead to debilitating toxic shock.

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Construction of the excretory system

The excretory system consists of:

1. kidney;
2. bladder;
3. ureters;
4. urethra.

Excretory system – kidneys

The kidneys are the main organ of the human excretory system. Each person has a pair of kidneys. They are located on each side of the spine at the level of the liver. They are protected by the ribs and back muscles, and in the case of an adult they are 5-7 cm wide, 10-12 cm long and weigh about 120-170 g.

Each kidney has an inner part called the kidney core and an outer part called the kidney cortex. The core of the kidney is made of tapered structures called pyramids. The top of each pyramid forms a renal papilla consisting of the orifices of the collecting tubes. The pyramids are separated by kidney columns known as Bertin columns.

The kidneys are made of nephrons, and each of them has as many as 1 million. The primary functions of nephrons are to conduct secretion and the excretion process. Each nephron has two parts: the glomerulus and the renal tubule.

1. Glomerulus – a collection of capillaries formed by afferent arterioles that absorb protein from the blood that travels through the body with a Malpighi body. Different arterioles transport blood from the glomerulus.
2. Kidney tubule – Bowman’s purse, which surrounds the glomeruli, forms the beginning of the renal tubule. The Malpighi body consists of a glomerulus and Bowman’s purse. The wrapped proximal tubule is a tightly coiled structure in the tubule adjacent to Bowman’s bag. The renal tubule consists of the proximal convoluted tubule (which is in the cortex and absorbs water, sodium and glucose back into the blood), the distal convoluted tubule (which reabsorbs sodium into the blood and also absorbs potassium and acid from the blood), and Henle’s loop . The Henle loop is a long U-shaped tube that has an ascending and descending arm and is another part of the tube. Many nephrons have distal, convoluted tubules that extend into the collection canal. It is mainly involved in the recovery of water and sodium chloride from the urine. Henle’s loop produces highly concentrated urine.

When talking about nephrons, it is worth noting that there are two types of nephrons, i.e. cortical nephrons, located higher in the cortex, with a short Henle loop that does not penetrate the core, and spinal nephrons, with a longer Henle loop, which runs deeper into the renal core.

Excretory system – urinary bladder

The urinary bladder is the organ that controls urination. It is a bag-like muscular structure present above the pubic bone that stores urine. The average volume of a human bladder is 400-600 ml. The urinary bladder retains urine up to its maximum capacity and expels it in the process of urination when it is full. The bladder is lined with muscle tissue that compresses when you urinate, allowing the urine to drain.

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Excretory system – ureter

Each kidney is connected to the renal pelvis by a thin and muscular tube. This tube is called the ureter. The function of the ureter is to periodically drain urine from the kidneys into the bladder.

Excretory system – urethra

The urethra is a tube made of fibromuscular tissue and emerges from the lower opening of the bladder and passes through the urogenital and pelvic diaphragms and opens out of the body through the outer opening of the urethra. It supports the removal of urine from the body. In men, it also carries sperm. The urethra is guarded by the sphincter, which relaxes when you urinate.

Other organs of excretion

In addition to the organs mentioned above, there are other organs that are involved in the excretion process.

1. Skin – is part of the integumentary system, but also plays a role in excretion through the production of sweat by the sweat glands in the dermis. Although the main role of sweat production is to cool the body and maintain temperature homeostasis, sweating also eliminates excess water and salt, as well as a small amount of urea. When sweating is profuse, intake of salt and water may be helpful in maintaining homeostasis.
2. Lungs – They are part of the respiratory system, but are also important excretory organs. They are responsible for the expulsion of gaseous waste from the body. The main waste gas released through the lungs is carbon dioxide, which is a waste product of cellular respiration in the cells of the entire body. Carbon dioxide diffuses from the blood into the air in the tiny alveoli of the lungs. By ejecting carbon dioxide from the blood, the lungs help maintain acid-base homeostasis. In fact, it is the pH of the blood that controls the rate of respiration. Water vapor is also captured from the lungs and other respiratory organs as the exhaled air passes through their moist linings and the water vapor is expelled along with the carbon dioxide. Traces of some other gases are also exhaled.
3. Liver – Has many major functions, including the secretion of bile to digest lipids, the synthesis of many proteins and other compounds, the storage of glycogen and other substances, and the secretion of endocrine hormones. In addition to all these functions, the liver is a very important excretory organ. The liver breaks down many substances in the blood, including toxins. For example, it converts ammonia, a poisonous by-product of protein catabolism, into urea, which is filtered from the blood by the kidneys and excreted in the urine. The liver also excretes bilirubin in the bile, a byproduct of hemoglobin catabolism, which is formed when red blood cells die. Bile travels to the small intestine and is then excreted with the faeces through the large intestine.
4. Large intestine – is an important part of the digestive system and the final organ of the digestive tract. As an excretory organ, its main function is to eliminate solid waste that remains after digesting food and extracting water from indigestible matter in the food waste. The large intestine also collects waste from the entire body (e.g., bile secreted into the gastrointestinal tract contains waste product bilirubin from the liver, which is the brown pigment that gives human faeces its characteristic brown color).

Excretory system – functions

The main function of the excretory system is to eliminate waste from the body, which is produced as by-products of metabolism. The excretory system works to maintain homeostasis. Homeostasis, in turn, is keeping the body in balance by maintaining a stable temperature and fluid balance. In addition to metabolic waste, there are also other chemical and hormonal wastes that are produced in the body and are excreted through various processes. However, the urinary system filters the blood from nitrogen urea, salt, and excess water and expels them from the body as urine. The kidneys also help reabsorb useful substances.

Blood filtration takes place in the nephrons in the kidneys. Millions of nephrons work together to absorb minerals such as glucose, amino acids, and salts and allow pure blood to flow to other parts of the body. The urea and excess water are converted into urine, which is passed into the bladder through the ureters and excreted from the body through the urethra. The urinary bladder holds the urine for a while until it is full and receives signals from the brain. Upon receiving the signal, the sphincters at the bladder opening relax and urine is expelled.

The excretory system – diagnostics

In the diagnosis of the excretory system, various types of tests or screening tests are used. It is important to know that the proper functioning of the urinary tract requires the coordination of the kidneys, ureters, bladder and urethra, therefore urological symptoms can have many possible causes. Your doctor may order a variety of diagnostic tests depending on your specific symptoms.

Diagnosis of the excretory system will be based, inter alia, on on urine collection and blood tests. In addition, imaging tests such as a pyelogram, cystography, CT or ultrasound of the kidneys, prostate / rectal ultrasound, and kidney angiogram are also used to provide an insight into the urinary tract for blockages, tumors, and other abnormalities. Cystometry and urine flow tests help doctors determine if your urine is working properly.

Excretory system – diseases

The excretory system may become damaged or suboptimal due to acute stress or chronic conditions.

Diseases of the excretory system – renal failure

Kidney failure is the inability of the kidneys to filter waste from the blood and maintain fluid homeostasis. It can be a result of diabetes (both type 1 and type 2) and high blood pressure, which can damage the glomerular capillaries. In addition, kidney failure can be caused by reduced blood flow caused by injury, infection in the body and bloodstream, diabetes insipidus (a disease resulting from a hormonal failure), medications, or kidney stones.

At first, symptoms of kidney failure are usually mild and may include swelling in the legs, indicating the kidney’s inability to maintain fluid homeostasis, or nausea and vomiting due to the presence of toxins in the blood. More serious symptoms of renal failure include anemia, weakness, somnolence and confusion due to changes in RBC metabolism and decreased renal excretion of erythropoietin. Kidney failure due to the excess of potassium ions can also lead to arrhythmias and changes in muscle tone and contractility.

Fortunately, kidney function can be restored by making long-term dietary and lifestyle changes. In the event that the kidneys are not working properly, efficient waste removal must be done using an external apparatus, called a dialysis machine. Sometimes a kidney transplant is also recommended.

Diseases of the excretory system – kidney stones

Kidney stones are small crystals made of minerals and salts that form in the kidneys and must eventually pass through the ureter, into the bladder, through the ureters, and ultimately from the urethra.

Kidney stones usually show no symptoms until they have moved to the ureter, where they block the flow of urine, causing the kidneys to swell and the ureter to contract. When the stones reach the ureter, you will feel pain very quickly, which may include pain in the side, back, lower abdomen, or groin. This pain comes and waves and changes in intensity. Kidney stones can also be symptoms of pain or burning when urinating, and the need to urinate more often.

Kidney stones can lead to complications such as urinary tract infections and may require surgery to remove them.

Diseases of the excretory system – kidney infections

A kidney infection, also known as pyelonephritis, is a type of urinary tract infection that reaches one or both of the kidneys.

Symptoms include fever, chills, frequent urination, persistent urge to urinate, burning sensation when urinating, nausea and vomiting, abdominal pain, blood in the urine, and mild or severe pain in the back, side, or groin.

In case of kidney infection, it is recommended that you contact your doctor as soon as possible. If left untreated, the infection can lead to permanent kidney damage or, if the bacteria spreads into the bloodstream, a life-threatening infection called blood poisoning (sepsis).

Diseases of the excretory system – urinary tract infections

Urinary tract infections are infections that occur in the kidneys, ureters, bladder, or urethra. They are caused by bacteria that enter the urinary tract through the urethra, multiplying rapidly when they reach the bladder. Urinary tract infections are quite common and generally quite painful. Urinary tract infections are easily treated with antibiotics.

Symptoms of urinary tract infections include burning when urinating, a persistent urge to urinate, passing small and frequent amounts of urine, pelvic pain, and urine that appears cloudy, red, or pale pink.

Urinary tract infections shouldn’t be taken lightly, as the bacteria that cause them tend to climb higher and higher in the urinary tract and can eventually reach the kidneys, leading to a kidney infection that can have serious consequences.

Diseases of the excretory system – glomerulonephritis

Glomerulonephritis is nothing more than glomerulonephritis, i.e. tiny capillaries in the kidneys that filter and remove excess fluid, electrolytes and waste from the blood and transport them to the urine. There are two forms of glomerulonephritis, chronic glomerulonephritis and acute glomerulonephritis with glomerulonephritis.

The former develops asymptomatically for several years, often leading to complete renal failure. Early symptoms may include blood in the urine, high blood pressure, swollen ankles or face, frequent nighttime urination, or foamy urine.

The latter develops suddenly and quickly. It can sometimes improve on its own, but if not, it can lead to acute kidney failure, chronic kidney disease, high blood pressure, or nephrotic syndrome if not treated quickly and properly. Early symptoms include facial swelling in the morning, blood in the urine, or passing urine less frequently than usual.

Glomerulonephritis can result from a wide variety of reasons, including bacterial infections (e.g. strep throat and staphylococcus), viral infections (e.g. HIV and hepatitis B and C), polyarteritis or granulomatosis, and immune disease (e.g. lupus, Goodpasture’s syndrome and Buerger’s disease).

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The excretory system – prophylaxis

In order to reduce the risk of problems with the excretory system, it is worth following these few tips.

The excretory system and proper hydration

It is assumed that a person should drink at least eight glasses of water a day. This water is filtered by the kidneys and then collected in the bladder until you feel the need to urinate. The urine in the bladder can thicken if not consumed enough water, which can lead to strong odors or irritate the bladder and make you visit the toilet more often. Concentrated urine can cause a burning sensation when urinating and increase the risk of bladder infections or kidney stones.

The excretory system and salt reduction

A salt-rich diet is associated with increased blood pressure, which in turn can lead to kidney damage. A salt-rich diet can also contribute to the development of kidney stones. To reduce your salt intake, you should pay attention to labels on processed foods, and also limit your consumption of canned soups and vegetables, cold cuts, sausages, and sausages.

The excretory system and the reduction of caffeine consumption

According to a 2011 study in the Urology Annals, drinking caffeinated beverages can irritate the bladder and act as a diuretic (increase the need to urinate by producing more urine). Too much caffeine can also cause dehydration, which can increase your risk of kidney stones, bladder infections, and other problems. Moreover, there is evidence that women with interstitial cystitis should avoid caffeine.

The excretory system and hydration in hot weather and exercise

During physical activity or in hot weather, we lose the most water from the body. The result is that we need more water than normal.

Urination and personal hygiene before and after sex

According to the Urology Care Foundation, bacteria can enter the urinary tract during sex, increasing the risk of urinary tract infections. Interestingly, urinating shortly after sex and wiping off have been shown to reduce the risk of developing an infection.

Urinary tract infections are believed to be more common in women after intercourse because they have shorter urethra than men. This makes it easier for the bacteria to enter the urinary tract. While rare, men can also become infected with urinary tract infections, and they can also transmit pathogens to women. The groin is a major source of bacteria, so men should clean their groin area as part of good personal hygiene.

Proper hygiene of intimate places after defecation

For women, it is very important for ladies to rub from front to back to ensure that bacteria do not come into contact with the vagina so urinary tract infections do not develop.

The excretory system and the bladder

The bladder is made of muscles that expand as it inflates and contract when it is time to empty. It’s best not to wait too long to urinate, which can stretch your bladder over time. Future problems can include incomplete emptying, recurring infections, and urine traveling all the way to the kidneys.

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Excretory system – how is urine formed?

Urine is generated in nephrons and the elimination process is divided into stages.

The first stage (glomerular filtration) of urine formation occurs in the glomeruli of the kidneys. Blood enters the glomerular capillaries through the afferent arterioles and exits through the efferent arterioles. In this process, excess water, ions, glucose, and waste products are removed from the blood into urine, which is then eliminated from the body. The glomerular filtrate consists of water, glucose and urea ions. Therefore, these essential substances must be reabsorbed by the body. This happens through reabsorption (reabsorption).

This is the second stage of urine formation and it is a very important step as it ensures that the necessary substances and ions are expelled from the body. In this process, ions and substances such as sodium ions, glucose, amino acids, water, etc. are absorbed. It also ensures less water loss. There are two types of transport that occur during reabsorption.

1. Active transport – glucose and ions are absorbed by active transport.
2. Passive transport – water is absorbed by passive transport.

Among the tubules carrying out the reabsorption process, the following elements are mentioned.

1. Kanalik proximalnywhich reabsorbs ions, water and nutrients from the filtrate. By releasing potassium, hydrogen and ammonia into the filtrate and reabsorbing bicarbonate ions from the filtrate. It also eliminates toxins from the filtrate, helps to regulate the ionic balance and pH of body fluids. thus maintaining the pH of the filtrate.
2. Ascending arm of Henle’s loopwhich enables the reabsorption of sodium and chlorine ions from the filtrate.
3. Descending arm of Henle’s loopwhich is impermeable to water but permeable to electrolytes. The transfer of electrolytes from the filtrate to the marrow fluid dilutes the filtrate. It allows the reabsorption of water.
4. Kanalik distalny, reabsorbing selective ions from the filtrate, including sodium chloride ions. It is also responsible for the reabsorption of water and sodium ions. It also helps to maintain pH and ion balance by secreting and reabsorbing ions such as PCT.
5. Cumulative channelwhich connects the nephron to the smaller renal calyx or renal pelvis and reabsorbs a significant amount of solutes and filtrate water.

With the third stage, waste ions such as hydrogen and potassium and ammonia are released, which are then mixed with urine and excreted from the body. After a series of these processes, the bladder fills with urine. After the signal from the brain, the bladder relaxes and releases urine from the body in the process of voiding or urinating.

Urination occurs when the bladder is stretched and filled with urine produced by the nephron. Receptors on the walls of the bladder transmit signals to the central nervous system, allowing the muscles of the sphincter to relax and pass urine.