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Our bodies produce several kinds of wastes, including sweat, carbon dioxide gas, feces (stool or poop), and urine (pee). These wastes leave the body in different ways. Sweat is released through pores in the skin. Water vapor and carbon dioxide are exhaled from the lungs. And undigested food materials are formed into feces in the intestines and excreted from the body as solid waste in bowel movements.
Urine, which is produced by the kidneys, contains the byproducts of metabolism — salts, toxins, and water — that end up in the blood. The kidneys and urinary tract (which includes the kidneys, ureters, bladder, and urethra) filter and eliminate these waste substances from our blood. Without the kidneys, waste products and toxins would soon build up in the blood to dangerous levels .The kidneys do a lot, but their most important job is to take waste out of the blood and make urine (pee). The urinary tract takes this waste out of the body when a person pees. Besides eliminating wastes, the kidneys and urinary tract also regulate many important body functions. For example, the kidneys monitor and maintain the body's balance of water, ensuring that our tissues receive enough water to work properly and be healthy.
When doctors take a urine sample, the results reveal how well the kidneys are working. For example, blood, protein, or white blood cells in pee may indicate injury, inflammation, or infection of the kidneys, and glucose in the urine may be an indication of diabetes.
Although the two kidneys work together to perform many vital functions, people can live a normal, healthy life with just one kidney. In fact, some people are born with just one of these bean-shaped organs. If one kidney is removed, the remaining one will enlarge within a few months to take over the role of filtering blood on its own.
Every minute, more than 1 quart (about 1 liter) of blood goes to the kidneys. About one fifth of the blood pumped from the heart goes to the kidneys at any one time.
Besides filtering blood, producing urine, and making that body tissues receive enough water, the kidneys also regulate blood pressure and the level of vital salts in the blood. By regulating salt levels through production of an enzyme called renin (as well as other substances), the kidneys ensure that blood pressure is regulated.
The kidneys also secrete the hormone erythropoietin, which stimulates and controls red blood cell production (red blood cells carry oxygen throughout the body). Plus, the kidneys help regulate the acid-base balance (or the pH) of the blood and body fluids, which is necessary for the body to function normally.
The kidneys are located just under the ribcage in the back, one on each side. The right kidney is below the liver, so it's a little lower than the left one. Each adult kidney is about the size of a fist. Each has an outer layer called the cortex, which contains the filtering units.
The center part of the kidney, the medulla, has 10 to 15 fan-shaped structures called pyramids. These drain urine into cup-shaped tubes called calyxes. A layer of fat surrounds the kidneys to cushion and help hold them in place.
Here's how the kidneys filter blood: Blood travels to each kidney through the renal artery, which enters the kidney at the hilus, the indentation in middle of the kidney that gives it its bean shape. As it enters the cortex, the artery branches to envelope the nephrons — 1 million tiny filtering units in each kidney that remove the harmful substances from the blood.
Each of the nephrons contain a filter called the glomerulus, which contains a network of tiny blood vessels known as capillaries. The fluid filtered from the blood by the glomerulus then travels down a tiny tube-like structure called a tubule, which adjusts the level of salts, water, and wastes that are excreted in the urine.
Filtered blood leaves the kidney through the renal vein and flows back to the heart.
The continuous blood supply entering and leaving the kidneys gives the kidneys their dark red color. While the blood is in the kidneys, water and some of the other blood components (such as acids, glucose, and other nutrients) are reabsorbed back into the bloodstream. Left behind is urine.
Urine is a concentrated solution of waste material containing water, urea (a waste product that forms when proteins are broken down), salts, amino acids, byproducts of bile from the liver, ammonia, and any substances that cannot be reabsorbed into the blood. Urine also contains urochrome, a pigmented breakdown product of blood that gives pee its yellowish color.
The renal pelvis, located near the hilus, collects the urine flowing from the calyxes. From the renal pelvis, urine is transported out of the kidneys through the ureters, tubes that carry the urine out of each kidney to be stored in the urinary bladder — a muscular collection sac in the lower abdomen.
The bladder expands as it fills and can hold about 2 cups (half a liter) of urine at any given time (an average adult produces about 6 cups, or 1½ liters, of urine per day). An adult needs to produce and excrete at least one third of this amount in order to adequately clear waste products from the body. Producing too much or not enough urine may be a sign of illness.
When the bladder is full, nerve endings in its wall send impulses to the brain. When a person is ready to urinate, the bladder walls contract and the sphincter (a ring-like muscle that guards the exit from the bladder to the urethra) relaxes. The pee is ejected from the bladder and out of the body through the urethra, another tube-like structure. The male urethra ends at the tip of the penis; the female urethra ends just above the vaginal opening.
Like other systems in the body, the entire urinary tract is subject to diseases and disorders.
In kids, the more common problems include:
Congenital problems of the urinary tract. As a fetus develops in the womb, any part of the urinary tract can grow to an abnormal size or in an abnormal shape or position. One common congenital abnormality (an abnormality that exists at birth) is duplication of the ureters, in which a kidney has two ureters coming from it instead of one. This defect happens in about 1 out of every 125 births and can cause the kidney to develop problems with repeated infections and scarring over time.
Another congenital problem is horseshoe kidney, where the two kidneys are fused (connected) into one arched kidney that usually works normally, but is more prone to problems later in life. This condition is found in 1 out of every 500 births.
Glomerulonephritis. This is an inflammation of the glomeruli, the parts of the filtering units (nephrons) of the kidney that contain a network of capillaries (tiny blood vessels). The most common form is post-streptococcal glomerulonephritis, which usually affects young children after a case of strep throat. Most kids with this type of nephritis recover fully, but a few can have permanent kidney damage that eventually requires dialysis or a kidney transplant.
High blood pressure (hypertension). High blood pressure can happen if the kidneys are harmed by disease. The kidneys control blood pressure by regulating the amount of salt in the body. They also produce the enzyme renin that, along with other substances, controls the constriction of muscle cells in the walls of the blood vessels, which affects a person's blood pressure.
Kidney (renal) failure. This can be acute (sudden) or chronic (happening over time and usually long lasting or permanent). In either form of kidney failure, the kidneys slow down or stop filtering blood effectively, causing waste products and toxic substances to build up in the blood.
Acute kidney failure may be due to many things, including bacterial infection, injury, shock, heart failure, poisoning, or drug overdose. Treatment includes correcting the problem that led to the failure and sometimes requires surgery or dialysis. Dialysis involves using a machine or other artificial device to remove the excess salts and water and other wastes from the body when the kidneys are unable to perform this function.
Chronic kidney failure involves a deterioration of kidney function over time. In children, it can result from acute kidney failure that fails to improve, birth defects of the kidney, chronic kidney diseases, repeated kidney infections, or chronic severe high blood pressure. If diagnosed early, chronic kidney failure in children can be treated but usually not reversed. The child may require a kidney transplant at some point in the future.
Kidney stones (nephrolithiasis). Kidney stones (also called calculi) are due to a buildup of crystallized salts and minerals such as calcium in the urinary tract. They also can form after an infection. Kidney stones that are large enough to block the kidney or ureter can cause severe abdominal pain. The stones usually pass through the urinary tract on their own, but some need to be removed surgically.
Nephritis is any inflammation of the kidney. This can be caused by infection, medicines, or an autoimmune disease (such as lupus), but sometimes the exact cause isn't known. Nephritis is usually detected when protein and blood are found in the urine.
Nephrotic syndrome. This type of kidney disease leads to loss of protein in the urine and swelling of the face (often the eyes) or body (often around the genitals). It's most common in children younger than 6 years old and affects more boys than girls. It's often treated with steroids.
Urinary tract infections (UTIs). Most UTIs are caused by intestinal bacteria (such as E. coli) that are normally found in feces. These bacteria can cause infections anywhere in the urinary tract, including the kidneys. Most UTIs happen in the lower urinary tract (the bladder and urethra). UTIs affect both boys and girls, but in school-age children, girls are more likely to develop them than boys. This might be because girls have shorter urethras than boys.
Vesicoureteral reflux (VUR). In this condition, pee abnormally flows backward (or refluxes) from the bladder into the ureters. It may even reach the kidneys, where infection and scarring can happen over time. VUR occurs in 1% of children and tends to run in families. It's often detected after a young child has a first urinary tract infection. Most kids outgrow mild forms of VUR, but some can develop permanent kidney damage and kidney failure later in life.
Wilms' tumor. The most common kidney cancer in children, it's most often diagnosed in kids between 2 and 5 years of age, and affects boys and girls equally.
The urinary tract is the body’s drainage system for removing urine, which is composed of wastes and extra fluid. In order for normal urination to occur, all body parts in the urinary tract need to work together in the correct order.
Kidneys. The kidneys are two bean-shaped organs, each about the size of a fist. They are located just below the rib cage, one on each side of the spine. Every day, the kidneys filter about 120 to 150 quarts of blood to produce about 1 to 2 quarts of urine. The kidneys work around the clock; a person does not control what they do.
Ureters. Ureters are the thin tubes of muscle—one on each side of the bladder—that carry urine from each of the kidneys to the bladder.
Bladder. The bladder, located in the pelvis between the pelvic bones, is a hollow, muscular, balloon-shaped organ that expands as it fills with urine. Although a person does not control kidney function, a person does control when the bladder empties. Bladder emptying is known as urination. The bladder stores urine until the person finds an appropriate time and place to urinate. A normal bladder acts like a reservoir and can hold 1.5 to 2 cups of urine. How often a person needs to urinate depends on how quickly the kidneys produce the urine that fills the bladder. The muscles of the bladder wall remain relaxed while the bladder fills with urine. As the bladder fills to capacity, signals sent to the brain tell a person to find a toilet soon. During urination, the bladder empties through the urethra, located at the bottom of the bladder.
Three sets of muscles work together like a dam, keeping urine in the bladder between trips to the bathroom.
The first set is the muscles of the urethra itself. The area where the urethra joins the bladder is the bladder neck. The bladder neck, composed of the second set of muscles known as the internal sphincter, helps urine stay in the bladder. The third set of muscles is the pelvic floor muscles, also referred to as the external sphincter, which surround and support the urethra.
To urinate, the brain signals the muscular bladder wall to tighten, squeezing urine out of the bladder. At the same time, the brain signals the sphincters to relax. As the sphincters relax, urine exits the bladder through the urethra.
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The urinary tract is important because it filters wastes and extra fluid from the bloodstream and removes them from the body. Normal, functioning kidneys
The ureters, bladder, and urethra move urine from the kidneys and store it until releasing it from the body.
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The amount of urine a person produces depends on many factors, such as the amounts of liquid and food a person consumes and the amount of fluid lost through sweat and breathing. Certain medications, medical conditions, and types of food can also affect the amount of urine produced. Children produce less urine than adults; the amount produced depends on their age.
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DEFINITION 2-
The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys filter the blood to remove wastes and produce urine. The ureters, urinary bladder, and urethra together form the urinary tract, which acts as a plumbing system to drain urine from the kidneys, store it, and then release it during urination. Besides filtering and eliminating wastes from the body, the urinary system also maintains the homeostasis of water, ions, pH, blood pressure, calcium...
Kidneys
The kidneys are a pair of bean-shaped organs found along the posterior wall of the abdominal cavity. The left kidney is located slightly higher than the right kidney because the right side of the liver is much larger than the left side. The kidneys, unlike the other organs of the abdominal cavity, are located posterior to the peritoneum and touch the muscles of the back. The kidneys are surrounded by a layer of adipose that holds them in place and protects them from physical damage. The kidneys filter metabolic wastes, excess ions, and chemicals from the blood to form urine.
Ureters
The ureters are a pair of tubes that carry urine from the kidneys to the urinary bladder. The ureters are about 10 to 12 inches long and run on the left and right sides of the body parallel to the vertebral column. Gravity and peristalsis of smooth muscle tissue in the walls of the ureters move urine toward the urinary bladder. The ends of the ureters extend slightly into the urinary bladder and are sealed at the point of entry to the bladder by the ureterovesical valves. These valves prevent urine from flowing back towards the kidneys.
Urinary Bladder
The urinary bladder is a sac-like hollow organ used for the storage of urine. The urinary bladder is located along the body’s midline at the inferior end of the pelvis. Urine entering the urinary bladder from the ureters slowly fills the hollow space of the bladder and stretches its elastic walls. The walls of the bladder allow it to stretch to hold anywhere from 600 to 800 milliliters of urine.
UrethraThe urethra is the tube through which urine passes from the bladder to the exterior of the body. The female urethra is around 2 inches long and ends inferior to the clitorisand superior to the vaginal opening. In males, the urethra is around 8 to 10 inches long and ends at the tip of the penis. The urethra is also an organ of the male reproductive system as it carries sperm out of the body through the penis.
The flow of urine through the urethra
is controlled by the internal and external urethral sphincter muscles. The internal urethral sphincter is made of smooth muscle and opens involuntarily when the bladder reaches a certain set level of distention. The opening of the internal sphincter results in the sensation of needing to urinate. The external urethral sphincter is made of skeletal muscle and may be opened to allow urine to pass through the urethra or may be held closed to delay urination.
Maintenance of Homeostasis
The kidneys maintain the homeostasis of several important internal conditions by controlling the excretion of substances out of the body.
Filtration
Inside each kidney are around a million tiny structures called nephrons. The nephron is the functional unit of the kidney that filters blood to produce urine. Arterioles in the kidneys deliver blood to a bundle of capillaries surrounded by a capsule called aglomerulus. As blood flows through the glomerulus, much of the blood’s plasma is pushed out of the capillaries and into the capsule, leaving the blood cells and a small amount of plasma to continue flowing through the capillaries. The liquid filtrate in the capsule flows through a series of tubules lined with filtering cells and surrounded by capillaries. The cells surrounding the tubules selectively absorb water and substances from the filtrate in the tubule and return it to the blood in the capillaries. At the same time, waste products present in the blood are secreted into the filtrate. By the end of this process, the filtrate in the tubule has become urine containing only water, waste products, and excess ions. The blood exiting the capillaries has reabsorbed all of the nutrients along with most of the water and ions that the body needs to function.
Storage and Excretion of Wastes
After urine has been produced by the kidneys, it is transported through the ureters to the urinary bladder. The urinary bladder fills with urine and stores it until the body is ready for its excretion. When the volume of the urinary bladder reaches anywhere from 150 to 400 milliliters, its walls begin to stretch and stretch receptors in its walls send signals to the brain and spinal cord. These signals result in the relaxation of the involuntary internal urethral sphincter and the sensation of needing to urinate. Urination may be delayed as long as the bladder does not exceed its maximum volume, but increasing nerve signals lead to greater discomfort and desire to urinate.
Urination is the process of releasing urine from the urinary bladder through the urethra and out of the body. The process of urination begins when the muscles of the urethral sphincters relax, allowing urine to pass through the urethra. At the same time that the sphincters relax, the smooth muscle in the walls of the urinary bladder contract to expel urine from the bladder.
Production of Hormones
The kidneys produce and interact with several hormones that are involved in the control of systems outside of the urinary system.
The urinary system is susceptible to a variety of infections and other problems, including blockages and injuries. These can be treated by a urologist or another health care professional who specializes in the renal system.
The urinary system works with the lungs, skin and intestines to maintain the balance of chemicals and water in the body. Adults eliminate about 27 to 68 fluid ounces (800 to 2,000 milliliters) per day based on typical daily fluid intake of 68 ounces (2 liters), National Institutes of Health (NIH). Other factors in urinary system function include fluid lost through perspiring and breathing. In addition, certain types of medications, such as diuretics that are sometimes used to treat high blood pressure, can also affect the amount of urine a person produces and eliminates. Some beverages, such as coffee and alcohol, can also cause increased urination in some people.The primary organs of the urinary system are the kidneys, which are bean-shaped organs that are located just below the rib cage in the middle of the back. The kidneys remove urea — waste product formed by the breakdown of proteins — from the blood through small filtering units called nephrons, according to the Cleveland Clinic. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.
From the kidneys, urine travels down two thin tubes, called ureters, to the bladder. The ureters are about 8 to 10 inches long (20 to 25 centimeters), according to the Cleveland Clinic.
Muscles in the ureter walls continuously tighten and relax to force urine away from the kidneys, according to the NIH. A backup of urine can cause a kidney infection. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds.
The bladder is a hollow, balloon-shaped organ that is located in the pelvis. It is held in place by ligaments attached to other organs and the pelvic bones, according to the Kidney & Urology Foundation of America. The bladder stores urine until the brain signals the bladder that the person is ready to empty it. A normal, healthy bladder can hold up to 16 ounces (almost half a liter) of urine comfortably for two to five hours.
To prevent leakage, circular muscles called sphincters close tightly around the opening of the bladder into the urethra, the tube that allows urine to pass outside the body. The only difference between the female and male urinary system is the length of the urethra, according to Merck Manuals. In females, the urethra is about 1.5 inches (3.8 cm) to 2 inches (5.1 cm) long and sits between the clitoris and the vagina. In males, it runs the length of the penis, is about 8 inches (20 cm) long and opens at the end of the penis. The male urethra is used to eliminate urine as well as semen during ejaculation.
Different specialists treat urinary system ailments. Nephrologists treat kidney diseases, while urologists treat problems with the urinary tract, including the kidneys, adrenal glands, ureters, bladder and urethra, according to the American Urological Association (AUA). Urologists also treat the male reproductive organs, while gynecologists often treat urinary diseases or disorders in females, including yeast infections. Nephrologists and urologists often work with endocrinologists or oncologists, depending on the disease.
Urinary tract infections (UTIs) occur when bacteria enters the urinary tract and can affect the urethra, bladder or even the kidneys. While UTIs are more common in women, they can occur in men. UTIs are typically treated with antibiotics, according to Dr. Oscar Aguirre, a urogynecologist in Denver.
Incontinence is another common disease of the urinary system. It can come in the form of a pelvic prolapse, which can result in leakage and can be the result of a vaginal delivery. Then there is the overactive bladder, “which we see a lot and is not related to having children or trauma,” Aguirre said. A third condition involves overflow, in which the bladder does not completely empty.
Some common treatments involve medications, physical therapy and pelvic mesh surgery, Aguirre noted. Vaginal laser surgery is also becoming a viable treatment option, he explained. “In another 10 to 15 years, vaginal laser surgery will be another common option for the treatment of urinary conditions.”
Interstitial cystitis (IC), also called painful bladder syndrome, is a chronic bladder condition, primarily in women, that causes bladder pressure and pain and, sometimes, pelvic pain to varying degrees, according to the Mayo Clinic. It can cause bladder scarring, and can make the bladder less elastic. While the cause isn’t known, many people with the condition also have a defect in their epithelium, the protective lining of the bladder.
Prostatitis is a swelling of the prostate gland and, therefore, can only occur in men. Often caused by advanced age, symptoms include urinary urgency and frequency, pelvic pain and pain during urination, the Mayo Clinic noted.
Kidney stones are clumps of calcium oxalate that can be found anywhere in the urinary tract. Kidney stones form when chemicals in the urine become concentrated enough to form a solid mass, according to the Cleveland Clinic. They can cause pain in the back and sides, as well as blood in the urine. Many kidney stones can be treated with minimally invasive therapy, such as extracorporeal shock wave lithotripsy, which disintegrates the kidney stones with shock waves.
Kidney failure, also called renal failure and chronic kidney disease, can be a temporary (often acute) condition or can become a chronic condition resulting in the inability of the kidneys to filter waste from the blood. Other conditions, such as diabetes and hypertension, can cause chronic kidney disease, according to the Mayo Clinic. Acute cases may be caused by trauma or other damage, and may improve over time with treatment. However, renal disease may lead to chronic kidney failure, which may require dialysis treatments or even a kidney transplant.
Bladder cancer is diagnosed in about 75,000 Americans each year and is more frequent in men and the elderly according to the American Cancer Society. The symptoms, including back or pelvic pain, difficulty urinating and urgent/and or frequent urination, mimic other diseases or disorders of the urinary system.
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How does the urinary system work?
What causes problems in the urinary system?Problems in the urinary system can be caused by aging, illness, or injury. As you get older, changes in the kidneys’ structure cause them to lose some of their ability to remove wastes from the blood. Also, the muscles in your ureters, bladder, and urethra tend to lose some of their strength. You may have more urinary infections because the bladder muscles do not tighten enough to empty your bladder completely. A decrease in strength of muscles of the sphincters and the pelvis can also cause incontinence, the unwanted leakage of urine. Illness or injury can also prevent the kidneys from filtering the blood completely or block the passage of urine. How are problems in the urinary system detected?Urinalysis is a test that studies the content of urine for abnormal substances such as protein or signs of infection. This test involves urinating into a special container and leaving the sample to be studied. What are some disorders of the urinary system?Disorders of the urinary system range in severity from easy to treat to life threatening. Who can help me with a urinary problem?Your primary doctor can help you with some urinary problems. Your pediatrician may be able to treat some of your child’s urinary problems. But some problems may require the attention of a urologist, a doctor who specializes in treating problems of the urinary system and the male reproductive system. A gynecologist is a doctor who specializes in the female reproductive system and may be able to help with some urinary problems. A urogynecologist is a gynecologist who specializes in the female urinary system. A nephrologist specializes in treating diseases of the kidney. Points to Remember
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