The Urinary SystemThe Urinary System

Section 2Section 2

What You Will LearnWhat You Will Learn

••Describe the parts and functions of the Describe the parts and functions of the urinary system.urinary system.

Explain how the kidneys filter blood.Explain how the kidneys filter blood.••

Describe three disorders of the urinary Describe three disorders of the urinary system.system.

The Urinary SystemThe Urinary System

As blood travels through the tissues, it picks up As blood travels through the tissues, it picks up waste produced by the body’s cells. Your blood is waste produced by the body’s cells. Your blood is like a train that comes to town to drop off supplies like a train that comes to town to drop off supplies and take away garbage. If the waste is not removed, and take away garbage. If the waste is not removed, your body can actually be poisoned.your body can actually be poisoned.ExcretionExcretion is the process of removing waste products is the process of removing waste products from the body. Three of your body systems have a from the body. Three of your body systems have a role in excretion. Your integumentary system role in excretion. Your integumentary system releases waste products and water when you sweat. releases waste products and water when you sweat. Your respiratory system releases carbon dioxide Your respiratory system releases carbon dioxide and water when you exhale. Finally, the and water when you exhale. Finally, the urinary urinary systemsystem contains the organs that remove waste contains the organs that remove waste products from your blood.products from your blood.

The Urinary SystemThe Urinary System

Cleaning the BloodCleaning the BloodAs your body performs As your body performs the chemical activities the chemical activities that keep you alive, waste that keep you alive, waste products, such as carbon products, such as carbon dioxide and ammonia, are dioxide and ammonia, are made. Your body has to made. Your body has to get rid of these waste get rid of these waste products to stay healthy. products to stay healthy. The urinary system, The urinary system, shown in shown in Figure 1,Figure 1, removes these waste removes these waste products from the blood.products from the blood.

Figure 1 Urinary System

The Urinary SystemThe Urinary System

The Kidneys as FiltersThe Kidneys as FiltersThe The kidneyskidneys are a pair of organs that constantly clean are a pair of organs that constantly clean the blood. Your kidneys filter about 2,000 L of blood the blood. Your kidneys filter about 2,000 L of blood each day. Your body holds only 5.6 L of blood, so your each day. Your body holds only 5.6 L of blood, so your blood cycles through your kidneys about 350 times per blood cycles through your kidneys about 350 times per day!day!Inside each kidney, shown in Inside each kidney, shown in Figure 2,Figure 2, are more than 1 are more than 1 million nephrons. million nephrons. NephronsNephrons are microscopic filters in the are microscopic filters in the kidney that remove wastes from the blood. Nephrons kidney that remove wastes from the blood. Nephrons remove many harmful substances. One of the most remove many harmful substances. One of the most important substances removed by nephrons is urea (yoo important substances removed by nephrons is urea (yoo REE uh), which contains nitrogen and is formed when REE uh), which contains nitrogen and is formed when cells use protein for energy.cells use protein for energy.

Figure 2 How the Kidneys Filter Blood

The Urinary SystemThe Urinary System

Water In, Water OutWater In, Water OutYou drink water every day. You lose water You drink water every day. You lose water every day in sweat and urine. You need to every day in sweat and urine. You need to get rid of as much water as you drink. If get rid of as much water as you drink. If you don’t, your body will swell up. So, how you don’t, your body will swell up. So, how does your body keep the water levels in does your body keep the water levels in balance? The balance of fluids is balance? The balance of fluids is controlled by chemical messengers in the controlled by chemical messengers in the body called body called hormoneshormones..

The Urinary SystemThe Urinary System

Sweat and ThirstSweat and Thirst

When you are too warm, as the boy in When you are too warm, as the boy in Figure 3Figure 3 is, you is, you lose a lot of water in the form of sweat. The evaporation lose a lot of water in the form of sweat. The evaporation of water from your skin cools you down. As the water of water from your skin cools you down. As the water content of the blood drops, the salivary glands produce content of the blood drops, the salivary glands produce less saliva. This is one of the reasons you feel thirsty.less saliva. This is one of the reasons you feel thirsty.

Figure 3 Drinking water when you exercise helps replace the water

you lose when you sweat.

The Urinary SystemThe Urinary System

Antidiuretic HormoneAntidiuretic HormoneWhen you get thirsty, other parts of your body react to the When you get thirsty, other parts of your body react to the water shortage, too. A hormone called water shortage, too. A hormone called antidiuretic hormoneantidiuretic hormone (AN tee DIE yoo RET ik HAWR MOHN), or ADH, is released. (AN tee DIE yoo RET ik HAWR MOHN), or ADH, is released. ADH signals the kidneys to take water from the nephrons. The ADH signals the kidneys to take water from the nephrons. The nephrons return the water to the bloodstream. Thus, the nephrons return the water to the bloodstream. Thus, the kidneys make less urine. When your blood has too much kidneys make less urine. When your blood has too much water, small amounts of ADH are released. The kidneys react water, small amounts of ADH are released. The kidneys react by allowing more water to stay in the nephrons and leave the by allowing more water to stay in the nephrons and leave the body as urine.body as urine.DiureticsDiureticsSome beverages contain caffeine, which is a Some beverages contain caffeine, which is a diureticdiuretic (DIE yoo (DIE yoo RET ik). Diuretics cause the kidneys to make more urine, RET ik). Diuretics cause the kidneys to make more urine, which decreases the amount of water in the blood. When you which decreases the amount of water in the blood. When you drink a beverage that contains water and caffeine, the drink a beverage that contains water and caffeine, the caffeine increases fluid loss. So, your body gets to use less of caffeine increases fluid loss. So, your body gets to use less of the water from the caffeinated beverage than from a glass of the water from the caffeinated beverage than from a glass of water.water.

The Urinary SystemThe Urinary System

Urinary System ProblemsUrinary System ProblemsThe urinary system regulates body fluids and removes The urinary system regulates body fluids and removes wastes from the blood. Any problems with water wastes from the blood. Any problems with water regulation can become dangerous for your body. Some regulation can become dangerous for your body. Some common urinary system problems are described below.common urinary system problems are described below.••Bacterial InfectionsBacterial Infections Bacteria can get into the bladder Bacteria can get into the bladder and ureters through the urethra and cause painful and ureters through the urethra and cause painful infections. Infections should be treated early, before they infections. Infections should be treated early, before they spread to the kidneys. Infections in the kidneys can spread to the kidneys. Infections in the kidneys can permanently damage the nephrons.permanently damage the nephrons.••Kidney DiseaseKidney Disease Damage to nephrons can prevent Damage to nephrons can prevent normal kidney functioning and can lead to kidney normal kidney functioning and can lead to kidney disease. If a person’s kidneys do not function properly, a disease. If a person’s kidneys do not function properly, a kidney machine can be used to filter waste from the kidney machine can be used to filter waste from the blood.blood.

The Urinary SystemThe Urinary System

••Kidney StonesKidney Stones Sometimes, salts and Sometimes, salts and other wastes collect other wastes collect inside the kidneys and inside the kidneys and form kidney stones like form kidney stones like the one in the one in Figure 4.Figure 4. Some kidney stones Some kidney stones interfere with urine flow interfere with urine flow and cause pain. Most and cause pain. Most kidney stones pass kidney stones pass naturally from the body, naturally from the body, but sometimes they must but sometimes they must be removed by a doctor.be removed by a doctor.

Figure 4 This kidney stone had to be removed from a patient’s urinary system.

The Urinary SystemThe Urinary System

Section SummarySection Summary The urinary system removes liquid waste as The urinary system removes liquid waste as urine. The filtering structures in the kidney are urine. The filtering structures in the kidney are called called nephrons.nephrons. Most of the water in the blood is returned to the Most of the water in the blood is returned to the bloodstream. Urine passes through the ureter, bloodstream. Urine passes through the ureter, into the bladder, and out of the body through the into the bladder, and out of the body through the urethra. urethra. Disorders of the urinary system include Disorders of the urinary system include infections, kidney stones, and kidney disease.infections, kidney stones, and kidney disease.