CK-12 Life Science

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by CK-12 Foundation


  Pneumonia is a disease in which the alveoli fill up with fluid. How might this affect the lungs’ ability to absorb oxygen?

  How can washing your hands help prevent you from catching a cold?

  Vocabulary

  acute disease

  A disease that lasts a short time.

  allergen

  Any antigen that is not an infectious organism, such as mold, dust, or pet hair.

  asthma

  A chronic illness in which the bronchioles are inflamed and become narrow.

  bronchodilators

  Drugs that reduce inflammation of the bronchioles allowing air through.

  bronchitis

  An inflammation of the bronchi.

  chronic bronchitis

  Having a cough that produces phlegm, for at least three months in a two-year period.

  chronic disease

  A disease that lasts for a long time, perhaps a few years or longer.

  chronic obstructive pulmonary disease (COPD)

  A disease of the lungs in which the airways become narrowed; leads to a limitation of the flow of air to and from the lungs causing shortness of breath.

  emphysema

  A chronic lung disease caused by loss of elasticity of the lung tissue.

  environmental tobacco smoke (ETS)

  Secondhand smoke, which greatly increases the risk of lung cancer and heart disease in nonsmokers.

  lifestyle disease

  A disease that is caused by choices that people make in their daily lives.

  lung cancer

  A disease where the cells that line the lungs grow out of control; the growing mass of cells pushes into nearby tissues and can affect how these tissues work.

  pathogen

  An organism that causes disease in another organism; certain bacteria, viruses, and fungi are pathogens of the respiratory system.

  pertussis

  Whooping cough; gets its name from the loud whooping sound that is made when the person inhales during a coughing fit.

  pneumonia

  An illness in which the alveoli become inflamed and flooded with fluid.

  respiratory disease

  A disease of the lungs, bronchial tubes, trachea, nose, and/or throat.

  tuberculosis (TB)

  A common and often deadly infectious disease caused by a type of bacterium called mycobacterium.

  Points to Consider

  The respiratory system gets rids of a certain type of wastes. What type of wastes do you think are removed by your respiratory system?

  Lesson 19.3: Excretory System

  Lesson Objectives

  Identify the functions of the excretory system.

  List the organs of the excretory system.

  Describe the parts of urinary system.

  Outline how the kidneys filter blood.

  Identify three disorders of the urinary system.

  Check Your Understanding

  What are some "wastes" that must be removed from your body?

  Do your circulatory and respiratory systems remove "waste?"

  Introduction

  One of the most important homeostatic jobs your body does is to keep the right amount of water and salts inside your body. Too much water and your cells would swell and burst. Too little water and your cells would shrivel up like an old apple. Either extreme would cause illness and death of cells, tissues, and organs. The organs of your excretory system help to keep the correct balance of water and salts within your body.

  Your body also needs to remove the wastes that build up from the metabolic activity of cells and digestion. These wastes include carbon dioxide, urea, and certain plant materials. If these wastes were not removed, your cells would stop working and you would get very sick. In this lesson you will learn how waste is removed from the body, and how the kidneys filter waste from the blood.

  The Excretory System

  The excretory system is the organ system that maintains homeostasis by keeping the correct balance of water and salts in your body. It also helps to release wastes from the body. Excretion is the process of removing wastes from the body. The organs of the excretory system are also parts of other organ systems. For example, your lungs are part of the respiratory system. Your lungs remove carbon dioxide from your body so they are also part of the excretory system. More organs of the excretory system, and the other organs systems of which they are part are listed in Table (below).

  Table 1: Organs of the Excretory System

  Organs of the Excretory System Organ(s) Function Other Organ System of which it is Part

  Lungs Remove carbon dioxide Respiratory system

  Skin Sweat glands remove water, salts, and other wastes Integumentary system

  Large intestine Removes solid waste and some water in the form of feces Digestive system

  Kidneys Remove urea, salts, and excess water from the blood Urinary system

  Functions of the Excretory System

  The excretory system controls the chemical make-up of body fluids. The organs of the excretory system remove metabolic wastes. They also maintain the proper concentrations of water, salts, and nutrients in the body. In this way the excretory system has an important homeostatic job.

  Your body takes nutrients from food and uses them for energy, growth, and repair. After your body has taken what it needs from the food, waste products are left behind in the blood and in the large intestine. These waste products need to be removed from the body. The kidneys work with the lungs, skin, and intestines to keep the correct balance of nutrients, salts and water in your body.

  The Urinary System

  Sometimes and confusingly, the urinary system is called the excretory system. But, the urinary system is only a part of the excretory system. Recall that the excretory system is made up of the skin, lungs, and large intestine as well as the kidneys. The urinary system is the organ system that makes, stores, and gets rid of urine. It includes two kidneys, two ureters, the bladder, and the urethra. The urinary system is shown in Figure below.

  Figure 19.13

  The kidneys filter the blood that passes through them and the urinary bladder stores the urine until it is released from the body.

  Organs of the Urinary System

  As you can see from Figure 1, the kidneys are two bean-shaped organs. The kidneys filter and clean the blood and form urine. They are about the size of your fists and are found near the middle of the back, just below your rib cage. The ureters are tube-shaped structures that bring urine from the kidneys to the urinary bladder. The urinary bladder is a hollow, muscular, and elastic-walled organ. It is shaped a little like a balloon. It is the organ that collects urine which comes from the kidneys. Urine leaves the body through the urethra.

  What is Urine?

  Urine is a liquid that is formed by the kidneys when they filter wastes from the blood. Urine contains mostly water and also dissolved salts and nitrogen-containing molecules. The amount of urine excreted from the body depends on many things. Some of these include the amounts of fluid and food a person consumes and how much fluid they have lost in sweat and breathing.

  Urine ranges from colorless to dark yellow, but is usually a pale yellow color. Dilute urine is light yellow in color. Concentrated urine is dark yellow or may be brown. The darker the urine, the less water it contains.

  The urinary system removes a type of waste called urea from your blood. Urea is a nitrogen-containing molecule that is made when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea and other wastes are carried in the bloodstream to the kidneys where they are removed and form urine.

  How the Kidneys Filter Wastes

  The kidneys are important organs in maintaining homeostasis. Kidneys perform a number of homeostatic functions:

  Maintain the volume of body fluids

  Maintain the balance of salt ions in body fluids

  Excrete harmful nitrogenous wastes (metabolic by-products) such as urea,
ammonia, and uric acid

  There are many blood vessels in the kidneys, as you can see in Figure below. The kidneys remove urea from the blood through tiny filtering units called nephrons. Nephrons are tiny, tube-shaped structures found inside each kidney. A nephron is shown in Figure below. Each kidney has up to a million nephrons. Each nephron collects a small amount of fluid and waste products from a small group of capillaries. If the body is in need of more water, water is removed from the fluid inside the nephron and is returned to the blood. The fluid within nephrons is carried out into a larger tube in the kidney called a ureter which you can see in Figure below. Urea, together with water and other wastes, forms the urine as it passes through the nephrons and the kidney.

  Figure 19.14

  Structures of the kidney; fluid leaks from the capillaries and into the nephrons where the fluid forms urine then moves to the ureter and on to the bladder.

  Figure 19.15

  The location of nephrons in the kidney; the glomerulus is the network of blood vessels that filter liquid into the nephron. The fluid collects in the nephron tubules, and moves to the bladder through the ureter.

  Formation of Urine

  The process of urine formation is as follows:

  Blood flows into the kidney through the renal artery, shown in Figure 2. The renal artery branches into capillaries inside the kidney. Capillaries and the nephrons lie very close to each other in the kidney.

  The blood pressure within the capillaries causes water and solutes such as salts, sugars, and urea to leave the capillaries and move into the nephron.

  The water and solutes move along through the tube-shaped nephron to a lower part of the nephron. At this point most of the water and solutes are returned to the capillaries that surround the nephron.

  The fluid that remains in the nephron at this point is called urine.

  The blood that leaves the kidney in the renal vein has much less waste than the blood that entered the kidney.

  The urine is collected in the ureters and is moved to the urinary bladder where it is stored.

  Nephrons filter 125 ml (about ¼ cup) of body fluid per minute. In a 24-hour period nephrons produce about 180 liters of filtrate, of which 178.5 liters are reabsorbed. The remaining 1.5 liters of fluid forms urine.

  Urine enters the bladder through the ureters. Similar to a balloon, the walls of the bladder are stretchy. The stretchy walls allow the bladder to hold a large amount of urine. The bladder can hold about 400 to 620 mL (about 1½ to 2½ cups) of urine, but may also hold more if the urine cannot be released immediately. Urination is the process of releasing urine from the body. Urine leaves the body through the urethra.

  Nerves in the bladder tell you when it is time to urinate. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The urge to urinate becomes stronger as the bladder continues to fill up.

  Kidneys play a large role in regulating the amount of water in urine. With the help of hormones such as antidiuretic hormone, aldosterone, and angiotensin II, when necessary the kidneys can reabsorb water and prevent it from being excreted. This is known as osmoregulation.

  Brain Control

  The kidneys never stop filtering waste products from the blood, so they are always producing urine. The amount of urine your kidneys produce is dependent on the amount of fluid in your body. Your body loses water through sweating, breathing, and urination. The water and other fluids you drink every day help to replace the lost water. This water ends up circulating in the blood because blood plasma is mostly water.

  The kidneys will normally adjust to the level of water a person drinks. For example, if a person suddenly increases their water intake, the kidneys will produce more diluted (watery) urine. If a person drinks much less fluid than they usually do, their urine will be more concentrated (contain much less water).

  The filtering action of the kidneys is controlled by the pituitary gland. The pituitary gland is about the size of a pea and is found below the brain, as shown in Figure below. The pituitary gland is also part of the endocrine system. The pituitary gland releases hormones which affect the ability of the kidneys to filter water from the blood.

  The absorption of water back into blood is controlled by a hormone called antidiuretic hormone (ADH). ADH is released from the pituitary gland in the brain. One of the most important roles of ADH is to control the body’s ability to hold onto water. If a person does not drink enough water, ADH is released and it causes the kidneys to remove more water from the urine. The urine is more concentrated and is less in volume.

  When too much fluid is present in the blood, the amount of ADH in the blood is reduced. This increases the amount of water that filters into the nephrons. The kidneys then produce a large volume of more dilute urine.

  Figure 19.16

  The pituitary gland is found directly below the brain and releases hormones that control the production of urine.

  Excretory System Problems

  The urinary system controls the amount of water in the body, and removes wastes, so any problem with the urinary system can badly affect many other body systems. Some common urinary system problems are described here.

  Kidney Stones

  In some cases, certain mineral wastes in urine crystallize and form kidney stones like the one shown inFigure below. Stones form in the kidneys and may be found anywhere in the urinary system. They vary in size. Some stones cause great pain while others cause very little pain. Some stones may need to be removed by surgery or ultrasound treatments.

  Figure 19.17

  A kidney stone; the stones can form anywhere in the urinary system.

  Kidney failure

  Kidney failure results when the kidneys are not able to regulate water and chemicals in the body or remove waste products from the blood. If the kidneys are unable to filter wastes from the blood, the wastes build up in the body. Homeostasis is disrupted because the ions and fluids in the body are out of balance.

  Kidney failure can be caused by an accident that injures the kidneys, the loss of a lot of blood, or it can be caused by some drugs or poisons. Kidney failure may lead to permanent loss of kidney function. But if the kidneys are not seriously damaged, they may recover. Chronic kidney disease is the gradual reduction of kidney function that may lead to permanent kidney failure.

  A person who has lost kidney function may need to undergo kidney dialysis. Kidney dialysis is the process of artificially filtering the blood of wastes. A dialysis machine (also called a hemodialyzer) filters the blood of waste by pumping it through a semipermeable membrane. The cleansed blood is then returned to the patient’s body. A dialysis machine is shown in Figure below.

  Figure 19.18

  During hemodialysis, a patients blood is sent through a filter that removes waste products and the clean blood is returned to the body.

  Urinary tract infections (UTIs)

  Urinary tract infections are bacterial infections of any part of the urinary tract. When bacteria get into the bladder or kidney and multiply in the urine, they cause a UTI. The most common type of UTI is a bladder infection. Women get UTIs more often than men. UTIs are often treated with antibiotics.

  Lesson Summary

  The excretory system controls the chemical make-up of body fluids. The organs of the excretory system remove metabolic wastes. They also maintain the proper concentrations of water, salts, and nutrients in the body.

  The lungs, skin, kidneys, and large intestine are all part of the excretory system. The urinary system is made up of the kidneys, the ureters, the bladder, and the urethra. The filtering structures of the kidneys are the nephrons.

  Water and waste molecules move out of the blood capillaries and into the nephrons. Most of the water returns to the blood. Urine collects in the nephron and moves to the urinary bladder through the ureters.

  The filtering action of the kidneys is controlled by the pituitary gland. ADH is the hormone that controls the uptake of water from the kidneys. Disorders of
the urinary system include kidney stones, kidney disease and urinary tract infections.

  Review Questions

  What are the functions of the excretory system?

  List the organs that make up the excretory system.

  What is the difference between the urinary system and the excretory system?

  What is urine made up of?

  Outline how the kidneys filter blood.

  What is the purpose of the urinary bladder?

  The walls of the urinary bladder are stretchy, what do you think is the advantage to having these stretchy walls?

  What connects the kidneys to the urinary bladder?

  What does antidiuretic hormone do?

  What is a urinary tract infection?

  Why is kidney failure such a serious health problem?

  Further Reading / Supplemental Links

  http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEXCRETE

  http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys

  http://en.wikipedia.org/wiki/Kidney_function

  Vocabulary

  antidiuretic hormone (ADH)

  Hormone that controls the absorption of water back into blood.

 

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