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L_0386 | the muscular system | T_2153 | You are less likely to have a muscle injury if you exercise regularly and have strong muscles. Stretching also helps prevent muscle injuries. Stretching improves the range of motion of muscles and tendons at joints. You should always warm up before stretching or doing any type of exercise. Warmed-up muscles and tendons are less likely to be injured. One way to warm up is to jog slowly for a few minutes. | text | null |
L_0387 | food and nutrients | T_2154 | Your body needs food for three purposes: 1. Food gives the body energy. You need energy for everything you do. The energy in food is measured in a unit called the Calorie. 2. Food provides building materials for the body. The body needs building materials for growth and repair. 3. Food contains substances that help control body processes. Body processes must be kept in balance for good health. | text | null |
L_0387 | food and nutrients | T_2155 | There are a variety of substances in foods that the body needs. Any substance in food that the body needs is called a nutrient. There are six major types of nutrients: carbohydrates, proteins, lipids, water, minerals, and vitamins. Carbohydrates, proteins, and lipids can be used for energy. Proteins also provide building materials. Proteins, minerals, and vitamins help control body processes. Water is needed by all cells just to stay alive. The six types of nutrients can be divided into two major categories based on how much of them the body needs. The categories are macronutrients and micronutrients. | text | null |
L_0387 | food and nutrients | T_2156 | Macronutrients are nutrients the body needs in relatively large amounts. They include carbohydrates, proteins, lipids, and water. | text | null |
L_0387 | food and nutrients | T_2157 | Carbohydrates include sugars, starches, and fiber. Sugars and starches are used by the body for energy. One gram of sugar or starch provides 4 Calories of energy. Fiber doesnt provide energy, but it is needed for other uses. At age 13 years, you need about 130 grams of carbohydrates a day. Figure 17.2 shows good food sources of each type. Sugars are small, simple carbohydrates. They are found in foods such as milk and fruit. Sugars in foods such as these are broken down by your digestive system to glucose, the simplest of all sugars. Glucose is taken up by cells for energy. Starches are larger, complex carbohydrates. They are found in foods such as grains and vegetables. Starches are broken down by your digestive system to glucose, which is used for energy. Fiber is a complex carbohydrate that consists mainly of cellulose and comes only from plants. High-fiber foods include whole grains and legumes such as beans. Fiber cant be broken down by the digestive system, but it plays important roles in the body. It helps keep sugar and lipids at normal levels in the blood. It also helps keep food waste moist so it can pass easily out of the body. | text | null |
L_0387 | food and nutrients | T_2158 | Proteins are nutrients made up of smaller molecules called amino acids. The digestive system breaks down proteins in food to amino acids, which are used for protein synthesis. Proteins synthesized from the amino acids in food serve many vital functions. They make up muscles, control body processes, fight infections, and carry substances in the blood. If you eat more protein than you need for these functions, the extra protein is used for energy. One gram of protein provides 4 Calories of energy, the same as carbohydrates. A 13-year-old needs to eat about 34 grams of protein a day. Figure 17.3 shows good food sources of protein. | text | null |
L_0387 | food and nutrients | T_2159 | Lipids are nutrients such as fats. They are used for energy and other important purposes. One gram of lipids provides the body with 9 Calories of energy, more than twice as much as carbohydrates or proteins. Lipids also make up cell membranes, protect nerves, control blood pressure, and help blood clot. You must consume some lipids for these purposes. Good food sources of lipids are shown in Figure 17.4. Any extra lipids you consume are stored as fat. A certain amount of stored fat is needed to cushion and protect internal organs and insulate the body. However, too much stored fat can lead to obesity and cause significant health problems. A type of lipid called trans fat is found in many processed foods. Trans fat is rare in nature but is manufactured and added to foods to preserve freshness. Eating foods that contain trans fat increases the risk of heart disease. Trans fat may be found in such foods as cookies, doughnuts, crackers, fried foods, ground beef, and margarine. | text | null |
L_0387 | food and nutrients | T_2159 | Lipids are nutrients such as fats. They are used for energy and other important purposes. One gram of lipids provides the body with 9 Calories of energy, more than twice as much as carbohydrates or proteins. Lipids also make up cell membranes, protect nerves, control blood pressure, and help blood clot. You must consume some lipids for these purposes. Good food sources of lipids are shown in Figure 17.4. Any extra lipids you consume are stored as fat. A certain amount of stored fat is needed to cushion and protect internal organs and insulate the body. However, too much stored fat can lead to obesity and cause significant health problems. A type of lipid called trans fat is found in many processed foods. Trans fat is rare in nature but is manufactured and added to foods to preserve freshness. Eating foods that contain trans fat increases the risk of heart disease. Trans fat may be found in such foods as cookies, doughnuts, crackers, fried foods, ground beef, and margarine. | text | null |
L_0387 | food and nutrients | T_2160 | Water is essential to life because chemical reactions within cells take place in water. Most people can survive only a few days without consuming water to replace their water losses. How do you lose water? You lose water in your breath each time you exhale. You lose water in urine. You lose water in sweat, especially if you are active in warm weather. The boy in Figure 17.5 is taking a water break while playing outside on a hot day. If he doesnt take in enough water to replace the water lost in sweat, he may become dehydrated. Symptoms of dehydration include dry mouth, headache, and dizziness. Dehydration can be very serious. It can even cause death. | text | null |
L_0387 | food and nutrients | T_2161 | Micronutrients are nutrients the body needs in relatively small amounts. They include minerals and vitamins. These nutrients dont provide the body with energy, but they are still essential for good health. | text | null |
L_0387 | food and nutrients | T_2162 | Minerals are chemical elements that dont come from living things or include the element carbon. Many minerals are needed in the diet for normal functioning of the body. Several minerals that are needed in relatively large amounts are listed in Table 17.1. As you can see from these examples, minerals have a diversity of important functions. Your body cant produce any of the minerals it needs, so you must get them from the food you eat. The table shows good food sources of the minerals. Mineral Calcium Chloride Magnesium Phosphorus Potassium Sodium Function strong bones and teeth salt-water balance strong bones strong bones and teeth muscle and nerve functions muscle and nerve functions Good Food Sources milk, green leafy vegetables table salt, most packaged foods whole grains, nuts poultry, whole grains meat, bananas table salt, most packaged foods Not getting enough minerals can cause health problems. For example, not getting enough calcium may cause osteoporosis. This is a disease in which the bones become porous so they break easily. Getting too much of some minerals can also cause health problems. Many people get too much sodium. Sodium is added to most packaged foods. People often add more sodium to their food by using table salt. Too much sodium has been linked to high blood pressure in some people. | text | null |
L_0387 | food and nutrients | T_2163 | The vitamins to watch out for are A, D, E, and K. These vitamins are stored by the body, so they can build up to high levels. | text | null |
L_0389 | the digestive system | T_2171 | The digestive system is the body system that breaks down food and absorbs nutrients. It also eliminates solid food wastes that remain after food is digested. The major organs of the digestive system are shown in Figure 17.10. For an entertaining overview of the digestive system and how it works, watch this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0389 | the digestive system | T_2172 | The organs in Figure 17.10 make up the gastrointestinal (GI) tract. This is essentially a long tube that connects the mouth to the anus. Food enters the mouth and then passes through the rest of the GI tract. Food waste leaves the body through the anus. In adults, the GI tract is more than 9 meters (30 feet) long! Organs of the GI tract are covered by muscles that contract to keep food moving along. A series of involuntary muscle contractions moves rapidly along the tract, like a wave travelling through a spring toy. The muscle contractions are called peristalsis. The diagram in Figure 17.11 shows how peristalsis works. | text | null |
L_0389 | the digestive system | T_2173 | As food is pushed through the GI tract by peristalsis, it undergoes digestion. Digestion is the process of breaking down food into nutrients. There are two types of digestion: mechanical digestion and chemical digestion. Mechanical digestion occurs when large chunks of food are broken down into smaller pieces. This is a physical process that happens mainly in the mouth and stomach. Chemical digestion occurs when large food molecules are broken down into smaller nutrient molecules. This is a chemical process that begins in the mouth and stomach but occurs mainly in the small intestine. | text | null |
L_0389 | the digestive system | T_2174 | After food is broken down into nutrient molecules, the molecules are absorbed by the blood. Absorption is the process in which nutrients or other molecules are taken up by the blood. Once absorbed by the blood, nutrients can travel in the bloodstream to cells throughout the body. | text | null |
L_0389 | the digestive system | T_2175 | Some substances in food cant be broken down into nutrients. They remain behind in the digestive system after the nutrients have been absorbed. Any substances in food that cant be digested pass out of the body as solid waste. This process is called elimination. | text | null |
L_0389 | the digestive system | T_2176 | Chemical digestion could not take place without the help of digestive enzymes and other substances secreted into the GI tract. An enzyme is a protein that speeds up a biochemical reaction. Digestive enzymes speed up the reactions of chemical digestion. Table 17.3 lists a few digestive enzymes, the organs that produce them, and their functions in digestion. Enzyme Amylase Pepsin Organ that Produces It mouth stomach Substance It Helps Digest starch protein Enzyme Lipase Ribonuclease Organ that Produces It pancreas pancreas Substance It Helps Digest fat RNA Most digestive enzymes are secreted into the GI tract by organs of the GI tract or from a nearby gland named the pancreas. Figure 17.12 shows where the pancreas is located. The figure also shows the locations of the liver and gall bladder. These organs produce or store other digestive secretions. The liver secretes bile acids. Bile acids help digest fat. Some liver bile is secreted directly into the small intestine. Some liver bile goes to the gall bladder. This sac-like organ stores and concentrates the liver bile before releasing it into the small intestine. | text | null |
L_0389 | the digestive system | T_2177 | Does the sight or smell of your favorite food make your mouth water? When this happens, you are getting ready for digestion. | text | null |
L_0389 | the digestive system | T_2178 | The mouth is the first digestive organ that food enters. The sight, smell, or taste of food stimulates the release of saliva and digestive enzymes by salivary glands inside the mouth. Saliva wets the food, which makes it easier to break up and swallow. The enzyme amylase in saliva begins the chemical digestion of starches to sugars. Your teeth help to mechanically digest food. Look at the different types of human teeth in Figure 17.13. Sharp teeth in the front of the mouth cut or tear food when you bite into it. Broad teeth in the back of the mouth grind food when you chew. Your tongue helps mix the food with saliva and enzymes and also helps you swallow. When you swallow, a lump of chewed food passes from the mouth into a tube in your throat called the pharynx. From the pharynx, the food passes into the esophagus. | text | null |
L_0389 | the digestive system | T_2179 | The esophagus is a long, narrow tube that carries food from the pharynx to the stomach. It has no other purpose. Food moves through the esophagus because of peristalsis. At the lower end of the esophagus, a circular muscle, called a sphincter, controls the opening to the stomach. The sphincter relaxes to let food pass into the stomach. Then the sphincter contracts to prevent food from passing back into the esophagus. | text | null |
L_0389 | the digestive system | T_2180 | The stomach is a sac-like organ at the end of the esophagus. It has thick muscular walls that contract and relax to squeeze and mix food. This helps break the food into smaller pieces. It also helps mix the food with enzymes and other secretions in the stomach. For example, the stomach secretes the enzyme pepsin, which helps digest proteins. Water, salt, and simple sugars can be absorbed into the blood from the lining of the stomach. However, most substances must undergo further digestion in the small intestine before they can be absorbed. The stomach stores the partly digested food until the small intestine is empty. Then a sphincter between the stomach and small intestine relaxes, allowing food to enter the small intestine. | text | null |
L_0389 | the digestive system | T_2181 | The small intestine is a narrow tube that starts at the stomach and ends at the large intestine. In adults, its about 7 meters (23 feet) long. Most chemical digestion and almost all nutrient absorption take place in the small intestine. The small intestine is made up of three parts: 1. The duodenum is the first part of the small intestine. It is also the shortest part. This is where most chemical digestion takes place. Many enzymes and other substances involved in digestion are secreted into the duodenum 2. The jejunum is the second part of the small intestine. This is where most nutrients are absorbed into the blood. The inside surface of the jejunum is covered with tiny projections called villi (villus, singular). The villi make the inner surface of the small intestine 1000 times greater than it would be without them. You can read in Figure 17.14 how villi are involved in absorption. 3. The ileum is the last part of the small intestine. It is covered with villi like the jejunum. A few remaining nutrients are absorbed in the ileum. From the ileum, any remaining food waste passes into the large intestine. | text | null |
L_0389 | the digestive system | T_2182 | The large intestine is a wide tube that connects the small intestine with the anus. In adults, the large intestine is about 1.5 meters (5 feet) long. It is larger in width but shorter in length than the small intestine. | text | null |
L_0389 | the digestive system | T_2183 | Food waste enters the large intestine from the small intestine in a liquid state. As the waste moves through the large intestine, excess water is absorbed from it. The remaining solid waste is called feces. After a certain amount of feces have collected, a sphincter relaxes to let the feces pass out of the body through the anus. This is elimination. | text | null |
L_0389 | the digestive system | T_2184 | Trillions of bacteria normally live in the large intestine. Dont worrymost of them are helpful. They have several important roles. For example, intestinal bacteria: produce vitamins B12 and K. control the growth of harmful bacteria. break down toxins in the large intestine. break down fiber and some other substances in food that cant be digested. | text | null |
L_0389 | the digestive system | T_2185 | Much of the time, you probably arent aware of your digestive system. It works well without causing any problems. But most people have problems with their digestive system at least once in a while. Did you ever eat something that didnt agree with you? Maybe you had a stomachache or felt sick to your stomach. Perhaps you had diarrhea. These can be symptoms of food poisoning. | text | null |
L_0389 | the digestive system | T_2186 | Food poisoning is the common term for foodborne illness. This type of illness occurs when harmful bacteria enter your digestive system in food and make you sick. The bacteriaor toxins they producemay cause cramping, vomiting, or other GI tract symptoms. Following these healthy practices may decrease your risk of foodborne illness: Wash your hands after handling raw foods such as meats, poultry, fish, or eggs. These foods often contain bacteria that your hands could transfer to your mouth. Cook meats, poultry, fish, or eggs thoroughly before eating them. The heat of cooking kills any bacteria the foods may contain so they cant make you sick. Keep hot foods hot and cold foods cold. This is especially important when food is packed for lunch or a picnic (see Figure 17.15). Maintaining the proper temperature slows the growth of bacteria in the food. | text | null |
L_0389 | the digestive system | T_2187 | Food allergies occur when the immune system reacts to harmless substances in food as though they were harmful germs. Food allergies are relatively common. Almost 10 percent of children have them. Some of the foods most likely to cause allergies include milk, shellfish, nuts, grains, and eggs. If you eat foods to which you are allergic, you may experience vomiting, diarrhea, or a rash. In some people, eating even tiny amounts of certain foods causes them to have serious symptoms, such as difficulty breathing. They need immediate medical attention. The best way to prevent food allergy symptoms is to avoid eating the offending food. This may require careful reading of food labels. | text | null |
L_0390 | overview of the cardiovascular system | T_2188 | The organs that make up the cardiovascular system are the heart and a network of blood vessels that run throughout the body. The blood in the cardiovascular system is a liquid connective tissue. Figure 18.1 shows the heart and major vessels through which blood flows in the system. The heart is basically a pump that keeps blood moving through the blood vessels. | text | null |
L_0390 | overview of the cardiovascular system | T_2189 | The main function of the cardiovascular system is transporting substances around the body. Figure 18.1 shows some of the substances that are transported in the blood. They include hormones, oxygen, nutrients from digested food, and cellular wastes. Transport of all these materials is necessary to maintain homeostasis of the body and life itself. The cardiovascular system also helps regulate body temperature by controlling where blood moves around the body. Blood is warm, so when more blood flows to the surface of the body, it warms the surface. This allows the body to lose excess heat from the surface. When less blood flows to the surface, it cools the surface. This allows the body to conserve heat and stay warm. You can see the role of blood vessels in the regulation of body temperature in this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0390 | overview of the cardiovascular system | T_2190 | The heart and blood vessels form a closed system through which blood keeps circulating. However, blood actually circulates in two different loops within this closed system. The two loops are called pulmonary circulation and systemic circulation. In both loops, blood passes through the heart. You can see a simple model of each circulation loop in Figure 18.2. As blood circulates through the body, it travels first through one loop and then the other loop, over and over again. | text | null |
L_0390 | overview of the cardiovascular system | T_2191 | Pulmonary circulation is the shorter loop of the cardiovascular system. It carries blood between the heart and lungs. Oxygen-poor blood flows from the heart to the lungs. In the lungs, the blood absorbs oxygen and releases carbon dioxide. Then the oxygen-rich blood returns to the heart. | text | null |
L_0390 | overview of the cardiovascular system | T_2192 | Systemic circulation is the longer loop of the cardiovascular system. It carries blood between the heart and the rest of the body. Oxygen-rich blood flows from the heart to cells throughout the body. As it passes cells, the blood releases oxygen and absorbs carbon dioxide. Then the oxygen-poor blood returns to the heart. | text | null |
L_0391 | heart and blood vessels | T_2193 | The heart is a muscular organ in the chest. It consists mainly of cardiac muscle tissue. It pumps blood by repeated, rhythmic contractions. This produces the familiar lub-dub sound of each heartbeat. For a good video introduction to the heart and how it works, watch this entertaining Bill Nye video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0391 | heart and blood vessels | T_2194 | The heart has four chambers, or rooms, which you can see in Figure 18.3. Each chamber is an empty space with muscular walls through which blood can flow. The top two chambers of the heart are called the left and right atria (atrium, singular). The atria of the heart receive blood from the body or lungs and pump it into the bottom chambers of the heart. The bottom two chambers of the heart are called the left and right ventricles. The ventricles receive blood from the atria and pump it out of the heart, either to the lungs or to the rest of the body. Flaps of tissue called valves separate the hearts chambers. Valves keep blood flowing in just one direction through the heart. For example, a valve at the bottom of the right atrium opens to let blood flow from the right atrium to the right ventricle. Then the valve closes so the blood cant flow back into the right atrium. | text | null |
L_0391 | heart and blood vessels | T_2195 | Blood flows through the heart in two paths. Trace these two paths in Figure 18.4 as you read about them below. You can also learn about how blood flows through the heart with this rap: MEDIA Click image to the left or use the URL below. URL: 1. One path of blood in the heart is through the right atrium and right ventricle. The right atrium receives oxygen- poor blood from the body. It pumps the blood into the right ventricle. Then the right ventricle pumps the blood out of the heart to the lungs. This path through the heart is part of the pulmonary circulation. 2. The other path of blood in the heart is through the left atrium and left ventricle. The left atrium receives oxygen-rich blood from the lungs. It pumps the blood into the left ventricle. Then the left ventricle pumps the blood out of the heart to the rest of the body. This path through the heart is part of the systemic circulation. | text | null |
L_0391 | heart and blood vessels | T_2196 | To move blood through the heart, cardiac muscles must contract in a certain sequence. First the atria must contract, followed quickly by the ventricles contracting. This series of contractions keeps blood moving continuously through the heart. Contractions of cardiac muscles arent under voluntary control. They are controlled by a cluster of special cells within the heart, commonly called the pacemaker. These cells send electrical signals to cardiac muscles so they contract in the correct sequence and with just the right timing. | text | null |
L_0391 | heart and blood vessels | T_2197 | Blood vessels are long, tube-like organs that consist mainly of muscle, connective, and epithelial tissues. They branch to form a complex network of vessels that run throughout the body. This network transports blood to all the bodys cells. | text | null |
L_0391 | heart and blood vessels | T_2198 | There are three major types of blood vessels: arteries, veins, and capillaries. You can see each type in Figure 18.5. You can watch a good video introduction to the three types at this link: MEDIA Click image to the left or use the URL below. URL: Arteries are muscular blood vessels that carry blood away from the heart. They have thick walls that can withstand the pressure of blood pumped by the heart. Arteries generally carry oxygen-rich blood. The largest artery is the aorta, which receives blood directly from the heart. It branches to form smaller and smaller arteries throughout the body. The smallest arteries are called arterioles. Veins are blood vessels that carry blood toward the heart. This blood is no longer under pressure, so veins have thinner walls. To keep the blood moving, many veins have valves that prevent the backflow of blood. Veins generally carry oxygen-poor blood. The smallest veins are called venules. They merge to form larger and larger veins. The largest vein is the inferior vena cava, which carries blood from the lower body directly to the heart. Capillaries are the smallest type of blood vessels. They connect the smallest arteries (arterioles) and veins (venules). Exchange of substances between cells and the blood takes place across the walls of capillaries, which may be only one cell thick. | text | null |
L_0391 | heart and blood vessels | T_2199 | Blood vessels help regulate body processes by either dilating (widening) or constricting (narrowing). This changes the amount of blood flowing to particular organs. For example, dilation of blood vessels in the skin allows more blood to flow to the surface of the body. This helps the body lose excess heat. Constriction of these blood vessels has the opposite effect and helps the body conserve heat. | text | null |
L_0391 | heart and blood vessels | T_2200 | Diseases of the cardiovascular system are common and may be life threatening. A healthy lifestyle can reduce the risk of such diseases developing. | text | null |
L_0391 | heart and blood vessels | T_2201 | Diseases of the heart and blood vessels are called cardiovascular diseases. The leading cause of cardiovascular disease is atherosclerosis. Atherosclerosis is a condition in which a material called plaque builds up inside arteries. Plaque consists of cell debris, cholesterol, and other substances. As plaque builds up in an artery, the artery narrows, as shown in Figure If plaque blocks coronary arteries that supply blood to the heart, coronary heart disease results. Poor blood flow to the heart may cause chest pain or a heart attack. A heart attack occurs when the blood supply to part of the heart muscle is completely blocked so that cardiac muscle cells die. Coronary heart disease is the leading cause of death in U.S adults. | text | null |
L_0391 | heart and blood vessels | T_2202 | Many factors influence your risk of developing cardiovascular diseases. Some of these factors you cant control. Older age, male gender, and a family history of cardiovascular disease all increase the risk and cant be controlled. However, you can control many other factors. To reduce the risk of cardiovascular disease, you can: avoid smoking. get regular physical activity. maintain a healthy percent of body fat. eat a healthy, low-fat diet. get regular checkups to detect and manage problems such as high blood pressure and high blood cholesterol. | text | null |
L_0392 | blood | T_2203 | Blood is a liquid connective tissue. It circulates throughout the body via blood vessels due to the pumping action of the heart. You couldnt survive without the approximately 4.5 to 5 liters of blood that are constantly being pumped through your blood vessels. | text | null |
L_0392 | blood | T_2204 | Blood consists of both liquid and cells. The liquid part of blood is called plasma. Plasma is a watery, golden-yellow fluid that contains many dissolved substances. Substances dissolved in plasma include glucose, proteins, and gases. Plasma also contains blood cells. There are three types of blood cells: red blood cells, white blood cells, and platelets. You can see all three types in Figure 18.8. 1. Red blood cells are shaped like flattened disks. There are trillions of red blood cells in your blood. Each red blood cell has millions of molecules of hemoglobin. Hemoglobin is a protein that contains iron. The iron in hemoglobin gives red blood cells their red color. It also explains how hemoglobin carries oxygen. The iron in hemoglobin binds with oxygen molecules so they can be carried by red blood cells. 2. White blood cells are larger than red blood cells, but there are far fewer of them. Their role is to defend the body in various ways. For example, white blood cells called phagocytes engulf and destroy microorganisms and debris in the blood. 3. Platelets are small, sticky cell fragments that help blood clot. A blood clot is a solid mass of cell fragments and other substances that plugs a leak in a damaged blood vessel. Platelets stick to tears in blood vessels and to each other, helping to form a clot at the site of injury. Platelets also release chemicals that are needed for clotting to occur. | text | null |
L_0392 | blood | T_2205 | The main function of blood is transport. Blood in arteries carries oxygen and nutrients to all the bodys cells. Blood in veins carries carbon dioxide and other wastes away from cells to be excreted. Blood also transports the chemical messengers called hormones to cells throughout the body where they are needed to regulate body functions. Blood has several other functions as well. For example, blood: defends the body against infections. repairs body tissues. controls the bodys pH. helps regulate body temperature. | text | null |
L_0392 | blood | T_2206 | Red blood cells carry proteins called antigens on their surface. People may vary in the exact antigens their red blood cells carry. The specific proteins are controlled by the genes they inherit from their parents. The particular antigens you inherit determine your blood type. Why does your blood type matter? Blood type is important for medical reasons. A patient cant safely receive a transfusion of blood containing antigens not found in the patients own blood. With foreign antigens, the transfused blood will be rejected by the persons immune system. This causes a reaction in the patients bloodstream, called agglutination. The transfused red blood cells clump together, as shown in Figure 18.9. The clumped cells block blood vessels and cause other life-threatening problems. There are many sets of antigens that determine different blood types. Two of the best known are the ABO and Rhesus antigens. Both are described below. You can also learn more about them by watching this video: | text | null |
L_0392 | blood | T_2207 | ABO blood type is determined by two common antigens, often called antigen A and antigen B. If your red blood cells carry only antigen A, you have blood type A. If your red blood cells carry only antigen B, you have blood type B. If your red blood cells carry both antigen A and antigen B, you have blood type AB. If your red blood cells carry neither antigen A nor antigen B, you have blood type O. | text | null |
L_0392 | blood | T_2208 | Another red blood cell antigen determines a persons Rhesus blood type. This blood type depends on a single common antigen, typically referred to as the Rhesus (Rh) antigen. If your red blood cells carry the Rhesus antigen, you have Rhesus-positive blood, or blood type Rh+. If your red blood cells lack the Rhesus antigen, you have Rhesus-negative blood, or blood type Rh-. | text | null |
L_0392 | blood | T_2209 | Some diseases affect mainly the blood or its components. They include anemia, leukemia, hemophilia, and sickle- cell disease. | text | null |
L_0392 | blood | T_2210 | Anemia is a disease that occurs when there is not enough hemoglobin (or iron) in the blood so it cant carry adequate oxygen to the cells. There are many possible causes of anemia. One possible cause is excessive blood loss due to an injury or surgery. Not getting enough iron in the diet is another possible cause. | text | null |
L_0392 | blood | T_2211 | Leukemia is a type of cancer in which bone marrow produces abnormal white blood cells. The abnormal cells cant do their job of fighting infections. Like most cancers, leukemia is thought to be caused by a combination of genetic and environmental factors. It is the most common cancer in children. | text | null |
L_0392 | blood | T_2212 | Hemophilia is a genetic disorder in which blood fails to clot properly because a normal clotting factor in the blood is lacking. In people with hemophilia, even a minor injury can cause a life-threatening loss of blood. Most cases of hemophilia are caused by a recessive gene on the X chromosome. The disorder is expressed much more commonly in males because they have just one X chromosome. | text | null |
L_0392 | blood | T_2213 | Sickle-Cell Disease is another genetic disorder of the blood. It is more common in people with African origins because it helps protect against malaria. Sickle-cell disease occurs in people who inherit two copies of the recessive mutant gene for hemoglobin. The abnormal hemoglobin that results causes red blood cells to take on a characteristic sickle shape under certain conditions. You can compare sickle-shaped and normal red blood cells in Figure 18.10. The sickle-shaped cells get stuck in tiny capillaries and block blood flow. This causes serious, painful symptoms. Watch this video animation to learn more about the genetic basis of sickle-cell disease: | text | null |
L_0393 | the respiratory system | T_2214 | The bodys exchange of oxygen and carbon dioxide with the air is called respiration. Respiration actually consists of two stages. In one stage, air is taken into the body and carbon dioxide is released to the outside air. In the other stage, oxygen is delivered to all the cells of the body and carbon dioxide is carried away from the cells. Another kind of respiration takes place within body cells. This kind of respiration is called cellular respiration. Its the process in which cells obtain energy by burning glucose. Both types of respiration are connected. Cellular respiration uses oxygen and produces carbon dioxide. Respiration by the respiratory system supplies the oxygen needed for cellular respiration. It also removes the carbon dioxide produced by cellular respiration. | text | null |
L_0393 | the respiratory system | T_2215 | You can see the main structures of the respiratory system in Figure 19.1. They include the nose, trachea, lungs, and diaphragm. Use the figure to trace how air moves through the respiratory system when you read about it below. You can also use this interactive to explore the respiratory system and see how it functions: http://science.nationalgeogr | text | null |
L_0393 | the respiratory system | T_2216 | Take in a big breath of air through your nose. As you breathe in, you may feel the air pass down through your throat and notice your chest expand. Now breathe out and observe the opposite events occurring. Breathing in and out may seem like simple actions, but they are just part of the complex process of respiration. Respiration actually occurs in four steps: 1. 2. 3. 4. breathing (inhaling and exhaling) gas exchange between the air and blood gas transport by the blood gas exchange between the blood and cells | text | null |
L_0393 | the respiratory system | T_2217 | Breathing is the process of moving air into and out of the lungs. The process depends on a muscle called the diaphragm. This is a large, sheet-like muscle below the lungs. You can see it in Figure 19.2. Inhaling, or breathing in, occurs when the diaphragm contracts. This increases the size of the chest, which decreases air pressure inside the lungs. The difference in air pressure between the lungs and outside air causes air to rush into the lungs. Exhaling, or breathing out, occurs when the diaphragm relaxes. This decreases the size of the chest, which increases air pressure inside the lungs. The difference in air pressure between the lungs and outside air causes air to rush out of the lungs. When you inhale, air enters the respiratory system through your nose and ends up in your lungs, where gas exchange with the blood takes place. What happens to the air along the way? In the nose, mucus and hairs trap any dust or other particles in the air. The air is also warmed and moistened so it wont harm delicate tissues of the lungs. Next, air passes through the pharynx, a passageway that is shared with the digestive system. From the pharynx, the air passes next through the larynx, or voice box. After the larynx, air moves into the trachea, or wind pipe. This is a long tube that leads down to the lungs in the chest. In the chest, the trachea divides as it enters the lungs to form the right and left bronchi (bronchus, singular). These passages are covered with mucus and tiny hairs called cilia. The mucus traps any remaining particles in the air. The cilia move and sweep the particles and mucus toward the throat so they can be expelled from the body. Air passes from the bronchi into smaller passages called bronchioles. The bronchioles end in clusters of tiny air sacs called alveoli (alveolus, singular). | text | null |
L_0393 | the respiratory system | T_2218 | The alveoli in the lungs are where gas exchange between the air and blood takes place. Each alveolus is surrounded by a network of capillaries. When you inhale, air in the alveoli has a greater concentration of oxygen than does blood in the capillaries. The difference in oxygen concentration causes oxygen to diffuse from the air into the blood. You can see how this occurs in Figure 19.3. Unlike oxygen, carbon dioxide is more concentrated in the blood in the capillaries surrounding the alveoli than it is in the air inside the alveoli. Therefore, carbon dioxide diffuses in the opposite direction. It moves out of the blood and into the air. | text | null |
L_0393 | the respiratory system | T_2219 | After the blood in the capillaries in the lungs picks up oxygen, it leaves the lungs and travels to the heart. The heart pumps the oxygen-rich blood into arteries, which carry it throughout the body. The blood passes eventually into capillaries that supply body cells. | text | null |
L_0393 | the respiratory system | T_2220 | The cells of the body have a lower concentration of oxygen that does blood in the capillaries that supply body cells. Therefore, oxygen diffuses from the blood into the cells. Carbon dioxide, which cells produce in cellular respiration, is more concentrated in the cells. Therefore, carbon dioxide diffuses out of the cells and into the blood. The carbon dioxide travels in capillaries to veins and then to the heart. The heart pumps the blood to the lungs, where the carbon dioxide diffuses into the alveoli. It passes out of the body during exhalation. This brings the process of respiration full circle. | text | null |
L_0393 | the respiratory system | T_2221 | No doubt youve had the common cold. When you did, you probably had respiratory system symptoms. For example, you may have had a stuffy nose that made it hard to breathe. While you may feel miserable when you have a cold, it is generally a relatively mild disease. Many other respiratory system diseases are more serious. | text | null |
L_0393 | the respiratory system | T_2222 | Common diseases of the respiratory system include asthma, pneumonia, and emphysema. All of them are diseases of the lungs. You can see some of the changes in the lungs that occur in each of these diseases in Figure 19.4. Asthma is a disease in which bronchioles in the lungs periodically swell and fill with mucus. Symptoms of asthma may include difficulty breathing, wheezing, coughing, and chest tightness. An asthma attack may be triggered by allergies, strenuous exercise, stress, or another respiratory illness such as a cold. Pneumonia is a disease in which some of the alveoli of the lungs fill with fluid so they can no longer exchange gas. Symptoms of pneumonia typically include coughing, chest pain, difficulty breathing, and fatigue. Pneumonia may be caused by an infection or an injury to the lungs. Emphysema is a disease in which the walls of the alveoli break down so less gas can be exchanged by the lungs. The main symptom of emphysema is shortness of breath. The damage to the alveoli is usually caused by smoking and is permanent. | text | null |
L_0393 | the respiratory system | T_2223 | The main way to keep your respiratory system healthy is to avoid smoking or breathing in the smoke of others. Smoking causes, or makes you more susceptible to, many respiratory diseases, including asthma, bronchitis, em- physema, and lung cancer. Other steps you can take to keep your respiratory system healthy are listed below. Eat well, get enough sleep, and be active every day. These healthy lifestyle choices will help keep your immune system healthy so it can fight off respiratory infections and other diseases. Wash your hands often. This will reduce your risk of picking up viruses or bacteria that could make you sick with colds or other respiratory infections. Avoid contact with other people when they are sick and stay home when you are sick. These steps will help reduce the spread of infectious diseases. | text | null |
L_0394 | the excretory system | T_2224 | Excretion is any process in which excess water or wastes are removed from the body. Excretion is the job of the excretory system. Besides the kidneys, other organs of excretion include the large intestine, liver, skin and lungs. The large intestine eliminates food wastes that remain after digestion takes place. The liver removes excess amino acids and toxins from the blood. Sweat glands in the skin excrete excess water and salts in sweat. The lungs exhale carbon dioxide and also excess water as water vapor. Each of the above organs of excretion is also part of another body system. For example, the large intestine and liver are part of the digestive system, and the lungs are part of the respiratory system. The kidneys are the main organs of excretion. They are part of the urinary system. | text | null |
L_0394 | the excretory system | T_2225 | The urinary system is shown in Figure 19.6. It includes two kidneys, two ureters, the urinary bladder, and the urethra. The main function of the urinary system is to filter waste products and excess water from the blood and excrete them from the body as urine. For a visual presentation on the urinary system and how it works, watch this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0394 | the excretory system | T_2226 | The kidneys are a pair of bean-shaped organs at each side of the body just above the waist. You can see a diagram of a kidney in Figure 19.7. The function of the kidneys is to filter blood and form urine. Tiny structures in the kidneys, called nephrons, perform this function. Each kidney contains more than a million nephrons. | text | null |
L_0394 | the excretory system | T_2226 | The kidneys are a pair of bean-shaped organs at each side of the body just above the waist. You can see a diagram of a kidney in Figure 19.7. The function of the kidneys is to filter blood and form urine. Tiny structures in the kidneys, called nephrons, perform this function. Each kidney contains more than a million nephrons. | text | null |
L_0394 | the excretory system | T_2227 | Blood with wastes enters each kidney through an artery, which branches into many capillaries. After passing through capillaries and being filtered, the clean blood leaves the kidney through a vein. The part of each nephron called the glomerulus is where blood in the capillaries is filtered. Excess water and wastes are filtered out of the blood. The tubule of the nephron collects these substances. Some of the water is reabsorbed. The remaining fluid is urine. | text | null |
L_0394 | the excretory system | T_2228 | From the kidneys, urine enters the ureters. These are two muscular tubes that carry urine to the urinary bladder. Contractions of the muscles of the ureters move the urine along by peristalsis. The urinary bladder is a sac-like organ that stores urine. When the bladder is about half full, a sphincter relaxes to let urine flow out of the bladder and into the urethra. The urethra is a muscular tube that carries urine out of the body through another sphincter. The process of urine leaving the body is called urination. The second sphincter and the process of urination are normally under conscious control. | text | null |
L_0394 | the excretory system | T_2229 | The kidneys help the body maintain homeostasis in several ways. They filter all the blood in the body many times each day and produce urine. They control the amount of water and dissolved substances in the blood by excreting more or less of them in urine. The kidneys also secrete hormones that help maintain homeostasis. For example, they produce a hormone that stimulates bone marrow to produce red blood cells when more are needed. They also secrete a hormone that regulates blood pressure and keeps it in a normal range. | text | null |
L_0394 | the excretory system | T_2230 | You need only one kidney to live a normal, healthy life. A single kidney can do all the work of filtering the blood and maintaining homeostasis. However, at least one kidney must function properly to maintain life. Diseases that threaten the health and functioning of the kidneys include kidney stones, infections, and diabetes. You can learn more about kidney diseases in this video: . MEDIA Click image to the left or use the URL below. URL: Kidney stones are mineral crystals that form in urine inside a kidney, as shown in Figure 19.8. The stones may be extremely painful. If a kidney stone blocks a ureter, it must be removed so urine can leave the kidney and be excreted. Bacterial infections of urinary organs, especially the urinary bladder, are common. They are called urinary tract infections. Generally, they can be cured with antibiotic drugs. However, if they arent treated, they can lead to more serious infections and damage to the kidneys. Untreated diabetes may damage capillaries in the kidneys so the nephrons can no longer filter blood. This is called kidney failure. The only cure for kidney failure is to receive a healthy transplanted kidney from a donor. Until that happens, a patient with kidney failure can be kept alive by artificially filtering the blood through a machine. This is called hemodialysis. You can see how it works in Figure 19.9. | text | null |
L_0396 | chemistry of living things | T_2237 | All known matter can be divided into a little more than 100 different substances called elements. | text | null |
L_0396 | chemistry of living things | T_2238 | An element is pure substance that cannot be broken down into other substances. Each element has a particular set of properties that, taken together, distinguish it from all other elements. Table 2.1 lists the major elements in the human body. As you can see, you consist mainly of the elements oxygen, carbon, and hydrogen. Element Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Percent of Body Mass 65 18 10 3 1.5 1.0 0.35 0.25 In your body, most elements are combined with other elements to form chemical compounds. A compound is a unique type of matter in which two or more elements are combined chemically in a certain ratio. For example, much of the oxygen and hydrogen in your body are combined in the chemical compound water, or H2O. | text | null |
L_0396 | chemistry of living things | T_2239 | The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. | text | null |
L_0396 | chemistry of living things | T_2239 | The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. | text | null |
L_0396 | chemistry of living things | T_2240 | Besides water, most of the compounds in living things are biochemical compounds. A biochemical compound is a carbon-based compound that is found in living organisms. Carbon is an element that has a tremendous ability to form large compounds. Each atom of carbon can form four chemical bonds with other atoms. A chemical bond is the sharing of electrons between atoms. Bonds hold the atoms together in chemical compounds. A carbon atom can form bonds with other carbon atoms or with atoms of other elements. | text | null |
L_0396 | chemistry of living things | T_2241 | Biochemical compounds make up the cells and tissues of living things. They are also involved in all life processes. Given their diversity of functions, its not surprising that there are millions of different biochemical compounds. Even so, all biochemical compounds can be grouped into just four main classes: carbohydrates, proteins, lipids, and nucleic acids. The classes are summarized in Table 2.1. Class Elements Examples Functions Class Carbohydrates Elements carbon hydrogen oxygen Examples sugars starch glycogen cellulose Proteins carbon hydrogen oxygen nitrogen sulfur carbon hydrogen oxygen carbon hydrogen oxygen nitrogen phosphorus enzymes hormones Lipids Nucleic acids fats oils phospholipids DNA RNA Functions provide energy to cells stores energy in plants stores energy in animals makes up the cell walls of plants speed up biochemical re- actions regulate life processes store energy in animals store energy in plants make up cell membranes stores genetic information in cells helps cells make proteins | text | null |
L_0396 | chemistry of living things | T_2242 | You can see from Table 2.1 that all biochemical compounds contain hydrogen and oxygen as well as carbon. They may also contain nitrogen, phosphorus, and/or sulfur. Almost all biochemical compounds are polymers. Polymers are large molecules that consist of many smaller, repeating molecules, called monomers. Most biochemical molecules are macromolecules. The prefix macro- means large, and many biochemical molecules are very large indeed. They may contain thousands of monomer molecules. The largest known biochemical molecule contains more than 34,000 monomers! | text | null |
L_0396 | chemistry of living things | T_2243 | Carbohydrates are biochemical compounds that include sugar, starch, glycogen, and cellulose. Sugars are simple carbohydrates with relatively small molecules. Glucose is the smallest of all the sugar molecules with its chemical formula of C6 H12 O6 . This means that a molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen. Plants and some other organisms make glucose in the process of photosynthesis. Living things that cannot make glucose can obtain it by consuming plants or organisms that consume plants. Starches are complex carbohydrates. They are polymers of glucose. Starches contain hundreds of glucose monomers. Plants make starches to store extra glucose. Consumers can get starches by eating plants. Common sources of starches in the human diet are pictured in the Figure 2.8. Our digestive system breaks down starches to sugar, which our cells use for energy. Like other animals, we store any extra glucose as the complex carbohydrate called glycogen. Glycogen is also a polymer of glucose. Cellulose is another complex carbohydrate found in plants that is a polymer of glucose. Cellulose molecules bundle together to form long, tough fibers. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to stems and tree trunks. | text | null |
L_0396 | chemistry of living things | T_2244 | Proteins are biochemical compounds that consist of one or more chains of small molecules called amino acids. Amino acids are the monomers of proteins. There are only about 20 different amino acids. The sequence of amino acids in chains and the number of chains in a protein determine the proteins shape. Shapes may be very complex. You can learn more about the shapes of proteins at this link: MEDIA Click image to the left or use the URL below. URL: The shape of a protein determines its function. Proteins have many different functions. For example, proteins: make up muscle tissues. speed up chemical reactions in cells. regulate life processes. help defend against infections. 2.2. Chemistry of Living Things transport materials around the body in the blood. blood How hemoglobin transports oxygen in the | text | null |
L_0396 | chemistry of living things | T_2245 | Lipids are biochemical compounds that living things use to store energy and make cell membranes. Types of lipids include fats, oils, and phospholipids. Fats are solid lipids that animals use to store energy. Examples of fats include butter and the fat in meat. Oils are liquid lipids that plants use to store energy. Examples of oils include olive oil and corn oil. Phospholipids contain the element phosphorus. They make up the cell membranes of living things. Lipids are made of long chains consisting almost solely of carbon and hydrogen. These long chains are called fatty acids. Fatty acids may be saturated or unsaturated. The Figure 2.10 shows an example of each type of fatty acid. | text | null |
L_0396 | chemistry of living things | T_2246 | Nucleic acids are biochemical compounds that include RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). Nucleic acids consist of chains of small molecules called nucleotides. Nucleotides are the monomers of nucleic 40 acids. A nucleotide is shown in Figure 2.11. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen. 2. a sugar, which is deoxyribose in DNA and ribose in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form bonds with each other. The bonded bases are called base pairs. Bonds form only between adenine and thymine, and between guanine and cytosine. They hold together the two chains of DNA and give it its characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 2.12. Sugars and phosphate groups form the backbone of each chain of DNA. Determining the structure of DNA was a huge scientific breakthrough. You can read the interesting story of its discovery and why it was so important at this link: DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in DNAs nucleotide chains. RNA copies and interprets the genetic code in DNA. RNA is also involved in the synthesis of proteins based on the code. You can watch these events unfolding at this link: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0396 | chemistry of living things | T_2246 | Nucleic acids are biochemical compounds that include RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). Nucleic acids consist of chains of small molecules called nucleotides. Nucleotides are the monomers of nucleic 40 acids. A nucleotide is shown in Figure 2.11. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen. 2. a sugar, which is deoxyribose in DNA and ribose in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form bonds with each other. The bonded bases are called base pairs. Bonds form only between adenine and thymine, and between guanine and cytosine. They hold together the two chains of DNA and give it its characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 2.12. Sugars and phosphate groups form the backbone of each chain of DNA. Determining the structure of DNA was a huge scientific breakthrough. You can read the interesting story of its discovery and why it was so important at this link: DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in DNAs nucleotide chains. RNA copies and interprets the genetic code in DNA. RNA is also involved in the synthesis of proteins based on the code. You can watch these events unfolding at this link: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0396 | chemistry of living things | T_2247 | The student athlete in Figure 2.13 is practically flying down the track! Running takes a lot of energy. But you dont have to run a race to use energy. All living things need energy all the time just to stay alive. The energy is produced in chemical reactions. A chemical reaction is a process in which some substances, called reactants, change chemically into different substances, called products. Reactants and products may be elements or compounds. Chemical reactions that take place inside living things are called biochemical reactions. Living things depend on biochemical reactions for more than just energy. Every function and structure of a living organism depends on thousands of biochemical reactions taking place in each cell. | text | null |
L_0396 | chemistry of living things | T_2248 | The sum of all of an organisms biochemical reactions is called metabolism. Biochemical reactions of metabolism can be divided into two general categories: catabolic reactions and anabolic reactions. You can watch an animation showing how the two categories of reactions are related at this link: Anabolic reactions involve forming bonds. Smaller molecules combine to form larger ones. These reactions require energy. For example, it takes energy to build starches from sugars. Catabolic reactions involve breaking bonds. Larger molecules break down to form smaller ones. These reactions release energy. For example, energy is released when starches break down to sugars. | text | null |
L_0396 | chemistry of living things | T_2249 | Each of the trillions of cells in your body is continuously performing thousands of anabolic and catabolic reactions. Thats an amazing number of biochemical reactionsfar more than the number of chemical reactions that might take place in a science lab or chemical plant. So many biochemical reactions can take place simultaneously in our cells because biochemical reactions occur very quickly. Thats because of enzymes. Enzymes are proteins that increase the rate of biochemical reactions. Enzymes arent changed or used up in the reactions, so they can be used to speed up the same reaction over and over again. Enzymes are highly specific for certain chemical reactions, so they are very effective. A reaction that would take years to occur without its enzyme might occur in a split second with the enzyme. | text | null |
L_0396 | chemistry of living things | T_2250 | Some of the most important biochemical reactions are the reactions involved in photosynthesis and cellular respira- tion. Photosynthesis is the process in which producers capture light energy from the sun and use it to make glucose. This involves anabolic reactions. Cellular respiration is the process in which energy is released from glucose and stored in smaller amounts in other molecules that cells can use for energy. This involves catabolic reactions. Photosynthesis and cellular respiration together provide energy to almost all living cells. Figure 2.14 shows how photosynthesis and cellular respiration are related. You can read more about both processes in the chapter Cell Functions. | text | null |
L_0398 | the nervous system | T_2257 | Controlling muscles and maintaining balance are just two of the functions of the human nervous system. What else does the nervous system do? It senses the surrounding environment with sense organs that include the eyes and ears. It senses the bodys own internal environment, including its temperature. It controls internal body systems to make sure the body maintains homeostasis. It prepares the body to fight or flee in the case of an emergency. It allows thinking, learning, memory, and language. Remember Hakeem the skater from the first page of the chapter? When Hakeem started to fall off the railing, his nervous system sensed that he was losing his balance. It responded by sending messages to his muscles. Some muscles contracted while other relaxed. As a result, Hakeem gained his balance again. How did his nervous system accomplish all of this in just a split second? You need to know how the nervous system transmits messages to answer that question. | text | null |
L_0398 | the nervous system | T_2258 | The nervous system is made up of nerves. A nerve is a bundle of nerve cells. A nerve cell that carries messages is called a neuron. The messages carried by neurons are called nerve impulses. A nerve impulse can travel very quickly because it is an electrical signal. Think about flipping on a light switch when you enter a room. When you flip the switch, electricity flows to the light through wires inside the walls. The electricity may have to travel many meters to reach the light. Nonetheless, the light still comes on as soon as you flip the switch. Nerve impulses travel just as quickly through the network of nerves inside the body. | text | null |
L_0398 | the nervous system | T_2259 | The structure of a neuron suits it for its function of transmitting nerve impulses. You can see what a neuron looks like in Figure 20.2. It has a special shape that lets it pass electrical signals to and from other cells. A neuron has three main parts: cell body, dendrites, and axon. 1. The cell body contains the nucleus and other organelles. 2. Dendrites receive nerve impulses from other cells. A single neuron may have thousands of dendrites. 3. The axon passes on the nerve impulses to other cells. It branches at the end into multiple nerve endings so it can transmit impulses to many other cells. | text | null |
L_0398 | the nervous system | T_2260 | There are three basic types of neurons: sensory neurons, motor neurons, and interneurons. All three types must work together to receive and respond to information. 1. Sensory neurons transmit nerve impulses from sense organs and internal organs to the brain via the spinal cord. In other words, they carry information about the inside and outside environment to the brain. 2. Motor neurons transmit nerve impulses from the brain via the spinal cord to internal organs, glands, and muscles. In other words, they carry information from the brain to the body, telling the body how to respond. 3. Interneurons carry nerve impulses back and forth between sensory and motor neurons. | text | null |
L_0398 | the nervous system | T_2261 | The nerve endings of an axon dont actually touch the dendrites of other neurons. The messages must cross a tiny gap between the two neurons, called the synapse. Chemicals called neurotransmitters carry the message across this gap. When a nerve impulse arrives at the end of an axon, neurotransmitters are released. They travel across the synaptic gap to a dendrite of another neuron. The neurotransmitters bind to the membrane of the dendrite, triggering a nerve impulse in the next neuron. You can see how this works in Figure 20.3 and in this animation: The transmission of nerve impulses between neurons is like the passing of a baton between runners in a relay race. After the first runner races, she passes the baton to the second runner. Then the second runner takes over. Instead of a baton, a neuron passes neurotransmitters to the next neuron. | text | null |
L_0398 | the nervous system | T_2262 | The nervous system has two main parts, called the central nervous system and the peripheral nervous system. The peripheral nervous system is described later in this lesson. The central nervous system is shown in Figure 20.4. It includes the brain and spinal cord. | text | null |
L_0398 | the nervous system | T_2263 | The human brain is an amazing organ. It is the most complex organ in the human body. By adulthood, the brain weighs about 3 pounds and consists of billions of neurons. All those cells need a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body! The brain serves as the control center of the nervous system and the body as a whole. It lets us understand what we see, hear, or sense in other ways. It allows us to learn, think, remember, and use language. It controls all the organs and muscles in our body. | text | null |
L_0398 | the nervous system | T_2264 | The brain consists of three major parts, called the cerebrum, cerebellum, and brain stem. You can see these three parts of the brain in Figure 20.5. You can use this interactive animation to explore these parts of the brain: http://s 1. The cerebrum is the largest part of the brain. It controls conscious functions, such as thinking, sensing, speaking, and voluntary muscle movements. Whether you are chatting with a friend or playing a video game, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It controls body position, coordination, and balance. Hakeems cerebellum kicked in when he started to lose his balance on the railing in the opening photo. It allowed him to regain his balance. 3. The brain stem (also called the medulla) is the smallest part of the brain. It controls involuntary body functions such as breathing, heartbeat, and digestion. It also carries nerve impulses back and forth between the rest of the brain and the spinal cord. | text | null |
L_0398 | the nervous system | T_2265 | The cerebrum is divided down the middle from the front to the back of the head. The two halves of the cerebrum are called the right and left hemispheres. The two hemispheres are very similar but not identical. They are connected to each other by a thick bundle of axons deep within the brain. These axons allow the two hemispheres to communicate with each other. Did you know that the right hemisphere of the cerebrum controls the left side of the body, and vice versa? This can happen because of the connections between the two hemispheres. Each hemisphere is further divided into four parts, called lobes, as you can see in Figure 20.6. Each lobe has different functions. One function of each lobe is listed in the figure. | text | null |
L_0398 | the nervous system | T_2266 | The spinal cord is a long, tube-shaped bundle of neurons. It runs from the brain stem to the lower back. The main job of the spinal cord is to carry nerve impulses back and forth between the body and brain. The spinal cord is like a two-way road. Messages about the body, both inside and out, pass through the spinal cord to the brain. Messages from the brain pass in the other direction through the spinal cord to tell the body what to do. | text | null |
L_0398 | the nervous system | T_2267 | All the other nervous tissues in the body are part of the peripheral nervous system. If you look again at Figure 20.1, you can see the major nerves of the peripheral nervous system. They include nerves that run through virtually every part of the body, both inside and out, except for the brain and spinal cord. The peripheral nervous system has two main divisions: the sensory division and the motor division. The divisions carry messages in opposite directions. Figure 20.7 shows these divisions of the peripheral nervous system. | text | null |
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