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L_0375 | fish | T_2045 | There are about 28,000 living species of fish. They are placed in five different classes. The classes are commonly called hagfish, lampreys, cartilaginous fish, ray-finned fish, and lobe-finned fish. Table 13.2 shows pictures of fish in each class. It also provides additional information about the classes. Class Hagfish Lampreys Cartilaginous Fish Distinguishing Traits Hagfish are very primitive fish. They lack scales and fins. They even lack a backbone, but they do have a cranium. They secrete large amounts of thick, slimy mucus. This makes them slippery, so they can slip out of the jaws of predators. Lampreys lack scales but have fins and a partial backbone. Their mouth is surrounded by a large round sucker with teeth. They use the sucker to suck the blood of other fish. Example hagfish Cartilaginous fish include sharks, rays, and ratfish. Their endoskele- ton is made of cartilage instead of bone. They also lack a swim blad- der. However, they have a complete vertebral column and jaws. They also have a relatively big brain. shark lampreys Class Ray-Finned Fish Lobe-Finned Fish Distinguishing Traits Ray-finned fish make up the ma- jority of living fish species. They are a type of bony fish, with an en- doskeleton made of bone instead of cartilage. Their fins consist of webs of skin over flexible bony spines, called rays. They have a swim blad- der. Lobe-finned fish include only coelacanths and lungfish. They are bony fish with an endoskeleton made of bone. Their fleshy fins contain bone and muscle. Lungfish are named for a lung-like organ that they can use for breathing air. It evolved from the swim bladder. It allows them to survive for long periods of time out of water. Example puffer lungfish | text | null |
L_0375 | fish | T_2046 | Fish vary in the types of places they live and what they eat. Many fish live in the salt water of the ocean. Other fish live in freshwater lakes, ponds, rivers, or streams. Most fish are predators, but they may differ in their prey and how they get it. Hagfish are deep-ocean bottom dwellers. They feed on other fish, either living or dead. They enter the body of their prey through the mouth or anus. Then they literally eat their prey from the inside out. Lampreys generally live in shallow water, either salty or fresh. They eat small invertebrates or suck the blood of larger fish. Cartilaginous fish, such as sharks, mainly live in the ocean. They prey on other fish and aquatic mammals, or else they eat plankton. Their jaws and teeth allow them to eat large prey. Bony fish, such as ray-finned or lobe-finned fish, may live in salt water or fresh water. They may eat algae, smaller fish like the butterfly fish in Figure 13.10, or dead organisms. To see how one species of predatory bony fish catches its prey, watch this amazing video: http://video.nationalgeographic.com/video/stonefish- MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0383 | introduction to the human body | T_2121 | The basic building blocks of the human body are cells. Human cells are organized into tissues, tissues are organized into organs, and organs are organized into organ systems. | text | null |
L_0383 | introduction to the human body | T_2122 | The average human adult consists of an incredible 100 trillion cells! Cells are the basic units of structure and function in the human body, as they are in all living things. Each cell must carry out basic life processes in order to survive and help keep the body alive. Most human cells also have characteristics for carrying out other, special functions. For example, muscle cells have extra mitochondria to provide the energy needed to move the body. You can see examples of these and some other specialized human cells in Figure 16.1. To learn more about specialized human cells and what they do, watch this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0383 | introduction to the human body | T_2123 | Specialized cells are organized into tissues. A tissue is a group of specialized cells of the same kind that perform the same function. There are four basic types of human tissues: connective, epithelial, muscle, and nervous tissues. The four types are shown in Figure 16.2. Connective tissue consists of cells that form the bodys structure. Examples include bone and cartilage, which protect and support the body. Blood is also a connective tissue. It circulates and connects cells throughout the body. Epithelial tissue consists of cells that cover inner and outer body surfaces. Examples include skin and the linings of internal organs. Epithelial tissue protects the body and its internal organs. It also secretes substances such as hormones and absorbs substances such as nutrients. Muscle tissue consists of cells that can contract, or shorten. Examples include skeletal muscle, which is attached to bones and makes them move. Other types of muscle include cardiac muscle, which makes the heart beat, and smooth muscle, which is found in other internal organs. Nervous tissue consists of nerve cells, or neurons, which can send and receive electrical messages. Nervous tissue makes up the brain, spinal cord, and other nerves that run throughout the body. | text | null |
L_0383 | introduction to the human body | T_2124 | The four types of tissues make up all the organs of the human body. An organ is a structure composed of two or more types of tissues that work together to perform the same function. Examples of human organs include the skin, brain, lungs, kidneys, and heart. Consider the heart as an example. Figure 16.3 shows how all four tissue types work together to make the heart pump blood. | text | null |
L_0383 | introduction to the human body | T_2124 | The four types of tissues make up all the organs of the human body. An organ is a structure composed of two or more types of tissues that work together to perform the same function. Examples of human organs include the skin, brain, lungs, kidneys, and heart. Consider the heart as an example. Figure 16.3 shows how all four tissue types work together to make the heart pump blood. | text | null |
L_0383 | introduction to the human body | T_2125 | Human organs are organized into organ systems. An organ system is a group of organs that work together to carry out a complex function. Each organ of the system does part of the overall job. For example, the heart is an organ in the circulatory system. The circulatory system also includes the blood vessels and blood. There are many different human organ systems. Figure 16.4 shows six of them and gives their functions. | text | null |
L_0383 | introduction to the human body | T_2126 | The organ systems of the body work together to carry out life processes and maintain homeostasis. The body is in homeostasis when its internal environment is kept more-or-less constant. For example, levels of sugar, carbon dioxide, and water in the blood must be kept within narrow ranges. This requires continuous adjustments. For example: After you eat and digest a sugary snack, the level of sugar in your blood quickly rises. In response, the endocrine system secretes the hormone insulin. Insulin helps cells absorb sugar from the blood. This causes the level of sugar in the blood to fall back to its normal level. When you work out on a hot day, you lose a lot of water through your skin in sweat. The level of water in the blood may fall too low. In response, the excretory system excretes less water in urine. Instead, the water is returned to the blood to keep water levels from falling lower. What happens if homeostasis is not maintained? Cells may not get everything they need, or toxic wastes may build up in the body. If homeostasis is not restored, it may cause illness or even death. | text | null |
L_0384 | the integumentary system | T_2127 | From the outside, the skin looks plain and simple, as you can see in Figure 16.5. But at a cellular level, theres nothing plain or simple about it. A single square inch of skin contains about 20 blood vessels, hundreds of sweat glands, and more than a thousand nerve endings. It also contains tens of thousands of pigment-producing cells. Clearly, there is much more to skin than meets the eye! For a dramatic introduction to the skin, watch this video: MEDIA Click image to the left or use the URL below. URL: The skin is only about 2 mm thick, or about as thick as the cover of a book. Although it is very thin, it consists of two distinct layers, called the epidermis and the dermis. You can see both layers and some of their structures in Figure 16.6. Refer to the figure as you read about the epidermis and dermis below. | text | null |
L_0384 | the integumentary system | T_2127 | From the outside, the skin looks plain and simple, as you can see in Figure 16.5. But at a cellular level, theres nothing plain or simple about it. A single square inch of skin contains about 20 blood vessels, hundreds of sweat glands, and more than a thousand nerve endings. It also contains tens of thousands of pigment-producing cells. Clearly, there is much more to skin than meets the eye! For a dramatic introduction to the skin, watch this video: MEDIA Click image to the left or use the URL below. URL: The skin is only about 2 mm thick, or about as thick as the cover of a book. Although it is very thin, it consists of two distinct layers, called the epidermis and the dermis. You can see both layers and some of their structures in Figure 16.6. Refer to the figure as you read about the epidermis and dermis below. | text | null |
L_0384 | the integumentary system | T_2128 | The epidermis is the outer layer of skin. It consists almost entirely of epithelial cells. There are no blood vessels, nerve endings, or glands in this skin layer. Nonetheless, this layer of skin is very active. It is constantly being renewed. How does this happen? 1. The cells at the bottom of the epidermis are always dividing by mitosis to form new cells. 2. The new cells gradually move up through the epidermis toward the surface of the body. As they move, they produce the tough, fibrous protein called keratin. 3. By the time the cells reach the surface, they have filled with keratin and died. On the surface, the dead cells form a protective, waterproof layer. 4. Dead cells are gradually shed from the surface of the epidermis. As they are shed, they are replaced by other dead cells that move up from below. The epidermis also contains cells called melanocytes. You can see a melanocyte in Figure 16.7. Melanocytes produce melanin. Melanin is a brown pigment that gives skin much of its color. Everyones skin has about the same number of melanocytes per square inch. However, the melanocytes of people with darker skin produce more melanin. The amount of melanin that is produced depends partly on your genes and partly on how much ultraviolet light strikes your skin. The more light you get, the more melanin your melanocytes produce. This explains why skin tans when its exposed to sunlight. | text | null |
L_0384 | the integumentary system | T_2129 | The dermis is the inner layer of skin. It is made of tough connective tissue. The dermis is attached to the epidermis by fibers made of the protein collagen. The dermis is where most skin structures are located. Look again at Figure pain, pressure, and temperature. If you cut your skin and it bleeds, the cut has penetrated the dermis and damaged a blood vessel. The cut probably hurts as well because of the nerve endings in this skin layer. The dermis also contains hair follicles and two types of glands. You can see some of these structures in Figure 16.8. Hair follicles are structures where hairs originate. Each hair grows out of a follicle, passes up through the epidermis, and extends above the skin surface. Sebaceous glands are commonly called oil glands. They produce an oily substance called sebum. Sebum is secreted into hair follicles. Then it makes its way along the hair shaft to the surface of the skin. Sebum waterproofs the hair and skin and helps prevent them from drying out. Sweat glands produce the salty fluid known as sweat. Sweat contains excess water, salts, and other waste products. Each sweat gland has a duct that passes through the epidermis. Sweat travels from the gland through the duct and out through a pore on the surface of the skin. | text | null |
L_0384 | the integumentary system | T_2130 | You couldnt survive without your skin. It has many important functions. In several ways, it helps maintain homeostasis. The main function of the skin is controlling what enters and leaves the body. It prevents the loss of too much water from the body. It also prevents bacteria and other microorganisms from entering the body. Melanin in the epidermis absorbs ultraviolet light. This prevents the light from reaching and damaging the dermis. The skin helps maintain a constant body temperature. It keeps the body cool in two ways. Sweat from sweat glands in the skin evaporates to cool the body. Blood vessels in the skin dilate, or widen, increasing blood flow to the body surface. This allows more heat to reach the surface and radiate into the environment. The opposite happens to retain body heat. Blood vessels in the skin constrict, or narrow, decreasing blood flow to the body surface. This reduces the amount of heat that reaches the surface so less heat is lost to the environment. | text | null |
L_0384 | the integumentary system | T_2131 | What can you do to keep your skin healthy? The most important step you can take is to protect your skin from sun exposure. On sunny days, wear long sleeves and pants and a hat with a brim. Also apply sunscreen to exposed areas of skin. Protecting your skin in these ways will reduce damage to your skin by ultraviolet light. This is important because skin that has been damaged by ultraviolet light is at greater risk of developing skin cancer. This is true whether the damage is due to sunlight or the light in tanning beds. About 85 percent of teens develop acne, like the boy in Figure 16.9. Acne is a condition in which pimples form on the skin. It is caused by a bacterial infection. It happens when the sebaceous glands secrete too much sebum. The excess oil provides a good place for bacteria to grow. Keeping the skin clean helps prevent acne. Over-the-counter products or prescription drugs may be needed if the problem is serious or doesnt clear up on its own. | text | null |
L_0384 | the integumentary system | T_2132 | You may spend a lot of time and money on your hair and nails. You may think of them as accessories, like clothes or jewelry. However, like the skin, the hair and nails also play important roles in helping the body maintain homeostasis. | text | null |
L_0384 | the integumentary system | T_2133 | Only mammals have hair. Hair is a fiber made mainly of the tough protein keratin. The cells of each hair are filled with keratin and no longer alive. The dead cells overlap each other, almost like shingles on a roof. They work like shingles as well, by helping shed water from hair. Head hair helps protect the scalp from sun exposure. It also helps insulate the body. It traps air so heat cant escape from the head. Hair in eyelashes and eyebrows helps keep water and dust out of the eyes. Hairs inside the nostrils of the nose trap dust and germs in the air so they cant reach the lungs. | text | null |
L_0384 | the integumentary system | T_2134 | Fingernails and toenails are made of specialized cells that grow out of the epidermis. They too are filled with keratin. The keratin makes them tough and hard. Their job is to protect the ends of the fingers and toes. They also make it easier to feel things with the sensitive fingertips by acting as a counterforce when things are handled. | text | null |
L_0385 | the skeletal system | T_2135 | Bones are the main organs of the skeletal system. In adults, the skeleton consists of a whopping 206 bones, many of them in the hands and feet. You can see many of the bones of the human skeleton in Figure 16.10. The skeletal system also includes cartilage and ligaments. Cartilage is a tough, flexible connective tissue that contains the protein collagen. It covers the ends of bones where they meet. The gray tissue in Figure 16.10 is cartilage. A ligament is a band of fibrous connective tissue. Ligaments connect bones of the skeleton and hold them together. | text | null |
L_0385 | the skeletal system | T_2136 | Your skeletal system supports your body and gives it shape. What else does it do? The skeletal system makes blood cells. Most blood cells are produced inside certain types of bones. The skeletal system stores calcium and helps maintain normal levels of calcium in the blood. Bones take up and store calcium when blood levels of calcium are high. They release some of the stored calcium when blood levels of calcium are low. The skeletal system works with muscles to move the body. Try to walk without bending your knees and youll see how important the skeletal system is for movement. The skeletal system protects the soft organs of the body. For example, the skull surrounds and protects the brain. The ribs protect the heart and lungs. | text | null |
L_0385 | the skeletal system | T_2137 | Some people think bones are like chalk: dead, dry, and brittle. In reality, bones are very much alive. They consist of living tissues and are supplied with blood and nerves. | text | null |
L_0385 | the skeletal system | T_2138 | Bones are organs. Like other organs, they are made up of more than one kind of tissue. There are four different kinds of tissues in bones, as shown in Figure 16.11. From the outside of the bone to the center, the tissues are periosteum, compact bone, spongy bone, and bone marrow. Periosteum is a tough, fibrous membrane that covers and protects the outer surfaces of bone. Compact bone lies below periosteum. It is very dense and hard. Compact bone gives bones their strength. Spongy bone lies below compact bone. It is less dense than compact bone. Spongy bone contains many tiny holes, or pores, which provide spaces for blood vessels and bone marrow. Bone marrow is a soft connective tissue inside pores and cavities in spongy bone. Bone marrow makes blood cells. | text | null |
L_0385 | the skeletal system | T_2139 | Early in the development of a human fetus, the skeleton is made entirely of cartilage. The relatively soft cartilage gradually changes to hard bone through ossification. This is a process in which mineral deposits replace cartilage in bone. At birth, several areas of cartilage remain, including the ends of the long bones in the arms and legs. This allows these bones to keep growing in length during childhood. By the late teens or early twenties, all of the cartilage has been replaced by bone. Bones cannot grow in length after this point has been reached. However, bones can continue to grow in width. They are stimulated to grow thicker when they are put under stress by muscles. Weight-bearing activities such as weight lifting can increase growth in bone width. | text | null |
L_0385 | the skeletal system | T_2140 | A joint is a place where two or more bones of the skeleton meet. There are three different types of joints based on the degree to which they allow movement of the bones: immovable, partly movable, and movable joints. Immovable joints do not allow the bones to move at all. In these joints, the bones are fused together by very tough collagen. Examples of immovable joints include the joints between bones of the skull. You can see them in Figure 16.12. Partly movable joints allow very limited movement. In these joints, the bones are held together by cartilage, which is more flexible than collagen. Examples of partly moveable joints include the bones of the rib cage. Movable joints allow the greatest movement and are the most common. In these joints, the bones are connected by ligaments. The surfaces of the bones at the joints are covered with a smooth layer of cartilage. It reduces friction between the bones when they move. The space between the bones is also filled with a liquid called synovial fluid. It helps to cushion the bones. There are several different types of movable joints. You can see three of them in Figure 16.13. Move these three joints in your own skeleton to experience the range of motion each allows. | text | null |
L_0385 | the skeletal system | T_2140 | A joint is a place where two or more bones of the skeleton meet. There are three different types of joints based on the degree to which they allow movement of the bones: immovable, partly movable, and movable joints. Immovable joints do not allow the bones to move at all. In these joints, the bones are fused together by very tough collagen. Examples of immovable joints include the joints between bones of the skull. You can see them in Figure 16.12. Partly movable joints allow very limited movement. In these joints, the bones are held together by cartilage, which is more flexible than collagen. Examples of partly moveable joints include the bones of the rib cage. Movable joints allow the greatest movement and are the most common. In these joints, the bones are connected by ligaments. The surfaces of the bones at the joints are covered with a smooth layer of cartilage. It reduces friction between the bones when they move. The space between the bones is also filled with a liquid called synovial fluid. It helps to cushion the bones. There are several different types of movable joints. You can see three of them in Figure 16.13. Move these three joints in your own skeleton to experience the range of motion each allows. | text | null |
L_0385 | the skeletal system | T_2141 | What you eat as a teen can affect how healthy your skeletal system is not only now but also in the future. Eating a diet with plenty of calcium and vitamin D can help keep your bones strong. If you dont get enough calcium and vitamin D in your diet as a teen, you will be more likely to develop osteoporosis when you are older. | text | null |
L_0385 | the skeletal system | T_2142 | Osteoporosis is a disease in which the bones become porous and weak because they do not contain enough calcium. The graph in Figure 16.14 shows how the mass of calcium in bone peaks around age 30 and declines after that, especially in women. Maximizing the calcium in your bones while youre young will reduce your risk of developing osteoporosis later in of life. | text | null |
L_0385 | the skeletal system | T_2143 | People with osteoporosis have an increased risk of bone fractures. A bone fracture is a crack or break in bone. Even if you have healthy bones, you may fracture a bone if too much stress is placed on it. This could happen in a car crash or while playing a sport. Wearing a seatbelt when you ride in a motor vehicle and wearing safety gear when you play sports may help prevent bone fractures. Bone fractures heal naturally as new bone tissue forms at the site of the fracture. However, the bone may have to be placed in a cast or have rods or screws inserted into it to keep it correctly aligned until it heals. The healing process usually takes several weeks or even months. | text | null |
L_0385 | the skeletal system | T_2144 | Another type of skeletal system injury is a sprain. A sprain is a strain or tear in a ligament that has been twisted or stretched too far. Ankle sprains are a common type of sprain. Athletes often strain a ligament in the knee called the ACL. Warming up adequately and stretching before playing sports may reduce the risk of a sprain. Ligament injuries can take a long time to heal. Rest, ice, compression, and elevation of the sprained area may help the healing process. | text | null |
L_0386 | the muscular system | T_2145 | Muscles are the main organs of the muscular system. Muscles are composed primarily of cells called muscle fibers. A muscle fiber is a very long, thin cell, as you can see in Figure 16.16. It contains multiple nuclei and many mitochondria, which produce ATP for energy. It also contains many organelles called myofibrils. Myofibrils allow muscles to contract, or shorten. Muscle contractions are responsible for virtually all the movements of the body, both inside and out. | text | null |
L_0386 | the muscular system | T_2145 | Muscles are the main organs of the muscular system. Muscles are composed primarily of cells called muscle fibers. A muscle fiber is a very long, thin cell, as you can see in Figure 16.16. It contains multiple nuclei and many mitochondria, which produce ATP for energy. It also contains many organelles called myofibrils. Myofibrils allow muscles to contract, or shorten. Muscle contractions are responsible for virtually all the movements of the body, both inside and out. | text | null |
L_0386 | the muscular system | T_2146 | To understand how a muscle contracts, you need to dive deeper into the structure of muscle fibers. You can see in Figure 16.16 that a muscle fiber is full of myofibrils. Each myofibril is made up of two types of proteins, called actin and myosin. These proteins form thread-like filaments. The myosin filaments use energy from ATP to pull on the actin filaments. This causes the actin filaments to slide over the myosin filaments and shorten a section of the myofibril. You can see a simple animation of the process at this link: http://commons.wikimedia.org/wiki/File:Actin_Myosin.gif The sliding-and-shortening process occurs all along many myofibrils and in many muscle fibers. It causes the muscle fibers to shorten and the muscle to contract. | text | null |
L_0386 | the muscular system | T_2147 | There are three different types of muscle tissue in the human body: cardiac, smooth, and skeletal muscle tissues. All three types consist mainly of muscle fibers, but the fibers have different arrangements. You can see how each type of muscle tissue looks in Figure 16.17. Cardiac muscle is found only in the walls of the heart. It is striated, or striped, because its muscle fibers are arranged in bundles. Contractions of cardiac muscle are involuntary. This means that they are not under conscious control. When cardiac muscle contracts, the heart beats and pumps blood. Smooth muscle is found in the walls of other internal organs such as the stomach. It isnt striated because its muscle fibers are arranged in sheets rather than bundles. Contractions of smooth muscle are involuntary. When smooth muscles in the stomach contract, they squeeze food inside the stomach. This helps break the food into smaller pieces. Skeletal muscle is attached to the bones of the skeleton. It is striated like cardiac muscle because its muscle fibers are arranged in bundles. Contractions of skeletal muscle are voluntary. This means that they are under conscious control. Whether you are doing pushups or pushing a pencil, you are using skeletal muscles. Skeletal muscles are the most common type of muscles in the body. You can read more about them below. | text | null |
L_0386 | the muscular system | T_2148 | The human body has more than 600 skeletal muscles. You can see some of them in Figure 16.18. A few of the larger muscles are labeled in the figure. | text | null |
L_0386 | the muscular system | T_2149 | You can see the bundles of muscle fibers that make up a skeletal muscle in Figure 16.19. You can also see in the figure how the muscle is attached to a bone by a tendon. Tendons are tough connective tissues that anchor skeletal muscles to bones throughout the body. Many skeletal muscles are attached to the ends of bones where they meet at a joint. The muscles span the joint and connect the bones. When the muscles contract, they pull on the bones, causing them to move. | text | null |
L_0386 | the muscular system | T_2149 | You can see the bundles of muscle fibers that make up a skeletal muscle in Figure 16.19. You can also see in the figure how the muscle is attached to a bone by a tendon. Tendons are tough connective tissues that anchor skeletal muscles to bones throughout the body. Many skeletal muscles are attached to the ends of bones where they meet at a joint. The muscles span the joint and connect the bones. When the muscles contract, they pull on the bones, causing them to move. | text | null |
L_0386 | the muscular system | T_2150 | Muscles can only contract. They cant actively lengthen. Therefore, to move bones back and forth at a joint, skeletal muscles must work in pairs. For example, the bicep and triceps muscles of the upper arm work as a pair. You can see how this pair of muscles works in Figure 16.20. When the bicep muscle contracts, it bends the arm at the elbow. When the triceps muscle contracts, it straightens the arm. | text | null |
L_0386 | the muscular system | T_2151 | Did you ever hear the saying, Use it or lose it? Thats certainly true when it comes to muscles. If you dont exercise your muscles, they will actually shrink in size. They will also become weaker and more prone to injury. | text | null |
L_0386 | the muscular system | T_2152 | Exercising muscles increases their size, and bigger muscles have greater strength. What type of exercises should you do? For all-round muscular health, you should do two basic types of exercise. To increase the size and strength of skeletal muscles, you need to make these muscles contract against a resisting force. For example, you can do sit-ups or pushups, where the resisting force is your own body weight. You can see another way to do it in Figure 16.21. To exercise cardiac muscle and increase muscle endurance, you need to do aerobic exercise. Aerobic exercise increases the size and strength of muscles in the heart and helps all your muscles develop greater endurance. This means they can work longer without getting tired. Aerobic exercise is any exercise such as running, biking, or swimming that causes an increase in your heart rate. You can see another example of aerobic exercise in Figure 16.22. Lifting weights is one way to pit skeletal muscles against a resisting force. Snowshoeing is a fun way to get aerobic exercise. | text | null |
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_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 |
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