lessonID
stringclasses 666
values | lessonName
stringclasses 631
values | ID
stringlengths 6
21
| content
stringlengths 10
6.57k
⌀ | media_type
stringclasses 2
values | ImagePath
stringlengths 28
76
⌀ |
|---|---|---|---|---|---|
L_0398 | the nervous system | T_2268 | The sensory division of the peripheral nervous system carries messages from sense organs and internal organs to the central nervous system. For example, it carries messages about images from the eyes to the brain. Once the messages reach the brain, the brain interprets the information. | text | null |
L_0398 | the nervous system | T_2269 | The motor division of the peripheral nervous system carries messages from the central nervous system to muscles, internal organs, and glands throughout the body. The brain sends commands to these tissues, telling them how to respond. As you can see in Figure 20.7, the motor division is divided into additional parts. The autonomic part of the motor division controls involuntary responses. It sends messages to organs and glands. These messages control the body both during emergencies (sympathetic division) and during none- mergencies (parasympathetic division). The somatic part of the motor division controls voluntary responses. It sends messages to the skeletal muscles for movements that are under conscious control. | text | null |
L_0398 | the nervous system | T_2270 | Nervous system problems include diseases and injuries. Most nervous system diseases cant be prevented. But you can take steps to decrease your risk of nervous system injuries. | text | null |
L_0398 | the nervous system | T_2271 | Bacteria and viruses can infect the brain or spinal cord. An infection of the brain is called encephalitis. An infection of the membranes that cover the brain and spinal cord is called meningitis. A vaccine is available to prevent meningitis caused by viruses (see Figure 20.8). Encephalitis and meningitis arent very common, but they can be extremely serious. They may cause swelling of the brain, which can be fatal. Thats why its important to know the symptoms of these diseases. Both encephalitis and meningitis typically cause a severe headache and a fever. Meningitis also causes a stiff neck. Both require emergency medical treatment. | text | null |
L_0398 | the nervous system | T_2272 | Epilepsy is a disease in which seizures occur. A seizure is a period of lost consciousness that may include violent muscle contractions. It is caused by abnormal electrical activity in the brain. Epilepsy may result from an infection, injury, or tumor. In many cases, however, the cause cant be identified. There is no known cure for epilepsy, but the seizures often can be prevented with medicine. Sometimes children with epilepsy outgrow it by adulthood. | text | null |
L_0398 | the nervous system | T_2273 | A stroke occurs when a blood clot blocks blood flow to part of the brain. Brain cells die quickly when their oxygen supply is cut off. Therefore, a stroke may cause permanent loss of normal mental functions. Many stroke patients suffer some degree of paralysis, or loss of the ability to feel or move certain parts of the body. If medical treatment is given very soon after a stroke occurs, some of the damage may be reversed. Strokes occur mainly in older adults. | text | null |
L_0398 | the nervous system | T_2274 | Alzheimers disease is another disease that occurs mainly in older adults. In Alzheimers disease, a person gradually loses most normal mental functions. The patient typically suffers from increasing memory loss, confusion, and mood swings. The cause of Alzheimers isnt known for certain, but it appears to be associated with certain abnormal changes in the brain. There is no known cure for this devastating disease, but medicines may be able to slow its progression. | text | null |
L_0398 | the nervous system | T_2275 | The brain and spinal cord are protected within bones of the skeletal system, but injuries to these organs still occur. With mild injuries, there may be no lasting effects. With severe injuries, there may be permanent disability or even death. Brain and spinal cord injuries most commonly occur because of car crashes or athletic activities. Fortunately, many injuries can be prevented by wearing seat belts and safety helmets (see Figure 20.9). Avoiding unnecessary risks, such as doing stunts on a bike or diving into shallow water, can also reduce the chances of brain and spinal cord injuries. The most common type of brain injury is a concussion. This is a bruise on the surface of the brain. It may cause temporary symptoms such as headache and confusion. Most concussions heal on their own in a few days or weeks. However, repeated concussions can lead to permanent changes in the brain. More serious brain injuries also often cause permanent brain damage. Spinal cord injuries may cause paralysis. Some people recover from spinal cord injuries. However, many people remain paralyzed for life. This happens when the spinal cord can no longer transmit nerve impulses between the body and brain. | text | null |
L_0398 | the nervous system | T_2276 | A drug is any chemical substance that affects the body or brain. Some drugs are medicines. Although these drugs are helpful when used properly, they can be misused like any other drug. Drugs that arent medicines include both legal and illegal drugs. Both can do harm. | text | null |
L_0398 | the nervous system | T_2277 | Many drugs affect the brain and influence how a person feels, thinks, or acts. Such drugs are called psychoactive drugs. They include legal drugs such as caffeine and alcohol, as well as illegal drugs such as cocaine and heroin. They also include certain medicines, such as antidepressant drugs and medical marijuana. Some psychoactive drugs, such as caffeine, stimulate the central nervous system. They may make the user feel more alert. Some psychoactive drugs, such as alcohol, depress the central nervous system. They may make the user feel more relaxed. Still other psychoactive drugs, such as marijuana, are hallucinogenic drugs. They may make the user have altered sensations, perceptions, or thoughts. | text | null |
L_0398 | the nervous system | T_2278 | Psychoactive drugs may bring about changes in mood that users find desirable. These drugs may be abused. Drug abuse is use of a drug without the advice of a medical professional and for reasons not originally intended. Continued use of a psychoactive drug may lead to drug addiction. This occurs when a drug user is unable to stop using the drug. Over time, a drug user may need more of the drug to get the desired effect. This can lead to drug overdose and death. | text | null |
L_0399 | the senses | T_2279 | The ability to see is called vision. It depends on both the eyes and the brain. The eyes sense light and form images. The brain interprets the images formed by the eyes and tells us what we are seeing. For a fascinating account of how the brain helps us see, watch this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0399 | the senses | T_2280 | Did you ever use 3-D glasses to watch a movie, like the teens in Figure 20.11? If you did, then you know that the glasses make images on the flat screen seem more realistic by giving them depth. The images seem to jump right out of the screen toward you. Unlike many other animals, human beings and other primates normally see the world around them in three dimen- sions. Thats because we have two eyes that face the same direction but are a few inches apart. Both eyes focus on the same object at the same time but from slightly different angles. The brain uses the different images from the two eyes to determine the distance to the object. Human beings and other primates also have the ability to see in color. We have special cells inside our eyes that can distinguish different wavelengths of visible light. Visible light is light in the range of wavelengths that the human eye can sense. The exact wavelength of visible light determines its color. | text | null |
L_0399 | the senses | T_2281 | The function of the eye is to focus light and form images. We see some objects, such as stars and light bulbs, because they give off their own light. However, we see most objects because they reflect light from another source such as the sun. We form images of the objects when some of the reflected light enters our eyes. Look at the parts of the eye in Figure 20.12. Follow the path of light through the eye as you read about it below. 1. Light from an object passes first through the cornea. This is a clear, protective covering on the outside of the eye. 2. Then light passes through the pupil, an opening in the center of the eye. The pupil, which looks black, is surrounded by the colored part of the eye, called the iris. 3. Light entering through the pupil next passes through the lens. The lens is a clear, curved structure, like the lens of a magnifying glass. Along with the cornea, the lens focuses the light on the back of the eye. 4. The back of the eye is covered by a thin layer called the retina. This is where the image of the object normally forms. The retina consists of special light-sensing cells called rods and cones. Rods sense dim light. Cones sense different colors of light. 5. Nerve impulses from rods and cones travel to the optic nerve. It carries the nerve impulses to the brain. | text | null |
L_0399 | the senses | T_2282 | You probably know people who need eyeglasses or contact lenses to see clearly. Maybe you need them yourself. Lenses are used to correct vision problems. Two of the most common vision problems in young people are myopia and hyperopia. You can compare myopia and hyperopia in Figure 20.13. To learn about astigmatism, another common vision problem, watch this very short video: . MEDIA Click image to the left or use the URL below. URL: Myopia is commonly called nearsightedness. People with myopia can see nearby objects clearly, but distant objects appear blurry. Myopia occurs when images focus in front of the retina because the eyeball is too long. This vision problem can be corrected with concave lenses, which curve inward. The lenses focus images correctly on the retina. Hyperopia is commonly called farsightedness. People with hyperopia can see distant objects clearly, but nearby objects appear blurry. Hyperopia occurs when images focus in back of the retina because the eyeball is too short. This vision problem can be corrected with convex lenses, which curve outward. The lenses focus images correctly on the retina. | text | null |
L_0399 | the senses | T_2283 | Vision is just one of several human senses. Other human senses include hearing, touch, taste, and smell. Imagine shopping at the fruit market in Figure 20.14. It would stimulate all of these senses. You would hear the noisy bustle of the market. You could feel the smooth skin of the fruit. If you tried a sample, you could smell the fruity aroma and taste its sweet flavor. | text | null |
L_0399 | the senses | T_2284 | What do listening to music and riding a bike have in common? Both activities depend on the ears. The ears are organs that sense sound. They also sense the position of the body and help maintain balance. Hearing is the ability to sense sound. Sound travels through the air in waves. Suppose a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves enter your ears and cause vibrations. The vibrations trigger nerve impulses that travel to the brain through the auditory nerve. You can learn how this happens in Figure 20.15. The brain then interprets the impulses and tells you what you are hearing. To find out how the brain determines where a sound is coming from, watch this amusing video: MEDIA Click image to the left or use the URL below. URL: The parts of the ears involved in balance are the semicircular canals. These are the curved structures above the cochlea in the inner ear in Figure 20.15. Like the cochlea, the semicircular canals contain liquid and are lined with tiny hair cells. As the head changes position, the liquid moves. This causes the hair cells to bend. The bending of the hair cells triggers nerve impulses that travel to the cerebellum in the brain. The cerebellum uses the information to maintain balance. | text | null |
L_0399 | the senses | T_2285 | Touch is the ability to sense pain, pressure, or temperature. Nerve cells that sense touch are found mainly in the skin. The skin on the palms, soles, face, and lips has the most neurons. Neurons that sense pain are also found inside the body inside the body in the tongue, joints, muscles, and other organs. Suppose you wanted to test the temperature of bath water before getting into the tub. You might stick one toe in the water. Neurons in the skin on your toe would sense the temperature of the water and send a message about it to the brain through the spinal cord. The brain would process the information. It might decide that the water is too hot and send a message to your muscles to pull your toe out of the water. | text | null |
L_0399 | the senses | T_2286 | The sense of taste is controlled by sensory neurons on the tongue. They are grouped in bundles called taste buds. You can see taste buds on the tongue in Figure 20.16. Taste neurons sense chemicals in food. They can detect five different tastes: sweet, salty, sour, bitter, and umami, which is a meaty taste. When taste neurons sense chemicals, they send messages to the brain about them. The brain then decides what you are tasting. The sense of smell also involves sensory neurons that sense chemicals. These neurons are found in the nose, and they sense chemicals in the air. Unlike taste neurons, smell neurons can detect thousands of different odors. Your sense of smell plays a big role in your sense of taste. You can use your sense of taste alone to learn that a food is sweet. However, you have to use your sense of smell as well to learn that the food tastes like apple pie. | text | null |
L_0400 | the endocrine system | T_2287 | The endocrine system is a system of glands that release chemical messenger molecules into the blood stream. The messenger molecules are called hormones. Hormones act slowly compared with the rapid transmission of electrical impulses of the nervous system. Endocrine hormones must travel through the bloodstream to the cells they control, and this takes time. On the other hand, because endocrine hormones are released into the bloodstream, they travel to cells everywhere in the body. For a good visual introduction to the endocrine system, watch this short video: http MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0400 | the endocrine system | T_2288 | An endocrine gland is a gland that secretes hormones into the bloodstream for transport around the body (instead of secreting hormones locally, like sweat glands in the skin). Major glands of the endocrine system are shown in Figure 20.17. The glands are the same in males and females except for the ovaries and testes. | text | null |
L_0400 | the endocrine system | T_2289 | The hypothalamus is actually part of the brain, but it also secretes hormones. Some of its hormones go directly to the pituitary gland in the endocrine system. These hypothalamus hormones tell the pituitary to either secrete or stop secreting its hormones. In this way, the hypothalamus provides a link between the nervous and endocrine systems. The hypothalamus also produces hormones that directly regulate body processes. For example, it produces antid- iuretic hormone. This hormone travels to the kidneys and stimulates them to conserve water by producing more concentrated urine. | text | null |
L_0400 | the endocrine system | T_2290 | The pea-sized pituitary gland is just below the hypothalamus and attached directly to it. The pituitary receives hormones from the hypothalamus. It also secretes its own hormones. Most pituitary hormones control other endocrine glands. Thats why the pituitary gland is called the master gland of the endocrine system. Table Pituitary Hormone Adrenocorticotropic (ACTH) hormone Target Glands/Cells adrenal glands Thyroid-stimulating (TSH) Growth hormone (GH) hormone thyroid gland Follicle-stimulating (FSH) hormone body cells ovaries or testes Luteinizing hormone (LH) ovaries or testes Prolactin (PRL) mammary glands Effects(s) Stimulates the cortex (outer layer) of the adrenal glands to secrete their hormones Stimulates the thyroid gland to se- crete its hormones Stimulates body cells to make pro- teins and grow Stimulates the ovaries to develop mature eggs; stimulates the testes to produce sperm Stimulates the ovaries or testes to secrete sex hormones; stimulates the ovaries to release eggs Stimulates the mammary glands to produce milk | text | null |
L_0400 | the endocrine system | T_2291 | There are several other endocrine glands. Find them in Figure 20.17 as you read about them below. The thyroid gland is a relatively large gland in the neck. Hormones secreted by the thyroid gland include thyroxin. Thyroxin increases the rate of metabolism in cells throughout the body. The pancreas is a large gland located near the stomach. Hormones secreted by the pancreas include insulin. Insulin helps cells absorb glucose from the blood. It also stimulates the liver to take up and store excess glucose. The two adrenal glands are glands located just above the kidneys. Each adrenal gland has an outer layer (cortex) and inner layer (medulla) that secrete different hormones. The hormone adrenaline is secreted by the inner layer. It prepares the body to respond to emergencies. For example, it increases the amount of oxygen and glucose going to the muscles. The gonads are glands that secrete sex hormones. Male gonads are called testes. They secrete the male sex hormone testosterone. The female gonads are called ovaries. They secrete the female sex hormone estrogen. Sex hormones stimulate the changes of puberty. They also control the production of sperm or eggs by the gonads. | text | null |
L_0400 | the endocrine system | T_2292 | Endocrine hormones travel throughout the body in the blood. However, each endocrine hormone affects only certain cells, called target cells. | text | null |
L_0400 | the endocrine system | T_2293 | A target cell is the type of cell on which a given endocrine hormone has an effect. A target cell is affected by a given hormone because it has proteins on its surface to which the hormone can bind. When the hormone binds to target cell proteins, it causes changes inside the cell. For example, binding of the hormone might cause the release of enzymes inside the cell. The enzymes then influence cell processes. | text | null |
L_0400 | the endocrine system | T_2294 | Endocrine hormones control many cell activities, so they are very important for homeostasis. But what controls the hormones? Most endocrine hormones are controlled by feedback loops. In a feedback loop, the hormone produced by a gland feeds back to control its own production by the gland. A feedback loop can be negative or positive. Most endocrine hormones are controlled by negative feedback loops. .Negative feedback occurs when rising levels of a hormone feed back to decrease secretion of the hormone or when falling levels of the hormone feed back to increase its secretion. You can see an example of a negative feedback loop in Figure 20.18. It shows how levels of thyroid hormones regulate the thyroid gland. This loop involves the hypothalamus and pituitary gland as well as the thyroid gland. Low levels of thyroid hormones in the blood cause the release of hormones by the hypothalamus and pituitary gland. These hormones stimulate the thyroid gland to secrete more hormones. The opposite happens with high levels of thyroid hormones in the blood. The hypothalamus and pituitary gland stop releasing hormones that stimulate the thyroid. | text | null |
L_0400 | the endocrine system | T_2295 | Diseases of the endocrine system are fairly common. An endocrine disease usually involves the secretion of too much or not enough hormone by an endocrine gland. This may happen because the gland develops an abnormal lump of cells called a tumor. For example, a tumor of the pituitary gland can cause secretion of too much growth hormone. If this occurs in a child, it may result in very rapid growth and unusual tallness by adulthood. This is called gigantism. Type 1 diabetes is another endocrine system disease. In this disease, the bodys own immune system attacks insulin- secreting cells of the pancreas. As a result, not enough insulin is secreted to maintain normal levels of glucose in the blood. Patients with type 1 diabetes must regularly check the level of glucose in their blood. When it gets too high, they must give themselves an injection of insulin to bring it under control. You can learn more about glucose, insulin, and type 1 diabetes by watching this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0401 | infectious diseases | T_2296 | An infectious disease is a disease that is caused by a pathogen. A pathogen is an organism or virus that causes disease in another living thing. Pathogens are commonly called germs. Watch this dramatic video for an historic perspective on infectious diseases and their causes: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0401 | infectious diseases | T_2297 | There are several types of pathogens that cause diseases in human beings. They include bacteria, viruses, fungi, and protozoa. The different types are described in Table 21.1. The table also lists several diseases caused by each type of pathogen. Many infectious diseases caused by these pathogens can be cured with medicines. For example, antibiotic drugs can cure most diseases caused by bacteria. | text | null |
L_0401 | infectious diseases | T_2298 | Different pathogens spread in different ways. Some are easy to catch. Others are much less contagious. Some pathogens spread through food or water. When harmful bacteria contaminate food, they cause foodborne illness, commonly called food poisoning. An example of a pathogen that spreads through water is the protozoan named Giardia lamblia, described in Table 21.1. It causes a disease called giardiasis. Some pathogens spread through sexual contact. In the U.S., the pathogen most commonly spread this way is HPV, or human papillomavirus. It may cause genital warts and certain types of cancer. A vaccine can prevent the spread of this pathogen. Many pathogens spread by droplets in the air. Droplets are released when a person coughs or sneezes, as you can see in Figure 21.2. The droplets may be loaded with pathogens. Other people may get sick if they breathe in the pathogens on the droplets. Viruses that cause colds and flu can spread this way. Other pathogens spread when they are deposited on objects or surfaces. The fungus that causes athletes food spreads this way. For example, you might pick up the fungus from the floor of a public shower. You can also pick up viruses for colds and flu from doorknobs and other commonly touched surfaces. Still other pathogens are spread by vectors. A vector is an organism that carries pathogens from one person or animal to another. Most vectors are insects such as ticks or mosquitoes. They pick up pathogens when they bite an infected animal and then transmit the pathogens to the next animal they bite. Ticks spread the bacteria that cause Lyme disease. Mosquitoes spread the protozoa that cause malaria. | text | null |
L_0401 | infectious diseases | T_2299 | What can you do to avoid infectious diseases? Eating well and getting plenty of sleep are a good start. These habits will help keep your immune system healthy. With a healthy immune system, you will be able to fight off many pathogens. Vaccines are available for some infectious diseases. For example, there are vaccines to prevent measles, mumps, whooping cough, and chicken pox. These vaccines are recommended for infants and young children. You can also take the following steps to avoid picking up pathogens or spreading them to others. Watch this video for additional information on preventing the spread of infectious diseases: MEDIA Click image to the left or use the URL below. URL: Wash your hands often with soap and water. Spend at least 20 seconds scrubbing with soap. See Figure 21.3 for effective hand washing tips. Avoid touching your eyes, nose, or mouth with unwashed hands. Avoid close contact with people who are sick. This includes kissing, hugging, shaking hands, and sharing cups or eating utensils. Cover your coughs and sneezes with a tissue or shirt sleeve, not your hands. Disinfect frequently touched surfaces, such as keyboards and doorknobs, especially if someone is sick. Stay home when you are sick. The best way to prevent diseases spread by vectors is to avoid contact with the vectors. For example, you can wear long sleeves and long pants to avoid tick and mosquito bites. Using insect repellent can also reduce your risk of insect bites. | text | null |
L_0402 | noninfectious diseases | T_2300 | Cancer is a disease in which cells divide out of control. Normally, the body has ways to prevent cells from dividing out of control. However, in the case of cancer, these ways fail. The rapidly dividing cells may form a mass of abnormal tissue called a tumor. This is illustrated in Figure 21.4. Watch this video for an animated introduction to cancer: . MEDIA Click image to the left or use the URL below. URL: As a tumor increases in size, it may harm normal tissues around it. Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are carried throughout the body. Then the cells may start growing in other tissues. This is usually how cancer spreads from one part of the body to another. Once this happens, cancer is very hard to stop. | text | null |
L_0402 | noninfectious diseases | T_2301 | Most cancers are caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually occur in genes that control the cell cycle. Because of the mutations, abnormal cells are allowed to divide. Some mutations that lead to cancer may be inherited. However, most of the mutations are caused by environmental factors. Anything in the environment that can cause cancer is called a carcinogen. Common carcinogens include certain chemicals and some types of radiation. Many different chemicals can cause cancer. For example, tobacco contains dozens of chemicals, including nicotine, that have been shown to cause cancer. Figure 21.5 shows some of these chemicals. Smoking tobacco or using smokeless tobacco increases the risk of cancer of the lung, mouth, throat, and urinary bladder. Types of radiation that cause cancer include ultraviolet (UV) radiation and radon. UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon is a naturally occurring radioactive gas that escapes from underground rocks. It may seep into the basements of buildings. It can cause lung cancer. | text | null |
L_0402 | noninfectious diseases | T_2302 | Cancer occurs most often in adults, especially adults over the age of 50. The most common types of cancer in adults differ between males and females. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. About one third of all cancers in men are prostate cancers. The most common type of cancer in adult females is cancer of the breast. About one third of all cancers in women are breast cancers. In both men and women, the second most common type of cancer is lung cancer. Most cases of lung cancer develop in people who smoke. Childhood cancer is rare. The main type of cancer in children is leukemia. It makes up about one third of all childhood cancers. It occurs when the body makes abnormal white blood cells. | text | null |
L_0402 | noninfectious diseases | T_2303 | Many cases of cancer can be cured if the cancer is diagnosed and treated early. Treatment often involves removing a tumor with surgery. This may be followed by other types of treatments. These treatments may include drugs and radiation, both of which target and kill cancer cells. Its important to know the warning signs of cancer so it can be diagnosed as early as possible. Having warning signs doesnt mean that you have cancer, but you should check with a doctor to be sure. Warning signs of cancer include: a change in bowel or bladder habits. a sore that doesnt heal. unusual bleeding or discharge. a lump in the breast or elsewhere. frequent, long-term indigestion. difficulty swallowing. obvious changes in a wart or mole. persistent cough or hoarseness. | text | null |
L_0402 | noninfectious diseases | T_2304 | Making healthy lifestyle choices can help prevent some types of cancer. For example, you can reduce your risk of lung cancer by not smoking. You can reduce your risk of skin cancer by using sunscreen (see Figure 21.6). | text | null |
L_0402 | noninfectious diseases | T_2305 | Diabetes is another type of noninfectious disease. Diabetes occurs when the pancreas doesnt make enough insulin or else the bodys cells are resistant to the effects of insulin. Insulin is a hormone that helps cells absorb glucose from the blood. When there is too little insulin or cells do not respond to it, the blood contains too much glucose. High glucose levels in the blood can damage blood vessels and other cells in the body. The kidneys work harder to filter the extra glucose from the blood and excrete it in urine. This leads to frequent urination, which in turn causes excessive thirst. Watch this short video for an animated introduction to diabetes, its causes, and its consequences: MEDIA Click image to the left or use the URL below. URL: There are two main types of diabetes: type 1 diabetes and type 2 diabetes. The two types of diabetes have different causes. | text | null |
L_0402 | noninfectious diseases | T_2306 | Type 1 diabetes is caused by the immune system attacking and destroying normal cells of the pancreas. As a result, the cells can no longer produce insulin. Why the immune system acts this way is not known for certain. Its possible that a virus may trigger the attack. This type of diabetes usually develops in childhood or adolescence. At present, there is no known way to prevent the development of type 1 diabetes. However, it is a treatable disease. Treatment of type 1 diabetes includes: taking several insulin injections every day or using an insulin pump (see Figure 21.7). monitoring blood glucose levels several times a day. eating a healthy diet that spreads out carbohydrate intake throughout the day. regular physical activity, which helps the body use insulin more efficiently. regular medical checkups. | text | null |
L_0402 | noninfectious diseases | T_2307 | Type 2 diabetes is much more common than type 1 diabetes. Type 2 diabetes occurs when body cells no longer respond normally to insulin. The pancreas still makes insulin, but the cells of the body cant use it. Being overweight and having high blood pressure increase the chances of developing type 2 diabetes. This type of diabetes usually develops in adulthood. However, it is becoming more common in teens and children because more young people are overweight now than ever before. You can greatly reduce your risk of developing type 2 diabetes by maintaining a healthy body weight. Some cases of type 2 diabetes can be cured with weight loss. However, most people with the disease need to take medicine to control their blood glucose. Regular exercise and balanced eating also help. Like people with type 1 diabetes, people with type 2 diabetes must frequently check their blood glucose. | text | null |
L_0402 | noninfectious diseases | T_2308 | The immune system is the body system that normally fights infections and defends against other causes of disease. When the immune system is working well, it usually keeps you from getting sick. But like any other body system, the immune system can have problems and develop diseases. Two types of immune system diseases are autoimmune diseases and allergies. | text | null |
L_0402 | noninfectious diseases | T_2309 | An autoimmune disease is a disease in which the immune system attacks the bodys own cells. Why this happens is not known for certain, but a combination of genetic and environmental factors are likely to be responsible. Type 1 diabetes is an example of an autoimmune disease. In this case, the immune system attacks cells of the pancreas. Two other examples are multiple sclerosis and rheumatoid arthritis. In multiple sclerosis, the immune system attacks nerve cells. This causes weakness and pain that gradually get worse over time. In rheumatoid arthritis, the immune system attacks joints. This causes joint damage and pain. These diseases cant be prevented and have no known cure. However, they can be treated with medicines that weaken the immune systems attack on normal cells. | text | null |
L_0402 | noninfectious diseases | T_2310 | An allergy is a disorder in which the immune system responds to a harmless substance as though it was a pathogen. Any substance that causes an allergy is called an allergen. The most common allergens are pollen, dust mites, mold, animal dander, insect stings, latex, and certain foods and medications. To see in greater detail how allergies occur, watch this animated video: . MEDIA Click image to the left or use the URL below. URL: Did you ever hear of hay fever? Its not really a fever, and it may have nothing to do with hay. Its actually an allergy to plant pollens. People with this type of allergy generally have seasonal allergies that come back year after year. Symptoms commonly include watery eyes and nasal congestion. Ragweed, shown blooming in Figure 21.8, causes more pollen allergies than any other plant. Allergy symptoms can range from mild to severe. Mild symptoms might include itchy eyes, sneezing, and a runny nose. Severe symptoms can cause difficulty breathing, which may be life threatening. Keep in mind that it is the immune system and not the allergen that causes the allergy symptoms. Allergy symptoms can be treated with medications such as antihistamines. Severe allergic reactions may require an injection of the hormone epinephrine. These treatments lessen or counter the immune systems response. Often, allergy symptoms can be prevented. One way is to avoid exposure to the allergens that cause your symptoms. If you are allergic to pollen, for example, you can reduce your exposure by staying inside when pollen levels are highest. Some people receive allergy shots to help prevent allergic reactions. The shots contain tiny amounts of allergens. After many months or years of shots, the immune system gets used to the allergens and no longer reacts to them. | text | null |
L_0405 | male reproductive system | T_2327 | The male reproductive system has two main functions: producing sperm and releasing testosterone. Sperm are male gametes, or reproductive cells. Sperm form when certain cells in the male reproductive system divide by meiosis to form haploid cells. Being haploid means they have half the number of chromosomes of other cells in the body. An adult male may produce millions of sperm each day! Testosterone is the major sex hormone in males. Testosterone has two primary roles: 1. During adolescence, testosterone causes most of the changes associated with puberty. It causes the reproduc- tive organs to mature. It also causes other adult male traits to develop. For example, it causes the voice to deepen and facial hair to start growing. 2. During adulthood, testosterone is needed for the production of sperm. | text | null |
L_0405 | male reproductive system | T_2328 | The male reproductive organs include the penis, testes, epididymis, vas deferens, and prostate gland. These organs are shown in Figure 22.1. The figure also shows some other parts of the male reproductive system. Find each organ in the drawing as you read about it below. For a cartoon about the male reproductive system, watch this video: http MEDIA Click image to the left or use the URL below. URL: The penis is an external, cylinder-shaped organ that contains the urethra. The urethra is the tube that carries urine out of the body. It also carries sperm out of the body. The two testes (testis, singular) are oval organs that produce sperm and secrete testosterone. They are located inside a sac called the scrotum that hangs down outside the body. The scrotum also contains the epididymis. | text | null |
L_0405 | male reproductive system | T_2329 | Sperm are tiny cells. In fact, they are the smallest of all human cells. They have a structure that suits them well to perform their function. | text | null |
L_0405 | male reproductive system | T_2330 | As you can see in Figure 22.2, a sperm has three main parts: the head, connecting piece (or midpiece), and tail. 1. The head of the sperm contains the nucleus. The nucleus holds the chromosomes. In humans, the nucleus of a sperm cell contains 23 chromosomes. The acrosome on the head contains enzymes that help the sperm penetrate an egg. 2. The connecting piece of the sperm is packed with mitochondria. Mitochondria are organelles in cells that produce energy. Sperm use the energy to move. 3. The tail of the sperm moves like a propeller. It spins around and around and pushes the sperm forward. Sperm can travel about 30 inches per hour. | text | null |
L_0405 | male reproductive system | T_2331 | It takes up to two months for mature sperm to form. The process occurs in several steps: 1. Special cells in the testes go through mitosis to make identical copies of themselves. 2. The copies of the original cells divide by meiosis. This results in haploid cells called spermatids. These cells lack tails and cannot yet swim. 3. Spermatids move from the testes to the epididymis, where they slowly mature. For example, they grow a tail and lose some of the cytoplasm from the head. 4. Once sperm are mature, they can swim. The mature sperm remain in the epididymis until it is time for them to leave the body. Sperm leave the epididymis through the vas deferens. As they travel through the vas deferens, they pass by the prostate and other glands. The sperm mix with secretions from these glands, forming semen. Semen travels through the urethra and leaves the body through the penis. A teaspoon of semen may contain as many as half a billion sperm! | text | null |
L_0406 | female reproductive system | T_2332 | Two functions of the female reproductive system are similar to the functions of the male reproductive system: producing gametes and secreting a major sex hormone. In the case of females, however, the gametes are eggs, and they are produced by the ovaries. The hormone is estrogen, which is the main sex hormone in females. Estrogen has two major roles: During adolescence, estrogen causes the changes of puberty. It causes the reproductive organs to mature. It also causes other female traits to develop. For example, it causes the breasts to grow and the hips to widen. During adulthood, estrogen is needed for a woman to release eggs from the ovaries. The female reproductive system has another important function, which is not found in males. It supports a baby as it develops before birth. It also gives birth to the baby at the end of pregnancy. | text | null |
L_0406 | female reproductive system | T_2333 | The female reproductive organs include the ovaries, fallopian tubes, uterus, and vagina. These organs are shown in Figure 22.3, along with some other structures of the female reproductive system. Find each organ in the drawing as you read about it below. For a cartoon about the female reproductive system, watch this video: http://education-por The two ovaries are small, oval organs on either side of the abdomen. Each ovary contains thousands of eggs. However, the eggs do not develop fully until a female has gone through puberty. Then, about once a month, an egg is released by one of the ovaries. The ovaries also secrete estrogen. The two fallopian tubes are thin tubes that are connected to the uterus and extend almost to the ovaries. The upper end of each fallopian tube has fingers (called fimbriae) that sweep an egg into the fallopian tube when it is released by the ovary. The egg then passes through the fallopian tube to the uterus. If an egg is fertilized, this occurs in the fallopian tube. The uterus is a hollow organ with muscular walls. The uterus is where a baby develops until birth. The walls of the uterus stretch to accommodate the growing fetus. The muscles in the walls contract to push the baby out during birth. The uterus is connected to the vagina by a small opening called the cervix. The vagina is a cylinder-shaped organ that opens to the outside of the body. The other end joins with the uterus. Sperm deposited in the vagina swim up through the cervix, into the uterus, and from there into a | text | null |
L_0406 | female reproductive system | T_2334 | When a baby girl is born, her ovaries contain all of the eggs they will ever produce. But these eggs are not fully developed. They develop only after the female reaches puberty at about age 12 or 13. Then, just one egg develops each month until she reaches her 40s or early 50s. | text | null |
L_0406 | female reproductive system | T_2335 | Human eggs are very large cells. In fact, they are the largest of all human cells. You can even see an egg without a microscope. Its almost as big as the period at the end of this sentence. Like a sperm cell, an egg cell is a haploid cell with half the number of chromosomes of other cells in the body. Unlike a sperm cell, the egg lacks a tail and contains a lot of cytoplasm. | text | null |
L_0406 | female reproductive system | T_2336 | Egg production takes place in the ovaries. It occurs in several steps: 1. Before birth, special cells in the ovaries go through mitosis to make identical daughter cells. 2. The daughter cells then start to divide by meiosis. However, they go though only the first of the two cell divisions of meiosis at this time. They remain in that stage until the girl goes through puberty. 3. After puberty, an egg develops in an ovary about once a month. As you can see in Figure 22.4, the egg rests in a nest of cells called a follicle. The follicle and egg grow larger and go through other changes. 4. After a couple of weeks, the egg bursts out of the follicle and through the wall of the ovary. This is called ovulation. After ovulation occurs, the moving fingers of the nearby fallopian tube sweep the egg into the tube. Fertilization may occur if sperm reach the egg while it is passing through the fallopian tube. If this happens, the egg finally completes meiosis. This results in two daughter cells that differ in size. The smaller cell is called a polar body. It soon breaks down and disappears. The larger cell is the fertilized egg, which will develop into a new human being. | text | null |
L_0406 | female reproductive system | T_2337 | Egg production in the ovary is part of the menstrual cycle. The menstrual cycle is a series of changes in the reproductive system of mature females that repeats every month on average. These changes include the development of an egg and follicle in the ovary. While the egg is developing, other changes are taking place in the uterus. It develops a thick lining that is full of tiny blood vessels. The lining prepares the uterus to receive a fertilized egg if fertilization actually takes place. If fertilization doesnt occur, the egg passes through the uterus and vagina and out of the body. The lining of the uterus also breaks down. Blood and other tissues from the lining pass through the vagina and leave the body. This is called menstruation. Menstruation is also called a menstrual period. It typically lasts about 4 days. When the menstrual period ends, the cycle begins repeats. | text | null |
L_0407 | reproduction and life stages | T_2338 | When a sperm penetrates the cell membrane of an egg, it triggers the egg to complete meiosis. The sperm also undergoes changes. Its tail falls off, and its nucleus fuses with the nucleus of the egg. The resulting cell, called a zygote, contains the diploid number of chromosomes. Half of the chromosomes come from the egg, and half come from the sperm. You can watch the process of fertilization and the development of a baby until birth in this amazing video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0407 | reproduction and life stages | T_2339 | The zygote spends the next few days traveling down the fallopian tube toward the uterus, where it will take up residence. As it travels, it divides many times by mitosis. It soon forms a tiny, fluid-filled ball of cells called a blastocyst. The blastocyst has an inner and outer layer of cells, as you can see in Figure 22.5. The inner layer, called the embryoblast, will develop into the new human being. The outer layer, called the trophoblast, will develop into other structures needed to support the new organism. | text | null |
L_0407 | reproduction and life stages | T_2340 | The blastocyst continues down the fallopian tube until it reaches the uterus, about 4 or 5 days after fertilization. When the outer cells of the blastocyst contact cells lining the uterus (the endometrium in Figure 22.5), the blastocyst embeds itself in the uterine lining. This process is called implantation. It generally occurs about a week after fertilization. | text | null |
L_0407 | reproduction and life stages | T_2341 | After implantation occurs, the blastocyst is called an embryo. The embryonic stage lasts from the end of the first week following fertilization through the end of the eighth week. During this time, the embryo grows in size and becomes more complex. It develops specialized cells and tissues. Most organs also start to form. You can see some of the specific changes that take place during weeks four to eight of the embryonic period in Figure 22.6. By the end of week eight, the embryo is about 30 millimeters (just over 1 inch) in length. It may also have begun to move. | text | null |
L_0407 | reproduction and life stages | T_2342 | From the eighth week following fertilization until birth, the developing human being is called a fetus. Birth typically occurs at about 38 weeks after fertilization, so the fetal period generally lasts about 30 weeks. During this time, the organs complete their development. The fetus also grows rapidly in length and weight. Some of the specific changes that occur during the fetal stage are listed in Figure 22.7. By the 38th week, the fetus is fully developed and ready to be born. A 38-week fetus normally ranges from about 36 to 51 centimeters (1420 inches) in length and weighs between 2.7 and 4.6 kilograms (about 610 pounds). | text | null |
L_0407 | reproduction and life stages | T_2343 | The fetus could not grow and develop without oxygen and nutrients from the mother. Wastes from the fetus also must be removed in order for it to survive. The exchange of these substances between the mother and fetus occurs through the placenta. The placenta is a temporary organ that starts to form shortly after implantation. It forms from the trophoblast layer of cells in the blastocyst and from maternal cells in the uterus. The placenta continues to develop and grow to meet the needs of the growing fetus. A fully developed placenta, like the one in Figure 22.8, is made up of a large mass of blood vessels from both mother and fetus. The maternal and fetal vessels are close together but separated by tiny spaces. This allows the mothers and fetuss blood to exchange substances across their capillary walls without the blood actually mixing. The fetus is connected to the placenta through the umbilical cord. This is a long tube that contains two arteries and a vein. Blood from the fetus enters the placenta through the umbilical arteries. It exchanges gases and other substances with the mothers blood. Then it travels back to the fetus through the umbilical vein. Another structure that supports the fetus is the amniotic sac. This is a membrane that surrounds and protects the fetus. It contains amniotic fluid, which consists of water and dissolved substances. The fluid allows the fetus to move freely until it grows to fill most of the available space. The fluid also cushions the fetus and helps protect it from injury. | text | null |
L_0407 | reproduction and life stages | T_2344 | Pregnancy is the carrying of one or more offspring from the time of implantation until birth. It is the development of an embryo and fetus from the expectant mothers point of view. | text | null |
L_0407 | reproduction and life stages | T_2345 | The pregnant mother plays a critical role in the development of the embryo and fetus. She must avoid toxic substances such as alcohol, which can damage the developing offspring. She also must provide all the nutrients and other substances needed for normal growth and development. Most nutrients are needed in greater amounts by a pregnant woman because she is literally eating for two people. Thats why its important for a woman to eat plenty of nutritious foods during pregnancy. The pregnant woman in Figure 22.9 is eating a variety of fresh fruits, which provide energy, vitamins, and other nutrients. | text | null |
L_0407 | reproduction and life stages | T_2346 | Near the time of birth, the amniotic sac breaks in a gush of liquid. Labor usually begins within a day of this event. Labor involves contractions of the muscular walls of the uterus. With the mothers help, the contractions eventually push the fetus out of the uterus and through the vagina. Within seconds of birth, the umbilical cord is cut. Without this connection to the placenta, the baby cant exchange gases, so carbon dioxide quickly builds up in the babys blood. This stimulates the babys brain to trigger breathing, and the newborn takes her first breath. | text | null |
L_0407 | reproduction and life stages | T_2347 | For the first year after birth, a baby is referred to as an infant. Childhood begins at the age of two years and continues until puberty. Adolescence begins with puberty and lasts until adulthood. | text | null |
L_0407 | reproduction and life stages | T_2348 | The first year of life after birth is called infancy. During infancy, a baby grows very quickly. The babys length typically doubles and her weight triples by her first birthday. Many other important changes also occur during infancy: The baby starts smiling, usually by about 6 weeks of age (see Figure 22.10). The baby starts noticing people and grabbing toys and other objects The baby teeth start to come in, usually by 6 months of age. The baby begins making babbling sounds. By the end of the first year, the baby may be saying a few words, such as Mama and Dada. The baby learns to sit, crawl, and stand. By the end of the first year, the baby may be starting to walk. | text | null |
L_0407 | reproduction and life stages | T_2349 | Childhood begins after the babys first birthday and continues until puberty. Between 1 and 3 years of age, a child is called a toddler. During the toddler stage, growth is still very rapid, but not as rapid as it was during infancy. Toddlers learn many new words and starts putting them together in simple sentences. Motor skills also develop quickly during the toddler stage. By the age of 3 years, most children can run and climb steps. They can hold crayons and scribble with them. They can also feed themselves, and most can use the toilet. From age 3 until puberty, growth slows down. The body also changes shape. The arms and legs grow longer relative to the trunk. Children continue to develop new motor skills. For example, many young children learn how to ride a tricycle and then a bicycle. Most learn how to play games and sports. By the age of 6 years, children start losing their baby teeth. Permanent teeth come in to replace them. Most children have started school by this age. They typically start learning to read and write around age 6 or 7 (see Figure 22.11). During the later years of childhood, children also start to develop friendships and become less dependent on their parents. | text | null |
L_0407 | reproduction and life stages | T_2350 | Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 10 to 16 years of age in girls and from about 12 to 18 years of age in boys. In both girls and boys, puberty begins when the pituitary gland signals the gonads (ovaries or testes) to start secreting sex hormones (estrogen in girls, testosterone in boys). Sex hormones, in turn, cause many other changes to take place. In girls, estrogen causes the following changes to occur: The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen and the breasts develop. In boys, testosterone causes these changes to take place: The penis and testes grow. The testes start producing sperm. Pubic and facial hair grow. The shoulders broaden. The voice becomes deeper as the larynx in the throat grows larger (see Figure 22.12). Girls and boys of the same age are similar in height during childhood. In both girls and boys, growth in height and weight is very fast during puberty. But boys grow more quickly that girls do, and their period of rapid growth also lasts longer. In addition, boys generally start puberty later than girls, so they have a longer period of childhood growth. For all these reasons, by the end of puberty, the average height of boys is 10 centimeters (about 4 inches) greater than the average height of girls. | text | null |
L_0407 | reproduction and life stages | T_2351 | Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members. | text | null |
L_0407 | reproduction and life stages | T_2351 | Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members. | text | null |
L_0407 | reproduction and life stages | T_2352 | Adulthood doesnt have a definite starting point. Teens may become physically mature by the age 16 years, but they are not adults in a legal sense until they are older. For example, in the U.S., you must be 18 years old to vote or serve in the armed forces. You must be 21 years old before you can take on many legal and financial responsibilities. Once adulthood begins, it can be divided into three stages: early, middle, and late adulthood. | text | null |
L_0407 | reproduction and life stages | T_2353 | Early adulthood refers to the 20s and early 30s. During early adulthood, most people are at their physical peak, and they are usually in good health. Often, they are completing their education and getting established in the workforce. Many people become engaged or marry during this time. | text | null |
L_0407 | reproduction and life stages | T_2354 | Middle adulthood is the period from the mid-30s to the mid-60s. During this stage of life, people start showing signs of aging. Their hair may thin and slowly turn gray. Their skin develops wrinkles. The risk of serious health problems increases. For example, cardiovascular diseases, cancer, and type 2 diabetes become more common in people of middle age. This is also the stage when many people raise a family and strive to attain career goals. | text | null |
L_0407 | reproduction and life stages | T_2355 | Late adulthood begins in the mid-60s and continues until death. This is the stage of life when most people retire from work. This frees up their time for hobbies, grandchildren, or other interests. For example, the man in Figure During late adulthood, the risk of developing diseases such as cardiovascular diseases and cancer continues to rise. Most people also have a decline in strength and stamina. Their senses may start failing, and their reflex time typically increases. Their immune system also doesnt work as well as it used to. As a result, common diseases like the flu may become more serious and even lead to death. The majority of late adults develop arthritis, and as many as one in four develop Alzheimers disease. Despite problems such as these, many people remain healthy and active into their 80s and even 90s. Do you want | text | null |
L_0408 | reproductive system health | T_2356 | A sexually transmitted infection (STI) is a disease that spreads mainly through sexual contact. STIs are caused by pathogens that enter the body through the reproductive organs. Many STIs also spread through body fluids such as blood. For example, a shared tattoo needle is one way that some STIs can spread. Some STIs can also spread from a mother to her infant during birth. | text | null |
L_0408 | reproductive system health | T_2357 | STIs are more common in teens and young adults than in older people. One reason is that young people are more likely to engage in risky behaviors. They also may not know how STIs spread. Instead, they may believe myths about STIs, like those in Table 22.1. Knowing the facts is important to prevent the spread of STIs. Myth If you are sexually active with just one person, then you cant get STIs. If you dont have any symptoms, then you dont have an STI. Getting STIs is no big deal, because they can be cured with medicines. Fact The only sure way to avoid getting STIs is to practice abstinence from sexual activity. Many STIs do not cause symptoms, especially in fe- males. Only some STIs can be cured with medicines; others cannot be cured. | text | null |
L_0408 | reproductive system health | T_2358 | A number of STIs are caused by bacteria. Bacterial STIs can usually be cured with antibiotics. However, some people with bacterial STIs may not have symptoms so they fail to get treatment. Left untreated, these infections may damage reproductive organs and lead to an inability to have children. Three bacterial STIs are chlamydia, gonorrhea, and syphilis. Chlamydia is the most common bacterial STI in the U.S. Females are more likely to develop it than males. Symptoms may include burning during urination and a discharge from the vagina or penis. Gonorrhea is another common bacterial STI. Symptoms may include painful urination and a discharge from the vagina or penis. Syphilis is a very serious STI but somewhat less common than chlamydia or gonorrhea. It usually begins with a small sore on the genitals. This is followed a few months later by a rash and flu-like symptoms. If syphilis isnt treated, it can eventually damage the heart, brain, and other organs and even cause death. | text | null |
L_0408 | reproductive system health | T_2359 | Several STIs are caused by viruses. Viral STIs cant be cured with antibiotics. Other drugs may help control the symptoms of viral STIs, but the infections usually last for life. Three viral STIs are genital warts, genital herpes, and AIDS. Genital herpes is a common STI caused by a herpes virus. The virus causes painful blisters on the penis or near the vaginal opening. The blisters generally go away on their own, but they may return repeatedly throughout life. There is no cure for genital herpes, but medicines can help prevent or shorten outbreaks. Acquired Immunodeficiency Syndrome (AIDS) is caused by human immunodeficiency virus (HIV). HIV destroys lymphocytes that normally fight infections. AIDS develops if the number of lymphocytes drops to a very low level. People with AIDS come down with diseasessuch as certain rare cancersthat almost never occur in people with a healthy immune system. Medicines can delay the progression of an HIV infection and may prevent AIDS from developing. Genital warts is an STI caused by human papilloma virus (HPV), which is pictured in Figure 22.15. This is one of the most common STIs in U.S. teens. Genital warts cant be cured, but a vaccine can prevent most HPV infections. The vaccine is recommended for boys and girls starting at 11 or 12 years of age. Its important to prevent HPV infections because they may lead to cancer later in life. | text | null |
L_0408 | reproductive system health | T_2360 | Other reproductive system disorders include injuries and noninfectious diseases. These are different in males and females. | text | null |
L_0408 | reproductive system health | T_2361 | Most common disorders of the male reproductive system involve the testes. They include injuries and cancer. Injuries to the testes are very common. In teens, such injuries occur most often while playing sports. Injuries to the testes are likely to be very painful and cause bruising and swelling. However, they generally subside fairly quickly. Cancer of the testes is most common in males aged 15 to 35. It occurs when cells in the testes grow out of control and form a tumor. If found early, cancer of the testes usually can be cured with surgery. | text | null |
L_0408 | reproductive system health | T_2362 | Disorders of the female reproductive system may involve the vagina, uterus, or ovaries. They may also affect the breasts. Vaginitis is a very common disorder. Symptoms include redness and itching of the vagina. It may be caused by soap or bubble bath. Another possible cause is a yeast infection. Yeast normally grow in the vagina. If they multiple too quickly, they may cause irritation. A yeast infection can be treated with medication. Cysts may develop in the ovaries. A cyst is a sac filled with fluid or other material. Ovarian cysts are usually harmless and often disappear on their own. However, some cysts may be painful and require surgery. Many females experience abdominal cramps during menstruation. This is usually normal and not a cause for concern. Exercise, heat, or medication may help relieve the pain. In severe cases, prescription medicine may be needed. Breast cancer is the most common type of cancer in females. It occurs when cells in the breast grow out of control and form a tumor. Breast cancer is rare in teens but becomes more common as females get older. Regular screening is recommended for most women starting around age 40. If found early, breast cancer usually can be cured with surgery. | text | null |
L_0408 | reproductive system health | T_2363 | Maintaining overall good health will help keep your reproductive system healthy. You should eat right, get regular exercise, and follow other healthy lifestyle behaviors. In addition, the following practices will help keep the reproductive system healthy: Keep the genitals clean. A daily shower or bath is all thats needed. Avoid harsh soaps or other personal hygiene products that may be irritating. Avoid risky behaviors. This includes contact with blood or dirty needles as well as sexual activity. If you are a girl and use tampons, be sure to change them every 4 to 6 hours. This will reduce your risk of toxic shock syndrome. This is a very dangerous condition that may occur if tampons are left in too long. If you are a boy, wear a protective cup if you play a contact sport. This will help protect the testes from injury. You should also learn how to check yourself for testicular cancer (see Figure 22.16). You can learn how by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0409 | what is ecology | T_2364 | Organisms are individual living things. They range from microscopic bacteria to gigantic blue whales (see Figure must be obtained from the environment. Biotic factors are all of the living or once-living aspects of the environment. They include all the organisms that live there as well as the remains of dead organisms. Abiotic factors are all of the aspects of the environment that have never been alive. They include factors such as sunlight, minerals in soil, temperature, and moisture. | text | null |
L_0409 | what is ecology | T_2365 | Ecologists study organisms and environments at several different levels, from the individual to the biosphere. The levels are depicted in Figure 23.2 and described below. For a video introduction to the levels of organization in ecology, click on this link: . MEDIA Click image to the left or use the URL below. URL: An individual is an organism, or single living thing. A population is a group of individuals of the same species that live in the same area. Members of the same population generally interact with each other. A community is made up of all the populations of all the species that live in the same area. Populations in a community also generally interact with each other. | text | null |
L_0410 | populations | T_2366 | Population size is the number of individuals in a population. Population size influences the chances of a species surviving or going extinct. If a species populations become very small, the species may be at risk of going extinct. | text | null |
L_0410 | populations | T_2367 | Another sign of a species state of health is the density of its populations. Population density is the average number of individuals in a population for a given area. Density is a measure of how crowded or spread out the individuals in a population are on average. For example, a population of 100 deer that live in an area of 10 square kilometers has a population density of 10 deer per square kilometer. Population density is an average measure. Often, individuals in a population are not spread out evenly. Instead, they may live in clumps or some other pattern. How individuals in a population are distributed, or spread throughout their area, is called population distribution. You can see different patterns of population distribution in Figure 23.3. Different patterns characterize different species and types of environments, as you can read in the figure. | text | null |
L_0410 | populations | T_2368 | Whether its populations are growing or shrinking in size may be another indicator of a species health. Individuals may be added to a population through births and the migration of individuals into the population. Individuals may be lost from a population through deaths and the migration of individuals out of the population. The population growth rate is how quickly a population changes in size over time. The rate of growth of a population may be positive or negative. A positive growth rate means that the population is increasing in size because more people are being added than lost. A negative growth rate means that the population is decreasing in size because more people are being lost than added. Populations may show different patterns of growth. The growth pattern depends partly on the conditions under which a population lives. Two common growth patterns are exponential growth and logistic growth. Both are represented in Figure 23.4. With exponential growth, the population starts out growing slowly. As population size increases, the growth rate also increases. The larger the population becomes, the more quickly it grows. This type of growth generally occurs only when a population is living under ideal conditions. However, it cant continue for very long. With logistic growth, the population starts out growing slowly, and then the rate of growth increasesbut only to a point. The rate of growth tapers off as the population size approaches its carrying capacity. Carrying capacity is the largest population size that can be supported in an area without harming the environment. This type of growth characterizes many populations. | text | null |
L_0410 | populations | T_2369 | Another way of describing a population is its age-sex structure. This refers to the numbers of individuals of each sex and age in the population. The age-sex structure of a population may influence the population growth rate. This is because only individuals of certain ages are able to reproduce, and because individuals of certain ages may be more likely to die. For example, if there are many individuals of reproductive age, there are likely to be many births, causing the population to grow rapidly. The age-sex structure of a population is often represented with a special bar graph called a population pyramid. You can see an example of a population pyramid in Figure 23.5. The graph in the figure actually has a pyramid shape because the bars become narrower from younger to older ages. However, this is not always the case. In some populations, for example, there may be more people at older than younger ages, resulting in a top-heavy population pyramid. Learn more about population pyramids and what you can learn from them, watch this TED video: http://w MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0410 | populations | T_2370 | Human beings have been called the most successful weed species on Earth. Like garden weeds, populations of human beings grow quickly and disperse rapidly. Human beings have colonized almost every terrestrial part of the planet. Overall, the human population has had a pattern of exponential growth, as you can see in Figure 23.6. The early human population grew very slowly. However, as the population grew larger, it started to grow more rapidly. | text | null |
L_0410 | populations | T_2370 | Human beings have been called the most successful weed species on Earth. Like garden weeds, populations of human beings grow quickly and disperse rapidly. Human beings have colonized almost every terrestrial part of the planet. Overall, the human population has had a pattern of exponential growth, as you can see in Figure 23.6. The early human population grew very slowly. However, as the population grew larger, it started to grow more rapidly. | text | null |
L_0410 | populations | T_2371 | The earliest members of the human species evolved around 200,000 years ago in Africa. Early humans lived in small populations of nomadic hunters and gatherers. Human beings remained in Africa until about 40,000 years ago. After that, they spread throughout Europe, Asia, and Australia. By 10,000 years ago, the first human beings colonized the Americas. During this long period of time, the total number of human beings increased very slowly. Birth rates were fairly high but so were death rates, producing low rates of population growth. Human beings invented agriculture about 10,000 years ago. This provided a bigger, more dependable food supply. It also allowed people to settle down in villages and cities for the first time. Birth rates went up because there was more food and settled life had other advantages. Death rates also rose because of crowded living conditions and diseases that spread from domestic animals. Because the higher birth rates were matched by higher death rates, the human population continued to grow very slowly. | text | null |
L_0410 | populations | T_2372 | Major changes in the human population first began in the 1700s. These changes occurred mainly in Europe, North America, and a few other places that became industrialized. First death rates fell. Then, somewhat later, birth rates also fell. These changes in death and birth rates affected the rate of population growth and are referred to as the demographic transition. The graph in Figure 23.7 shows the stages in which the demographic transition occurred. You can learn more about the stages by watching this video: http://education-portal.com/academy/lesson/what-is-d In Stage 1, both birth and death rates were high so population growth was slow. In Stage 2, death rates fell while birth rates remained high. Why did death rates fall? There were several reasons, including new scientific knowledge of the causes of disease. Water supplies were cleaned up and sewage was disposed of more safely. Better farming techniques and machines increased the food supply and the distribution of food. For all these reasons, death rates fell, especially in children. Birth rates, on the other hand, remained high. This resulted in faster population growth. Before long, birth rates also started to fall. People started having fewer children because large families became too expensive. For example, with better farming machines, farm families no longer needed as many children to work in the fields. Laws were also passed that required children to go to school. They could no longer work and help support the family. Having many children became too costly. Eventually, birth rates fell to match death rates (Stage 4). As a result, population growth slowed down. | text | null |
L_0410 | populations | T_2373 | Just as they did in Europe and North America, death rates have fallen throughout the world. No country today remains in Stage 1 of the demographic transition. However, birth rates are still high in many of the poorest countries of the world. These populations seem to be stuck in Stage 2 or 3 of the demographic transition. They have high population growth rates because low death rates are not matched by equally low birth rates. Whether these populations will ever enter Stage 4 and attain very low rates of population growth is uncertain. | text | null |
L_0410 | populations | T_2374 | As of 2014, there were more than 7 billion human beings on planet Earth. That number is increasing rapidly. More than 200,000 people are added to the human population each day! At this rate, the human population will pass 9 billion by 2050. Many experts think that the human population has reached its carrying capacity. It has already harmed the environ- ment. An even larger human population may cause severe environmental problems. It could also lead to devastating outbreaks of disease, starvation, and war. To solve these problems, two approaches may be needed: Slow down human population growth so there are fewer people. Distribute Earths resources more fairly so that everyone has enough. Hopefully, we will act before its too late. Otherwise, the planet may be ruined for future generations of human beings and other species. | text | null |
L_0413 | biomes | T_2389 | Terrestrial biomes are land-based biomes. They range from arctic tundra to tropical rainforests. Figure 23.18 shows the locations of the worlds major terrestrial biomes. | text | null |
L_0413 | biomes | T_2390 | Plants are the primary producers in terrestrial biomes. They make food for themselves and other organisms by photosynthesis. The major plants in a given biome, in turn, help determine the types of animals and other organisms that can live there. Which plants grow in a given biome depends mainly on climate. Climate is the average weather in a place over a long period of time. The major climatic factors affecting plant growth are temperature and moisture. | text | null |
L_0413 | biomes | T_2391 | You can read about three different terrestrial biomes in Figure 23.19: tropical rainforest, temperate grassland, and tundra. You can learn more about these and other terrestrial biomes by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0413 | biomes | T_2392 | Aquatic biomes are water-based biomes. They include both freshwater biomes, such as rivers and lakes, and marine biomes, which are salt-water biomes in the ocean. The primary producers in most aquatic biomes are phytoplankton. Phytoplankton consist of microscopic bacteria and tiny algae that make food by photosynthesis. Unlike terrestrial biomes, which are determined mainly by temperature and moisture, aquatic biomes are determined mainly by sunlight and dissolved substances in the water. These factors, in turn, depend mainly on depth of water and distance from shore. | text | null |
L_0413 | biomes | T_2393 | Only the top 200 meters or so of water receive enough sunlight for photosynthesis. This part of the water is called the photic zone. Below 200 meters, there is too little sunlight for photosynthesis to take place. This part of the water is called the aphotic zone. In this zone, food must come from other sources. It may be made by chemosynthesis, in which microorganisms use energy in chemicals instead of sunlight to make food. Or, food may drift down from the water above. | text | null |
L_0413 | biomes | T_2394 | In addition to sunlight, aquatic producers also need dissolved oxygen and nutrients. Water near the surface generally contains more dissolved oxygen than deeper water. Many nutrients enter the water from the land. Therefore, water nearer shore usually contains more dissolved nutrients than water farther from shore. | text | null |
L_0413 | biomes | T_2395 | A lake is an example of a freshwater biome. Water in a lake generally forms three different zones based on water depth and distance from shore. The shallow water near the shore is called the littoral zone. It has diverse community of organisms. There is adequate light for photosynthesis and plenty of dissolved oxygen and nutrients. Producers include algae and aquatic plants (see Figure 23.20). Animals in this zone may include insects, crustaceans, fish, and turtles. The top layer of water farther from shore is called the limnetic zone. There is enough light for photosynthesis and plenty of dissolved oxygen. However, dissolved nutrients tend not to be as plentiful as they are in the littoral zone. Producers here are mainly phytoplankton. A variety of zooplankton and fish also occupy this zone. The deeper water of a lake makes up the profundal zone. There isnt enough light for photosynthesis in this zone, so most organisms here eat dead organisms that drift down from the water above. Organisms in the profundal zone may include clams, snails, and some species of fish. | text | null |
Subsets and Splits