Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
3.3 As you have learned, specialized cells are organized into tissues. For example, muscle tissue is made up of cells that contract to help the body move. Nerve tissue is made up of cells that carry signals to and from the brain. Tissues can be classified into four major types. Figure 1 summarizes the four major types of tissue. Figure 1 The four major types of animal tissue 72 Chapter 3 • How the Body Works NEL Coverings, Connections, and Support Two types of tissue, epithelial tissue and connective tissue, provide coverings, connections, and support within the body. Epithelial Tissue Epithelial tissue (epithelium) is made up of tightly packed cells that cover body surfaces and line the body’s internal organs and cavities. Epithelium can be a single layer of cells, or it can be many layers of cells (Figure 2). Epithelial tissue made up of a single layer of cells allows materials to pass through the layer. For example, it forms the air sacs of the lungs, where oxygen is exchanged for carbon dioxide. (a) ▶▶ epithelial tissue (epithelium): sheets of tightly packed cells covering surfaces and lining internal organs (b) Figure 2 Epithelium can be made up of (a) a single layer of cells, or (b) many layers of cells. Epithelium with many layers covers parts of the body that need greater protection from injury. Human skin contains layers of epithelial tissue. These cells help protect areas beneath the skin. Connective Tissue Connective tissue supports, protects, and connects the body’s organs. Connective tissue is made up of both specialized cells and non-living substances. Perhaps most surprising of all, blood is a type of connective tissue. Blood connects body systems by bringing oxygen and nutrients and removing wastes. ▶▶ connective tissue: tissue composed of living cells and non-living materials that supports, protects, and connects the body’s organs ▶▶ bone: tissue made up of living bone cells surrounded by non-living material Bone and Other Connective Tissue The most obvious type of connective tissue is bone. Bone is made up of living bone cells surrounded by hard, non-living material (Figure 3). Bones are connected to each other by strong elastic bands of connective tissue called ligaments. Tough, inelastic connective tissue, called tendons, attaches muscles to bones. Between the ends of the bones at a joint, such as your elbow, connective Figure 3 Living bone tissue called cartilage cells are surrounded by forms a cushioning pad non-living bone. (Figure 4). NEL Figure 4 Connective tissues holds our tissues and organs together. 3.3 Animal Tissues 73 Figure 5 The ACL is located in the front of the knee. When it becomes torn, the knee becomes less stable. dig deeper Did You Know? Injuries on the Rise Society’s interest in physical fitness has increased greatly. The bad news is that doctors are seeing more patients with torn ACLs and other connective tissue injuries. ▶▶ nerve tissue: specialized tissue that makes up the brain, nerves, and spinal cord, and carries electric signals to and from the brain to control body functions Cartilage is also found in other parts of the body. You can feel cartilage in your ears and nose. Cartilage cells are suspended in a dense network of fibres that make the tissue strong, yet flexible. Another type of connective tissue connects the skin to the muscles and fat underneath. Connective Tissue Injuries Do you know anyone who has injured an Achilles tendon, had tennis elbow, or suffered a torn ACL? A torn ACL is one of the most common sports knee injuries. ACL stands for “anterior cruciate ligament.” It is one of the ligaments holding the knee joint together. Overstretching or suddenly twisting the knee can tear the ACL (Figure 5). Repair often requires surgery. Sensing and Responding As you know, specialized cells in our ears, eyes, skin, nose, and mouth help to collect information about our surroundings. The eye contains light-sensitive cells. The ear contains hair cells that are sensitive to sound vibrations. The tongue contains taste buds, and the nose has cells that detect tastes and smells. The skin contains cells that respond to temperature, touch, pain, and pressure. How is this information carried to the brain? How do we respond to it? These are the tasks of the other two types of tissue: nerve tissue and muscle tissue. Nerve Tissue nerve connective tissue bundle of nerve cells nerve cell Figure 6 Nerve cells transmit signals around the body. If your hand gets close to something too hot, you pull your hand away. Your body can feel because your skin contains millions of nerve cells that make up nerve tissue. Nerve tissue is the most complex tissue in the body. It makes up the brain, spinal cord, and nerves. The brain is responsible for all thinking, language, and memory, as well as directing routine body functions. Nerve tissue transmits signals throughout the body (Figure 6). There are three kinds of nerve cells. One kind of nerve carries information from the body to the brain or spinal cord. These are the nerves in your skin or sense organs that inform you about the outside world. They are called sensory neurons. A second kind of nerve carries instructions from the brain or spinal cord to another body part—usually the muscles. These are called motor neurons. The third kind of nerve connects the sensory and motor neurons and are called interneurons. The brain and the spinal cord are made up of interneurons. 74 Chapter 3 • How the Body Works NEL Let's say your hand gets close to a hot stove. The sensory neurons in your hand sense the hot stove and send a signal to the brain. The interneurons in your brain interpret the signal and send a return signal to motor neurons in your arm and hand. The motor neurons interact with the arm and hand muscles, making you pull your hand away from the hot stove. All of this happens in less than a second. The signals between your body and brain can travel very fast. Some nerve signals can travel at more than 100 m/s! Muscle Tissue Muscle tissue is made up of cells that contract, or get shorter. When each end of a muscle is attached to a different bone, the contracting muscle pulls the two bones toward each other. This allows us to move. Muscle tissue also enables the organs to function. For example, heart muscle tissue allows the heart to pump blood. Stomach muscle tissue allows the stomach to squeeze and churn food to break it down. ▶▶ muscle tissue: specialized tissue made up of cells that shorten or contract to allow movement There are three kinds of muscle tissue (Figure 7). Actions such as walking or throwing a ball are voluntary. That means you decide to move those body parts. The muscles that you control are skeletal muscles. These muscles are made up of striated muscle tissue. Smooth muscle tissue is the second kind of muscle tissue. Smooth muscle lines the walls of arteries, veins, and body organs. Think about when you eat. You cannot “tell” your stomach to squeeze and churn the food you eat! It just does so automatically. Smooth muscle is also called involuntary muscle because it contracts and relaxes without your conscious thought. This is very important because if it were not involuntary, we would spend all of our time thinking about things like breathing and digesting food. The third kind of muscle tissue is cardiac muscle tissue. Cardiac muscle tissue is an involuntary striated muscle that lines the walls of the heart. NEL Figure 7 The three types of muscle tissue: (a) striated; (b) smooth; and (c) cardiac 3.3 Animal Tissues 75 Research This Multiple Sclerosis Research Skills: Researching, Analyzing the Issue, Communicating, Evaluating 4.A., 4.B. Imagine not being able to move your legs the way you want to, or having a difficult time moving your mouth the right way to form words. Multiple sclerosis (MS) is a disease of the brain and spinal cord. In this disease, the nerve cells are damaged. As a result, signals do not travel smoothly between nerve cells. This can cause a wide range of symptoms including vision problems, numbness, tingling, and muscle weakness. 2.Research the incidence of MS in different provinces and territories of Canada. Determine if there are significant differences among the provinces and territories. The occurrence of this disease in Canada is very high. In Crowsnest Pass, Alberta, for example, there are 217 cases per 100 000 people. This is in contrast to the South American rate of less than 30 cases per 100 000. A.Use a map of Canada to show the incidence of MS in the different provinces and territories. T/ I 1.Research how MS affects people’s lives, including the symptoms and how fast it progresses. 3.Find out what kind of research on MS is being carried out in Canada and how this research might benefit people with MS. C B.Write a summary of current MS research in Canada. T/I C C.Make a poster or draw a diagram that details the different ways MS can affect the body, and how new treatments might help. T/I C go to Nelson Science 3.3 Wrap Up • Epithelial tissue covers and lines parts of the body. Epithelial tissue is made up of either a single layer of cells or many layers of cells. • Connective tissue supports, protects, and connects the body’s organs. Bone is specialized connective tissue that provides the body with support and protection. • Nerve tissue sends signals between the body and the brain. The brain receives sensory information from the body and sends instructions to the muscles. • Muscle tissues enable movement. There are three kinds of muscle tissue: striated, smooth, and cardiac muscle tissue. Check Your Learning 1.List the four types of tissue and give an example of each. Describe its function and where it can be found. K/U C 2.Name and describe the three types of muscle. Give an example of each type. K /U C 76 Chapter 3 • How the Body Works 3.How is connective tissue different from the other kinds of tissues? Give an example. K/U C 4.Why is it important that some types of muscles can contract and relax without our having to think about it? K/U C NEL