DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A Human Systems CHAPTER 28 and Homeostasis BIg IdEa The human body is organized into different systems that interact in a coordinated way to maintain homeostasis. 28.1 Levels of Organization 10C 28.2 Mechanisms of Homeostasis 4B, 10A, 11A 28.3 Interactions among Systems 10A, 10C data analysis INtErprEtINg INvErSE rELatIONSHIpS 2G Online BiOlOgy HMDScience.com ONLINE Labs ■■ Homeostasis and Exercise ■■ QuickLab Negative Feedback Loop ■■ Examining Human Cells ■■ Hormones and Homeostasis ■■ Negative and Positive Feedback ■■ Open Inquiry Lab Interactions Among Systems (t) ©Ken Redding/Corbis 814 Unit 9: Human Biology DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A Q How does this ice climber hang on to his body temperature? This climber has to concentrate on every move—one slip could mean serious injury or even death. His body is working just as hard on the inside to provide energy and to maintain a stable body temperature. The climber’s clothes help prevent heat loss, while his body’s internal systems increase his body heat. r E a d IN g T o o L b o x this reading tool can help you learn the material in the following pages. USINg LaNgUAGE YOUr tUrN analogies Analogies compare words that have similar Use information found in the chapter to complete the relationships. You can write analogies with words or with following analogies. colons. For example, the analogy “up is related to down in 1. heart : pump :: kidney : _____ the same way that top is related to bottom” can be written 2. nervous system : nerves :: endocrine system : _____ “up : down :: top : bottom.” To answer an analogy problem, you must figure out how the words are related. In the example given, up is above down and top is above bottom. Chapter 28: Human Systems and Homeostasis 815 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A 28.1 Levels of Organization 10C KEy cONcEPT The human body has five levels of organization. maiN idEas vOcabuLary Specialized cells develop from a single zygote. determination Specialized cells function together in tissues, organs, organ systems, and the cell differentiation whole organism. tissue organ organ system Connect to Your World Climbing a wall of ice requires careful interaction among all parts of the body. You probably know that the brain and muscles work together to coordinate the climber’s 10C analyze the levels of organization in biological systems movements. The heart and lungs also have to work together to help provide energy and relate the levels to each other for the climb. Yet every human body starts out as a single cell, a fertilized zygote. and to the whole system How does a single cell give rise to all the different types of cells, tissues, and organs in the human body? Further, how do such different parts coordinate their activities to keep the body functioning? maiN idEa specialized cells develop from a single zygote. If you were to watch an emergency medical team in action, you would quickly notice that each person has a special job. One keeps in radio contact with the main hospital. Another monitors the patient’s vital signs. Still others perform life-saving procedures. All emergency teams are made up of people, but each person within the group has a different job. Likewise, multicellular organisms are made up of cells, but different cells in the organism have different functions. Take a moment to study the images of the blood cells and nerve cells, or neurons, in FIGURE 1.1. You will notice that the red blood cells are round with a concave center. This structure gives them more surface area to help deliver oxygen to all parts of the body. In contrast, neurons develop extensions that transmit and receive messages from other neurons. Humans, like almost all multicellular organisms, are collections of special- ized cells that work together. These cells arise from a single cell, the zygote, which is formed by the union of an egg and sperm. The zygote divides and differentiates into more than 200 different types of human cells. These cells allow you to do everything from lifting a glass, to learning people’s names, to maintaining your body temperature on a cold day. Cell specialization involves two main steps: determination and differentiation. Figure 1.1 The disk-shaped red blood cells (top) carry oxygen to all parts of the body. The neuron determination (bottom), through its extensions, The cells produced during the first few divisions of the zygote are known as receives and transmits messages embryonic stem cells. These cells have the potential to become any type of from and to other neurons. (colored SEMs; magnifications: blood cells specialized cell in the body. Within a few weeks, however, a process called 28003; neuron about 16003) determination occurs, in which most stem cells become committed to develop (tl) ©Susumu Nishinaga/Photo Inc.; Researchers, (b) ©David McCarthy/Photo Inc. Researchers, 816 Unit 9: Human Biology DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A into only one type of cell. For instance, a stem cell might become a cardiac r E a d i N G TO OLB Ox muscle cell or a spinal neuron. These committed cells still retain all of the TaKiNG NOTEs ©Carolina genetic information needed to build an entire organism. However, during Use a supporting main ideas determination, they lose their ability to express some of this information. strategy to take notes about Once a cell is committed to becoming a specialized cell, it will develop into processes such as cell only that type of cell. For instance, a cell that will become a neuron can only specialization. be a neuron, even if it is transplanted into another part of the body. During Specialized cells develop normal development, determination cannot be reversed. from embryonic stem cells. New-Human bone marrow cells determination—cells differentiation are committed to be one type of cell cell differentiation is the process by which committed cells acquire the struc- tures and functions of highly specialized cells. Cell differentiation occurs cell differentiation because specific genes in each cell are turned on and off in a complex, regu- supporting detail lated pattern. The different structures of these specialized cells, such as those ©CNRI/Photo Inc.; Researchers, shown in FIGURE 1.2, allow them to perform specific functions within the body. The specialization enabled by differentiation is what allows different types of cells to have different functions. The function of muscle cells, for example, is group of sperm to produce movement by contracting and relaxing. However, skeletal muscle and smooth muscle cells have different structures. Skeletal muscle cells align in bands of orderly rows and contain many nuclei. They are responsible for nearly all voluntary muscle movements, FIGURE 1.2 Cell differentiation such as lifting your foot to kick a ball. In contrast, smooth muscle cells develop specialized structures and functions during differentiation. cells are shorter and have only one nucleus. They perform involuntary Connective cells ©Dr. Yorgos Nikas/Photo Inc; Researchers, Yorgos ©Dr. Smooth muscle cells in movements, such as raising the in skin intestinal wall zygote hairs on your arm. Other cells have even more specialized structures and func- tions. Sperm cells, for instance, develop whiplike tails that enable Bone Skeletal them to swim. Cells lining the gut cells muscle GOT ©Ed Reschke/Peter Arnold, Inc.; Arnold, ©Ed Reschke/Peter are elongated and tightly packed to Zy E cells provide more surface area for the absorption of nutrients. ©Educational Images/Custom Medical Stock Photos Not all cells continue to develop into specialized cells. The process areolar tissue of programmed cell death, called apoptosis (ap-uhp-TOH-sihs), is also a normal part of development. Epithelial cells Epithelial For example, when your hands in skin cells in stomach first formed, your fingers resem- lining bled a mitten. The death of cells between the fingers allowed Sperm cells individual fingers to develop. analyze Why do multicellular contrast How do the structures of sperm cells and epithelial cells in organisms need specialized cells? the stomach differ? Biological Supply company/Phototake Inc./Alamy Ltd; skeletal muscle tissue, smooth muscle, skeletal stratifiedsmooth muscle tissue, columnar muscle, epithelium, epithelium, Chapter 28: Human Systems and Homeostasis 817 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A maiN idEa 10C specialized cells function together in tissues, organs, organ systems, and the whole organism. Specialized, or differentiated, cells are only the first level of organization in a multicellular organism. Scientists organize multicellular structures into five basic levels, beginning with cells and moving to increasingly complex levels— tissues, organs, organ systems, and the whole organism. These five levels in the human body are shown in FIGURE 1.3. 1 Cells Each type of specialized cell has a particular structure and a chemical makeup that enable it to perform a specific task. Some cells in the lungs, for instance, are involved in the exchange of gases. Others secrete mucus that helps to trap foreign particles and to protect the lungs from pathogens, such as bacteria and viruses. 2 Tissues A group of similar cells that work together to perform a specialized function are known as tissue. The human body is made up of four general types of tissues. cONNEcT TO • Epithelial tissue consists of protective sheets of tightly packed cells digesTion aNd connected by special junctions. The skin and the membranes that line ELimiNaTion the stomach, the lungs, and other organs are epithelial tissues. In addition to serving as a protective layer, epithelial tissue • Connective tissue serves to support, bind together, and protect other can absorb materials and secrete tissues and organs.