Anatomy and Physiology Chapter 1 PDF

CHAPTER 1 An Introduction to the Human Body Figure 1.1 Blood Pressure A progciency in anatomy and physiology is fundamental to any career in the health professions. (credit: Bryan Mason/flickr) CHAPTER OBJECTIVES After studying this chapter, you will be able to: Distinguish between anatomy and physiology, and identify several branches of each Describe the structure of the body, from simplest to most complex, in terms of the six levels of organization Identify the functional characteristics of human life Identify the four requirements for human survival De*ne homeostasis and explain its importance to normal human functioning Use appropriate anatomical terminology to identify key body structures, body regions, and directions in the body Compare and contrast at least four medical imaging techniques in terms of their function and use in medicine INTRODUCTION Though you may approach a course in anatomy and physiology strictly as a requirement for your geld of study, the knowledge you gain in this course will serve you well in many aspects of your life. An understanding of anatomy and physiology is not only fundamental to any career in the health professions, but it can also benegt your own health. Familiarity with the human body can help you make healthful choices and prompt you to take appropriate action when signs of illness arise. Your knowledge in this geld will help you understand news about nutrition, medications, medical devices, and procedures and help you understand genetic or infectious diseases. At some point, everyone will have a problem with some aspect of their body and your knowledge can help you to be a better parent, spouse, partner, friend, colleague, or caregiver. This chapter begins with an overview of anatomy and physiology and a preview of the body regions and functions. It then covers the characteristics of life and how the body works to maintain stable conditions. It introduces a set of standard terms for body structures and for planes and positions in the body that will serve as a foundation for more comprehensive information covered later in the text. It ends with examples of medical imaging used to see inside the living body. 8 1 An Introduction to the Human Body 1.1 Overview of Anatomy and Physiology LEARNING OBJECTIVES By the end of this section, you will be able to: Compare and contrast anatomy and physiology, including their specializations and methods of study Discuss the fundamental relationship between anatomy and physiology Human anatomy is the scientigc study of the body’s structures. Some of these structures are very small and can only be observed and analyzed with the assistance of a microscope. Other larger structures can readily be seen, manipulated, measured, and weighed. The word “anatomy” comes from a Greek root that means “to cut apart.” Human anatomy was grst studied by observing the exterior of the body and observing the wounds of soldiers and other injuries. Later, physicians were allowed to dissect bodies of the dead to augment their knowledge. When a body is dissected, its structures are cut apart in order to observe their physical attributes and their relationships to one another. Dissection is still used in medical schools, anatomy courses, and in pathology labs. In order to observe structures in living people, however, a number of imaging techniques have been developed. These techniques allow clinicians to visualize structures inside the living body such as a cancerous tumor or a fractured bone. Like most scientigc disciplines, anatomy has areas of specialization. Gross anatomy is the study of the larger structures of the body, those visible without the aid of magnigcation (Figure 1.2 a). Macro- means “large,” thus, gross anatomy is also referred to as macroscopic anatomy. In contrast, micro- means “small,” and microscopic anatomy is the study of structures that can be observed only with the use of a microscope or other magnigcation devices (Figure 1.2 b). Microscopic anatomy includes cytology, the study of cells and histology, the study of tissues. As the technology of microscopes has advanced, anatomists have been able to observe smaller and smaller structures of the body, from slices of large structures like the heart, to the three-dimensional structures of large molecules in the body. FIGURE 1.2 Gross and Microscopic Anatomy (a) Gross anatomy considers large structures such as the brain. (b) Microscopic anatomy can deal with the same structures, though at a different scale. This is a micrograph of nerve cells from the brain. LM × 1600. (credit a: “WriterHound”/Wikimedia Commons; credit b: Micrograph provided by the Regents of University of Michigan Medical School © 2012) Anatomists take two general approaches to the study of the body’s structures: regional and systemic. Regional anatomy is the study of the interrelationships of all of the structures in a specigc body region, such as the abdomen. Studying regional anatomy helps us appreciate the interrelationships of body structures, such as how muscles, nerves, blood vessels, and other structures work together to serve a particular body region. In contrast, systemic anatomy is the study of the structures that make up a discrete body system—that is, a group of structures that work together to perform a unique body function. For example, a systemic anatomical study of the muscular system would consider all of the skeletal muscles of the body. Whereas anatomy is about structure, physiology is about function. Human physiology is the scientigc study of the chemistry and physics of the structures of the body and the ways in which they work together to support the functions of life. Much of the study of physiology centers on the body’s tendency toward homeostasis. Homeostasis is the state of steady internal conditions maintained by living things. The study of physiology certainly includes observation, both with the naked eye and with microscopes, as well as manipulations and measurements. However, current advances in physiology usually depend on carefully designed laboratory experiments that reveal the Access for free at openstax.org 1.2 Structural Organization of the Human Body 9 functions of the many structures and chemical compounds that make up the human body. Like anatomists, physiologists typically specialize in a particular branch of physiology. For example, neurophysiology is the study of the brain, spinal cord, and nerves and how these work together to perform functions as complex and diverse as vision, movement, and thinking. Physiologists may work from the organ level (exploring, for example, what different parts of the brain do) to the molecular level (such as exploring how an electrochemical signal travels along nerves). Form is closely related to function in all living things. For example, the thin flap of your eyelid can snap down to clear away dust particles and almost instantaneously slide back up to allow you to see again. At the microscopic level, the arrangement and function of the nerves and muscles that serve the eyelid allow for its quick action and retreat. At a smaller level of analysis, the function of these nerves and muscles likewise relies on the interactions of specigc molecules and ions. Even the three-dimensional structure of certain molecules is essential to their function. Your study of anatomy and physiology will make more sense if you continually relate the form of the structures you are studying to their function. In fact, it can be somewhat frustrating to attempt to study anatomy without an understanding of the physiology that a body structure supports. Imagine, for example, trying to appreciate the unique arrangement of the bones of the human hand if you had no conception of the function of the hand. Fortunately, your understanding of how the human hand manipulates tools—from pens to cell phones—helps you appreciate the unique alignment of the thumb in opposition to the four gngers, making your hand a structure that allows you to pinch and grasp objects and type text messages. 1.2 Structural Organization of the Human Body LEARNING OBJECTIVES By the end of this section, you will be able to: Describe the structure of the human body in terms of six levels of organization List the eleven organ systems of the human body and identify at least one organ and one major function of each Before you begin to study the different structures and functions of the human body, it is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. It is convenient to consider the structures of the body in terms of fundamental levels of organization that increase in complexity: subatomic particles, atoms, molecules, organelles, cells, tissues, organs, organ systems, organisms and biosphere (Figure 1.3). 10 1 An Introduction to the Human Body FIGURE 1.3 Levels of Structural Organization of the Human Body The organization of the body often is discussed in terms of six distinct levels of increasing complexity, from the smallest chemical building blocks to a unique human organism. The Levels of Organization To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms and molecules. All matter in the universe is composed of one or more unique pure substances called elements, familiar examples of which are hydrogen, oxygen, carbon, nitrogen, calcium, and iron. The smallest unit of any of these pure substances (elements) is an atom. Atoms are made up of subatomic particles such as the proton, electron and neutron. Two or more atoms combine to form a molecule, such as the water molecules, proteins, and sugars found in living things. Molecules are the chemical building blocks of all body structures. A cell is the smallest independently functioning unit of a living organism. Even bacteria, which are extremely small, independently-living organisms, have a cellular structure. Each bacterium is a single cell. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells. Access for free at openstax.org 1.2 Structural Organization of the Human Body 11 A human cell typically consists of flexible membranes that enclose cytoplasm, a water-based cellular fluid together with a variety of tiny functioning units called organelles. In humans, as in all organisms, cells perform all functions of life. A tissue is a group of many similar cells (though sometimes composed of a few related types) that work together to perform a specigc function. An organ is an anatomically distinct structure of the body composed of two or more tissue types. Each organ performs one or more specigc physiological functions. An organ system is a group of organs that work together to perform major functions or meet physiological needs of the body. This book covers eleven distinct organ systems in the human body (Figure 1.4 and Figure 1.5). Assigning organs to organ systems can be imprecise since organs that “belong” to one system can also have functions integral to another system. In fact, most organs contribute to more than one system. In this book and throughout your studies of biological sciences, you will often read descriptions related to similarities and differences among biological structures, processes, and health related to a person's biological sex. People often use the words "female" and "male" to describe two different concepts: our sense of gender identity, and our biological sex as determined by our chromosomes, hormones, organs, and other physical characteristics. For some people, gender identity is different from biological sex or their sex assigned at birth. Throughout this book, "female" and "male" refer to sex only, and the typical anatomy and physiology of XX and XY individuals is discussed. 12 1 An Introduction to the Human Body FIGURE 1.4 Organ Systems of the Human Body Organs that work together are grouped into organ systems. Access for free at openstax.org 1.2 Structural Organization of the Human Body 13 FIGURE 1.5 Organ Systems of the Human Body (continued) Organs that work together are grouped into organ systems. The organism level is the highest level of organization. An organism is a living being that has a cellular structure and that can independently perform all physiologic functions necessary for life. In multicellular organisms, including humans, all cells, tissues, organs, and organ systems of the body work together to maintain the life and health of the 14 1 An Introduction to the Human Body organism. 1.3 Functions of Human Life LEARNING OBJECTIVES By the end of this section, you will be able to: Explain the importance of organization to the function of the human organism Distinguish between metabolism, anabolism, and catabolism Provide at least two examples of human responsiveness and human movement Compare and contrast growth, differentiation, and reproduction The different organ systems each have different functions and therefore unique roles to perform in physiology. These many functions can be summarized in terms of a few that we might consider degnitive of human life: organization, metabolism, responsiveness, movement, development, and reproduction. Organization A human body consists of trillions of cells organized in a way that maintains distinct internal compartments. These compartments keep body cells separated from external environmental threats and keep the cells moist and nourished. They also separate internal body fluids from the countless microorganisms that grow on body surfaces, including the lining of certain passageways that connect to the outer surface of the body. The intestinal tract, for example, is home to more bacterial cells than the total of all human cells in the body, yet these bacteria are outside the body and cannot be allowed to circulate freely inside the body. Cells, for example, have a cell membrane (also referred to as the plasma membrane) that keeps the intracellular environment—the fluids and organelles—separate from the extracellular environment. Blood vessels keep blood inside a closed circulatory system, and nerves and muscles are wrapped in connective tissue sheaths that separate them from surrounding structures. In the chest and abdomen, a variety of internal membranes keep major organs such as the lungs, heart, and kidneys separate from others. The body’s largest organ system is the integumentary system, which includes the skin and its associated structures, such as hair and nails. The surface tissue of skin is a barrier that protects internal structures and fluids from potentially harmful microorganisms and other toxins. Metabolism The grst law of thermodynamics holds that energy can neither be created nor destroyed—it can only change form. Your basic function as an organism is to consume (ingest) energy and molecules in the foods you eat, convert some of it into fuel for movement, sustain your body functions, and build and maintain your body structures. There are two types of reactions that accomplish this: anabolism and catabolism. Anabolism is the process whereby smaller, simpler molecules are combined into larger, more complex substances. Your body can assemble, by utilizing energy, the complex chemicals it needs by combining small molecules derived from the foods you eat Catabolism is the process by which larger more complex substances are broken down into smaller simpler molecules. Catabolism releases energy. The complex molecules found in foods are broken down so the body can use their parts to assemble the structures and substances needed for life. Taken together, these two processes are called metabolism. Metabolism is the sum of all anabolic and catabolic reactions that take place in the body (Figure 1.6). Both anabolism and catabolism occur simultaneously and continuously to keep you alive. Access for free at openstax.org 1.3 Functions of Human Life 15 FIGURE 1.6 Metabolism Anabolic reactions are building reactions, and they consume energy. Catabolic reactions break materials down and release energy. Metabolism includes both anabolic and catabolic reactions. Every cell in your body makes use of a chemical compound, adenosine triphosphate (ATP), to store and release energy. The cell stores energy in the synthesis (anabolism) of ATP, then moves the ATP molecules to the location where energy is needed to fuel cellular activities. Then the ATP is broken down (catabolism) and a controlled amount of energy is released, which is used by the cell to perform a particular job. INTERACTIVE LINK View this animation (http://openstax.org/l/metabolic) to learn more about metabolic processes. Which organs of the body likely carry out anabolic processes? What about catabolic processes? Responsiveness Responsiveness is the ability of an organism to adjust to changes in its internal and external environments. An example of responsiveness to external stimuli could include moving toward sources of food and water and away from perceived dangers. Changes in an organism’s internal environment, such as increased body temperature, can cause the responses of sweating and the dilation of blood vessels in the skin in order to decrease body temperature, as shown by the runners in Figure 1.7. Movement Human movement includes not only actions at the joints of the body, but also the motion of individual organs and even individual cells. As you read these words, red and white blood cells are moving throughout your body, muscle cells are contracting and relaxing to maintain your posture and to focus your vision, and glands are secreting chemicals to regulate body functions. Your body is coordinating the action of entire muscle groups to enable you to move air into and out of your lungs, to push blood throughout your body, and to propel the food you have eaten through your digestive tract. Consciously, of course, you contract your skeletal muscles to move the bones of your skeleton to get from one place to another (as the runners are doing in Figure 1.7), and to carry out all of the activities of your daily life. 16 1 An Introduction to the Human Body FIGURE 1.7 Marathon Runners Runners demonstrate two characteristics of living humans—responsiveness and movement. Anatomic structures and physiological processes allow runners to coordinate the action of muscle groups and sweat in response to rising internal body temperature. (credit: Phil Roeder/flickr) Development, growth and reproduction Development is all of the changes the body goes through in life. Development includes the process of differentiation, in which unspecialized cells become specialized in structure and function to perform certain tasks in the body. Development also includes the processes of growth and repair, both of which involve cell differentiation. Growth is the increase in body size. Humans, like all multicellular organisms, grow by increasing the number of existing cells, increasing the amount of non-cellular material around cells (such as mineral deposits in bone), and, within very narrow limits, increasing the size of existing cells. Reproduction is the formation of a new organism from parent organisms. In humans, reproduction is carried out by the male and female reproductive systems. Because death will come to all complex organisms, without reproduction, the line of organisms would end. 1.4 Requirements for Human Life LEARNING OBJECTIVES By the end of this section, you will be able to: Discuss the role of oxygen and nutrients in maintaining human survival Explain why extreme heat and extreme cold threaten human survival Explain how the pressure exerted by gases and fluids influences human survival Humans have been acclimating to life on Earth for at least the past 200,000 years. Earth and its atmosphere have provided us with air to breathe, water to drink, and food to eat, but these are not the only requirements for survival. Although you may rarely think about it, you also cannot live outside of a certain range of temperature and pressure that the surface of our planet and its atmosphere provides. The next sections explore these four requirements of life. Oxygen Atmospheric air is only about 20 percent oxygen, but that oxygen is a key component of the chemical reactions that keep the body alive, including the reactions that produce ATP. Brain cells are especially sensitive to lack of oxygen because of their requirement for a high-and-steady production of ATP. Brain damage is likely within gve minutes without oxygen, and death is likely within ten minutes. Access for free at openstax.org 1.4 Requirements for Human Life 17 Nutrients A nutrient is a substance in foods and beverages that is essential to human survival. The three basic classes of nutrients are water, the energy-yielding and body-building nutrients, and the micronutrients (vitamins and minerals). The most critical nutrient is water. Depending on the environmental temperature and our state of health, we may be able to survive for only a few days without water. The body’s functional chemicals are dissolved and transported in water, and the chemical reactions of life take place in water. Moreover, water is the largest component of cells, blood, and the fluid between cells, and water makes up about 70 percent of an adult’s body mass. Water also helps regulate our internal temperature and cushions, protects, and lubricates joints and many other body structures. The energy-yielding nutrients are primarily carbohydrates and lipids, while proteins mainly supply the amino acids that are the building blocks of the body itself. You ingest these in plant and animal foods and beverages, and the digestive system breaks them down into molecules small enough to be absorbed. The breakdown products of carbohydrates and lipids can then be used in the metabolic processes that convert them to ATP. Although you might feel as if you are starving after missing a single meal, you can survive without consuming the energy-yielding nutrients for at least several weeks. Water and the energy-yielding nutrients are also referred to as macronutrients because the body needs them in large amounts. In contrast, micronutrients are vitamins and minerals. These elements and compounds participate in many essential chemical reactions and processes, such as nerve impulses, and some, such as calcium, also contribute to the body’s structure. Your body can store some of the micronutrients in its tissues, and draw on those reserves if you fail to consume them in your diet for a few days or weeks. Some others micronutrients, such as vitamin C and most of the B vitamins, are water-soluble and cannot be stored, so you need to consume them every day or two. Narrow Range of Temperature You have probably seen news stories about athletes who died of heat stroke, or hikers who died of exposure to cold. Such deaths occur because the chemical reactions upon which the body depends can only take place within a narrow range of body temperature, from just below to just above 37°C (98.6°F). When body temperature rises well above or drops well below normal, certain proteins (enzymes) that facilitate chemical reactions lose their normal structure and their ability to function and the chemical reactions of metabolism cannot proceed. That said, the body can respond effectively to short-term exposure to heat (Figure 1.8) or cold. One of the body’s responses to heat is, of course, sweating. As sweat evaporates from skin, it removes some thermal energy from the body, cooling it. Adequate water (from the extracellular fluid in the body) is necessary to produce sweat, so adequate fluid intake is essential to balance that loss during the sweat response. Not surprisingly, the sweat response is much less effective in a humid environment because the air is already saturated with water. Thus, the sweat on the skin’s surface is not able to evaporate, and internal body temperature can get dangerously high. 18 1 An Introduction to the Human Body FIGURE 1.8 Extreme Heat Humans acclimate to some degree to repeated exposure to high temperatures. (credit: McKay Savage/flickr) The body can also respond effectively to short-term exposure to cold. One response to cold is shivering, which is random muscle movement that generates heat. Another response is increased breakdown of stored energy to generate heat. When that energy reserve is depleted, however, and the core temperature begins to drop signigcantly, red blood cells will lose their ability to give up oxygen, denying the brain of this critical component of ATP production. This lack of oxygen can cause confusion, lethargy, and eventually loss of consciousness and death. The body responds to cold by reducing blood circulation to the extremities, the hands and feet, in order to prevent blood from cooling there and so that the body’s core can stay warm. Even when core body temperature remains stable, however, tissues exposed to severe cold, especially the gngers and toes, can develop frostbite when blood flow to the extremities has been much reduced. This form of tissue damage can be permanent and lead to gangrene, requiring amputation of the affected region. Everyday Connection Controlled Hypothermia As you have learned, the body continuously engages in coordinated physiological processes to maintain a stable temperature. In some cases, however, overriding this system can be useful, or even life-saving. Hypothermia is the clinical term for an abnormally low body temperature (hypo- = “below” or “under”). Controlled hypothermia is clinically induced hypothermia performed in order to reduce the metabolic rate of an organ or of a person’s entire body. Controlled hypothermia often is used, for example, during open-heart surgery because it decreases the metabolic needs of the brain, heart, and other organs, reducing the risk of damage to them. When controlled hypothermia is used clinically, the patient is given medication to prevent shivering. The body is then cooled to 25–32°C (79–89°F). The heart is stopped and an external heart-lung pump maintains circulation to the patient’s body. The heart is cooled further and is maintained at a temperature below 15°C (60°F) for the duration of the surgery. This very cold temperature helps the heart muscle to tolerate its lack of blood supply during the surgery. Some emergency department physicians use controlled hypothermia to reduce damage to the heart in patients who have suffered a cardiac arrest. In the emergency department, the physician induces coma and lowers the patient’s body temperature to approximately 91 degrees. This condition, which is maintained for 24 hours, slows the patient’s metabolic rate. Because the patient’s organs require less blood to function, the heart’s workload is reduced. Access for free at openstax.org 1.4 Requirements for Human Life 19 Narrow Range of Atmospheric Pressure Pressure is a force exerted by a substance that is in contact with another substance. Atmospheric pressure is pressure exerted by the mixture of gases (primarily nitrogen and oxygen) in the Earth’s atmosphere. Although you may not perceive it, atmospheric pressure is constantly pressing down on your body. This pressure keeps gases within your body, such as the gaseous nitrogen in body fluids, dissolved. If you were suddenly ejected from a space ship above Earth’s atmosphere, you would go from a situation of normal pressure to one of very low pressure. The pressure of the nitrogen gas in your blood would be much higher than the pressure of nitrogen in the space surrounding your body. As a result, the nitrogen gas in your blood would expand, forming bubbles that could block blood vessels and even cause cells to break apart. Atmospheric pressure does more than just keep blood gases dissolved. Your ability to breathe—that is, to take in oxygen and release carbon dioxide—also depends upon a precise atmospheric pressure. Altitude sickness occurs in part because the atmosphere at high altitudes exerts less pressure, reducing the exchange of these gases, and causing shortness of breath, confusion, headache, lethargy, and nausea. Mountain climbers carry oxygen to reduce the effects of both low oxygen levels and low barometric pressure at higher altitudes (Figure 1.9). FIGURE 1.9 Harsh Conditions Climbers on Mount Everest must accommodate extreme cold, low oxygen levels, and low barometric pressure in an environment hostile to human life. (credit: Melanie Ko/flickr) HOMEOSTATIC IMBALANCES Decompression Sickness Decompression sickness (DCS) is a condition in which gases dissolved in the blood or in other body tissues are no longer dissolved following a reduction in pressure on the body. This condition affects underwater divers who surface from a deep dive too quickly, and it can affect pilots flying at high altitudes in planes with unpressurized cabins. Divers often call this condition “the bends,” a reference to joint pain that is a symptom of DCS. In all cases, DCS is brought about by a reduction in barometric pressure. At high altitude, barometric pressure is much less than on Earth’s surface because pressure is produced by the weight of the column of air above the body pressing down on the body. The very great pressures on divers in deep water are likewise from the weight of a column of water pressing down on the body. For divers, DCS occurs at normal barometric pressure (at sea level), but it is brought on by the relatively rapid decrease of pressure as divers rise from the high pressure conditions of deep water to the now low, by comparison, pressure at sea level. Not surprisingly, diving in deep mountain lakes, where barometric pressure at the surface of the lake is less than that at sea level is more likely to result in DCS than diving in water at sea level. In DCS, gases dissolved in the blood (primarily nitrogen) come rapidly out of solution, forming bubbles in the blood and in other body tissues. This occurs because when pressure of a gas over a liquid is decreased, the amount of gas that can remain dissolved in the liquid also is decreased. It is air pressure that keeps your normal blood gases 20 1 An Introduction to the Human Body dissolved in the blood. When pressure is reduced, less gas remains dissolved. You have seen this in effect when you open a carbonated drink. Removing the seal of the bottle reduces the pressure of the gas over the liquid. This in turn causes bubbles as dissolved gases (in this case, carbon dioxide) come out of solution in the liquid. The most common symptoms of DCS are pain in the joints, with headache and disturbances of vision occurring in 10 percent to 15 percent of cases. Left untreated, very severe DCS can result in death. Immediate treatment is with pure oxygen. The affected person is then moved into a hyperbaric chamber. A hyperbaric chamber is a reinforced, closed chamber that is pressurized to greater than atmospheric pressure. It treats DCS by repressurizing the body so that pressure can then be removed much more gradually. Because the hyperbaric chamber introduces oxygen to the body at high pressure, it increases the concentration of oxygen in the blood. This has the effect of replacing some of the nitrogen in the blood with oxygen, which is easier to tolerate out of solution. The dynamic pressure of body fluids is also important to human survival. For example, blood pressure, which is the pressure exerted by blood as it flows within blood vessels, must be great enough to enable blood to reach all body tissues, and yet low enough to ensure that the delicate blood vessels can withstand the friction and force of the pulsating flow of pressurized blood. 1.5 Homeostasis LEARNING OBJECTIVES By the end of this section, you will be able to: Discuss the role of homeostasis in healthy functioning Contrast negative and positive feedback, giving one physiologic example of each mechanism Maintaining homeostasis requires that the body continuously monitor its internal conditions. From body temperature to blood pressure to levels of certain nutrients, each physiological condition has a particular set point. A set point is the physiological value around which the normal range fluctuates. A normal range is the restricted set of values that is optimally healthful and stable. For example, the set point for normal human body temperature is approximately 37°C (98.6°F) Physiological parameters, such as body temperature and blood pressure, tend to fluctuate within a normal range a few degrees above and below that point. Control centers in the brain and other parts of the body monitor and react to deviations from homeostasis using negative feedback. Negative feedback is a mechanism that reverses a deviation from the set point. Therefore, negative feedback maintains body parameters within their normal range. The maintenance of homeostasis by negative feedback goes on throughout the body at all times, and an understanding of negative feedback is thus fundamental to an understanding of human physiology. Negative Feedback A negative feedback system has three basic components (Figure 1.10a). A sensor, also referred to a receptor, is a component of a feedback system that monitors a physiological value. This value is reported to the control center. The control center is the component in a feedback system that compares the value to the normal range. If the value deviates too much from the set point, then the control center activates an effector. An effector is the component in a feedback system that causes a change to reverse the situation and return the value to the normal range. Access for free at openstax.org 1.5 Homeostasis 21 FIGURE 1.10 Negative Feedback System In a negative feedback system, a stimulus—a deviation from a set point—is resisted through a physiological process that returns the body to homeostasis. (a) A negative feedback system has gve basic parts. (b) Body temperature is regulated by negative feedback. In order to set the system in motion, a stimulus must drive a physiological parameter beyond its normal range (that is, beyond homeostasis). This stimulus is “heard” by a specigc sensor. For example, in the control of blood glucose, specigc endocrine cells in the pancreas detect excess glucose (the stimulus) in the bloodstream. These pancreatic beta cells respond to the increased level of blood glucose by releasing the hormone insulin into the bloodstream. The insulin signals skeletal muscle gbers, fat cells (adipocytes), and liver cells to take up the excess glucose, removing it from the bloodstream. As glucose concentration in the bloodstream drops, the decrease in concentration—the actual negative feedback—is detected by pancreatic alpha cells, and insulin release stops. This prevents blood sugar levels from continuing to drop below the normal range. Humans have a similar temperature regulation feedback system that works by promoting either heat loss or heat gain (Figure 1.10b). When the brain’s temperature regulation center receives data from the sensors indicating that the body’s temperature exceeds its normal range, it stimulates a cluster of brain cells referred to as the “heat-loss center.” This stimulation has three major effects: Blood vessels in the skin begin to dilate allowing more blood from the body core to flow to the surface of the skin allowing the heat to radiate into the environment. As blood flow to the skin increases, sweat glands are activated to increase their output. As the sweat evaporates from the skin surface into the surrounding air, it takes heat with it. The depth of respiration increases, and a person may breathe through an open mouth instead of through the nasal passageways. This further increases heat loss from the lungs. In contrast, activation of the brain’s heat-gain center by exposure to cold reduces blood flow to the skin, and blood returning from the limbs is diverted into a network of deep veins. This arrangement traps heat closer to the body core and restricts heat loss. If heat loss is severe, the brain triggers an increase in random signals to skeletal muscles, causing them to contract and producing shivering. The muscle contractions of shivering release heat while using up ATP. The brain triggers the thyroid gland in the endocrine system to release thyroid hormone, which increases metabolic activity and heat production in cells throughout the body. The brain also signals the adrenal glands to release epinephrine (adrenaline), a hormone that causes the breakdown of glycogen into glucose, which can be used as an energy source. The breakdown of glycogen into glucose also results in increased metabolism and heat production. 22 1 An Introduction to the Human Body INTERACTIVE LINK Water concentration in the body is critical for proper functioning. A person’s body retains very tight control on water levels without conscious control by the person. Watch this video (http://openstax.org/l/H2Ocon) to learn more about water concentration in the body. Which organ has primary control over the amount of water in the body? Positive Feedback Positive feedback intensiges a change in the body’s physiological condition rather than reversing it. A deviation from the normal range results in more change, and the system moves farther away from the normal range. Positive feedback in the body is normal only when there is a degnite end point. Childbirth and the body’s response to blood loss are two examples of positive feedback loops that are normal but are activated only when needed. Childbirth at full term is an example of a situation in which the maintenance of the existing body state is not desired. Enormous changes in a person’s body are required to expel the baby at the end of pregnancy. And the events of childbirth, once begun, must progress rapidly to a conclusion or the life of a person giving bith and the baby are at risk. The extreme muscular work of labor and delivery are the result of a positive feedback system (Figure 1.11). FIGURE 1.11 Positive Feedback Loop Normal childbirth is driven by a positive feedback loop. A positive feedback loop results in a change in the body’s status, rather than a return to homeostasis. The grst contractions of labor (the stimulus) push the baby toward the cervix (the lowest part of the uterus). The cervix contains stretch-sensitive nerve cells that monitor the degree of stretching (the sensors). These nerve cells send messages to the brain, which in turn causes the pituitary gland at the base of the brain to release the hormone oxytocin into the bloodstream. Oxytocin causes stronger contractions of the smooth muscles in of the uterus (the effectors), pushing the baby further down the birth canal. This causes even greater stretching of the cervix. The cycle of stretching, oxytocin release, and increasingly more forceful contractions stops only when the baby is born. At this point, the stretching of the cervix halts, stopping the release of oxytocin. A second example of positive feedback centers on reversing extreme damage to the body. Following a penetrating wound, the most immediate threat is excessive blood loss. Less blood circulating means reduced blood pressure and reduced perfusion (penetration of blood) to the brain and other vital organs. If perfusion is severely reduced, vital organs will shut down and the person will die. The body responds to this potential catastrophe by releasing substances in the injured blood vessel wall that begin the process of blood clotting. As each step of clotting occurs, Access for free at openstax.org 1.6 Anatomical Terminology 23 it stimulates the release of more clotting substances. This accelerates the processes of clotting and sealing off the damaged area. Clotting is contained in a local area based on the tightly controlled availability of clotting proteins. This is an adaptive, life-saving cascade of events. 1.6 Anatomical Terminology LEARNING OBJECTIVES By the end of this section, you will be able to: Demonstrate the anatomical position Describe the human body using directional and regional terms Identify three planes most commonly used in the study of anatomy Distinguish between the posterior (dorsal) and the anterior (ventral) body cavities, identifying their subdivisions and representative organs found in each Describe serous membrane and explain its function Anatomists and health care providers use terminology that can be bewildering to the uninitiated. However, the purpose of this language is not to confuse, but rather to increase precision and reduce medical errors. For example, is a scar “above the wrist” located on the forearm two or three inches away from the hand? Or is it at the base of the hand? Is it on the palm-side or back-side? By using precise anatomical terminology, we eliminate ambiguity. Anatomical terms derive from ancient Greek and Latin words. Because these languages are no longer used in everyday conversation, the meaning of their words does not change. Anatomical terms are made up of roots, pregxes, and sufgxes. The root of a term often refers to an organ, tissue, or condition, whereas the pregx or sufgx often describes the root. For example, in the disorder hypertension, the pregx “hyper-” means “high” or “over,” and the root word “tension” refers to pressure, so the word “hypertension” refers to abnormally high blood pressure. Anatomical Position To further increase precision, anatomists standardize the way in which they view the body. Just as maps are normally oriented with north at the top, the standard body “map,” or anatomical position, is that of the body standing upright, with the feet at shoulder width and parallel, toes forward. The upper limbs are held out to each side, and the palms of the hands face forward as illustrated in Figure 1.12. Using this standard position reduces confusion. It does not matter how the body being described is oriented, the terms are used as if it is in anatomical position. For example, a scar in the “anterior (front) carpal (wrist) region” would be present on the palm side of the wrist. The term “anterior” would be used even if the hand were palm down on a table. 24 1 An Introduction to the Human Body FIGURE 1.12 Regions of the Human Body The human body is shown in anatomical position in an (a) anterior view and a (b) posterior view. The regions of the body are labeled in boldface. A body that is lying down is described as either prone or supine. Prone describes a face-down orientation, and supine describes a face up orientation. These terms are sometimes used in describing the position of the body during specigc physical examinations or surgical procedures. Regional Terms The human body’s numerous regions have specigc terms to help increase precision (see Figure 1.12). Notice that the term “brachium” or “arm” is reserved for the “upper arm” and “antebrachium” or “forearm” is used rather than “lower arm.” Similarly, “femur” or “thigh” is correct, and “leg” or “crus” is reserved for the portion of the lower limb between the knee and the ankle. You will be able to describe the body’s regions using the terms from the ggure. Directional Terms Certain directional anatomical terms appear throughout this and any other anatomy textbook (Figure 1.13). These terms are essential for describing the relative locations of different body structures. For instance, an anatomist might describe one band of tissue as “inferior to” another or a physician might describe a tumor as “supergcial to” a deeper body structure. Commit these terms to memory to avoid confusion when you are studying or describing the locations of particular body parts. Anterior (or ventral) Describes the front or direction toward the front of the body. The toes are anterior to the foot. Posterior (or dorsal) Describes the back or direction toward the back of the body. The popliteus is posterior to the patella. Superior (or cranial) describes a position above or higher than another part of the body proper. The orbits are superior to the oris. Access for free at openstax.org 1.6 Anatomical Terminology 25 Inferior (or caudal) describes a position below or lower than another part of the body proper; near or toward the tail (in humans, the coccyx, or lowest part of the spinal column). The pelvis is inferior to the abdomen. Lateral describes the side or direction toward the side of the body. The thumb (pollex) is lateral to the digits. Medial describes the middle or direction toward the middle of the body. The hallux is the medial toe. Proximal describes a position in a limb that is nearer to the point of attachment or the trunk of the body. The brachium is proximal to the antebrachium. Distal describes a position in a limb that is farther from the point of attachment or the trunk of the body. The crus is distal to the femur. SuperJcial describes a position closer to the surface of the body. The skin is supergcial to the bones. Deep describes a position farther from the surface of the body. The brain is deep to the skull. FIGURE 1.13 Directional Terms Applied to the Human Body Paired directional terms are shown as applied to the human body. Body Planes A section is a two-dimensional surface of a three-dimensional structure that has been cut. Modern medical imaging devices enable clinicians to obtain “virtual sections” of living bodies. We call these scans. Body sections and scans can be correctly interpreted, however, only if the viewer understands the plane along which the section was made. A plane is an imaginary two-dimensional surface that passes through the body. There are three planes commonly referred to in anatomy and medicine, as illustrated in Figure 1.14. The sagittal plane is the plane that divides the body or an organ vertically into right and left sides. If this vertical plane runs directly down the middle of the body, it is called the midsagittal or median plane. If it divides the body into unequal right and left sides, it is called a parasagittal plane or less commonly a longitudinal section. The frontal plane is the plane that divides the body or an organ into an anterior (front) portion and a posterior (rear) portion. The frontal plane is often referred to as a coronal plane. (“Corona” is Latin for “crown.”) The transverse plane is the plane that divides the body or organ horizontally into upper and lower portions. 26 1 An Introduction to the Human Body Transverse planes produce images referred to as cross sections. FIGURE 1.14 Planes of the Body The three planes most commonly used in anatomical and medical imaging are the sagittal, frontal (or coronal), and transverse plane. Body Cavities and Serous Membranes The body maintains its internal organization by means of membranes, sheaths, and other structures that separate compartments. The dorsal (posterior) cavity and the ventral (anterior) cavity are the largest body compartments (Figure 1.15). These cavities contain and protect delicate internal organs, and the ventral cavity allows for signigcant changes in the size and shape of the organs as they perform their functions. The lungs, heart, stomach, and intestines, for example, can expand and contract without distorting other tissues or disrupting the activity of nearby organs. FIGURE 1.15 Dorsal and Ventral Body Cavities The ventral cavity includes the thoracic and abdominopelvic cavities and their subdivisions. The dorsal cavity includes the cranial and spinal cavities. Access for free at openstax.org 1.6 Anatomical Terminology 27 Subdivisions of the Posterior (Dorsal) and Anterior (Ventral) Cavities The posterior (dorsal) and anterior (ventral) cavities are each subdivided into smaller cavities. In the posterior (dorsal) cavity, the cranial cavity houses the brain, and the spinal cavity (or vertebral cavity) encloses the spinal cord. Just as the brain and spinal cord make up a continuous, uninterrupted structure, the cranial and spinal cavities that house them are also continuous. The brain and spinal cord are protected by the bones of the skull and vertebral column and by cerebrospinal fluid, a colorless fluid produced by the brain, which cushions the brain and spinal cord within the posterior (dorsal) cavity. The anterior (ventral) cavity has two main subdivisions: the thoracic cavity and the abdominopelvic cavity (see Figure 1.15). The thoracic cavity is the more superior subdivision of the anterior cavity, and it is enclosed by the rib cage. The thoracic cavity contains the lungs and the heart, which is located in the mediastinum. The diaphragm forms the floor of the thoracic cavity and separates it from the more inferior abdominopelvic cavity. The abdominopelvic cavity is the largest cavity in the body. Although no membrane physically divides the abdominopelvic cavity, it can be useful to distinguish between the abdominal cavity, the division that houses the digestive organs, and the pelvic cavity, the division that houses the organs of reproduction. Abdominal Regions and Quadrants To promote clear communication, for instance about the location of a patient’s abdominal pain or a suspicious mass, health care providers typically divide up the cavity into either nine regions or four quadrants (Figure 1.16). FIGURE 1.16 Regions and Quadrants of the Peritoneal Cavity There are (a) nine abdominal regions and (b) four abdominal quadrants in the peritoneal cavity. The more detailed regional approach subdivides the cavity with one horizontal line immediately inferior to the ribs and one immediately superior to the pelvis, and two vertical lines drawn as if dropped from the midpoint of each clavicle (collarbone). There are nine resulting regions. The simpler quadrants approach, which is more commonly used in medicine, subdivides the cavity with one horizontal and one vertical line that intersect at the patient’s umbilicus (navel). Membranes of the Anterior (Ventral) Body Cavity A serous membrane (also referred to a serosa) is one of the thin membranes that cover the walls and organs in the thoracic and abdominopelvic cavities. The parietal layers of the membranes line the walls of the body cavity (pariet- refers to a cavity wall). The visceral layer of the membrane covers the organs (the viscera). Between the parietal and visceral layers is a very thin, fluid-glled serous space, or cavity (Figure 1.17). 28 1 An Introduction to the Human Body FIGURE 1.17 Serous Membrane Serous membrane lines the pericardial cavity and reflects back to cover the heart—much the same way that an underinflated balloon would form two layers surrounding a gst. There are three serous cavities and their associated membranes. The pleura is the serous membrane that encloses the pleural cavity; the pleural cavity surrounds the lungs. The pericardium is the serous membrane that encloses the pericardial cavity; the pericardial cavity surrounds the heart. The peritoneum is the serous membrane that encloses the peritoneal cavity; the peritoneal cavity surrounds several organs in the abdominopelvic cavity. The serous membranes form fluid-glled sacs, or cavities, that are meant to cushion and reduce friction on internal organs when they move, such as when the lungs inflate or the heart beats. Both the parietal and visceral serosa secrete the thin, slippery serous fluid located within the serous cavities. The pleural cavity reduces friction between the lungs and the body wall. Likewise, the pericardial cavity reduces friction between the heart and the wall of the pericardium. The peritoneal cavity reduces friction between the abdominal and pelvic organs and the body wall. Therefore, serous membranes provide additional protection to the viscera they enclose by reducing friction that could lead to inflammation of the organs. 1.7 Medical Imaging LEARNING OBJECTIVES By the end of this section, you will be able to: Discuss the uses and drawbacks of X-ray imaging Identify four modern medical imaging techniques and how they are used For thousands of years, fear of the dead and legal sanctions limited the ability of anatomists and physicians to study the internal structures of the human body. An inability to control bleeding, infection, and pain made surgeries infrequent, and those that were performed—such as wound suturing, amputations, tooth and tumor removals, skull drilling, and cesarean births—did not greatly advance knowledge about internal anatomy. Theories about the function of the body and about disease were therefore largely based on external observations and imagination. During the fourteenth and gfteenth centuries, however, the detailed anatomical drawings of Italian artist and anatomist Leonardo da Vinci and Flemish anatomist Andreas Vesalius were published, and interest in human anatomy began to increase. Medical schools began to teach anatomy using human dissection; although some resorted to grave robbing to obtain corpses. Laws were eventually passed that enabled students to dissect the corpses of criminals and those who donated their bodies for research. Still, it was not until the late nineteenth century that medical researchers discovered non-surgical methods to look inside the living body. X-Rays German physicist Wilhelm Röntgen (1845–1923) was experimenting with electrical current when he discovered that a mysterious and invisible “ray” would pass through his flesh but leave an outline of his bones on a screen coated with a metal compound. In 1895, Röntgen made the grst durable record of the internal parts of a living human: an “X-ray” image (as it came to be called) of his wife’s hand. Scientists around the world quickly began their own experiments with X-rays, and by 1900, X-rays were widely used to detect a variety of injuries and diseases. In 1901, Röntgen was awarded the grst Nobel Prize for physics for his work in this geld. The X-ray is a form of high energy electromagnetic radiation with a short wavelength capable of penetrating solids Access for free at openstax.org 1.7 Medical Imaging 29 and ionizing gases. As they are used in medicine, X-rays are emitted from an X-ray machine and directed toward a specially treated metallic plate placed behind the patient’s body. The beam of radiation results in darkening of the X-ray plate. X-rays are slightly impeded by soft tissues, which show up as gray on the X-ray plate, whereas hard tissues, such as bone, largely block the rays, producing a light-toned “shadow.” Thus, X-rays are best used to visualize hard body structures such as teeth and bones (Figure 1.18). Like many forms of high energy radiation, however, X-rays are capable of damaging cells and initiating changes that can lead to cancer. This danger of excessive exposure to X-rays was not fully appreciated for many years after their widespread use. FIGURE 1.18 X-Ray of a Hand High energy electromagnetic radiation allows the internal structures of the body, such as bones, to be seen in X-rays like these. (credit: Trace Meek/flickr) Regnements and enhancements of X-ray techniques have continued throughout the twentieth and twenty-grst centuries. Although often supplanted by more sophisticated imaging techniques, the X-ray remains a “workhorse” in medical imaging, especially for viewing fractures and for dentistry. The disadvantage of irradiation to the patient and the operator is now attenuated by proper shielding and by limiting exposure. Modern Medical Imaging X-rays can depict a two-dimensional image of a body region, and only from a single angle. In contrast, more recent medical imaging technologies produce data that is integrated and analyzed by computers to produce three- dimensional images or images that reveal aspects of body functioning. Computed Tomography Tomography refers to imaging by sections. Computed tomography (CT) is a noninvasive imaging technique that uses computers to analyze several cross-sectional X-rays in order to reveal minute details about structures in the body (Figure 1.19a). The technique was invented in the 1970s and is based on the principle that, as X-rays pass through the body, they are absorbed or reflected at different levels. In the technique, a patient lies on a motorized platform while a computerized axial tomography (CAT) scanner rotates 360 degrees around the patient, taking X-ray images. A computer combines these images into a two-dimensional view of the scanned area, or “slice.” 30 1 An Introduction to the Human Body FIGURE 1.19 Medical Imaging Techniques (a) The results of a CT scan of the head are shown as successive transverse sections. (b) An MRI machine generates a magnetic geld around a patient. (c) PET scans use radiopharmaceuticals to create images of active blood flow and physiologic activity of the organ or organs being targeted. (d) Ultrasound technology is used to monitor pregnancies because it is the least invasive of imaging techniques and uses no electromagnetic radiation. (credit a: Akira Ohgaki/flickr; credit b: “Digital Cate”/flickr; credit c: “Raziel”/Wikimedia Commons; credit d: “Isis”/Wikimedia Commons) Since 1970, the development of more powerful computers and more sophisticated software has made CT scanning routine for many types of diagnostic evaluations. It is especially useful for soft tissue scanning, such as of the brain and the thoracic and abdominal viscera. Its level of detail is so precise that it can allow physicians to measure the size of a mass down to a millimeter. The main disadvantage of CT scanning is that it exposes patients to a dose of radiation many times higher than that of X-rays. In fact, children who undergo CT scans are at increased risk of developing cancer, as are adults who have multiple CT scans. INTERACTIVE LINK A CT or CAT scan relies on a circling scanner that revolves around the patient’s body. Watch this video (http://openstax.org/l/CATscan) to learn more about CT and CAT scans. What type of radiation does a CT scanner use? Magnetic Resonance Imaging Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic gelds and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the grst MRI scanning device, which was in use clinically by the early 1980s. The early MRI scanners were crude, but advances in digital computing and electronics led to their advancement over any other technique for precise imaging, especially to discover tumors. MRI also has the major advantage of not exposing patients to radiation. Drawbacks of MRI scans include their much higher cost, and patient discomfort with the procedure. The MRI scanner subjects the patient to such powerful electromagnets that the scan room must be shielded. The patient Access for free at openstax.org 1.7 Medical Imaging 31 must be enclosed in a metal tube-like device for the duration of the scan (see Figure 1.19b), sometimes as long as thirty minutes, which can be uncomfortable and impractical for ill patients. The device is also so noisy that, even with earplugs, patients can become anxious or even fearful. These problems have been overcome somewhat with the development of “open” MRI scanning, which does not require the patient to be entirely enclosed in the metal tube. Patients with iron-containing metallic implants (internal sutures, some prosthetic devices, and so on) cannot undergo MRI scanning because it can dislodge these implants. Functional MRIs (fMRIs), which detect the concentration of blood flow in certain parts of the body, are increasingly being used to study the activity in parts of the brain during various body activities. This has helped scientists learn more about the locations of different brain functions and more about brain abnormalities and diseases. INTERACTIVE LINK A patient undergoing an MRI is surrounded by a tube-shaped scanner. Watch this video (http://openstax.org/l/MRI) to learn more about MRIs. What is the function of magnets in an MRI? Positron Emission Tomography Positron emission tomography (PET) is a medical imaging technique involving the use of so-called radiopharmaceuticals, substances that emit radiation that is short-lived and therefore relatively safe to administer to the body. Although the grst PET scanner was introduced in 1961, it took 15 more years before radiopharmaceuticals were combined with the technique and revolutionized its potential. The main advantage is that PET (see Figure 1.19c) can illustrate physiologic activity—including nutrient metabolism and blood flow—of the organ or organs being targeted, whereas CT and MRI scans can only show static images. PET is widely used to diagnose a multitude of conditions, such as heart disease, the spread of cancer, certain forms of infection, brain abnormalities, bone disease, and thyroid disease. INTERACTIVE LINK PET relies on radioactive substances administered several minutes before the scan. Watch this video (http://openstax.org/l/PET) to learn more about PET. How is PET used in chemotherapy? Ultrasonography Ultrasonography is an imaging technique that uses the transmission of high-frequency sound waves into the body to generate an echo signal that is converted by a computer into a real-time image of anatomy and physiology (see Figure 1.19d). Ultrasonography is the least invasive of all imaging techniques, and it is therefore used more freely in sensitive situations such as pregnancy. The technology was grst developed in the 1940s and 1950s. Ultrasonography is used to study heart function, blood flow in the neck or extremities, certain conditions such as gallbladder disease, and fetal growth and development. The main disadvantages of ultrasonography are that the image quality is heavily operator-dependent and that it is unable to penetrate bone and gas. 32 1 Key Terms Key Terms abdominopelvic cavity division of the anterior divides the body or organ into anterior and posterior (ventral) cavity that houses the abdominal and portions pelvic viscera gross anatomy study of the larger structures of the anabolism assembly of more complex molecules body, typically with the unaided eye; also referred to from simpler molecules macroscopic anatomy anatomical position standard reference position growth process of increasing in size used for describing locations and directions on the homeostasis steady state of body systems that living human body organisms maintain anatomy science that studies the form and inferior describes a position below or lower than composition of the body’s structures another part of the body proper; near or toward the anterior describes the front or direction toward the tail (in humans, the coccyx, or lowest part of the front of the body; also referred to as ventral spinal column); also referred to as caudal anterior cavity larger body cavity located anterior to lateral describes the side or direction toward the side the posterior (dorsal) body cavity; includes the of the body serous membrane-lined pleural cavities for the magnetic resonance imaging (MRI) medical imaging lungs, pericardial cavity for the heart, and peritoneal technique in which a device generates a magnetic cavity for the abdominal and pelvic organs; also geld to obtain detailed sectional images of the referred to as ventral cavity internal structures of the body catabolism breaking down of more complex medial describes the middle or direction toward the molecules into simpler molecules middle of the body caudal describes a position below or lower than metabolism sum of all of the body’s chemical another part of the body proper; near or toward the reactions tail (in humans, the coccyx, or lowest part of the microscopic anatomy study of very small structures spinal column); also referred to as inferior of the body using magnigcation cell smallest independently functioning unit negative feedback homeostatic mechanism that of all organisms; in animals, a cell contains tends to stabilize an upset in the body’s cytoplasm, composed of fluid and organelles physiological condition by preventing an excessive computed tomography (CT) medical imaging response to a stimulus, typically as the stimulus is technique in which a computer-enhanced cross- removed sectional X-ray image is obtained normal range range of values around the set point control center compares values to their normal that do not cause a reaction by the control center range; deviations cause the activation of an effector nutrient chemical obtained from foods and cranial describes a position above or higher than beverages that is critical to human survival another part of the body proper; also referred to as organ functionally distinct structure composed of two superior or more types of tissues cranial cavity division of the posterior (dorsal) cavity organ system group of organs that work together to that houses the brain carry out a particular function deep describes a position farther from the surface of organism living being that has a cellular structure and the body that can independently perform all physiologic development changes an organism goes through functions necessary for life during its life pericardium sac that encloses the heart differentiation process by which unspecialized cells peritoneum serous membrane that lines the become specialized in structure and function abdominopelvic cavity and covers the organs found distal describes a position farther from the point of there attachment or the trunk of the body physiology science that studies the chemistry, dorsal describes the back or direction toward the biochemistry, and physics of the body’s functions back of the body; also referred to as posterior plane imaginary two-dimensional surface that passes dorsal cavity posterior body cavity that houses the through the body brain and spinal cord; also referred to the posterior pleura serous membrane that lines the pleural cavity body cavity and covers the lungs effector organ that can cause a change in a value positive feedback mechanism that intensiges a frontal plane two-dimensional, vertical plane that change in the body’s physiological condition in Access for free at openstax.org 1 Chapter Review 33 response to a stimulus optimally healthful, that is, within its parameters of positron emission tomography (PET) medical homeostasis imaging technique in which radiopharmaceuticals spinal cavity division of the dorsal cavity that houses are traced to reveal metabolic and physiological the spinal cord; also referred to as vertebral cavity functions in tissues superJcial describes a position nearer to the surface posterior describes the back or direction toward the of the body back of the body; also referred to as dorsal superior describes a position above or higher than posterior cavity posterior body cavity that houses the another part of the body proper; also referred to as brain and spinal cord; also referred to as dorsal cranial cavity supine face up pressure force exerted by a substance in contact with systemic anatomy study of the structures that another substance contribute to specigc body systems prone face down thoracic cavity division of the anterior (ventral) cavity proximal describes a position nearer to the point of that houses the heart, lungs, esophagus, and attachment or the trunk of the body trachea regional anatomy study of the structures that tissue group of similar or closely related cells that act contribute to specigc body regions together to perform a specigc function renewal process by which worn-out cells are transverse plane two-dimensional, horizontal plane replaced that divides the body or organ into superior and reproduction process by which new organisms are inferior portions generated ultrasonography application of ultrasonic waves to responsiveness ability of an organisms or a system to visualize subcutaneous body structures such as adjust to changes in conditions tendons and organs sagittal plane two-dimensional, vertical plane that ventral describes the front or direction toward the divides the body or organ into right and left sides front of the body; also referred to as anterior section in anatomy, a single flat surface of a three- ventral cavity larger body cavity located anterior to dimensional structure that has been cut through the posterior (dorsal) body cavity; includes the sensor (also, receptor) reports a monitored serous membrane-lined pleural cavities for the physiological value to the control center lungs, pericardial cavity for the heart, and peritoneal serosa membrane that covers organs and reduces cavity for the abdominal and pelvic organs; also friction; also referred to as serous membrane referred to as anterior body cavity serous membrane membrane that covers organs and X-ray form of high energy electromagnetic radiation reduces friction; also referred to as serosa with a short wavelength capable of penetrating set point ideal value for a physiological parameter; solids and ionizing gases; used in medicine as a the level or small range within which a physiological diagnostic aid to visualize body structures such as parameter such as blood pressure is stable and bones Chapter Review 1.1 Overview of Anatomy and Physiology 1.2 Structural Organization of the Human Human anatomy is the scientigc study of the body’s Body structures. In the past, anatomy has primarily been Life processes of the human body are maintained at studied via observing injuries, and later by the several levels of structural organization. These include dissection of anatomical structures of cadavers, but in the chemical, cellular, tissue, organ, organ system, and the past century, computer-assisted imaging the organism level. Higher levels of organization are techniques have allowed clinicians to look inside the built from lower levels. Therefore, molecules combine living body. Human physiology is the scientigc study of to form cells, cells combine to form tissues, tissues the chemistry and physics of the structures of the body. combine to form organs, organs combine to form organ Physiology explains how the structures of the body systems, and organ systems combine to form work together to maintain life. It is difgcult to study organisms. structure (anatomy) without knowledge of function (physiology). The two disciplines are typically studied 1.3 Functions of Human Life together because form and function are closely related Most processes that occur in the human body are not in all living things. 34 1 Interactive Link Questions consciously controlled. They occur continuously to response until an end point is reached. build, maintain, and sustain life. These processes include: organization, in terms of the maintenance of 1.6 Anatomical Terminology essential body boundaries; metabolism, including Ancient Greek and Latin words are used to build energy transfer via anabolic and catabolic reactions; anatomical terms. A standard reference position for responsiveness; movement; and growth, mapping the body’s structures is the normal differentiation, reproduction, and renewal. anatomical position. Regions of the body are identiged using terms such as “occipital” that are more precise 1.4 Requirements for Human Life than common words and phrases such as “the back of Humans cannot survive for more than a few minutes the head.” Directional terms such as anterior and without oxygen, for more than several days without posterior are essential for accurately describing the water, and for more than several weeks without relative locations of body structures. Images of the carbohydrates, lipids, proteins, vitamins, and minerals. body’s interior commonly align along one of three Although the body can respond to high temperatures planes: the sagittal, frontal, or transverse. The body’s by sweating and to low temperatures by shivering and organs are organized in one of two main increased fuel consumption, long-term exposure to cavities—dorsal (also referred to posterior) and ventral extreme heat and cold is not compatible with survival. (also referred to anterior)—which are further sub- The body requires a precise atmospheric pressure to divided according to the structures present in each maintain its gases in solution and to facilitate area. The serous membranes have two layers—parietal respiration—the intake of oxygen and the release of and visceral—surrounding a fluid glled space. Serous carbon dioxide. Humans also require blood pressure membranes cover the lungs (pleural serosa), heart high enough to ensure that blood reaches all body (pericardial serosa), and some abdominopelvic organs tissues but low enough to avoid damage to blood (peritoneal serosa). vessels. 1.7 Medical Imaging 1.5 Homeostasis Detailed anatomical drawings of the human body grst Homeostasis is the activity of cells throughout the body became available in the gfteenth and sixteenth to maintain the physiological state within a narrow centuries; however, it was not until the end of the range that is compatible with life. Homeostasis is nineteenth century, and the discovery of X-rays, that regulated by negative feedback loops and, much less anatomists and physicians discovered non-surgical frequently, by positive feedback loops. Both have the methods to look inside a living body. Since then, many same components of a stimulus, sensor, control center, other techniques, including CT scans, MRI scans, PET and effector; however, negative feedback loops work to scans, and ultrasonography, have been developed, prevent an excessive response to the stimulus, providing more accurate and detailed views of the form whereas positive feedback loops intensify the and function of the human body. Interactive Link Questions 1. View this animation (http://openstax.org/l/ 3. A CT or CAT scan relies on a circling scanner that metabolic) to learn more about metabolic revolves around the patient’s body. Watch this processes. What kind of catabolism occurs in the video (http://openstax.org/l/CATscan) to learn more heart? about CT and CAT scans. What type of radiation 2. Water concentration in the body is critical for does a CT scanner use? proper functioning. A person’s body retains very 4. A patient undergoing an MRI is surrounded by a tight control on water levels without conscious tube-shaped scanner. Watch this video control by the person. Watch this video (http://openstax.org/l/MRI) to learn more about (http://openstax.org/l/H2Ocon) to learn more about MRIs. What is the function of magnets in an MRI? water concentration in the body. Which organ has 5. PET relies on radioactive substances administered primary control over the amount of water in the several minutes before the scan. Watch this video body? (http://openstax.org/l/PET) to learn more about PET. How is PET used in chemotherapy? Access for free at openstax.org 1 Review Questions 35 Review Questions 6. Which of the following specialties might focus on 13. Cancer cells can be characterized as “generic” studying all of the structures of the ankle and foot? cells that perform no specialized body function. a. microscopic anatomy Thus cancer cells lack ________. b. muscle anatomy a. differentiation c. regional anatomy b. reproduction d. systemic anatomy c. responsiveness d. both reproduction and responsiveness 7. A scientist wants to study how the body uses foods and fluids during a marathon run. This scientist is 14. Humans have the most urgent need for a most likely a(n) ________. continuous supply of ________. a. exercise physiologist a. food b. microscopic anatomist b. nitrogen c. regional physiologist c. oxygen d. systemic anatomist d. water 8. The smallest independently functioning biological 15. Which of the following statements about nutrients unit of an organism is a(n) ________. is true? a. cell a. All classes of nutrients are essential to human b. molecule survival. c. organ b. Because the body cannot store any d. tissue micronutrients, they need to be consumed nearly every day. 9. A collection of similar tissues that performs a c. Carbohydrates, lipids, and proteins are specigc function is an ________. micronutrients. a. organ d. Macronutrients are vitamins and minerals. b. organelle c. organism 16. C.J. is stuck in their car during a bitterly cold d. organ system blizzard. Their body responds to the cold by ________. 10. The body system responsible for structural a. increasing the blood to the hands and feet support and movement is the ________. b. becoming lethargic to conserve heat a. cardiovascular system c. breaking down stored energy b. endocrine system d. signigcantly increasing blood oxygen levels c. muscular system d. skeletal system 17. After you eat lunch, nerve cells in your stomach respond to the distension (the stimulus) resulting 11. Metabolism can be degned as the ________. from the food. They relay this information to a. adjustment by an organism to external or ________. internal changes a. a control center b. process whereby all unspecialized cells b. a set point become specialized to perform distinct c. effectors functions d. sensors c. process whereby new cells are formed to replace worn-out cells 18. Stimulation of the heat-loss center causes d. sum of all chemical reactions in an organism ________. a. blood vessels in the skin to constrict 12. Adenosine triphosphate (ATP) is an important b. breathing to become slow and shallow molecule because it ________. c. sweat glands to increase their output a. is the result of catabolism d. All of the above b. release energy in uncontrolled bursts c. stores energy for use by body cells d. All of the above 36 1 Critical Thinking Questions 19. Which of the following is an example of a normal 23. The heart is within the ________. physiologic process that uses a positive feedback a. cranial cavity loop? b. mediastinum a. blood pressure regulation c. posterior (dorsal) cavity b. childbirth d. All of the above c. regulation of fluid balance 24. In 1901, Wilhelm Röntgen was the grst person to d. temperature regulation win the Nobel Prize for physics. For what discovery 20. What is the position of the body when it is in the did he win? “normal anatomical position?” a. nuclear physics a. The person is prone with upper limbs, b. radiopharmaceuticals including palms, touching sides and lower c. the link between radiation and cancer limbs touching at sides. d. X-rays b. The person is standing facing the observer, 25. Which of the following imaging techniques would with upper limbs extended out at a ninety- be best to use to study the uptake of nutrients by degree angle from the torso and lower limbs rapidly multiplying cancer cells? in a wide stance with feet pointing laterally a. CT c. The person is supine with upper limbs, b. MRI including palms, touching sides and lower c. PET limbs touching at sides. d. ultrasonography d. None of the above 26. Which of the following imaging studies can be 21. To make a banana split, you halve a banana into used most safely during pregnancy? two long, thin, right and left sides along the a. CT scans ________. b. PET scans a. coronal plane c. ultrasounds b. longitudinal plane d. X-rays c. midsagittal plane d. transverse plane 27. What are two major disadvantages of MRI scans? a. release of radiation and poor quality images 22. The lumbar region is ________. b. high cost and the need for shielding from the a. inferior to the gluteal region magnetic signals b. inferior to the umbilical region c. can only view metabolically active tissues and c. superior to the cervical region inadequate availability of equipment d. superior to the popliteal region d. release of radiation and the need for a patient to be congned to metal tube for up to 30 minutes Critical Thinking Questions 28. Name at least three reasons to study anatomy and 32. Explain why the smell of smoke when you are physiology. sitting at a campgre does not trigger alarm, but 29. For whom would an appreciation of the structural the smell of smoke in your residence hall does. characteristics of the human heart come more 33. Identify three different ways that growth can easily: an alien who lands on Earth, abducts a occur in the human body. human, and dissects his heart, or an anatomy and 34. When you open a bottle of sparkling water, the physiology student performing a dissection of the carbon dioxide gas in the bottle form bubbles. If heart on her very grst day of class? Why? the bottle is left open, the water will eventually 30. Name the six levels of organization of the human “go flat.” Explain these phenomena in terms of body. atmospheric pressure. 31. The and the testes are a part of which body 35. On his midsummer trek through the desert, Josh system? Can these organs be members of more ran out of water. Why is this particularly than one organ system? Why or why not? dangerous? Access for free at openstax.org 1 Critical Thinking Questions 37 36. Identify the four components of a negative 39. If a bullet were to penetrate a lung, which three feedback loop and explain what would happen if anterior thoracic body cavities would it enter, and secretion of a body chemical controlled by a which layer of the serous membrane would it negative feedback system became too great. encounter grst? 37. What regulatory processes would your body use if 40. Which medical imaging technique is most you were trapped by a blizzard in an unheated, dangerous to use repeatedly, and why? uninsulated cabin in the woods? 41. Explain why ultrasound imaging is the technique 38. In which direction would an MRI scanner move to of choice for studying fetal growth and produce sequential images of the body in the development. frontal plane, and in which direction would an MRI scanner move to produce sequential images of the body in the sagittal plane?

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