Anatomy & Physiology_Unit 1 - Chapter 2 PDF

2 Introduction to the Human Body Hareluya/Shutterstock.c...

2 Introduction to the Human Body Hareluya/Shutterstock.com Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 15   Chapter Introduction An understanding of anatomy and physiology is not only fundamental to any career in the health professions, but it can also benefit you personally. The knowledge and understanding you gain in this course may help you act as an advocate for your own health as well as the health of your family members. Mastery of the language of anatomy and physiology will help you converse with your healthcare providers. Your knowledge and critical thinking skills in this field will help you understand and critique news about nutrition, medications, medical devices, procedures, and both infectious and non infectious diseases. This chapter begins with an overview of anatomy and physiology and a preview of the body regions and functions. It introduces a set of standard terms for body structures and for planes and positions in the body that will serve as a foun- dation for more comprehensive information covered later in the text. 2.1 Overview of Anatomy and Physiology Learning Objectives: By the end of this section, you will be able to: 2.1.1 Define the terms anatomy and physiology. 2.1.2 Give specific examples to show the interrelationship between anatomy and physiology. Human anatomy is the scientific study of the body’s structures. Some of these struc- tures are very small and can only be observed and analyzed with the assistance of a microscope (microscopic anatomy). Larger structures can readily be seen, manipu- lated, measured, and weighed (gross anatomy). Our visual understanding of the body gross anatomy extends far beyond these two levels of detail. We also have many ways of “seeing” inside (macroscopic anatomy) the bodies of living individuals with great precision (such as the use of Magnetic Reso- nance Imaging and X-rays). The “Digging Deeper” feature discusses the physics behind these imaging techniques. Figure 2.1 illustrates their differences by comparing a view of the brain and cranium using a variety of techniques. Figure 2.1A is a gross anatomi- cal view of an intact human brain. Functional Magnetic Resonance Imaging (fMRI, Figure 2.1C) as well as ultrasonography (Figure 2.1D), however, do allow us to see func- tions in real time, which microscopic anatomy does not. X-ray imaging is best for hard structures such as bones; notice that we cannot visualize the brain through the cranium using an X-ray (Figure 2.1E). CT scans is an imaging technique that uses multiple angles of X-rays at once to produce a more detailed image (Figure 2.1F). Microscopic anatomy (Figure 2.1B) can only be done on cells and tissues removed from the body (which isn’t optimal when it comes to brain tissue!). 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. Anatomists take two general approaches to the study of the body’s structures: regional and systemic. Regional anatomy is the study of the interrelationships The Human Anatomy and Physiology Society includes more than 1,700 educators who work together to promote excellence in the teaching of this subject area. The HAPS A&P Learning Outcomes measure student mastery of the content typically covered in a two-semester Human A&P curriculum at the undergraduate level. The full Learning Outcomes are available at https://www.hapsweb.org. Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 16 Unit 1 Levels of Organization Figure 2.1 Anatomical Structures in a Variety of Imaging Techniques (A) Gross anatomy of the brain considers structures visible with the naked eye. (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. (C) Functional MRI (fMRI) shows regions of the brain active during particular activities. (D) Ultrasound visualization of the fetal brain. (E) X-rays are best for illustrating hard structures such as the skull. (F) CT scans show brain and body structures in a variety of planes. Rattiya Thongdumhyu/Shutterstock.com Jesada Sabai/Shutterstock.com A B Cavallini James/BSIP SA/Alamy Stock Photo Kul Bhatia/Science Source C D Puwadol Jaturawutthichai/Shutterstock.com Oksana2010/Shutterstock.com E F Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 17   of all of the structures in a specific body region, such as the abdomen. Studying regional anatomy helps us appreciate the relatedness of body structures, such as how muscles, nerves, blood vessels, and other structures work together to serve a particular body region. A significant goal of those learning regional anatomy is to build a three-dimensional understanding of the placement and relationships among structures in their minds so that, when presented with images taken from a various perspectives or while performing surgery or dissection, anatomists are able to understand the images. 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 ana- tomical study of the muscular system would consider all of the skeletal muscles of the body. Whereas anatomy is about structure (the where of the body’s components), physiology is about function (the how of the body’s components). Human physiology is the scientific 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 LO 2.1.1 life. For example, if we were examining human sweat, an anatomist would be able to draw the structures of a sweat gland, describe where these glands are found, and compare and contrast different types of sweat glands. A physiologist, on the other hand, would be able to explain how sweat was made, relate sweating to its impacts on the body, and predict what might change about the sweating process in LO 2.1.2 various conditions such as dehydration. Like anatomists, physiologists typically specialize in a particular branch of physiol- ogy. 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 Learning Connection example, what different parts of the brain do) to the molecular level (such as exploring Anatomy relies heavily on memorization how an electrochemical signal travels along neurons). and understanding skills. Learning physi- ology relies more heavily on skills such as understanding, analysis, and applica- tion. Very little physiology content can be Cultural Connection memorized. “We are the ones we have been waiting for.” This line is from Poem for South African Women by June Jordan. From climate change to racial disparities in healthcare, the world is starving for science advocacy. Scientists (and most of us humans!) have a lot of demands on their time, but it is paramount that scientific understanding and data literacy be used to inform public policy and funding. The time for change is now and the wheels of change are pushed by people like you! Student and work- force populations encourage greater creativity, innovation, productivity, and critical thinking in scientific research, healthcare, and public policy. For effective advocacy, consider what it is about healthcare or public policy that makes you passionate. Do you want to see greater gen- der inclusivity? Do you think our nation should spend more research dollars on a particular heathcare concern? Are you eager to see more attention given to women’s healthcare issues? You can bring your scientific knowledge and strong communication skills and get involved at the local, regional, national, and international levels. To learn more about how to get involved in science and healthcare advocacy, check out: the Annie E. Casey Foundation, the Human Anatomy and Physiology Society, the American Association for the Advancement of Science, and the American Association of Anatomists. 2.1a The Themes of Anatomy and Physiology There are a few central themes that will appear frequently throughout your study of anatomy and physiology. You can think of these themes as tools that you will pull out Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 18 Unit 1 Levels of Organization and use to build your understanding in different contexts or places within the body. These themes are: Structure and function Evolution and human variation Flow Homeostasis 2.2 Structure and Function Learning Objectives: By the end of this section, you will be able to: 2.2.1* Describe, compare, and contrast various 2.2.2* Relate the commonly found branching structure–function relationships from structure to function of an organ. molecular to organ level. * Objective is not a HAPS Learning Goal. LO 2.2.1 Form is closely related to function in all living things. The harmony between form and function can be seen in every aspect of human life from molecular structure to physical traits of the whole organism. As we will examine in Chapter 3, proteins have the most diverse structural variation of all molecules. Protein structure is intimately tied to protein function, and changes in protein shape alter the function of those proteins. A classic example of these changes can be seen when proteins are phosphorylated (a negatively charged phosphate group is added onto a protein). The addition of this negative charge typically changes the shape of the entire protein by drawing positively charged regions of the molecule toward the new addition. Phos- phorylation is the most common form of molecular regulation in animal cells. Using phosphorylation, we can turn on or off the activity of enzymes, signaling molecules, or transcription factors (Figure 2.2). We will see many examples of structure and function at every level of organization in this book. One gross anatomical example that is unique to humans is the shape of our pelvises. Humans are the only adult mammals that walk predominately on two feet (bipedalism). When early humans evolved to move primarily as bipeds instead of as our tree-dwelling primate ancestors, we evolved a restructured pelvis, one that could support the weight of our abdominal organs as well as accommodate the much larger gluteal (buttock) muscles that were required for stabilization of our torso and efficient forward motion. If we had not needed the function of the pelvis to accommodate Figure 2.2 Phosphorylation Induces Shape Changes in Proteins + Phosphate group Enzyme Enzyme with altered activity Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 19   Figure 2.3 Human versus Ape Pelvis Figure 2.4 The Branching Pattern of the Lungs As early humans evolved to become bipedal walkers, the shape of Examples of branching structure to maximize surface area can be their pelvises had to change to support their new function. seen throughout all living organisms. BSIP/Universal Images Group/Getty Images bipedalism, we would not have observed the structural change of the pelvis over time (Figure 2.3). A common theme throughout, not just anatomy and physiology but all living LO 2.2.2 things, is that branching structures are efficient for maximizing surface area. From tree branches to vasculature and respiratory conduction tubes, this format is plentiful in anatomy (Figure 2.4). Cultural Connection Checking Our Lenses What we know about human evolution is the product of arduous and careful investigative work by archeologists and anthropologists. Occasionally when we look at the past, we see things through a modern lens. Many scientists and science advocates are working to check where assumptions and biases may have worked their way into representations of the past. Lucy, a famous 3.2-million-year-old skeleton, belongs to the species Aus- tralopithecus afarensis. The discovery of this species was fundamental to our scientific understanding of how bipedalism evolved, A. afarensis is hypothesized to be a nonhomi- nid ape that was bipedal—a link, if you will, between tree-dwelling ancestors and bipedal humans. Lucy and her species have been recently reimagined after a careful look at how this species has been portrayed. In most artistic imaginings of Lucy, she is typically drawn with one or two small children and a male Australopithecus nearby. In many represen- tations of this family, the male is hunting or fishing while Lucy is tending to children. However, evolutionary data indicate that small, nuclear families are a very recent feature of human history. Lucy may or may not have had children or lived with male members of their species; we do not even know if Australopithecus were monogamous or polyga- mous, but the frequent representation of them with one male mate and children is decid- edly modern and misogynistic. Given the deep roots of racism and sexism in our society, it is important that we reexamine representations of the past to remove modern bias. Recently, an international team of scientists have sought to reimagine Lucy and other historic finds in ways that are free of bias and rooted in the evolutionary data. Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 20 Unit 1 Levels of Organization 2.3 Evolution and Human Variation Learning Objectives: By the end of this section, you will be able to: 2.3.1* Define the term and explain the concept of 2.3.2* Contrast the impact of selection on traits that evolution. affect reproduction and traits that do not; use this to explain examples of anatomical and physiological variation. * Objective is not a HAPS Learning Goal. LO 2.3.1 Evolution is a change in gene expression that occurs from generation to generation. Evolution specifically entails genetic changes and does not occur within one’s lifetime but across the lifetimes of generations of humans or other organisms. Genetic changes occur randomly and with relative frequency, but they become more common among the individuals of a population when they confer an advantage in a particular environ- ment. The key here to remember is that what is or is not advantageous has to do with the immediate environment. For example, let’s examine our human relationship with UV radiation in sunlight. UV radiation is required for the synthesis of vitamin D, a nutrient that is central to the structure of our bones, as we will learn more about it in Chapter 7. UV radiation is harmful, however, to the structure of a nutrient known as folate. Folate is essential for sperm production and embryonic development. As early humans evolved, they expressed lower and lower amounts of body hair. This likely had to do with these early humans spending less time in trees and more time under the hot sun. Without body hair, these early humans may have been cooler, but they also were at much higher risk of folate damage from UV radiation. Therefore, as successive generations of early humans had less and less body hair, the expression of the skin pigment melanin increased. Producing and expressing the skin pigment melanin conferred a tremen- dous advantage to humans who evolved over generations near the equator or at high altitudes, where UV radiation is the highest. Through genetic changes these popula- tions evolved to express and maintain melanin levels that protected their cells from the strong UV rays of equatorial sunlight, while allowing sufficient UV radiation for the manufacturing of vitamin D. However, as humans migrated to locations with less intense UV radiation, their skin cells developed the adaptation to digest some of the expressed melanin pigment, leading to lighter skin such that vitamin D manufacturing was still possible with lower amounts of UV radiation. We now can see the influence of environment on evolution and genetic change as we look about at the beautiful diver- sity of skin shades present in our modern human population. The story of melanin is explained in a bit more detail in Chapter 6. LO 2.3.2 In genetic changes that impact reproduction or the likelihood of living to reproductive age, we tend to see less anatomical or physiological variation among individuals. However, anatomical or physiological variation that does not influence reproduction does not tend to be selected for or against; therefore, a wider degree of variation exists. If we looked inside all of the bodies in a college classroom, for example, we would find many individuals with four pulmonary veins, but some individuals with two and some with three. Most bodies in the classroom would have five lumbar verte- brae, but some may have four, others six. A much wider array of anatomical variation is present in our human population than is represented in most anatomy textbooks. Physiological variation is much more diverse and widespread. Physiological variables will differ not just from one individual to another, but also between children and adults, women and men, and depending on age. This physiological variation is very important to understand and remember as it can lead to grave consequences in Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 21   the recognition and treatment of disease. For example, for many years medical students learned that one of the central symptoms of a heart attack is pain in the left shoulder. This was observed over years of studying heart attacks in biological men. As it turns out, this symptom is rarely seen in female heart attack patients; the most common symptom of heart attack in women is nausea. We will never know how many women suffered more significant clinical outcomes because of the delay in or complete failure to recog- nize their symptoms. Therefore, it is essential to include diverse populations of humans whenever health is being studied. In 2020, when the world raced to develop vaccines to prevent the disease caused by the novel coronavirus, SARS-CoV-2, vaccine developers realized they needed to study the vaccine’s efficacy and side effects in many populations of humans, and these clinical trials were among the most diverse ever established. Learning Check 1. Barbra is learning about the various structures in the area of the body called the pelvic girdle. They are learning about the pelvic joints, the organs within the pelvis such as the urinary bladder, and the muscles of this area. Which type of anatomical study is Barbra using? a. Regional anatomy c. Cytology b. Systemic anatomy d. Histology 2. True or False: The shape of a structure will determine the function, but the function will not determine the shape. a. True b. False 3. Which type of variable would you expect to have the broadest range between adults and infants? a. Anatomical variables b. Physiological variables 2.4 Flow Learning Objectives: By the end of this section, you will be able to: 2.4.1* Describe how a gradient determines flow 2.4.2* Predict how changes in a gradient will affect between two regions, and give examples flow rate. of gradients that exist in different levels of organization in the body. 2.4.3* Predict how differences in resistance will affect flow rate. * Objective is not a HAPS Learning Goal. In your study of anatomy and physiology you will examine the flow of materials in many LO 2.4.1 different contexts. Some of these include: the flow of ions across the membrane of muscle Student Study Tip cells, the flow of air through the lungs, and the flow of blood through the vessels of your body. While the substances and the scale of flow vary widely among these examples, the Molecules diffusing across a membrane principles of flow can be applied universally. Substances, whether they are air or sodium act like a crowd leaving a concert: a larger crowd will rush to exit (larger concen- ions, flow according to gradients. The three types of gradients that drive flow in physi- tration gradient). If smaller, people will ological contexts are concentration, electrical, and pressure gradients. Pressure gradients take their time. If the exit door is smaller drive the flow of fluids and gasses; the pressure generated by the pumping of the heart (membrane surface area), diffusion and drives the flow of blood. Concentration gradients drive the flow (here called diffusion) of exiting will be more difficult. If there is individual molecules (for example, sodium ions will flow from areas where they are more farther to go, as in a large venue, it will be concentrated to areas where they are less concentrated). Electrical gradients will influence harder to cross the exit/membrane. the flow of charged particles, including ions. In all examples of flow, there are also factors LO 2.4.2 Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 22 Unit 1 Levels of Organization Figure 2.5 F low Rate and Its Determining that oppose, or resist, flow. We can summarize the rate of flow as being determined by the Factors size of the gradient divided by the resistance (Figure 2.5). For example, in the flow of liq- uids and gasses, the diameter and length of the tubes provide resistance to flow. Different Flow is proportional to the size of the gradi- types of flow are illustrated in the “Anatomy of Flow” feature. In Chapter 4 we will look ent and inversely proportional to resistance. carefully at the flow of molecules across membranes and examine the factors of resistance Gradient Flow ~ Resistance that oppose these types of flow. In Chapters 20, 22, and 23 we will examine flow and resis- tance under various physiological and anatomical constraints. LO 2.4.3 Anatomy of... Anatomy of Flow A Molecules ˜ow down their concentration gradients. B Muscle contraction propels food to ˜ow through the digestive tract. C Contractions of the heart muscle walls push blood to ˜ow through blood vessels. D Contractions of the diaphragm and intercostals drive air˜ow in the lungs. Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 23   2.5 Homeostasis Learning Objectives: By the end of this section, you will be able to: 2.5.1 Define the following terms as they relate 2.5.4 List the steps in a feedback mechanism to homeostasis: setpoint, variable, receptor (loop) and explain the function of each step. (sensor), effector (target), and control (integrating) center. 2.5.5 Compare and contrast positive and negative feedback in terms of the relationship 2.5.2 Explain why negative feedback is the most between stimulus and response, and common mechanism used to maintain describe examples of each. homeostasis. 2.5.3 List the main physiological variables for which the body attempts to maintain homeostasis. Much of the study of physiology centers on the body’s tendency toward homeostasis. Homeostasis is the state of dynamic stability of the body’s internal conditions. While our bodies are able to withstand a variety of external conditions, many internal condi- tions must stay stable for the health of our cells. Parameters such as oxygen levels, pH, nutrient availability, and temperature must remain constant for our molecules and cells to be able to survive and perform their functions. Maintaining homeostasis requires that the body continuously monitor its internal LO 2.5.1 conditions. From body temperature to blood pressure to levels of certain nutrients, each physiological condition has a particular setpoint. A setpoint is the physiological value around which the normal range fluctuates. For example, the setpoint for normal human body temperature is approximately 37°C (98.6°F). Of course, humans are diverse and so setpoints are diverse too. Temperature setpoints, for example, appear to vary widely based on metabolic rate, body mass, age, and biological sex. Typically, a range of values around the setpoint is acceptable; we consider a person to be in hypothermia, or danger- ously cold, when their body temperature falls below 35°C (95°F) and a person is consid- ered to have a fever when their body temperature registers above 38°C (100.4°F). While 37°C is the average, the range is 35°C to 38°C. Hypothermia and fever are disease states, but what happens when the body warms or cools under healthy conditions? Let’s say you go for a run on a summer day. Your body temperature quickly rises above the healthy range. Temperature sensors in your skin detect these changes and provide information about the increase in temperature to a control center, which often is in the brain. The control center takes action to reverse the increase in temperature by communicating with effectors, in this case, sweat glands in the skin, to take action to cool the body. This basic model of homeostasis and homeostatic mechanisms is represented in Figure 2.6. It is important to note that not all physiological variables are homeostatically regulated. Take the following options—blood sugar levels, thyroid hormone level, heart rate, and pH; can you pick out which of the variables is not homeostatically regulated? You may not be ready as a physiologist to debate all of these variables, but the one in this list that is not homeostatically regulated is heart rate. Heart rate in a resting adult can be as low as 60 or even 50 beats per minute, and in an exercising adult it may be 195 beats per minute or even higher! This wide variation is because the heart can (within limits) beat as fast or slow as the body needs it to in order to maintain homeostatic levels of blood pressure and oxygenation for healthy cells. In this case, the heart and how frequently it pumps blood is the effector, not the regu- lated variable. The main physiological variables for which homeostatic ranges are maintained by the body are listed in Table 2.1. Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 24 Unit 1 Levels of Organization Figure 2.6 A Model of Homeostasis and Homeostatic Mechanisms The homeostatic model includes a setpoint for the regulated variable, a sensor, control center, and effector. Set point Control center Sensor Effector Sweating Regulated variable Temperature Many of our variables are regulated in a common pattern known as negative LO 2.5.2 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 fundamen- Student Study Tip tal to an understanding of human physiology. In a negative feedback pattern, the Negative feedback is explained by an air action of the effectors “turns off ” the action of the sensor. An example of nega- conditioner set to a specific temperature: tive feedback is illustrated in Figure 2.7. In this example, the levels of sugar in the once it has been running for a while, blood fall in an individual who is between meals. This decrease in circulating blood it turns itself off once the setpoint is sugar could compromise the function of the body’s cells, particularly the brain. The reachieved! decrease is sensed by the pancreas, which releases a hormone called glucagon to alert the body of this dangerous decrease in nutrients. Upon receiving the glucagon signal, the liver begins to break down glycogen, a storage carbohydrate, and releas- ing the resulting sugars into the blood. Blood sugar levels rise, and the sensors in the pancreas stop sending signals (Figure 2.7C). A parallel system works to control blood glucose levels from going too high. After a meal or glycogen breakdown, blood glucose levels rise. The pancreas releases a hormone known as insulin which LO 2.5.3 Table 2.1 Physiological Variables of Homeostatic Ranges Maintained by the Body Variable Examples Blood gas levels CO2, O2 Nutrient levels Blood glucose Electrolyte levels Na+, Ca2+, K+ pH H+ Blood pressure Body temperature Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 25   Figure 2.7 Negative Feedback Loop LO 2.5.4 In a negative feedback loop, a stimulus—a deviation from a setpoint—is resisted through a physiological process that returns the body to homeosta- sis. (A) A negative feedback loop has four basic parts. (B) Blood sugar levels are regulated by negative feedback. (C) If we graph blood sugar levels over time, we can see how homeostatic mechanisms keep the levels close to the setpoint. * * relieves relieves Deviation in Decrease in blood controlled variable sugar level _ _ (detected by) (detected by) Sensor Pancreas (sensor) (informs) (informs) Control center Secretes glucagon (negative (negative feedback feedback (sends instructions to) shuts off (sends instructions to) shuts off system system responsible responsible for response) for response) Effector(s) Liver (effector) (brings about) (brings about) Breaks down glycogen into Compensatory response glucose, releases into the bloodstream (results in) (results in) * * Controlled variable blood sugar returns to restored to normal healthy level A Components of a negative B Components of a negative feedback control system feedback control system lnsulin secretion Blood glucose concentration Glucagon secretion Eat Setpoint Time C Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 26 Unit 1 Levels of Organization Apply to Pathophysiology Type I Diabetes Eliott is nine years old. Lately Eliott has been complaining to their parents of feeling tired. Sometimes lately Eliott gets very thirsty and their parents notice that Eliott can drink an astonishing amount. Orange juice is a particular favorite. Eventually Eliott goes to the doctor and the following is noted on their bloodwork: Test Patient value High/low/within range Healthy range Blood glucose 202 H 70–100 1. The doctors suspect that the hormones that control blood glucose are not functioning properly. Which hormone is likely not working? A) Glucagon B) Insulin C) Neither of these 2. The hormone you identified in question 1 can be delivered by an injection under the skin, but delivering the proper dose is critically impor- tant. If too much of this hormone were delivered to Eliott, which of the following could occur? A) Blood glucose levels would become too high. B) Blood glucose levels would sink too low. C) The cells of the body would not be able to access enough glucose to live. 3. What organ is not functioning well? A) Heart C) Liver B) Stomach D) Pancreas 4. Which type of variable is dysregulated in this scenario? A) Anatomical B) Physiological helps cells all over the body to take glucose out of the blood, bringing the blood glucose levels back within the homeostatic range. In either direction, the system effectively turns itself off (Figures 2.7A and 2.7B). A positive feedback system, in contrast, intensifies a change in the body’s physi- ological condition rather than reversing it. A deviation from the normal range results LO 2.5.5 in more change, and the system moves farther away from the normal range. A positive feedback cycle within the body will continue and intensify until there is an interrup- tion. Childbirth is one example of a positive feedback loop that is healthy, but does not work to maintain homeostasis. Enormous changes in the mother’s body are required to expel the fetus at the end of pregnancy. The events of childbirth, once begun, progress rapidly toward a conclu- sion at which the cycle finally comes to a stop once the fetus and placenta are outside the mother’s body. The extreme muscular work of labor and delivery are the result of a positive feedback system (Figure 2.8). The first contractions of labor (the stimulus) push the fetus toward the cervix (the lowest part of the uterus). The cervix contains 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 to release the hormone oxytocin into the bloodstream. Oxy- tocin causes stronger contractions of the smooth muscles in the uterus (the effectors), pushing the fetus further down the birth canal. This causes even greater stretching of the cervix. The cycle of stretching, oxytocin release, and increasingly more forceful contrac- tions stops only when the baby is born. At this point, the stretching of the cervix halts, and the cycle comes to a close. Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 27   Figure 2.8 Positive Feedback Loop Childbirth is driven by a positive feedback loop. A positive feedback loop continues on its own until the stimulus is removed or halted. Positive feedback loops do not result in a return to homeostasis. Contractions push the fetus toward the cervix. Oxytocin causes the Fetal head pushes smooth muscle within against the cervix, the uterus to contract. thinning it. Oxytocin is secreted Nerves within the from the pituitary gland in cervix send signals response to stimulation to the brain. from the brain. 2.6 Structural Organization of the Human Body Learning Objectives: By the end of this section, you will be able to: 2.6.1 Describe, in order from simplest to most 2.6.3 List the organ systems of the human body and complex, the major levels of organization in their major components. the human organism. 2.6.4 Describe the major functions of each organ 2.6.2 Give an example of each level of system. organization. In our study of the human body it is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. We will begin in Chapter 3 with the smallest pieces—subatomic particles, atoms, molecules—and build up to organelles and cells in Chapter 4, tissues in Chapter 5, and the organs in their organ systems in the subsequent chapters. As we go, we will build our understanding of the interconnectedness of the structures within a single human body and the organism with its environment (Figure 2.9). 2.6a The Levels of Organization 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 Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 28 Unit 1 Levels of Organization LO 2.6.1 Figure 2.9 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 whole human body. 2 Cellular level 3 Tissue level 1 Chemical level Cardiac muscle cell DNA Atoms Cardiac muscle tissue 4 Organ Heart level Cardiovascular system 6 Organism level 5 System level 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. We explore the relationships among molecules in much more detail in Chapter 3. A cell is the smallest independently functioning unit of a living organism. Even bacteria, which are extremely small, unicellular organisms, have a cellular structure. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells. LO 2.6.2 A human cell functions as its own tiny world encased in a protective membrane that encloses 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 cells that work together to perform a specific function. An organ is a structure of the body that is composed of two or more tissue types; each organ performs one or more specific 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 (Figures 2.10A and 2.10B). Assigning organs to organ systems can be imprecise since Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 29   Figure 2.10A Organ Systems of the Human Body LO 2.6.3 Organs that work together toward one or a set of functions can be grouped into organ systems. Integumentary system Skeletal system Muscular system Creates a barrier Supports and Creates the that protects the protects the body movement body from of the body pathogens and Contributes to ˜uid loss body temperature Sensory reception homeostasis Nervous system Endocrine system Cardiovascular system Acts as the sensor Secretes the Delivers oxygen, for homeostasis hormones that nutrients, hormones, Connects the regulate many and waste products brain to every bodily processes throughout the part of the body body Contributes to temperature regulation Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 30 Unit 1 Levels of Organization Figure 2.10B Organ Systems of the Human Body (continued) LO 2.6.4 Organs that work together toward one or a set of functions can be grouped into organ systems. Lymphatic system Respiratory system Digestive system Regulates ˜uid Exchanges air with Breaks down food balance in the body the atmosphere and absorbs Houses some of Provides surface nutrients into the the immune cells area for the body that defend the diffusion of oxygen body from and carbon pathogens dioxide with the blood Urinary system Reproductive systems Contributes to blood Produce and exchange pressure and pH gametes homeostasis House the fetus Removes waste until birth products from Lactation the body Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Introduction to the Human Body Chapter 2 31   organs that “belong” to one system can also have functions integral to another system. In fact, most organs contribute to more than one system. 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 organism. Learning Check 1. What is the goal of a positive feedback mechanism? a. To restore homeostasis b. To return body parameters to the setpoint c. To intensify body parameters until there is an interruption 2. Which of the following detects change in a body’s internal condition? a. Effectors c. Variable b. Sensor d. Setpoint 3. Which of the following organ systems is responsible for removing wastes from blood and excreting them? a. Reproductive system c. Urinary system b. Circulatory system d. Digestive system 2.7 Anatomical Terminology Learning Objectives: By the end of this section, you will be able to: 2.7.1 Describe the human body in anatomical 2.7.7* Classify images based on the section or plane position. they were taken in. 2.7.2 Describe how to use the terms right and left 2.7.8 Identify and describe the location of the in anatomical reference. body cavities and the major organs found in each cavity. 2.7.3 List and define the major directional terms used in anatomy. 2.7.9 Identify and describe the location of the four abdominopelvic quadrants and the 2.7.4 List and describe the location of the major nine abdominopelvic regions, and the major anatomical regions of the body. structures found in each. 2.7.5 Describe the location of body structures, using 2.7.10* Predict, based on location (quadrant, region) appropriate directional terminology. of symptoms or pain, what organ may be the 2.7.6 Identify and define the anatomic planes in issue. which a body might be viewed. 2.7.11* Describe the structure, function, and location of serous membranes. * Objective is not a HAPS Learning Goal. Anatomists and healthcare 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 anatomi- cal terminology, we eliminate ambiguity. Anatomical terms derive from ancient Greek and Latin words. Building an understanding of anatomically relevant Greek Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 32 Unit 1 Levels of Organization and Latin roots can facilitate your path through learning the language of anatomy and physiology. For example, in the disorder hypotension, the prefix “hypo-” means “low” or “under”; you will see this root attached to many terms. The hypodermis is the layer of skin under the dermis, hypoglycemia is low blood sugar (gly- is a root for sugar), and hyposecretion refers to an endocrine gland that is secreting less than its typical levels of hormone. 2.7a Anatomical Position Student Study Tip For precision, anatomists standardize the way in which they view the body. Imagine Anatomical position is important so no if you were looking at a body in the position you see in Figure 2.11. If you referred to a two bones are crossed and you can use structure just above the left hand, you would likely be talking about the left wrist. But anatomical directional terms without what if you were referring to a person with their arms crossed? “Above the left” might confusion! technically be the right arm. To eliminate confusion, we always discuss a body in a LO 2.7.1 standard position—anatomical position—when describing the relative position of one structure to another. Anatomical position, as illustrated in Figure 2.11, is that of the body standing upright, with the feet shoulder width apart and parallel, toes forward. The upper limbs are held out to each side, and the palms of the hands face forward with thumbs out to the sides. The terms right and left refer to the patient or cadaver’s LO 2.7.2 right and left, never to the observer’s right and left. Figure 2.11 illustrates the anatomi- cal position with regional terms. Body position can be described as 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 specific physical examinations or surgical procedures. 2.7b Regional Terms The human body’s numerous regions have specific terms to help increase precision (see Figure 2.11). 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 figure. Anterior (ventral) 2.7c Directional Terms Certain directional anatomical terms appear throughout this and any other anatomy Posterior (dorsal) textbook (Figure 2.12). 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 “superficial Superior (cranial) 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, and remember that we refer to the relative locations of the structures as if the body is in Inferior (caudal) anatomical position. Anterior Describes the front (belly) of the body. The toes are anterior to the foot. Posterior Describes the back of the body. The spine is posterior to the stomach. LO 2.7.3 Superior Describes a position above or higher than another part of the body proper. The neck is superior to the shoulders. Inferior Describes a position below or lower than another part of the body. The pelvis Student Study Tip is inferior to the abdomen. Latitude has the Latin root “lat-,” which Lateral Describes a structure toward the side of the body. The thumb (pollex) is lateral means side. Lateral is farther out to the to the digits. sides compared to medial, which has the Medial Describes the middle or direction toward the middle of the body. The hallux is root “medi-,” which means middle. the most medial toe. Copyright 2023 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.