The Human Body: An Orientation PDF

The Human Body: An Orientation 1 An Overview of Anatomy 38 Subdisciplines of Anatomy 38 Th...

The Human Body: An Orientation 1 An Overview of Anatomy 38 Subdisciplines of Anatomy 38 The Hierarchy of Structural Organization 38 Scale: Length, Volume, and Weight 42 Anatomical Terminology 42 Gross Anatomy: An Introduction 42 Regional and Directional Terms 42 Body Planes and Sections 43 The Human Body Plan 46 Body Cavities and Membranes 47 Abdominal Quadrants 49 Anatomical Variability 49 Microscopic Anatomy: An Introduction 49 Light and Electron Microscopy 49 Scanning Electron Microscopy 51 Artifacts 51 Clinical Anatomy: An Introduction to Medical Imaging Techniques 51 X-Ray Imaging 51 Advanced X-Ray Techniques 52 Positron Emission Tomography 53 Sonography 54 Magnetic Resonance Imaging 54 A s you read this book, you will learn about a subject that has for- ever fascinated people—their own bodies. The study of human anatomy is not only an interesting and highly personal experi- ence, but also a timely one. Almost every week, the news media report advances in medical science. Understanding how your body is built and how it works allows you to appreciate newly developed techniques for detecting and treating disease and to apply guidelines for staying healthy. If you are preparing for a career in the health sciences, your knowledge of human anatomy is the foundation of your clinical practice. Whole body scan of a woman (colored MRI). ▲ M01_MARI6798_08_GE_C01.indd 37 25/06/16 3:39 pm  38 Chapter 1 The Human Body: An Orientation AN OVERVIEW OF ANATOMY the muscles of the entire body. The systemic approach to anatomy is best for relating structure to function. Therefore, learning outcomes it is the approach taken in most college anatomy courses De!ne anatomy and physiology, and describe the and in this book. Medical schools, however, favor regional subdisciplines of anatomy. anatomy because many injuries and diseases involve speci!c Identify the levels of structural organization in the human body regions (sprained ankle, sore throat, heart disease); fur- body, and explain the interrelationships between each thermore, surgeons need extensive and detailed knowledge of level. each body region. List the organ systems of the body, and brie"y state their Another subdivision of gross anatomy is surface anatomy, functions. the study of shapes and markings (called landmarks) on the Use metric units to quantify the dimensions of cells, surface of the body that reveal the underlying organs. This tissues, and organs. knowledge is used to identify the muscles that bulge beneath the skin in weight lifters, and clinicians use it to locate blood Use the meaning of word roots to aid in understanding anatomical terminology. vessels for placing catheters, feeling pulses, and drawing blood. Clinically useful surface landmarks are described Anatomy is the study of the structure of the human body. It is throughout the text in reference to the organ system that also called morphology (mor″fol′o-je), the science of form. they relate to. (Chapter 11 concludes with a section on sur- An old and proud science, anatomy has been a !eld of serious face anatomy, which integrates the anatomical relationships intellectual investigation for at least 2300 years. It was the between skeletal and muscular structures.) most prestigious biological discipline of the 1800s and is still dynamic. Microscopic Anatomy Anatomy is closely related to physiology, the study of Microscopic anatomy, or histology (his-tol′o-je; “tissue body function. Although you may be studying anatomy and study”), is the study of structures that are so small they can be physiology in separate courses, the two are truly insepa- seen only with a microscope. These structures include cells rable, because structure supports function. For example, and cell parts; groups of cells, called tissues; and the micro- the lens of the eye is transparent and curved; it could not scopic details of the organs of the body (stomach, spleen, perform its function of focusing light if it were opaque and so on). A knowledge of microscopic anatomy is impor- and uncurved. Similarly, the thick, long bones in our legs tant because physiological and disease processes occur at the could not support our weight if they were soft and thin. This cellular level. textbook stresses the closeness of the relationship between structure and function. In almost all cases, a description of Other Branches of Anatomy the anatomy of a body part is accompanied by an explana- Two branches of anatomy explore how body structures form, tion of its function, emphasizing the structural characteris- grow, and mature. Developmental anatomy traces the struc- tics that contribute to that function. This approach is called tural changes that occur in the body throughout the life span functional anatomy. and the effects of aging. Embryology is the study of how body structures form and develop before birth. A knowledge Subdisciplines of Anatomy of embryology helps you understand the complex design Anatomy is a broad !eld of science consisting of several sub- of the adult human body and helps to explain birth defects, disciplines, or branches. Each branch of anatomy studies the which are anatomical abnormalities that occur during embry- body’s structures in a specialized way. onic development and are evident after birth. Some specialized branches of anatomy are used pri- Gross Anatomy marily for medical diagnosis and scienti!c research. Gross anatomy (gross = large) is the study of body struc- Pathological (pah-tho-loj′ ı̆-kal) anatomy deals with the tures that can be examined by the naked eye—the bones, structural changes in cells, tissues, and organs caused by lungs, and muscles, for example. An important technique disease. (Pathology is the study of disease.) Radiographic for studying gross anatomy is dissection (d ı̆-sek′shun; (ra″de-o′graf′ic) anatomy is the study of internal body “cut apart”), in which connective tissue is removed from structures by means of X-ray studies and other imag- between the body organs so that the organs can be seen ing techniques (see pp. 51–55). Functional morphology more clearly. Then the organs are cut open for viewing. explores the functional properties of body structures and The term anatomy is derived from Greek words meaning assesses the ef!ciency of their design. “to cut apart.” Studies of gross anatomy can be approached in several The Hierarchy of Structural different ways. In regional anatomy, all structures in a sin- Organization gle body region, such as the abdomen or head, are examined The human body has many levels of structural complexity as a group. In systemic (sis-tem′ik) anatomy, by contrast, as illustrated in Focus on Levels of Structural Organization all the organs with related functions are studied together. For (Figure 1.1). At the chemical level, atoms are tiny build- example, when studying the muscular system, you consider ing blocks of matter such as carbon, hydrogen, oxygen, and M01_MARI6798_08_GE_C01.indd 38 25/06/16 3:39 pm  FOCUS Levels of Structural Organization Figure 1.1 Recognizing connections between structural levels leads to better understanding of organismal function. Chemical level O H O Atoms combine to form molecules. Molecules combine to form the macromolecules (carbohydrates, lipids, C proteins, and nucleic acids). Atoms Molecule Hemoglobin, a protein (not to scale) Cellular level Cells and their surroundings are made up of molecules. For example, a phospholipid molecule is a structural component of the plasma membrane. Phospholipid Phospholipid Forms most of the plasma molecule membrane membrane of a cell Tissue level Epithelial tissue Tissues consist of similar types of cells and associated extracellular material. In this example, epithelial tissue forms the inner lining of blood vessels. Underlying extracellular layer Organ level Connective tissue Smooth An organ is a discrete structure made up of multiple muscle tissue tissue types. Examples include blood vessels, the Epithelial tissue liver, brain, and femur. Blood vessel (organ) Organ system level Blood vessels transport blood, which carries O2, An organ system is a unified group of organs and CO2, nutrients and tissues that perform a specific function. The wastes. example shown here is the cardiovascular system, showing blood vessels, blood, and the heart. The heart pumps blood. Organismal level The whole person is the most complex level of organization, the organismal level, resulting from the simpler levels working interdependently. 39 M01_MARI6798_08_GE_C01.indd 39 25/06/16 3:39 pm  40 Chapter 1 The Human Body: An Orientation Hair Skeletal muscles Skin Nails Bones Joint (a) Integumentary System (b) Skeletal System (c) Muscular System Forms the external body covering and Protects and supports body organs and Allows manipulation of the environment, protects deeper tissues from injury. provides a framework the muscles use locomotion, and facial expression. Synthesizes vitamin D and houses to cause movement. Blood cells are Maintains posture and produces heat. cutaneous receptors (pain, pressure, etc.) formed within bones. Bones store minerals. and sweat and oil glands. Pineal gland Brain Pituitary Thyroid gland gland Heart Thymus Adrenal gland Pancreas Testis Nerves Ovary Blood Spinal vessels cord (d) Nervous System (e) Endocrine System (f) Cardiovascular System As the fast-acting control system of the Glands secrete hormones that regulate Blood vessels transport blood, which body, it responds to internal and external processes such as growth, reproduction, carries oxygen, carbon dioxide, changes by activating appropriate and nutrient use (metabolism) by body nutrients, wastes, etc. The heart pumps muscles and glands. cells. blood. Figure 1.2 The body’s organ systems and their major functions. nitrogen. Atoms combine to form small molecules, such as functions of the cells as an energy source (carbohydrates), carbon dioxide (CO2) and water (H2O), and larger macro- as signaling molecules (proteins and lipid hormones), and as molecules (macro = big). Four classes of macromolecules catalysts (enzymes). Cells are the smallest living things in are found in the body: carbohydrates (sugars), lipids (fats), the body, and you have trillions of them. proteins, and nucleic acids (DNA, RNA). These macromol- The next level is the tissue level. A tissue is a group of cells ecules are the building blocks of the structures at the cellular that work together to perform a common function. Only four tis- level: the cells and their functional subunits, called cellular sue types make up all organs of the human body: epithelial tissue organelles. Macromolecules also contribute to the metabolic (epithelium), connective tissue, muscle tissue, and nervous M01_MARI6798_08_GE_C01.indd 40 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 41 Nasal Oral cavity Red bone cavity marrow Thymus Pharynx Esophagus Larynx Bronchus Lymphatic vessels Trachea Thoracic duct Lung Liver Stomach Small Spleen intestine Large intestine Lymph nodes Rectum Anus (g) Lymphatic System/Immunity (h) Respiratory System (i) Digestive System Picks up fluid leaked from blood vessels Keeps blood constantly supplied with Breaks down food into absorbable units and returns it to blood. Disposes oxygen and removes carbon dioxide. that enter the blood for distribution to of debris in the lymphatic stream. The gaseous exchanges occur through body cells. Indigestible foodstuffs are Houses white blood cells (lymphocytes) the walls of the air sacs of the lungs. eliminated as feces. involved in immunity. The immune response mounts the attack against foreign substances within the body. Mammary glands (in breasts) Kidney Ureter Prostate gland Ovary Penis Urinary bladder Testis Ductus deferens Uterine Urethra Scrotum Uterus tube Vagina (j) Urinary System (k) Male Reproductive System (l) Female Reproductive System Eliminates nitrogenous wastes from the Overall function is production of offspring. Testes produce sperm and male sex hormone, body. Regulates water, electrolyte, and and male ducts and glands aid in delivery of sperm to the female reproductive tract. Ovaries acid-base balance of the blood. produce eggs and female sex hormones. The remaining female structures serve as sites for fertilization and development of the fetus. Mammary glands of female breasts produce milk to nourish the newborn. Figure 1.2 The body’s organ systems and their major functions, continued. tissue. Each tissue plays a characteristic role in the body. than one tissue. Most organs contain all four tissues. The Brie"y, epithelium (ep″ ı̆-the′le-um) covers the body surface liver, brain, femur, and heart are good examples. You can and lines its cavities; connective tissue supports the body and think of each organ in the body as a functional center respon- protects its organs; muscle tissue provides movement; and sible for an activity that no other organ can perform. nervous tissue provides fast internal communication by trans- Organs that work closely together to accomplish a common mitting electrical impulses. purpose make up an organ system, the next level (Figure 1.2). Extremely complex physiological processes occur at the For example, organs of the cardiovascular system—the heart organ level. An organ is a discrete structure made up of more M01_MARI6798_08_GE_C01.indd 41 25/06/16 3:39 pm  42 Chapter 1 The Human Body: An Orientation and blood vessels—transport blood to all body tissues. Organs check your understanding of the digestive system—the mouth, esophagus, stomach, intes- 1. What is the difference between histology and tine, and so forth—break down the food we eat so that we can radiography? absorb the nutrients into the blood. The body’s organ systems 2. Use the word root de!nitions located in the end are the integumentary (skin), skeletal, muscular, nervous, endo- pages of this text to de!ne each of the terms listed: crine, cardiovascular, lymphatic, immune, respiratory, diges- pathology, hepatitis, brachial, leukocyte, pneumonia. tive, urinary, and reproductive systems.* The highest level of organization is the organismal level; 3. De!ne a tissue. List the four types of tissues in the for example, the human organism is a whole living person. The body, and brie"y state the function of each. organismal level is the result of all of the simpler levels work- 4. Name the organ system described in each of the ing in unison to sustain life. following: (a) eliminates wastes and regulates water and ion balance; (b) fast-acting control system that Scale: Length, Volume, and Weight integrates body activities; (c) supplies blood with To describe the dimensions of cells, tissues, and organs, anat- oxygen and removes carbon dioxide. omists need a precise system of measurement. The metric (For answers, see Appendix B.) system provides such precision (Appendix A). Familiarity with this system lets you understand the sizes, volumes, and weights of body structures. GROSS ANATOMY: An important unit of length is the meter (m), which is a little longer than a yardstick. If you are 6 feet tall, your height AN INTRODUCTION is 1.83 meters. Most adults are between 1.5 and 2 meters tall. A learning outcomes centimeter (cm) is a hundredth of a meter (cent = hundred). De!ne the anatomical position. You can visualize this length by remembering that a nickel is about 2 cm in diameter. Many of our organs are several cen- Use anatomical terminology to describe body directions, regions, and planes. timeters in height, length, and width. A micrometer (!m) is a millionth of a meter (micro = millionth). Cells, organelles Describe the basic structures that humans share with (structures found inside cells), and tissues are measured in other vertebrates. micrometers. Human cells average about 10 #m in diameter, Locate the major body cavities and their subdivisions. although they range from 5 #m to 100 #m. The human cell with Name the four quadrants of the abdomen, and the largest diameter, the egg cell (ovum), is about the size of the identify the visceral organs located within each tiniest dot you could make on this page with a pencil. quadrant. The metric system also measures volume and weight (mass). A liter (l) is a volume slightly larger than a quart; soft drinks are packaged in 1-liter and 2-liter bottles. A Regional and Directional Terms milliliter (ml) is one-thousandth of a liter (milli = thousandth). To accurately describe the various body parts and their loca- A kilogram (kg) is a mass equal to about 2.2 pounds, and a tions, you need to use a common visual reference point. This gram (g) is a thousandth of a kilogram (kilo = thousand). reference point is the anatomical position (Figure 1.3a). In this position, a person stands erect with feet "at on the Anatomical Terminology ground, toes pointing forward, and eyes facing forward. The palms face anteriorly with the thumbs pointed away from Most anatomical terms are based on ancient Greek or Latin the body. It is essential to learn the anatomical position because words. For example, the arm is the brachium (bra′ke-um; Greek most of the directional terminology used in anatomy refers to for “arm”), and the thigh bone is the femur (fe′mer; Latin for the body in this position. Additionally, the terms right and left “thigh”). This terminology, which came into use when Latin was always refer to those sides belonging to the person or cadaver the of!cial language of science, provides a standard nomencla- being viewed—not to the right and left sides of the viewer. ture that scientists can use worldwide, no matter what language Regional terms are the names of speci!c body areas. they speak. This text will help you learn anatomical terminol- The fundamental divisions of the body are the axial and ogy by explaining the origins of selected terms as you encoun- appendicular (ap″en-dik′u-lar) regions. The axial region, ter them. Dividing an unfamiliar term into its word roots will so named because it makes up the main axis of the body, help you understand its meaning. For example, the word hepati- consists of the head, neck, and trunk. The trunk, in turn, is tis is made up of hepata, “liver,” and itis, “in"ammation”; thus, divided into the thorax (chest), abdomen, and pelvis; the hepatitis is in"ammation of the liver. For further help, see the trunk also includes the region around the anus and exter- Glossary in the back of the book, and the list of word roots inside nal genitals, called the perineum (per″ ı̆-ne′um; “around the the back cover of the book.** anus”). The appendicular region of the body consists of *The cardiovascular and lymphatic systems are collectively known as the circu- latory system because of their interrelated roles in circulating "uids (blood and **For a guide to pronunciation, see the Glossary. lymph) through the body. M01_MARI6798_08_GE_C01.indd 42 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 43 Axial region Appendicular region Cephalic (head) Cephalic Frontal Otic Orbital Occipital (back Nasal of head) Oral Upper limb Mental Acromial Cervical Cervical (neck) Brachial (arm) Thoracic Antecubital Sternal Olecranal Back (dorsal) Axillary Antebrachial Scapular (forearm) Mammary Carpal (wrist) Vertebral Abdominal Umbilical Lumbar Manus (hand) Pelvic Pollex Sacral Inguinal Metacarpal (groin) Palmar Gluteal Digital Perineal (between Lower limb anus and external Coxal (hip) genitalia) Pubic (genital) Femoral (thigh) Patellar Popliteal Crural (leg) Sural (calf) Fibular or peroneal Pedal (foot) Thorax Tarsal (ankle) Abdomen Calcaneal Back (Dorsum) Metatarsal Digital Plantar Hallux (a) Anterior/Ventral (b) Posterior/Dorsal Figure 1.3 Anatomical position and regional terms. Practice art labeling the limbs, which are also called appendages or extremities. Body Planes and Sections The fundamental divisions of the body are subdivided into In the study of anatomy, the body is often sectioned (cut) smaller regions (as shown in Figure 1.3). along a "at surface called a plane. The most frequently used Standard directional terms are used by medical personnel body planes are sagittal, frontal, and transverse planes, which and anatomists to explain precisely where one body structure lie at right angles to one another (Figure 1.4). A section bears lies in relation to another. For example, you could describe the the name of the plane along which it is cut. Thus, a cut along relationship between the eyebrows and the nose informally by a sagittal plane produces a sagittal section. stating, “The eyebrows are at each side of the face to the right A sagittal plane (sag′ ı̆-tal; “arrow”) extends vertically and left of the nose and higher than the nose.” In anatomical and divides the body into left and right parts (Figure 1.4a). terminology, this is condensed to, “The eyebrows are lateral The speci!c sagittal plane that lies exactly in the midline is and superior to the nose.” Clearly, the anatomical terminology the median plane, or midsagittal plane. All other sagittal is less wordy and confusing. Most often used are the paired planes, offset from the midline, are parasagittal (para = terms superior/inferior, anterior (ventral)/posterior (dorsal), near). A frontal (coronal) plane also extends vertically and medial/lateral, and super"cial/deep (Table 1.1). divides the body into anterior and posterior parts (Figure 1.4b). A transverse (horizontal) plane runs horizontally M01_MARI6798_08_GE_C01.indd 43 25/06/16 3:39 pm  44 Chapter 1 The Human Body: An Orientation Table 1.1 Orientation and Directional Terms Term De!nition/Example Superior Superior Toward the head end or upper part of a (cranial) structure or the body; above The head is superior to the abdomen. Inferior Away from the head end or toward the (caudal) lower part of a structure or the body; Lung below The intestines are inferior to the liver. Heart Medial Toward or at the midline of the body; Liver on the inner side of The heart is medial to the lungs. Intestines Lateral Away from the midline of the body; on the outer side of The thumb is lateral to the pinky. Proximal Closer to the origin of the body part or the point of attachment of a limb to the body trunk The elbow is proximal to the wrist.# Distal Farther from the origin of a body part or the point of attachment of a limb to the Knee body trunk The knee is distal to the thigh. Ipsilateral On the same side The right hand and right foot are ipsilateral. Contralateral On opposite sides Right side The right hand and left foot are contralateral. Anterior Toward or at the front of the body; (ventral)* in front of The sternum is anterior to the heart. Whole body MRI, frontal section, anterior view Anterior Posterior Toward or at the back of the body; Sternum (dorsal)* behind The vertebra is posterior to the heart. Skin Muscle Super!cial Toward or at the body surface (external) The skin is super!cial to the skeletal muscles. Heart Deep Away from the body surface; more Lung (internal) internal Vertebra The lungs are deep to the skin. Posterior CT scan, transverse section through thorax *Whereas the terms ventral and anterior are synonymous in humans, this is not the case in four-legged animals. Ventral speci!cally refers to the “belly” of a vertebrate animal and thus is the inferior surface of four-legged animals. Likewise, although the dorsal and posterior surfaces are the same in humans, the term dorsal speci!cally refers to an animal’s back. Thus, the dorsal surface of four-legged animals is their superior surface. M01_MARI6798_08_GE_C01.indd 44 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 45 (a) Median (midsagittal) plane (b) Frontal (coronal) plane (c) Transverse plane Vertebral Right Left column lung Heart lung Liver Aorta Pancreas Spleen Rectum Intestines Liver Stomach Spleen Subcutaneous Spinal fat layer cord Figure 1.4 Planes of the body with corresponding magnetic resonance imaging (MRI) scans. from right to left, dividing the body into superior and inferior The ability to interpret sections through the body, espe- parts (Figure 1.4c). A transverse section is also called a cross cially transverse sections, is increasingly important in the section. clinical sciences. Many medical imaging devices (described Cuts made along any plane that lies diagonally between on pp. 52–55) produce sectional images rather than three- the horizontal and the vertical are called oblique sections. dimensional images. It can be dif!cult, however, to deci- Not frontal, transverse, or sagittal, such oblique sections are pher an object’s overall shape from a sectional view alone. dif!cult to interpret because the orientation of the view is not A cross section of a banana, for example, looks like a circle obvious. For this reason, oblique sections are seldom used. and gives no indication of the whole banana’s crescent shape. M01_MARI6798_08_GE_C01.indd 45 25/06/16 3:39 pm  46 Chapter 1 The Human Body: An Orientation Notochord Muscle segments Brain Spinal (myotomes) cord Brain Pharynx Muscle segments (muscles Pharyngeal between pouches Heart Digestive tube ribs) (a) Generalized vertebrate Spinal Lung cord bud Pharyngeal pouches Heart Spinal Vertebrae cord Notochord Disc between vertebrae Muscle segments Digestive (myotomes) tube Brain Heart Digestive tube (c) Adult human (b) Human embryo; 5 weeks postconception Inner tube Dorsal hollow nerve tube Figure 1.5 Basic human body plan, indicated by structures Segmented outer tube shared among all vertebrates. The bodies are shown as semitransparent to reveal the internal organs. Notochord Sometimes, you must mentally assemble a whole series of 2. Bilateral symmetry. The left half of the body is essen- sections to understand the true shape of an object. With prac- tially a mirror image of the right half. Most body struc- tice, you will gradually learn to relate two-dimensional sec- tures, such as the right and left hands, eyes, and ovaries, tions to three-dimensional shapes. occur in pairs. Structures in the median plane are unpaired, but they tend to have identical right and left The Human Body Plan sides (the nose is an example). Humans belong to the group of animals called vertebrates. This 3. Dorsal hollow nerve cord. All vertebrate embryos have group also includes cats, rats, birds, lizards, frogs, and !sh. An a hollow nerve cord running along their back in the understanding of the basic vertebrate body plan will aid your median plane. This cord develops into the brain and spi- understanding of the complexities of human anatomical structure. nal cord. All vertebrates share the following basic features (Figure 1.5): 4. Notochord and vertebrae. The notochord (no′to-kord; 1. Tube-within-a-tube body plan. The inner tube extends “back string”) is a stiffening rod in the back just deep from the mouth to the anus and includes the respiratory to the spinal cord. In humans, a complete notochord and digestive organs (yellow structures in Figure 1.5). forms in the embryo, although most of it is quickly The outer tube consists of the axial skeleton and associ- replaced by the vertebrae (ver′tĕ-bre), the bony pieces ated axial muscles that make up the outer body wall, and of the vertebral column, or backbone. Still, some of nervous structures. the notochord persists throughout life as the cores of M01_MARI6798_08_GE_C01.indd 46 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 47 Cranial Cranial cavity cavity (contains brain) Vertebral cavity Superior Dorsal body mediastinum Thoracic cavity cavity Pleural (contains cavity heart and lungs) Pericardial cavity within the mediastinum Vertebral cavity (contains spinal Diaphragm Ventral body cord) cavity (thoracic and Abdominal cavity abdominopelvic (contains digestive Abdomino- cavities) viscera) pelvic cavity Pelvic cavity (contains urinary Dorsal body cavity bladder, reproductive Ventral body cavity organs, and rectum) (a) Lateral view (b) Anterior view Figure 1.6 Dorsal and ventral body cavities and their subdivisions. Practice art labeling the discs between the vertebrae (see the description Dorsal Body Cavity of nucleus pulposus, p. 207). The dorsal body cavity is subdivided into a cranial cavity, 5. Segmentation. The “outer tube” of the body shows evi- which lies in the skull and encases the brain, and a vertebral dence of segmentation. Segments are repeating units of cavity, which runs through the vertebral column to enclose similar structure that run from the head along the full the spinal cord. The hard, bony walls of this cavity protect the length of the trunk. In humans, the ribs and the mus- contained organs. cles between the ribs are evidence of segmentation, as are the many nerves branching off the spinal cord. The Ventral Body Cavity bony vertebral column, with its repeating vertebrae, is The more anterior and larger of the closed body cavities is also segmented. the ventral body cavity (Figure 1.6). The organs it contains, 6. Pharyngeal pouches. Humans have a pharynx (far′ingks), such as the lungs, heart, intestines, and kidneys, are called which is the throat region of the digestive and respiratory visceral organs or viscera (vis′er-ah). The ventral body cav- tube. In the embryonic stage, the human pharynx has a set ity has two main divisions: (1) a superior thoracic cavity, of outpocketings called pharyngeal (far-rin′je-al) pouches surrounded by the ribs and the muscles of the chest wall; and that correspond to the clefts between the gills of !sh. Such (2) an inferior abdominopelvic (ab-dom″ ı̆-no-pel′vic) cavity pouches give rise to some structures in the head and neck. surrounded by the abdominal walls and pelvic girdle. The An example is the middle ear cavity, which runs from the thoracic and abdominal cavities are separated from each other eardrum to the pharynx. by the diaphragm, a dome-shaped muscle used in breathing. The thoracic cavity has three parts: (a) two lateral parts, each containing a lung surrounded by a pleural cavity (ploo′- Body Cavities and Membranes ral; “the side, a rib”), and (b) a central band of organs called the Within the body are two large cavities called the dorsal and mediastinum (me″de-ah-sti′num; “in the middle”). The medi- ventral cavities (Figure 1.6). These are closed to the outside, astinum contains the heart surrounded by a pericardial cavity and each contains internal organs. Think of them as !lled (per″ ı̆-kar′de-al; “around the heart”). It also houses other major cavities, like toy boxes containing toys. thoracic organs, such as the esophagus and trachea (windpipe). M01_MARI6798_08_GE_C01.indd 47 25/06/16 3:39 pm  48 Chapter 1 The Human Body: An Orientation Lung Ribs Heart Parietal pleura Parietal pericardium Pleural cavity Pericardial cavity with serous fluid with serous fluid Visceral pleura Visceral pericardium Diaphragm (a) Serosae associated with the lungs: pleura (b) Serosae associated with the heart: pericardium Anterior Visceral peritoneum Liver Peritoneal Outer balloon wall cavity (with (comparable to parietal serosa) serous fluid) Air (comparable to serous cavity) Stomach Parietal Inner balloon wall peritoneum Kidney (comparable to visceral serosa) (retroperitoneal) Wall of Posterior body trunk (c) Serosae associated with the abdominal viscera: peritoneum (d) Model of the serous membranes and serous cavity Figure 1.7 The serous cavities and their associated membranes. The abdominopelvic cavity is divided into two parts. serous pericardium, and peritoneum, respectively. The The superior part, called the abdominal cavity, contains part of a serosa that forms the outer wall of the cavity is the liver, stomach, kidneys, and other organs. The inferior called the parietal (pah-ri′ĕ-tal; “wall”) serosa. The parietal part, or pelvic cavity, contains the bladder, some repro- serosa is continuous with the inner, visceral serosa, which ductive organs, and the rectum. These two parts are con- covers the visceral organs. You can visualize the relation- tinuous with each other, not separated by any muscular or ship of the serous membranes by pushing your !st into a membranous partition. Many organs in the abdominopel- limp balloon (Figure 1.7d): vic cavity are surrounded by a peritoneal (per″ ı̆-to-ne′al) The part of the balloon that clings to your !st represents cavity. the visceral serosa on the organ’s (your !st’s) outer Serous Cavities surface. The previous section mentioned the pleural cavity around The outer wall of the balloon represents the parietal the lung, the pericardial cavity around the heart, and the serosa. peritoneal cavity around the viscera in the abdominopel- The balloon’s thin airspace represents the serous cavity vic cavity. Each of these serous cavities is a slitlike space itself. lined by a serous (se′rus) membrane, or serosa (se-ro′- Serous cavities contain a thin layer of serous #uid sah; plural, serosae) (Figure 1.7). These serous membranes (serous = watery). This "uid is produced by both serous (indicated by the red lines in Figure 1.7) are named pleura, membranes. The slippery serous "uid allows the visceral M01_MARI6798_08_GE_C01.indd 48 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 49 Liver Diaphragm Spleen Gallbladder Stomach Right upper Left upper Transverse colon quadrant quadrant Ascending colon of large intestine of large intestine (RUQ) (LUQ) Small intestine Descending colon of large intestine Right lower Left lower Cecum Initial part of quadrant quadrant sigmoid colon (RLQ) (LLQ) Appendix Urinary bladder (a) The four abdominopelvic quadrants (b) Anterior view of the four quadrants showing the superficial organs Figure 1.8 Abdominal quadrants. In (a), the two planes through the abdominopelvic cavity, one horizontal and one vertical, intersect at the navel. organs to slide with little friction across the cavity walls of place,” or a small muscle may be missing. Such minor as they carry out their routine functions. This freedom of variations are unlikely to confuse you, however, because movement is extremely important for organs that move or well over 90% of all structures present in any human body change shape, such as the pumping heart and the churning match the textbook descriptions. Extreme anatomical var- stomach. iations are seldom seen, because they are incompatible with life. For example, no living person could be missing Abdominal Quadrants the blood vessels to the brain. Because the abdominopelvic cavity is large and contains check your understanding many organs, it is helpful to divide it into smaller areas for study. To localize organs in a general way, the abdomen 5. Using directional terms, describe the location of the is divided into four quadrants (“quarters”) by drawing liver in reference to the heart (see Figure 1.8 and one vertical and one horizontal plane through the navel Table 1.1). (Figure 1.8a). Knowledge of which abdominal organs are 6. Which tube of the body shows evidence of located within each quadrant (Figure 1.8b) aids clinicians segmentation, the outer tube or the inner tube? in diagnosing disorders or injuries. 7. What is the outer layer of serous membrane that lines The rib cage is commonly thought of as protection for the pleural cavity called? the thoracic organs, but it also protects the organs in the most (For answers, see Appendix B.) superior part of the abdomen. The liver and the spleen, two blood-rich organs particularly vulnerable to injury, are pro- tected by the surrounding rib cage on the right and left sides, MICROSCOPIC ANATOMY: respectively. The kidneys, located along the posterior abdom- inal wall, are also protected by the inferior ribs. AN INTRODUCTION learning outcomes Anatomical Variability Explain how human tissue is prepared and examined for You know from looking at the faces and body shapes of its microscopic structure. the people around you that humans differ in their external Distinguish tissue viewed by light microscopy from that anatomy. The same kind of variability holds for internal viewed by electron microscopy. organs as well. Thus, not every structural detail described in an anatomy book is true of all people or of all the cadav- Light and Electron Microscopy ers (dead bodies) you observe in the anatomy lab. In some Microscopy is the examination of small structures with bodies, for example, a certain blood vessel may branch off a microscope. When microscopes were introduced in the higher than usual, a nerve or vessel may be somewhat “out early 1600s, they opened up a tiny new universe whose M01_MARI6798_08_GE_C01.indd 49 25/06/16 3:39 pm  50 Chapter 1 The Human Body: An Orientation existence was unsuspected before that time. Two main types of microscopes are now used to investigate the !ne structure of organs, tissues, and cells: the light microscope Cytoplasm (LM) and the transmission electron microscope (TEM or just EM). Light microscopy illuminates body tissue with a Cell nuclei beam of light, whereas electron microscopy uses a beam of electrons. LM is used for lower-magni!cation viewing; EM, Extracellular for higher magni!cation (Figure 1.9a and b, respectively). material Light microscopy can produce sharp, detailed images of tis- sues and cells, but not of the small structures within cells (a) Light micrograph (190×) (organelles). A light microscope’s low resolution—its ina- bility to reveal small structures clearly—remains its basic limitation, despite technical advances that have greatly improved the quality of LM images. EM, by contrast, uses electron beams of much smaller wavelength to produce sharp images at much greater magni!cation, thus revealing the !ne details of cells and tissues. Elaborate steps are taken to prepare tissue for micro- scopic viewing. The specimen must be "xed (preserved) and then cut into sections (slices) thin enough to transmit light or electrons. Finally, the specimen must be stained to enhance contrast. The stains used in light microscopy are beautifully colored organic dyes, most of which were origi- nally developed by clothing manufacturers in the mid-1800s (Figure 1.9a). These dyes helped to usher in the golden age of microscopic anatomy from 1860 to 1900. The stains come in almost all colors. Many consist of charged molecules (b) Transmission electron micrograph (2250×) (negative or positive molecules) of dye that bind within the tissue to macromolecules of the opposite charge. This elec- trical attraction is the basis of staining. Dyes with negatively charged molecules stain the positively charged structures of the cell or tissue, and thus they are called acidic stains. Positively charged dyes, by contrast, are called basic stains because they bind to, and stain, negatively charged struc- tures. Because different parts of cells and tissues take up dif- ferent dyes, the stains distinguish the different anatomical structures. One of the most commonly used histological stains is a combination of two dyes, hematoxylin and eosin (H&E stain). Hematoxylin is a basic stain that binds to the acidic structures of the cell (the nucleus, ribosomes, rough ER) and colors them a dark blue to purple hue. Eosin, an acidic stain, binds to basic cytoplasmic structures and extracellular com- ponents, coloring them red to pink. Many of the micrographs throughout this text show tissues stained with H&E. (In (c) Scanning electron micrograph, artificially colored (2500×) Figure 1.9a, for example, the dark, almost black, spots are the cell nuclei, the cellular cytoplasm is magenta, and the extra- Figure 1.9 Cells viewed by three types of microscopy. cellular material in the bottom half of the image is stained a (a) Light micrograph of ciliated epithelium. (b) Transmission lighter pink.) A variety of other stains can be used to visual- electron micrograph showing enlarged area of the cell ize speci!c structures. Some of these stains create strikingly region that is indicated in the box in part (a). (c) Scanning beautiful images illuminating detailed histological structure. electron micrograph: surface view of cells lining the trachea, For transmission electron microscopy, tissue sections are or windpipe. The long, grasslike structures on the surfaces stained with heavy-metal salts. These metals de"ect electrons of these cells are cilia, and the tiny knoblike structures are in the beam to different extents, thus providing contrast in microvilli (Chapter 4, p. 112). the image. Electron-microscope images contain only shades of gray because color is a property of light, not of electron View Histology waves. The image may be arti!cially colored to enhance con- trast (Figure 1.9c). M01_MARI6798_08_GE_C01.indd 50 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 51 Clavicles (collarbones) Ribs Air in lungs (black) Heart Diaphragm (a) Radiograph of the chest (b) Lower GI with barium contrast medium, normal Figure 1.10 X-ray images. Scanning Electron Microscopy 9. Which type of microscopy produces detailed three- dimensional images of the surface features of a The types of microscopy introduced so far are used to view structure? cells and tissue that have been sectioned. Another kind of elec- tron microscopy, scanning electron microscopy (SEM), (For answers, see Appendix B.) provides three-dimensional pictures of whole, unsectioned sur- faces with striking clarity (Figure 1.9c). First, the specimen is preserved and coated with !ne layers of carbon and gold dust. CLINICAL ANATOMY: AN Then, an electron beam scans the specimen, causing other, INTRODUCTION TO MEDICAL secondary electrons to be emitted from its surface. A detec- tor captures these emitted electrons and assembles them into a IMAGING TECHNIQUES three-dimensional image on a video screen, based on the prin- learning outcome ciple that more electrons are produced by the higher points on Describe the medical imaging techniques that are used the specimen surface than by the lower points. Although arti- to visualize structures inside the body. !cially constructed, the SEM image is accurate and looks very real. Like all electron-microscopy images, the original is in Physicians have long sought ways to examine the body’s black and white, although it can be colored arti!cially to high- internal organs for evidence of disease without subjecting light structural details (Figure 1.9c). the patient to the risks of exploratory surgery. Physicians can identify some diseases and injuries by feeling the patient’s Artifacts deep organs through the skin or by using traditional X rays. Powerful new techniques for viewing the internal anatomy of The preserved tissue seen under the microscope has been living people continue to be developed. These imaging tech- exposed to many procedures that alter its original condition. niques not only reveal the structure of functioning internal Because each preparatory step introduces minor distortions, organs but also can yield information about cellular activity. called artifacts, most microscopic structures viewed by anat- The new techniques all rely on powerful computers to con- omists are not exactly like those in living tissue. Furthermore, struct images from raw data transmitted by electrical signals. the human and animal corpses studied in the anatomy labora- tory have also been preserved, so their organs have a drab- ber color and a different texture from those of living organs. X-Ray Imaging Keep these principles in mind as you look at the micrographs Before considering the newer techniques, you need to under- (pictures taken with a microscope) and the photos of human stand traditional X-ray images, because these still play the cadavers in this book. major role in medical diagnosis (Figure 1.10a). Discovered quite by accident in 1895 and used in medicine ever since, check your understanding X rays are electromagnetic waves of very short wavelength. 8. In tissue stained with H&E stain, what color are the When X rays are directed at the body, some are absorbed. cellular nuclei? The amount of absorption depends on the density of the M01_MARI6798_08_GE_C01.indd 51 25/06/16 3:39 pm  52 Chapter 1 The Human Body: An Orientation Right Left Liver Stomach Colon View Inferior vena cava Aorta Spleen Left kidney Thoracic vertebra Figure 1.11 Computed tomography (CT). CT scan through the upper abdomen. CT sections are conventionally oriented as if viewed from an inferior direction, with the posterior surface of the body directed toward the inferior part of the picture; therefore, the patient’s right side is at the left side of the picture. matter encountered. X rays that pass through the body expose top of another. Even more problematic, denser organs block a piece of !lm behind the patient. The resulting image (radio- the less dense organs that lie in the same path. For improved graph) is a negative: The darker, exposed areas on the !lm images, particularly of soft tissues, clinicians use computer- represent soft organs, which are easily penetrated by X rays, assisted imaging techniques that produce sectional images of whereas light, unexposed areas correspond to denser struc- the body’s interior. tures, such as bones, which absorb most X rays. X-ray images are best for visualizing bones and for Advanced X-Ray Techniques locating abnormal dense structures, such as some tumors Computed Tomography and tuberculosis nodules in the lungs. Mammography (“breast image”) uses low-dose X rays to screen for tumors One of the more useful modern imaging techniques is a re!ned in the breast, and bone density scans use X rays of the X-ray technology called computed tomography (CT), or lower back and hip to screen for osteoporosis (“porous computed axial tomography (CAT) (Figure 1.11). A CT bone”). X-ray examination of hollow soft tissue organs scanner is shaped like a square metal nut (as in “nuts and is enhanced by the use of a contrast medium, a liquid bolts”) standing on its side. The patient lies in the cen- that contains atoms of a heavy element such as barium tral hole, situated between an X-ray tube and a recorder, that absorb more passing X rays. The contrast medium both of which are in the scanner. The tube and recorder is injected or ingested, depending on the structure to be rotate to take about 12 successive X-ray images around examined, to !ll organs of interest and allow better visual- the person’s full circumference. Because the fan-shaped ization of these soft tissue structures. The gastrointestinal X-ray beam is thin, all pictures are con!ned to a single (“stomach intestine”) tract is commonly examined using transverse body plane about 0.3 cm thick. This explains this procedure (upper and lower GI imaging) to screen for the term axial tomography, which literally means “pic- ulcers or tumors (Figure 1.10b). tures of transverse sections taken along the body axis.” In many instances, conventional X-ray images are very Information is obtained from all around the circumfer- informative; however, conventional X-ray studies have several ence so that every organ is recorded from its best angle, limitations that have prompted clinicians to seek more with the fewest structures blocking it. The computer trans- advanced imaging techniques. First, X-ray images, especially lates all the recorded information into a detailed picture of those of soft tissues, can be blurry. Second, conventional the body section, which it displays on a viewing screen. X-ray images "atten three-dimensional body structures into CT produces superb images of soft tissue as well as of bone two dimensions. Consequently, organs appear stacked one on and blood vessels. CT is a fast and relatively inexpensive M01_MARI6798_08_GE_C01.indd 52 25/06/16 3:39 pm  Chapter 1 The Human Body: An Orientation 53 Brain Narrowing of artery Heart Artery supplying Liver heart Kidney Colon Urinary bladder Figure 1.12 Digital subtraction angiography (DSA). A DSA image of the arteries that supply the heart. (a) PET scan before (b) PET scan after treatment treatment. Tumors visible in right breast and in liver test. It can be used quickly and readily in trauma situations Figure 1.13 Positron emission tomography (PET). PET to assess internal injury. CT does use X rays to produce scans are used in oncology to assess tumor size, location, and images, so it does pose some, although minimal, concern response to treatment. about radiation exposure. CT is less useful for nervous tis- sue structures and for joint images, particularly the knee and shoulder, because bone can obscure the joint details. However, because it is less costly than magnetic resonance For example, radioactively tagged sugar or water molecules imaging (MRI, described on p. 54), and its use less restric- are injected into the bloodstream and traced to the body tive, CT is an essential diagnostic tool for clinicians. areas that take them up in the greatest quantity. This proce- dure identi!es the body’s most active cells and pinpoints the Angiography body regions that receive the greatest supply of blood. As the Angiography (“vessel image”) is a technique that produces radioactive material decays, it gives off energy in the form images of blood vessels. A contrast medium is injected into of gamma rays. Sensors within the doughnut-shaped scan- a vessel and distributed via the vascular system. Images