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1Introduction and Basic Conceptsabdomen, p 11abdominal, p 13amplifier, p 16anatomical position, p 9anatomy, p 2anterior, p 9brachial, p 11cardiovascular physiology, p 8carpal, p 11caudal, p 9cavities, p 13cell-to-cell

communication, p 2cellular physiology, p 8control, p 17coronal, p 13cranial, p 13cytology, p 4developmental anatomy, p 4diaphragm, p 13dorsal, p 9effector, p 16

embryology, p 4epigastric, p 12etymology, p 9feed-forward loop, p 18gain, p 17gross anatomy, p 4histology, p 4homeostasis, p 1hypochondriac, p 12hypogastric, p 12iliac, p 12inferior, p 9longitudinal, p 13lumbar, p 12mediastinum, p 13mesenteries, p 14midsagittal, p 13nasal, p 13negative feedback loops, p 17neurophysiology, p 8normal range, p 16oblique, p 13

parasagittal, p 13parietal, p 14parietal pericardium, p 14parietal peritoneum, p 14parietal pleura, p 14pathology, p 8pathophysiologies, p 8pelvic, p 11pericardial, p 14pericardial cavity, p 14pericardial fluid, p 14physiology, p 8pleural, p 14pleural fluid, p 14positive feedback loops, p 17posterior, p 9prone, p 9regional anatomy, p 4resolution, p 17sagittal, p 13sensor, p 16serous membranes, p 14

sinuses, p 13solvent, p 15spinal, p 13structure dictates

function, p 1superficial anatomy, p 4superior, p 9supine, p 9systemic anatomy, p 4systemic physiology, p 8thoracic, p 13thorax, p 11transverse, p 13trunk, p 11umbilical, p 12variable, p 16ventral, p 9visceral, p 14visceral pericardium, p 14visceral peritoneum, p 14visceral pleura, p 14

Key Terms

Learning Objectives• Understand key terms and basic concepts of anatomy and physiology.• Define anatomical position and explain its importance in understanding physiology.• Identify and define the directional terms, parts, and planes of the human body.• Name the major trunk cavities of the body.• Identify and characterize the body’s serous membranes.• Understand how structures affect physiological function.• Describe the key role that homeostasis plays in the anatomy and physiology of many processes.• Understand the role of cell-to-cell communication in physiological processes.

IntroductionThis textbook examines the structures and processes that underlie the marvelous ma-chine that is the human body. How we imagine the body has changed throughout history from the Renaissance (fig. 1.1a) the modern-day view of the body as a marvelous machine (fig. 1.1b). The organization of this textbook differs from most other books of this type in that we begin by discussing basic concepts that are essential for life. We then carry the discussion of these concepts throughout the book as a unifying theme, relating human anatomy to bodily functions.

The basic concepts essential to life have powerful impacts on how the body works. The first of these concepts is a simple one, structure dictates function, and its impact can be seen in something as simple as an elbow or the knee. The second concept, homeostasis

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Property of Kendall Hunt Publishing Ch. 1 from Crivello's Human Anatomy & Physiology ISBN: 978-0-7575-8738-2 | 2010 www.kendallhunt.com/crivello

2 Chapter 1—Introduction and Basic Concepts

(G. homoios, similar, and stasis, standing), involves cells, tissues, and the body striving to maintain a constant internal environment in the face of a changing external environment. The body spends an enormous amount of energy striving to maintain homeostasis. The third concept, cell-to-cell communication, is a process in which cells communicate and coordinate their functions to allow cells within the body to do things that would otherwise be impossible, like riding a bike.

Knowledge of how these concepts interrelate and work in the human body is an impor-tant foundation of modern medicine and is essential for students planning a career in the health sciences. This knowledge is also beneficial to nonprofessionals because it helps them understand overall health, wellness, and disease. An awareness of the human body and its processes allows individuals to make an educated assessment of the ever-increasing barrage of medical facts and, sometimes, misinformation.

Students who study the human body will quickly realize that they are learning a new lan-guage. Most medical students and nurses will learn 15,000 new terms, when they study the human body. This textbook is full of new terms, and the key to understanding them is understanding their roots from other languages. That is why as new terms are introduced, their etymology (origin or history of words) is included.

In this chapter, we define and discuss anatomy, physiology, and the three basic concepts. We also examine the human body’s structural and functional organization.

Anatomy and PhysiologyAnatomyAnatomy (L. anatomia, dissection) is the scientific discipline that examines the structure and organization of the human body. The root of this term lies in the Latin word for dis-section and reflects the need to delve beyond the surface of the skin to understand how the human body works. It provides a detailed description of the smallest to the largest of the

Figure 1.1 Different historical views of the human body. (a) The Renaissance view of the body by da Vinci. (b) A modern view of the body with associated muscles.

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Chapter 1—Introduction and Basic Concepts 3

body’s components and, in many cases, provides a road map of how different structures are interrelated. As an example, anatomical information describes the specific pathway by which pain travels from the foot to the brain when a person steps on a tack.

Anatomy also provides information about the first basic concept, structure dictates function, because it describes the structure of key components in a way that can be related to their function (fig. 1.2). Examination of the elbow makes it obvious why it acts like a door hinge and allows your hand to scratch your nose. A cursory examination of the human knee also makes it clear how we can walk, run and jump—it also acts like a hinge. At a macro (large) scale, anatomy describes body structures that can be seen with the unaided eye; at a micro

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A. Nuclear envelope

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Outer and inner membranes

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Figure 1.2 Levels of structural organization. The digestive system is used to illustrate structural organization and the associated branch of anatomy. (a) Chemical level: Molecules are formed from atoms. The branch of anatomy is microanatomy. (b) Cellular level: Cells are composed of molecules. The branch of anatomy is cytology. (c) Tissue level: Tissues are made up of cells. The branch of anatomy is histology. (d) Organ level: Organs contain several different types of tissues. The branch of anatomy is anthropotomy. (e) System level: Systems include organs with similar functions. The branch of anatomy is gross anatomy.

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(small) scale, it describes structures that can be seen with light microscopes or more power-ful imaging tools. Anatomy also applies to the nano (G. nanos, dwarf) scale of structures that cannot be imaged easily; the structure of molecules or proteins.

As a scientific discipline, anatomy is considered at many different levels (fig. 1.2), from a very small to a large scale (table 1.1), and specific terms relate to the scale examined. Cytology (L. cyto, cell, and ology, study) examines cell structure; histology (L. histo, tissue and study) examines tissue structure; embryology (embryo and study) studies anatomical changes that occur from egg fertilization to the eighth week of fetal development; and developmental anatomy studies changes that occur from egg fertilization through adulthood.

Gross anatomy examines body structures seen with the unaided eye. Systemic anatomy studies gross anatomy at a level that includes different tissues that underlie some com-plex function. Systemic anatomy might examine the respiratory system (breathing) or the urinary system (production of urine). It is also possible to examine regional anatomy, an examination of the body’s anatomy area by area, for example, an examination of the left arm or right leg. Superficial anatomy examines body surfaces like the shape of the ears or surface of the skin.

Anatomic Variations

The tools now available to scientists and physicians to examine the human body have revo-lutionized anatomy. By using these imaging tools, scientists and physicians have discov-ered that humans are not structurally identical (fig. 1.3). That may seem to be so obvious a point that it does not bear mention, but it underscores several important factors about human anatomy. This is especially frustrating to new students studying gross anatomy of human cadavers, when they realize that standard anatomy textbooks at best describe 60% to 70% of humans, with fully a third of people having significant anatomical differ-ences. The greatest differences are found in the size, shape, and attachments of muscles, ligaments, and tendons, as well as the size and shape of bones, arteries, and nerves. Even though no two individuals are structurally identical, all humans are designed with the same basic structure. It is the correct organization and working of these structures that is required for our continued good health.

An examination of 100 typical college students demonstrates that the human body has an axis of symmetry running through the body center. The left side of the body is almost a mirror image of the right side. There are obvious exceptions to this rule. Each individual

Figure 1.3 Difference in hu-man height as a demonstra-tion of anatomical variability.

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Table 1.1

AnATOmICAL STudIeSLevel of Organization Branch of Anatomy Chapter(s)

Chemical Microanatomy 2

Cellular Cytology 3

Tissue Histology 4

Organ Anthropotomy 5–29

System Gross 5–28

Organism Gross 1




The ability to see anatomical structures within the body, without significant harm to the patient, has revolutionized medicine and greatly increased our un-derstanding of how the body works and the nature of disease. Technologies that seemed amazing only a few years ago now routinely allow physicians to look in-side the body with little risk to the patient.

Internal anatomical imaging really started in 1895 (Wilhelm Conrad Röntgen coined the term X-ray) with the use of X-rays to see inside the human body. X-rays are a type of radiation that can pass through the body and develop images on film. Dense objects within the body, like bones, appear white (under exposed)

Clinical—In Context: A Deeper Look: Imaging Toolsbecause they absorb a high percentage of the passing X-rays, whereas less-dense objects, like fat, appear dark (overexposed) on X-ray film because they allow a high percentage of the X-rays to pass through (fig. 1.4a). X-rays are limited as a diagnostic tool because radiation is inherently dangerous, and the images produced are a two-dimensional representation of a three-dimensional structure (think of looking at the surface of a piece of toast and try to image how you would reconstruct the shape of the entire loaf). Medical radiography, which uses X-rays, is composed of fluoroscopy and radio-graphs. Fluoroscopy (fig 1.4b) produces real-time im-ages of internal tissues with lower doses of radiation than radiographs. Fluoroscopy exploits contrast media,

(a)

(b)

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Figure 1.4 Visualization of the human body. (a) X-rays of the right hand. X-rays are a form of high-energy radiation that penetrates soft tissues. In the most common procedure, a beam of X-rays travels through the body and strikes a photographic plate. Not all of the projected X-rays reach the film: some are absorbed or deflected as they pass through the body. The resistance to X-ray penetration is known as radiodensity. Radiodensity in-creases in the following sequence: air , adipose , liver , blood , muscle , bone. Radiodense tissues appear as white, and less radiodense tissues appear in shades of gray to black. (b) A barium contrast fluoroscope of the upper gastrointestinal tract. Barium is a radioactively dense material that highlights sharp outlines and con-trasts within soft tissues and the distribution of fluids within soft tissues or the movements of internal organs. (c) A fetal sonogram.

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like barium, to help visualize soft tissues that would not normally be seen in a radiograph, like in a barium enema used to visualize the lower intestinal tract. Fluo-roscopy is also employed in cases when physicians need to guide instruments or probes to specific locations within the body. Radiographs, which use more radia-tion, are commonly used to detect bone fractures. They can also be done with contrast media to increase the visualization of soft tissues.

Ultrasound, developed in the 1950s as an adaptation of World War II sonar technology, uses high-frequency sound waves (megahertz range) to characterize struc-tures. The high-frequency sound waves are reflected from different surfaces within the body, making it possible to reconstruct by computer the information from these reflections into a picture of internal body components. Ultrasound is commonly used because there is little evidence that these sound waves harm soft tissues. Ultrasounds are well-known for their role in imaging fetuses (fig 1.4c), but are commonly used to image a wide range of body tissues—such as the heart, breasts, liver, muscles, and arteries. Ultrasounds have another advantage in that they produce real-time images, which is especially valuable in imaging the heart (i.e., an echocardiogram). A sonogram is a static im-age produced by ultrasound and is the type of picture expectant families bring home from the obstetrician to show their relatives the unborn baby.

Digital subtraction angiography (DSA) compares two images, one obtained from the patient before adding contrast media and the other after contrast media, to study the patient’s blood vessels. The advantage of this approach is that it greatly enhances differences (con-trast) in tissues that are otherwise hard to visualize (like blood vessels). Radiologists or cardiologists rou-tinely use DSA to guide catheters into the carotid ar-tery during angioplasty (the surgical repair of a blood vessel, either by inserting a balloon-tipped catheter to unblock it or by reconstructing or replacing part of the vessel, see discussion in Chapter 19).

Magnetic resonance imaging (MRI) is capable of producing high-quality images of internal structures of the hu-man body (fig. 1.5a). MRI is based on the principles of nuclear magnetic resonance (NMR), which uses power-ful magnets to excite hydrogen nuclei (protons) within molecules. When a magnetic field is applied to the hu-man body, it causes atoms to align themselves with the external field, like small metal shavings are aligned by a simple bar magnet. When the field is removed, the

molecules relax (or return) to their native state. Pro-tons relax at different rates, dependent on the molecules around them, and this information can be reconstructed into three-dimensional images by sophisticated com-puter programs. The human body is approximately

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Figure 1.5 Common scanning techniques. (a) Magnetic resonance image of the head showing the sinuses and nasal cavity. (b) Computed tomography scan of the lower abdo-men. (c) Synthetically produced technetium.

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63% hydrogen atoms, because of the large amounts of water and lipids, and magnetic resonance imaging primarily produces images from the relaxation of hy-drogen nuclei. Traditionally, MRIs produce a static two-dimensional view of tissues (like a slice through the body). The slices can be reassembled to produce three-dimensional images in a process known as tomography (G. tomos, section) (fig 1.5b). Tomography is commonly known as computed tomography (CT) scans. The CT scan uses a low- intensity X-ray beam that is rotated 360 degrees around the stationary patient. Each “slice” of the body produced by the X-ray beam can be recon-structed into a three-dimensional structure or displayed as static slices of the body.

Real-time, dynamic images of tissues can also be ob-tained by introducing short-lived radioactive isotopes, like technetium (Tc; G. teknetos, artificial) that are pref-erentially absorbed by biologically active tissues, like tumors or fractures (fig 1.5c). Technetium is a syn-thetically produced, radioactive, silvery gray metal. A common use of technetium is to couple it with phos-phate, a major component of bone, as an imaging tool in a bone scan. Bone scans, which provide much more information than typical X-ray films, can show sites of bone repair and can actually reveal the level of blood flow to bone tissue.

A special camera can detect the radiation given off by technetium. Positron emission tomography (PET) is commonly used to detect diseases of the heart and brain, and the presence of tumors within the body. Pa-tients are commonly given glucose substituted with

a positron-emitting radioisotopes (like 18F) that is preferentially absorbed by metabolically active tissues like a tumor. PET scans do not give detailed anatomi-cal information, so they are often compared with CT scans, but are the method of choice to determine the presence of tumor within a tissue, like the lung. PET scans are especially useful in neurological imaging of the brain while patients are singing, talking, or carry-ing out some complex function, and help to identify the different structure(s) in the brain that are involved in such tasks.

Current imaging techniques allow scientists to obtain information about the concentration of components within cells, map where the components reside, and monitor how they are transported. Cellular biologists now use molecular imaging to localize and image bio-logical molecules and structures inside a cell. They can also image when molecules are produced to track changes in cell metabolism. Current technologies for molecular imaging in cellular biology include fluores-cent in situ histology (FISH), green fluorescent protein (GFP) (fig. 1.6), and many other spectral techniques. Atomic force microscopy (AFM) is a new approach to resolving molecular structure at a small enough scale to image individual atoms. New techniques are be-ing developed to image viruses as they attach to cells and to image the movement of living cells. Three- dimensional body imaging is also becoming increas-ingly popular, both as a means of identifying faces at airports and for e-commerce, medicine, vehicle and tool design, industrial design, among other uses.

Figure 1.6 Current technologies for molecular imaging in cellu-lar biology. Green fluorescent protein (GFP) imaging of a protein expressed in one strain of mice.

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has one heart and one liver, not two, with one on each side of the body. Nonetheless, even with the same axis of symmetry, no two individuals are identical. The frequency of nor-mal variation in human gross anatomy (e.g., finger length, leg length, eye color) can be predicted. These variations arise primarily from our genetic composition, an inheritance carried over from our ancient origins. The aorta (a large artery that leaves the heart, see chapter 19) can vary in its position and extent without causing any health problems. The height of the aorta (aortic arch) may vary by as much as 12 cm (4 inches) within the chest cavity. Within the knee, a fibrocartilage disk known as the menisci is commonly C-shaped, but it can also have a flat, circular shape. Anatomical variations can also compromise nor-mal functioning to the point that they become life-threatening. In recent years, it has not uncommon for conjoined twins to travel to the United States for surgical separations or for teams of doctors and nurses to travel to other countries to perform cleft palate surgeries.

PhysiologyPhysiology is the scientific investigation of the processes that support life. These processes are key to survival of life and include ensuring an adequate supply of oxygen (respiratory system) or the removal of waste products from the blood (urinary system). Normal human physiology depends on key component structures; for example, the lung must be able to expand like a balloon to allow humans to bring oxygen-rich air into the lungs.

This relationship between the structure of a cell or component and physiologic processes is an example of how structure dictates function, one of the central conceptual themes of this book. Physiologic processes attempt to maintain homeostasis (the ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiologic processes, and another of the central conceptual themes of this book). Physiologic pro-cesses also depend on cell-to-cell communication. So normal physiology that is the basis of good health is absolutely dependent on the three conceptual themes running through this book.

Like anatomy, physiology is considered at many different levels. Cellular physiology ex-amines cellular processes (growth, division, metabolism, differentiation, excretion, and absorption), whereas systemic physiology examines organ system processes (breathing, the beating of the heart, the movement of food through the intestines, or moving our arms and legs). Neurophysiology examines nervous system processes (seeing, hearing, touch, language, memory, and abstract thought), and cardiovascular physiology examines heart and blood vessels processes (blood pressure and blood flow). Physiologic examinations are typically focused on tissue and organ systems, because they interact to maintain normal body functioning.

Pathology examines all aspects of disease (anatomical and physiologic), with an emphasis on the cause and development of abnormal conditions, as well as the structural and functional changes resulting from disease. Many diseases, or pathophysiologies, arise from an inability to maintain homeostasis (like diabetes), from a flaw in the normal cell-to-cell communi-cation pathways (cancer), or from a structural alteration that disrupts the expected function (like sickle cell anemia). To understand how the body operates, students must integrate anatomy with physiology, keeping in mind the three basic concepts of this book.

In Review . . .1.1 Define anatomy, physiology, and pathophysiology.

1.2 Why is it important to understand the relationship between anatomy and nor-mal physiology and/or pathophysiology?




Terminology and the Human Body PlanTerminologyThis book is filled with terms that may be confusing for students new to this field. Know-ing the sources, or etymology, of these terms makes understanding them much easier. Most of the terms are derived from Latin or Greek because these were the languages of the educated elite in Europe during the Renaissance, where the study of anatomy and physiol-ogy was extensively developed. As an example, myasthenia is derived from the Latin term for “fatigue” and gravis is derived from the Latin term for “severe.” Someone suffering from myasthenia gravis has symptoms of progressive fatigue and generalized weakness of the skeletal muscles, especially those of the face, neck, arms, and legs, caused by impaired transmission of nerve impulses. Prefixes and suffixes are added to words to expand their meanings. The suffix -itis means “inflammation,” so rhinitis is the inflammation of nasal tissues (rhin) common during a cold. The suffix -ology means the study of the word that precedes it, so physiology means the study of physio, or how the human body works, or embryology refers to the study of the embryo. A glossary and list of word roots, prefixes, and suffixes appear at the back of this textbook.

Body PositionThe anatomical language used to describe the human body is premised on several clear rules. Imagine the confusion that would ensue if you couldn’t use landmarks to tell your friends where they should meet for dinner in a new city. Anatomical positions are based on a person standing erect, facing forward, with the upper limbs hanging to the sides and the palms of the hand facing forward, which is known as the anatomical position (fig. 1.7). A person lying on his or her back is supine (L. supinus, to lay); when lying on the stomach, that person is prone (L. pronus, sloping). Even though healthcare workers all use the common anatomical position to standardize the location of different body parts, many anatomical descriptions are still relative. When standing erect, the elbow is inferior (below) the shoulder, but it is parallel to the shoulder when the person is supine or prone. To avoid confusion, relational descriptions are always based on the anatomical position.

Direction It is important to be able to describe the relationship between body parts. Sometimes it is obvious—the head is superior (or above) to the neck. Other times it is not so obvious—the inferior vena cava is a large vein that returns to the heart from tissues inferior (below) the heart (fig. 1.8). Table 1.2 lists the common directional terms used in this book. Some of the terms are commonly used, such as anterior (front) and posterior (rear), whereas others are not, such as caudal (toward the tail or coccyx bone), ventral (toward the belly), and dorsal (toward the back). It is possible to use two different terms, dorsal and posterior, to describe the relationship between two body parts; the esophagus is dorsal or posterior to the trachea.

Body Parts and RegionsThe human body can be subdivided into different regions that describe anatomically or physiologically functional areas (fig. 1.9). The lower limb is composed of the thigh, knee, leg, ankle, and foot, whereas the upper limb is composed of the upper arm, elbow, forearm, wrist, and hand. The central portions of the body are composed of the head, neck, and

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Figure 1.7 The anatomical standard position and direc-tional terms.




Table 1.2

COmmOn dIReCTIOnAL TeRmS fOR HumAn AnATOmyTerm Etymology Definition Example

Right Toward the right side of the body

The right ear

Left Toward the left side of the body

The left ear

Superior L. superus, upper

A structure above another The ear is superior the mouth

Inferior L. inferus, low A structure below another The mouth is inferior to the ear

Cephalic L. cephalicus, head

Synonymous with superior but also meaning closer to the head than another structure

The shoulder is cephalic to the elbow

Caudal L. cauda, tail Synonymous with inferior but also meaning closer to the tail than another structure

The sternum is caudal to the ear

Anterior L. ante, before The front of the body The nose is anterior to the ear

Posterior L. posterus, after

The back of the body The ear is posterior to the nose

Ventral L. ventralis, belly

Synonymous with anterior but means specifically toward the belly

The navel is ventral to the spine

Dorsal L. dorsum, back

Synonymous with posterior but means specifically toward the back

The spine is dorsal to the navel

Proximal L. proximus, nearest

Closer to a point of attachment to the body than something else

The elbow is proximal to the wrist

Distal L. di plussto Farther to a point of attachment to the body than something else

The wrist is distal to the elbow

Lateral L. latus, side Away from the body midline

The elbow is lateral to the ribs

Medial L. medialis, middle

Toward from the body midline

The sternum is medial to the shoulder

Superficial L. superficialis, surface

Toward the surface The skin is superficial to muscle

Deep O.E., deep Away from the surface The lungs are deep to the ribs




trunk. The trunk is divided into the thorax (chest), abdomen (region between the thorax and pelvic region), and pelvic region (the inferior end of the trunk associated with the hips). There are many alternative terms to describe body regions, such as brachial for the upper arm and carpal for the wrist.

The abdominal region is typically quartered by imaginary horizontal and vertical lines that intersect at the navel (fig. 1.10), forming four quadrants: upper right, upper left, lower right, and lower left. The abdomen can also be subdivided into nine regions by two

Orbital

NasalOral

Axillary

Thoracic

Abdominal

Digital

Pubic

Pelvic

Umbilical

Brachial

Cervical

Buccal

Carpal

Femoral

Tarsal

Figure 1.9 Subdivision of the body into anatomically or physiologically functional areas.

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Lateral View

Lateral(ventral)

Posterior(dorsal)

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Midline

Anterior or Ventral View

MedialLateral Lateral

Superior

Inferior

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Deep

Superficial

Rostral

Caudal

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Figure 1.8 Directional terms associated with the body.

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Frontal (Coronal) Plane

Horizontal (Transverse) Plane

Sagittal Plane

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Figure 1.11 (a) The human body divided into quadrants by imaginary horizontal and vertical lines. Division of the human body into different planes; (b) X-ray of the neck in the sagittal plane; (c) X-ray of the chest in the frontal plane; (d) computerized axial tomography scan of the brain in the transverse plane.

Adapted with permission from Anatomy I and Physiology Lecture Manual

Adapted with permission from Anatomy I and Physiology Lab Manual ANP101

Left Upper Quadrant

Left Lower Quadrant

Right Upper Quadrant

Right Lower Quadrant

RUQ

RLQ

LUQ

LLQ

Figure 1.10 External division of the abdomen into four quadrants: right upper quadrant, left upper quadrant, right lower quadrant, and left lower quadrant.

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imaginary vertical and horizontal lines. These regions—epigastric (over the belly), right and left hypochondriac (hypo in this context means “beneath,” which, in this case, is near the lower ribs on both sides), umbilical (center of the abdomen), right and left lumbar (between the lower ribs and hips), hypogastric (the lowest region), and right and left iliac (near the hips on both sides)—are used as reference points for the underlying organs. Para-medics use quadrants to describe the location of pain and regions to describe the location of injuries.




PlanesThe human body can be divided into different areas by flat, imaginary planes that pass through it (fig. 1.11). The planes can be used to reveal the organizational relationship between different body parts. The term sagittal (L. saggita, arrow) refers to a longitudinal (top to bottom) plane that divides the human body into symmetrical right and left sec-tions. A midsagittal plane divides the body into equal right and left halves (mirror image), whereas a parasagittal (G. para, beside) plane is offset to one side of the midline, result-ing in unequal halves. A transverse (L. transversus, turn around) plane runs parallel to the ground and divides the body into superior and inferior sections (i.e., top and bottom half). A coronal (L. coronalis, crown) plane runs through the body vertically, dividing the body into anterior and posterior sections (i.e., a front and back). If an organ is sectioned to reveal interior structure, a longitudinal section runs along the long axis, a transverse section runs at right angles to the longitudinal section, and an oblique (L. obliquus, slope) section runs at any other angle. For example, splitting an artery along its length would be a longitudi-nal section, whereas slicing across it like a loaf of bread would be a transverse section, and at an angle would be an oblique section.

CavitiesMany vital organs are suspended within internal cavities (hollow areas) that act to protect and cushion delicate organs from accidental shocks, bumps, or thumps when people walk, jump, or run (fig. 1.12). These cavities also allow the organs to change shape and size with-out causing damage. The activities of the heart and lungs require that they change size and shape, and the cavities that surround them allow them to do so. The body contains many different cavities including the nasal, cranial, thoracic, and abdominal cavities. Some cavities open to the outside of the body (sinuses) and others do not (thoracic). Introductory human anatomy and physiology textbooks sometimes describe a dorsal cavity that contains the brain and spinal cord, and a ventral cavity that contains the thoracic, abdominal, and pelvic cavities. This chapter limits the discussion to the major trunk cavities that do not open to the outside of the body.

The thoracic, abdominal, and pelvic cavities do not open to the outside (fig. 1.12). The thoracic and abdominal cavities are sepa-rated by the diaphragm, a dome-shaped muscle. The boundar-ies of the thoracic cavity are the neck (superior), ribs (lateral and medial), sternum (anterior or ventral), spinal cord (posterior or dorsal), and diaphragm (inferior). The thoracic cavity is divided into left and right sections by a middle line (mediastinum). The lungs are located on either side of the mediastinum; the heart, thymus, trachea, esophagus, and blood vessels lie beneath the me-diastinum. The abdominal cavity is marked by the diaphragm (superior), abdominal muscle (lateral, medial, anterior, or ven-tral), lower spine (posterior or dorsal), and pelvic region (inferior). The abdominal cavity contains many of the body’s largest organs including the liver, stomach, intestine, gallbladder, kidneys, and pancreas, but most of the pancreas is retroperitoneal (to the back of the cavity). Pelvic bones define the pelvic cavity. This small space encases the internal reproductive organs (ovaries, uterus, bulbourethral gland, etc.), urinary bladder, and part of the large intestine, and it is contiguous with the abdominal cavity. The skull bones define the cranial cavity, whereas the vertebrae and connective tissues define the spinal cavity.

DorsalCavity

ThoracicCavity

CranialCavity

SpinalCavity

PelvicCavity

AbdominalCavity

AbdominopelvicCavity

VentralCavity

Figure 1.12 Body cavities. A lateral view of the thoracic, abdominopelvic, and cranial cavities.

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Serous MembranesThe interiors of the trunk cavities are lined with serous (L. serum) membranes, which are double-walled structures (fig. 1.13). The serous membranes are named by the tissues with which they are associated. The visceral (of the viscera or internal areas) membrane has direct contact with the organ of interest; the parietal ( parietalis, of a wall) membrane has contact with the wall of the cavity. The serous membranes provide for physical contact between organs and a cavity in such a way that organs can move. The serous membrane is a sealed structure; the fluid it contains acts as a lubricant between the two membranes.

The thoracic cavity contains three distinct serous membranes (fig. 1.13). The pericardial (L. peri, around; cardi, the heart) membrane surrounds the heart and made up of the visceral and parietal pericardium. The visceral pericardium is in direct contact with the heart, and the parietal pericardium is in direct contact with the thoracic cavity. The space be-tween the two membranes (the pericardial cavity) is filled with pericardial fluid that reduces friction as the heart beats. The pericardium helps to anchor the heart in place, preventing excessive movement of the heart in the chest when body position changes. It protects the heart from infections and tumors that develop in, and may spread from, adja-cent tissues and may also help keep the heart from enlarging.

A pleural (L. pleura, side) membrane surrounds each lung, and is made up of the visceral and parietal pleura. The visceral pleura are in direct contact with the lungs, and parietal pleura are in direct contact with the inner surface of the thoracic wall, the lateral surfaces of the mediastinum, and the superior surface of the diaphragm. The two membranes form a pleural cavity that is filled with a pleural fluid. This fluid decreases friction when the lungs expand and contract during breathing.

The wall of the abdominal cavity, pelvic cavities, and inferior surfaces of the diaphragm are lined with the parietal peritoneum (G. peritonaion, stretched across). The internal organs, or viscera, are lined with the visceral peritoneum that forms the outer layer of most of the intestinal tract. The peritoneum forms sheets of greatly modified membranes called mesenteries (G. meso, middle, and enteron, intestine). Mesenteries hold the organs of the

Figure 1.13 Serous mem-branes are demonstrated by pushing a fist into a balloon (a). The hand within the balloon represents an organ surrounded by a serous membrane. (b) Heart serous membranes. (c) Lung serous membranes. (d) Abdominal serous membranes.

A

B

D

C

Outer Wall(comparable toparietal serosa)

Parietalpericardium

Heart

Pericardialfluid

Visceralpericardium

Parietal pleuralPleural fluid

Visceral pleural

Diaphragm

Posterior

Anterior

Air(comparable

to serous fluid) Inner Wall(comparable tovisceral serosa)

Lung

Wall of body trunk

Parietalperitoneum

Kidney(retroperitoneal)

Peritoneal cavitycontainingperitoneal fluid

Visceralperitoneum

thought questionWould you expect to find a serous membrane around an organ that does not move?




digestive tract in position and convey nerves, blood vessels, and lymphatic ducts to the organs. The space between the parietal and visceral membranes contains a watery fluid that permits the abdominal organs to slide freely against the abdominal wall.

In Review . . .1.3 What is the anatomical body position?

1.4 What is the difference between caudal and ventral?

1.5 What tissues mark the boundaries of the thoracic space?

1.6 Into what regions can the abdomen be divided?

1.7 How does a sagittal section differ from a transverse section?

1.8 How do serous membranes allow tissues to move without friction?

Concepts underlying Human Anatomy and PhysiologyStructure Dictates FunctionScientists and physicians can often predict the biological function (and normal physiologic role) of a newly characterized component if they thoroughly understand its structure. Some-times it is obvious and easy to make this connection, as with your opposable thumbs, but in many cases, it is extremely difficult, like with a newly identified protein. The inability to make this correlation is a limitation of our scientific understanding. This correlation can be made at all levels, from the smallest level all the way up to the largest level (bones, muscles, or tissues). The following are examples of how structure dictates function in a physiologic sense.

It is clear how the structures of the knee and elbow allow humans to make common move-ments. Both the knee and elbow bend and allow us to walk and touch our faces. The knee and elbow work like a hinge on a door. Though it is not apparent from a surface examina-tion, the structure of both the elbow and knee prevent it from moving in certain directions. These movements, if allowed, would cause severe damage to associated tissue, which hap-pens when a football player damages his knee during a game.

It may not be clear to most students why the human body is composed of up to 70% water. The body is made up of so much water because the structure of water gives it prop-erties that make it critical for life. Water is a powerful solvent (ability to dissolve solid compounds). Dissolving compounds accelerates the rate at which they can combine and change. Mixing dry yeast with dry salt, sugar, and flour does not result in bread dough. But if a small amount of water (acting as a solvent) is added to dissolve the yeast, sugar, salt, and flour, the chemical reactions carried out by the yeast are greatly accelerated and bread dough is formed.

Water aggregate in drops rather than spread out over a surface as a thin film (fig. 1.14a). Water aggregation is clearly demonstrated by the sweating athlete (fig. 1.14b). This phe-nomenon causes water to stick to the sides of vertical structures despite gravity’s downward pull and allows for the formation of water droplets and waves, and it helps water to move up the surface of structures (within a straw or blood vessel).

As anyone who has heated a pot of water knows, it takes a great deal of energy to change water temperature (fig. 1.14c). Because of this, water can absorb large amounts of heat before it begins to get hot. Water also releases heat slowly when situations cause it to cool, helping humans regulate their body temperature more effectively. All of these properties of water, and many other properties, are dependent on water’s structure. Life as we know it is not possible without water.




Feedback Controller Set Point

Receptor

Effector

Figure 1.15 Homeostasis acts to maintain a physiologic variable within a normal range. Changes in a physiologic variable are detected by a sensor that sends a signal to an integrating center, which, in turn, sends a signal to an effector. The effector response changes the physiologic variable back to a normal range. This type of control system is known as negative feedback.

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Figure 1.14 Examples of the surface tension of water. (a) Water forms drops instead of sheets because of hydrogen bonds. (b) On the skin of a sweating athlete, water forms droplets because of surface tension. (c) It takes a great deal of heat to evaporate water; therefore, splashing water on the body when temperatures increase acts to cool the young child. Water is the only biological mol-ecule that can be a solid, liquid, or a gas at commonly occurring environmental temperatures.

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HomeostasisHomeostasis (coined by American physiologist W. B. Cannon [1871–1945]) refers to the processes that allow the human body to maintain internal equilibrium by adjusting physi-ologic systems. The homeostatic concept arose in the nineteenth century when scientists determined that animals had many mechanisms preserving conditions favorable for life. The term homeostasis describes the processes by which living tissues maintain a distinct and rela-tively constant internal environment. This is one of the main conceptual focuses of this book. Homeostasis is critically important to the normal functioning of human (and all other ani-mal and plant) cells. So, how does homeostasis work, and why is it so critical for life?

Homeostatic mechanisms rely on several key components (fig. 1.15):

1. The physiological variable (L. vario, to differ) in question, such as body tempera-ture, blood pH, and blood chemistry, that changes in response to external or internal changes

2. An ideal value (or set point) and the normal range over which the variable oscillates (increases or decreases) around the set point

3. A sensor that can monitor the levels of the variable4. An amplifier (L. amplificatio, an enlarging), which increases the ability of the sensor

to detect small changes in the variable5. The ability to cause a change in the level of the variable (either 1 or 2) through an

effector (L. efficio, to accomplish)




Why does the body require this complicated process to maintain its internal environment? The components of the human body are designed to work optimally within a narrow range of conditions; outside of that range components would be nonfunctional and cells would die. It is advantageous, therefore, to provide homeostatic systems to allow components to function normally even when external conditions vary widely. A cost is associated with homeostatic sys-tems in that they can be complex and expensive to operate (require lots of energy). Homeostatic systems usually involve negative feedback loops. Negative feedback loops act to limit the change in a critical variable, making it return toward the desired value. There are a number of normal positive feedback loops in the body, but by their nature they are difficult to control.

Negative Feedback Loops

In a negative feedback system, changes in physiologic processes oppose, or negate, the origi-nal stimulus (hence negative feedback). Let us use as an example the maintenance of human blood pressure. A decrease in blood pressure is detected by cells in the carotid artery (see chapter 20 for a detailed discussion), which act as sensors. So blood pressure is the physiologic variable. This sensor sends information to cells in the central nervous system, which ampli-fies the signal (making it easier to detect small changes) and turns on an effector, which, in turn, causes the heart to increase cardiac output so that blood pressure returns to normal. This is an example of a negative feedback loop limiting swings in blood pressure. Most of the homeostatic processes in the body are negative feedback loops because they minimize changes in physiologic systems, keeping them within limits that are compatible with long-term survival.

It is possible for homeostatic mechanisms to have different levels of resolution and con-trol. If the temperature sensor cell within the body was only responsive to changes of at least 1°C (meaning that the temperature would have to increase or decrease by 1°C before any physiologic system began to change), we would expect the normal human body tem-perature to be from 36°C to 38°C (if the set point was 37°C). If you measured the internal body temperature of 100 college students 20 times during the day over a month, you would find that the internal body temperature varied by only 0.1°C, (from 36.9–37.1°C). A normal range of 0.1°C indicates that maintenance of temperature is critically important, because it takes a great deal more energy to regulate temperature over a 0.1°C range than a 1°C range. If a physiologic variable is critically important, as internal temperature ap-pears to be, the homeostatic process must be much more sensitive to small changes, but it would also be more energetically expensive. So only the most critical physiologic systems are regulated with very high resolution.

The rate at which the variable is corrected back to the set point (known as gain) is also controllable. If a physiologic system is critical, and small changes potentially disastrous, then it is to the benefit of the body to rapidly (with high gain) return the physiologic system to the correct set point. An example is provided when people stand up after sit-ting for long periods. While people are sitting, gravity causes blood to pool in their lower legs, when a person quickly stands up, there can be an insufficient amount of blood in the upper body to supply the needs of the brain. As a result, for a few brief moments, many people are light-headed and feel like they could fall. However, the sensation passes quickly and then the person feels normal. What has happened is that the heart and blood vessels have rapidly shifted the flow of blood through the body by a homeostatic process to compensate for the change of the effects of gravity on the body. If this system had low gain, then many people would fall down before the homeostatic system could adjust blood flow. Not all physiologic systems have high gain; as long as changes in a physiologic system are not dangerous, the body is satisfied with allowing a longer period to readjust.




In the human body, many of the negative feedback loops seem to anticipate changes in physiologic systems and start corrective action before there are significant swings in physi-ologic variables. This type of negative feedback loop is known as a feed-forward loop. An example of this is provided when someone runs to catch a bus. When a person runs for a few seconds to catch a bus, they are breathing heavily, their heart is beating rapidly, and their blood pressure has increased. Many people think that this is because they are out of shape, but it is due to a feed-forward system that is anticipating that we are about to exercise and preparing the heart and lungs for extended effort. This change prevents any significant changes in blood gases when a person is beginning to exercise, because changes in blood gases can have damaging effects. A feed-forward process acts to dampen changes before they occur, whereas a negative feedback loop dampens changes after they have occurred. Scien-tists are not sure exactly how feed-forward loops are initiated, but it is thought that sensory input triggers the response.

Positive Feedback Loops

A positive feedback loop is not as common. During a positive feedback process, a sensor detects changes in a physiologic variable, which then activates an effector cell, which, in turn, causes the variable to move farther away from a set point (in a positive direction). Pos-itive feedback loops are important in stimulating processes to completion (like childbirth or ejaculation).

By its very nature, a positive feedback loop is more difficult to control and causes physi-ologic variables to change from the set point. The dilation of the cervix during the birthing process is under the control of a positive feedback loop that stops as soon as the baby is born and before there is damage to the uterus. The formation of blood clots is caused by a pos-itive feedback loop. In this case, it is more important to rapidly change blood conditions so that a clot forms in response to an injury, because it is more dangerous to bleed uncon-trollably. However, blood clots must be prevented from occurring randomly throughout the body. To prevent unwanted clots, several systems limit their formation to only areas of damage. Positive feedback loops are important in how the nervous system controls and communicates with other cells.

Positive feedback loops can also occur in certain pathophysiologic (disease) states, such as heart disease caused by coronary artery blockages (see chapter 20). The heart is fed by blood flow from the coronary arteries. If those blood vessels become blocked or if a person suffers severe blood loss after an accident, the flow of blood (and O2) to the heart drops below its desired value. Normally, a homeostatic process would cause the heart to increase blood flow to compensate, but in this case, the heart muscle cannot function properly (it does not have enough O2). This further decreases the flow of blood through the coronary artery, making the situation worse. If this positive feedback loop continued, the heart muscle would die, as would the patient. Many pathophysiologic or disease states are characterized by failure of the normal negative feedback control pathways and initiation of a positive feedback pathway. Throughout this book, we will refer to the role of homeostatic processes in the regulation of key processes.

Energy Costs

Physiologists estimate that 40% to 60% of the energy an average person expends during a normal day is used to maintain homeostatic processes. Some homeostatic processes require the expenditure of greater amounts of energy than others. One of the most energetically expensive is the system that maintains the differences in fluid components found inside and outside of cells (almost 50% of all energy consumed by cells). The maintenance of these




differences consumes so much energy that it is one of the systems used to increase body heat in the late fall and early winter. When students are first exposed to 50°F temperatures in the fall, they are cold and bundle themselves up with sweaters and jackets. The same students, when exposed to 50°F temperatures in the spring, start to wear shorts. The difference is that in the fall, the body readjusts the physiologic set point maintaining the differences in fluid components between inside and outside cells in an effort to increase the production of heat to keep the body warm. In the spring, the increased production of heat makes students feel warm even though the same outside temperature made them feel cold in the fall.

Cell-to-Cell CommunicationThe process by which the body acts to limit changes in key physiologic variables is depen-dent on cell-to-cell communication. Any coordinated activity, whether a player on a soccer team or cells within the human body, requires the exchange of communication between different components so that they act in unison for the common good. College life for many students is inconceivable without cell phones and instant messaging or texting to coordi-nate activities with friends. Multicellular organisms must have cell-to-cell communication pathways to act in a coordinated fashion. There are two main types of pathways: nervous and hormonal (see chapters 8 and 17). There is also local communication between cells. There are specific requirements for a successful cell-to-cell communication pathway.

A cell must send a message in a form that is understood only by the cell that is meant to receive it. Many students have cell phones and a text message from one phone to another requires a specific phone number. The message is sent only to the correct phone so there is no confusion. The same is true when cells communicate, a cell sends a message in different forms (chemical or electrical) over small and long distances and, only the correct cell (target cell) has the ability to receive and understand the message. Cell-to-cell communication works because it is specific and cells respond only to the correct message, sensitive so that only very low levels of the message are needed, and accurate so that the message is correctly understood.

We will continuously refer to the concept of structure dictating function, homeostasis, and cell-to-cell communication throughout this book. As you read, apply these concepts to the new material you encounter to help you understand both the physiology and anatomy of the human body.

In Review . . .1.9 How does the structure of water affect its role within the body?

1.10 Why is myoglobin used as an oxygen storage protein?

1.11 Why is Na1 the primary extracellular ion in the body?

1.12 What does homeostasis strive to maintain?

1.13 What is the role of negative feedback loops in homeostasis?

1.14 What is a feed-forward loop?

1.15 What is an example of a positive feedback loop?

1.16 What are the components of a homeostatic system?

1.17 How does cell-to-cell communication allow multicellular organisms to coordi-nate their actions?




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Y


CHAP

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YCLInICAL TERMScomputerized axial tomography Reconstruction of two-dimensional X-ray images into a three-

dimensional image.

digital subtraction angiography Comparison of two images, one with dye and one without.

dynamic spatial reconstruction Reconstruction of a two-dimensional image from X-rays obtained through rotating cameras.

magnetic resonance imaging Production of high-quality images of the inside the human body by using nuclear magnetic resonance.

mediastinum A midline through the thoracic cavity.

pathology An examination of the causes and structural and functional changes resulting from disease.

positron emission tomography Measurement of the concentrations of positron-emitting radioisotopes within the tissue of living subjects.

serous membranes Double-walled structures that line the interior of cavities.

sonograms Static images produced by ultrasound.

ultrasound Use of high-frequency sound waves to characterize internal body structures.

CHAPTER SUMMARY• Anatomy is the scientific discipline that examines the structure and organization of the human body.• Physiology is the scientific investigation of the processes that support living creatures. It can be exam-

ined at a cellular or systems level.• Pathology deals with all aspects of disease.

Terminology and the Human Body PlanTerminology

• The anatomical language used to describe the human body is based on several clear rules. Many of the anatomical descriptions are relative.

Body Position• It is important to be able to describe the relationship between body parts.

Direction• It is important to provide information about the direction in which body parts are related (above or

below).

Body Parts and Regions• The human body can be subdivided into different regions that describe some anatomical or physiologic

functional area.




CHAPTER SUMM

ARYPlanes

• The human body can be divided into different areas by flat, imaginary planes that pass through it.

Cavities• The body contains many cavities (a hollow area within a body), some of which are in contact with the

outside world and some that are not.

Serous Membranes• The interior of the trunk cavities are lined with serous membranes, a sealed structure with a fluid that

acts as a lubricant between the two membranes.

Concepts Underlying Human Anatomy and PhysiologyStructure Dictates Function

• Scientists and physicians work to predict the biological function (and normal physiologic role) of a newly characterized component by thoroughly understanding its structure.

• The structure of water predicts its biological roles and is critical for life. • The structure of a protein, such as myoglobin, also predicts its physiologic role.• It is no accident that the two most common ions in the body are Na1 and K1, since they have proper-

ties that favor life.

Homeostasis• Homeostasis is the ability or tendency of an organism or cell to maintain internal equilibrium by ad-

justing its physiologic processes.• Homeostasis requires several key components: the physiologic variable in question, an ideal value, and

the normal range over which the variable changes. • Homeostatic processes also require a cell-based sensor that can monitor the levels of the variable; a

biochemically based amplifier, which increases the ability of the sensor to detect small changes in the variable; and the ability to elicit a change in the level of the variable.

• Most of the homeostatic processes in the body are negative feedback loops because they act to limit the oscillation of a variable around its set point.

• Feed-forward processes anticipate the oscillation of the physiologic variable around the set point and activate the effector pathway before there is an oscillation.

• A positive feedback loop, by its very nature, is uncontrollable and will cause the physiologic variable to oscillate widely outside the set point.

• Physiologists estimate that 40% to 60% of the energy an average person expends during a normal day is to maintain homeostatic processes throughout the body.

Cell-to-Cell Communication• The process by which a homeostatic mechanism acts to limit the change in physiologic variables requir-

ing cell-to-cell communication.• Cell-to-cell communication is initiated by afferent cells that transduce information into a form under-

standable by the cell.• At the receiving end is the target cell, which has the ability to receive, understand, and react to the

message.




CHAPTER REvIEwKnowledge and Comprehension

1. The hand is to the shoulder. a. anterior d. posterior b. caudal e. proximal c. distal

2. A homeostatic process would act to a. help to maintain animal movement. b. remove waste products from the blood. c. help an organism efficiently consume fuel. d. help an organism maintain internal environments. e. cause the body’s internal environments to change wildly.

3. Serous membranes a. reduce friction. b. are double-walled. c. are found surrounding tissue or organs that move. d. do all of the above. e. do none of the above.

4. Which of the following technologies, currently in use for the anatomical characterization of the human body, is capable of visualizing the smallest possible structures? a. Atomic force microscopy d. MRI b. CT scan e. X-rays c. Light microscopy

5. A feed-forward process a. normally occurs in the body. b. anticipates a change in a physiologic process. c. decreases the deviation(s) of physiologic processes. d. starts corrective action before a large change in a physiologic process. e. has all of the properties listed above.

6. The regulation of body temperature is a homeostatic negative feedback process that requires a. sweating and shivering. b. changes in core body temperature. c. thermally sensitive cells in the hypothalamus. d. all of the above. e. none of the above.

7. Which of the following describes the same relationship between two body parts? a. Superior and deep b. Posterior and anterior c. Superior and anterior d. Dorsal and posterior e. Ventral and posterior

8. Which of the following describes the opposite relationship between two body parts? a. Superior and deep d. Dorsal and posterior b. Posterior and anterior e. Ventral and posterior c. Superior and anterior




9. A patient with an upset stomach usually has pain in the region of the abdomen. a. epigastric c. lumbar b. hypogastric d. umbilical

10. A plane that cuts through your body at the level of your belt would be a. a sagittal section. d. below the pelvic region b. an oblique section. e. above the thoracic cavity. c. a transverse section.

11. The peritoneal cavity does not contain the a. gallbladder. d. liver. b. heart. e. stomach. c. intestinal tract.

12. In a homeostatic reflex, which component detects a change in a physiologic variable and sends information to other cells? a. Amplifier b. Target cell c. Sensor cell

Application and Analysis1. Why would it be medically worthwhile to perfect technologies that allow us to routinely look inside cells during

their normal and abnormal functioning? What advantages are gained by being able to see smaller and smaller cellular components?

2. Human anatomy is variable. How does this affect the treatment of disease? Does this variability also affect nor-mal physiologic functions?

3. Homeostatic mechanisms that provide precise regulation of physiologic systems are more energetically expen-sive that those with less gain. Are these types of homeostatic systems worth the energetic expenditure?

4. Scientists hope to be able one day to predict the physiologic function of a protein based purely on its structure. What would be the advantage of being able to predict the function of a new component? Would this predictive ability be of any value in treating a disease?

5. Can you think of a physiologic process that is not under the control of a homeostatic reflex system? Would there be any advantage for a physiologic system not to be homeostatically controlled? What are the disadvantages of having all physiologic systems under homeostatic control?

6. Is life possible without water? Could you replace water with a different solvent? If you look for life on other planets, should you first look for the presence of water? Why?

Synthesis and EvaluationA patient enters the emergency department and reports that his hands and feet tingle as if they were asleep. This has been going on for several days. What types of visualization technologies might be useful to examine what is wrong with this patient?





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