Quantitative Human Physiology. An Introduction

923 Pages·2012·77.989 MB·960\923

by  Joseph J. Feher (Auth.)

QUANTITATIVE HUMAN
PHYSIOLOGY
QUANTITATIVE
HUMAN PHYSIOLOGY
AN INTRODUCTION
Joseph Feher
Department of Physiology and Biophysics
Virginia Commonwealth University School of Medicine
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Preface
THIS TEXT IS A PHYSIOLOGY TEXT
able to articulate these relationships with words, but this
FIRST, AND A QUANTITATIVE text demands more. Mathematical statements—equa-
TEXT SECOND tions—are simply logical sentences. You can read an
equation in words. But the mathematical statement uses
First and foremost, this text is a physiology text, aneconomyofwords,andextrawordseithermakeitfalse
designed for students who have never been exposed to oraddnonewinformation,likeaddingzerotobothsides
it and who know neither the language nor the concepts ofanequation.Mathematicsalsohasspecificrulesforthe
of the subject. The text contains all elements of physiol- manipulationofthelogicalpartsofthesentences,sothat
ogy in nine units: physical and chemical foundations; rearrangementor combination of equations leads tonew
cell physiology; excitable tissue physiology; neurophysi- insight. This text uses lots of mathematics at the level of
ology; cardiovascular physiology; respiratory physiol- calculusandelementarydifferentialequations.Itispossi-
ogy; renal physiology; gastrointestinal physiology; and bletounderstandthetextbyusingonlythefinalresulting
endocrinology. The course was designed for a survey equations that describe physiologically relevant phenom-
course in quantitative physiology to undergraduate stu- ena,butstudentswanttoknowwherethingscomefrom,
dents majoring in Biomedical Engineering at Virginia notjustacceptthemfromsomehigherauthority.Thetext
Commonwealth University in a two-semester sequence, aims to convince them that these equations are right and
roughly inthe orderin the text. applicable. Once convinced, application of the equations
follows.
Secondly, this text aimstobe quantitative.Human physi-
ology is all about everything that happens in the body The text does not say what I tell my students about the
duringitsnormaloperationthatmakesthatoperationsta- applicability of equations in general. I tell my students
ble, smooth, and coordinated. Those things that happen in lecture that all of these equations are wrong. They are
haveflowsandforcesassociatedwiththem.Insomecases wrong in something of the same sense that Newtonian
the flows are rates of secretion or absorption, or move- mechanics is wrong. Relativity and quantum mechanics
mentofdissolvedsolutes,fluid,orionsfromoneplaceto supplant Newtonian mechanics (even in the macro-
another. How fast these movements occur is crucial, and scopic world), but Newtonian mechanics will still get
theirfunctioncannotbeunderstoodfullywithoutaquan- the rocket ship to the moon. So I tell them that these
titative approach. For some aspects of physiology, there equations are theoretically wrong but they give satis-
currently is not enough information to make a detailed factorily correct answers, in much the same way that
quantitative analysis; or an in-depth analysis is beyond Newtonian mechanics still does, even though theoreti-
the scope of this text. In these cases, this text is not very cally incomplete. Fick’s Law of Diffusion depends on
different from more traditional texts. Where possible, the continuum mathematics for an inherently discrete pro-
texttakesananalyticalandquantitativeapproach. cess. But the discreteness is so finely divided that the
distinction is unimportant.
THE TEXT USES MATHEMATICS
EXTENSIVELY NOT ALL THINGS WORTH KNOWING
ARE WORTH KNOWING WELL
Carl Frederick Gauss famously said, “Mathematics is the
queen of sciences.” The quantitative approach in this text Derivations themselves often bore and lose students. In
is not just about assigning values to the controlled para- manycases,thederivationsinthistextareplacedinsepa-
meters, or rate constants to reactions or values of forces rate appendices, at the end of the chapter instead of the
andflowsthatnormallyoccur;itisaboutdiscoveringthe end of the book. Students are encouraged to look at
relationshipsbetweentheforcesandflowsandthereason these, but in my view the derivations are not the point.
controlled parameters are what they are. These relation- Important derivations are in the text, but not all things
ships cannot be fully understood withwords alone. They worth knowing are worth knowing well, and some are
ix
require the language of mathematics. Students should be placed in the appendices. The point is the final equation
x PREFACE
and its application to real-world problems. The deriva- together they cover the breadth of physiology. The
tions develop understanding of how these equations chapter summaries review the most important concepts
came to be, and what assumptions were made in their in one page or less. These devices aid in understanding
construction, and what the variables in the equation by repetition in different words. Instructors, of course,
mean. These are useful in understanding the limits of are free to add or subtract from the list of learning
applicabilityofthefinalresults. objectives.
CLINICAL APPLICATIONS PIQUE
EXAMPLES AND PROBLEM SETS AID IN
INTEREST
QUANTITATIVE UNDERSTANDING
Pathological situations often illuminate normal phy-
There are several aids in the text to foster a quantitative
siology. Clinical Applications are scattered throughout
and analytical understanding. First, there are some
the text. Because it takes a lot of background material
worked calculations in the text that are set apart in text
to understand these clinical applications, Clinical
boxes as Examples. These aim to show the students how
Applications are less prevalent in the early parts of the
to apply some of the ideas presented in the text. Second,
text, which are foundational, than in the latter parts of
there are a total of 17 problem sets scattered throughout
the text. There are 50 such Clinical Applications. The
the text. All units have at least one, most have two, and
students like them because these Clinical Applications
the cardiovascular section has three. These are meant to
tell them that there is a reason for learning what might
cover about three chapters each, so that a problems set
otherwiseappear arcane.
can beassignedapproximatelyonce a week, for threelec-
tures per week. Students have told me that they want a HOW INSTRUCTORS CAN USE
solution set to the problems to see how they can do
THIS TEXT
them, but this makes them useless as a graded assign-
ment. There is something to be said for wrestling with
This text is meant for anyone with a fairly modest level
problems and thereby learning how to tackle a difficult
of mathematical skill, at the level of the calculus with
problem.
elementary differential equations. Students without this
The problems themselves are generally meant to cover level of training will find this book too difficult. I have
some new idea or concept that could not be, or was not, developed this book specifically with undergraduate
effectively covered in the text itself, and to expand on the Biomedical Engineering students in mind and have
student’s understanding of the material. They are not taught this material for 12 years. It is most useful in a
merely busy work or “plug and chug” exercises. The alert two-semester sequence, and I cover all chapters and all
student should not merely do the problem, but think problem sets in that time. The text would also be useful
about what theresult means. Inmanycasesthe problems for instructors with less time. UNIT 1, for example, cov-
are written as a sequence of questions, each of which sets ers physical and chemical foundations of physiology
up the student for further questions or insights. These that some instructors assume their students already
illustratetheprocessnecessaryforansweringalargerques- know well enough and will not cover. Some of my stu-
tion, breaking it up into parts of the answer that must dents take University Physics of Organic Chemistry con-
come first. This method aids the students in thinking currently, and they find this review helpful. It was not
aboutlargerproblems:breakitdownintoitssimplercom- originally constructed this way: student feedback caused
ponents.Somesubjectmatterunfortunatelydoesnotlend me to rework the sequence.
itselfeasilytosuchproblems,butIhaveattemptedtofind
Each chapter is intended to be a single lecture, and the
problemsthatstudentscando.Thestudentsinmyclasses
length of the chapter is meant to be readable in a sin-
find the problems challenging. I allow them to work on
gle sitting. There are 77 chapters, so this would be
them collaboratively because they are meant to be part of
impossible to cover in a single semester. However,
theinstructionandlessoftheevaluation,buttheproblem
the depth and breadth of coverage are variables that
sets are graded and contribute significantly to the final
can be adjusted. Chapter summaries give the broad
grades.Suchpoliciesare,ofcourse,setatthediscretionof
picture of what is happening with fewer of the details.
theinstructor.
It is entirely possible to cover the breadth of physiol-
ogy if the depth is reduced. This can be done by focus-
LEARNING OBJECTIVES, SUMMARIES,
ing on the chapter summaries and combining lectures,
AND REVIEW QUESTIONS GUIDE and possibly omitting some topics. In this regard, the
STUDENT LEARNING text is useful similarly to a cafeteria: the instructor is
free to choose those sections of most interest, and to
The Learning Objectives are meant as a guide to the downplay those of lesser interest. Some instructors
construction of examination questions, either directly or may feel that knowing how to think about problems is
indirectly. These learning objectives are fairly broad and the most important thing, and that the details of the
PREFACE xi
physiology are secondary. Such an instructor may want this question? How can you find out what is needed? If
to focus more on the appendices than on the chapter it is a physical constant, where can you find it? Do you
matter themselves, and more on the problems and know a relationship or equation that relates what is
how to solve them. being asked to what is given? Write it down and rear-
range it to give the desired answer. Plug and chug what
ANCILLARY MATERIALS FOR
is given and what else you have looked up to get a
INSTRUCTORS
numerical answer. It is very simple in principle but
sometimes verydifficult inexecution.
For instructors adopting this text for use in a course the
following ancillaries are available: PowerPoint lecture ANCILLARY MATERIALS FOR
slides, electronic images from the text, solutions manual STUDENTS
for the problem sets, and additional test questions. Please
visit http://booksite.academicpress.com/9780123821638 Student resources available with this text include a set
andclickonthe‘instructor’tabtoregisterforaccess. of online flashcards, a selection of animations based on
figuresinthetext,andonlinequizzesforself-study.Please
HOW STUDENTS CAN USE THIS TEXT
visit http://booksite.academicpress.com/9780123821638
andclickonthe‘student’tabforaccess.
A student’s goal ought to be to learn as much phys-
iology as possible within the constraints of available STUDENT FEEDBACK
time. This text is written with considerable detail. The
Learning Objectives and Review Questions set the stage Students who have completed the course regularly tell
for the kinds of things you should be able to do, and methatitisbothoneofthemostchallengingandoneof
the kinds of questions you should be able to answer. the most rewarding courses of their undergraduate
The chapter summaries encapsulate each chapter in an career. This is generally the case: what you get out of an
economy of words and detail. Start with the Learning educational enterprise is proportionate to what you put
Objectives, read the Summary, and then look at the in.Physiologyisanintegrativescience.Thereisgreatsat-
Review Questions. Then read the chapter and repeat isfaction inunderstanding how asystem worksfromthe
Learning Objectives, Summary, and Review Questions. cellularandsubcellularlevelallthewayuptotheorgan-
What you cannot answer at that point requires you to ism level. Human beings do not come with an owner’s
rereadthe pertinent sectionsasecondtime. manual.Theideathatthistextisafirstapproximationto
anowner’smanualresonateswiththestudents.
The approach to the problem sets is different. The first
job is: find a bright fellow student to work with. Joseph Feher
Second, read the question for understanding of what it
is asking. Then ask yourself, what is needed to answer
Acknowledgments
I would like to thank all the reviewers of the proposal Acquisition Editor; Fiona Geraghty, Editorial Project
and drafts of this project. Their feedback was very help- Manager; Eric DeCicco, Designer; and especially Renata
ful in improving the final version: Corbani,SeniorProjectManager.
VadimBackman NorthwesternUniversity Muchmoreindirectly,Iwishtothankalonglineofscien-
TrevorCardinal CaliforniaPolytechnicStateUniversity, tific mentors who instilled in me the academic integrity
SanLuisObispo
and the desire to be thorough and correct. Included in
LianneCartee NorthCarolinaStateUniversity
RonaldCechner CaseWesternReserveUniversity thislistareLemuelWright,andDonaldB.McCormick,of
JingjiaoGuan FAMU-FSU CornellUniversity,whoadvisedmeonmymaster’sthesis;
JohnK.Li RutgersUniversity
Robert Hall of Upstate Medical Center, with whom I
DonaldMcEachron DrexelUniversity
TomMilner UniversityofTexasatAustin worked for a short but meaningful time and who pro-
HorstvonRecum CaseWesternReserveUniversity videdtheepiphanyformypursuit ofanacademic career;
ScottSeidman UniversityofRochester
Robert Wasserman, of Cornell University, who first
GeorgeShoane RutgersUniversity
BradSutton UniversityofIllinoisatUrbana-Champaign inspired me to apply mathematics to transport processes;
Norm Briggs, of VCU School of Medicine, who first
I would also like toacknowledge the help and support of
thoughtIwouldbeagoodbetforatenuretrackposition;
my colleagues at the VCU School of Medicine, especially
DonMikulecky,whointroducedmetomanyideasofthe-
Clive Baumgarten and Ray Witorsch, for their criticism of
oretical biology; and Margaret Biber, who first presented
early drafts, and Margaret Biber, who expressed the confi-
mewiththedauntingtaskofdevelopingayear-longphys-
dence in publishing this text that kept me going. I would
iology sequence for BME students, with laboratories, that
like tothank George Ford, VCU School ofMedicine, who
formedthetext.
helpeddeveloptheearlyoutlinesofthecardiovascularsec-
tion;ScottWalsh,whoprovidedthebasisforsomeofthe Although I desire to be thorough and correct, often I
endocrine chapters; and Andy Anderson, who helped cri- am mistaken. I acknowledge the help of all those listed
tique multiple teaching efforts of mine. I especially above, but reserve to myself the blame for any errors in
acknowledgethefeedbackfrommanyyearsofsophomore the text. If the reader finds any errors of fact or analysis,
andjuniorBMEstudentswhopointedouterrorsanddiffi- I would appreciate them letting me know so that I can
culties in the material and suggested improvements to evaluate and correct it.
help their learning experience, which is really what this
Lastly, I express my deep appreciation for my wife, Lee,
text is all about. Special thanks go to students Woon
who put up with innumerable late nights and weekends
Chow, Yasha Mohajer, Matthew Caldwell, Matthew
with a husband glued to the chair in front of the com-
Painter, Mary Beth Bird, Richard Boe, Linda Scheider,
puter screen. Her support and encouragement made the
William Eggleston, Alex Sherwood, Ross Pollansch, Kate
workpossible.Duringthewritingofthemanuscript,the
Proffitt, and Roshan George. Teaching these students and
author’sfamilysufferedthelossofKarenEsterlineFeher,
many more like them, and getting to know them, has
who died in a tragic climbing accident in the New River
beentremendouslyrewarding.
Gorge of West Virginia. She left behind a husband and
I would like to thank the publishing team at Elsevier twoyoungchildren.Thetextisdedicatedtothememory
including Joe Hayton, Publisher; Steve Merken, Associate ofKarenandtothefutureofherbeautifulchildren.
xiii
1.1
The Core Principles of Physiology
REDUCTIONISM EXPLAINS SOMETHING
ON THE BASIS OF ITS PARTS
Learning Objectives
The process of explaining something on the basis of its
(cid:1) Definethedisciplineofphysiology parts is called reductionism. Thus, the behavior of the
(cid:1) Describeingeneraltermshoweachorgansystemcontri- bodycan beexplained bythe coordinated behaviorofits
butestohomeostasis component organ systems. In turn, each organ system
(cid:1) Definereductionismandcompareittoholism can be explained in terms of the behavior of the compo-
(cid:1) Describewhatismeantbyemergentproperties nent organs. In this reduction recursion, the behavior of
the component organs can be explained by their compo-
(cid:1) Definehomeostasis
nents, the individual cells that make up the organ. These
(cid:1) ListthefourAristoteliancausesanddefineteleology
cells, in turn, can be explained by the behavior of their
(cid:1) Definemechanism
component subcellular organelles; the subcellular orga-
(cid:1) Describehowevolutionisacauseofhumanformand
nelles can be explained by the macrochemicals and
function
biochemicalsthatmakeuptheseorganelles;thebiochem-
(cid:1) Writeequationsfortheconservationofmassandenergy icals can be explained by their component atoms; the
forthebody atoms can be explained by their component subatomic
(cid:1) Giveanexampleofsignalingattheorganorcellularlevel particles;thesubatomicparticlescanbeexplainedbyfun-
oforganization damental particles. According to this reductionist recur-
(cid:1) Listthecoreprinciplesofphysiology sion,wemightanticipatethatthefinalexplanationofour
own bodies lies in the physics of the fundamental parti-
cles.Beyondbeing impractical, there isa growing realiza-
tionthatitistheoreticallyimpossibletodescribecomplex
and complicated living beings solely on this basis offun-
HUMAN PHYSIOLOGY IS THE
damental physics, because at each step in the process
INTEGRATED STUDY OF THE NORMAL someinformationislost.
FUNCTION OF THE HUMAN BODY
PHYSIOLOGICAL SYSTEMS ARE PART OF
ORGAN SYSTEMS WORK TOGETHER TO
A HIERARCHY OF LEVELS OF ORGANIZATION
PRODUCE OVERALL BODY BEHAVIOR
The recursion of explanation described above for reduc-
The human body consists of parts. We consider an
tionism involves various levels of complexity in a hier-
assortment of parts that usually relate to each other in
archical description of living beings, as shown in
defined ways to be a system. In physiology a system is
Figure 1.1.1 Understanding any particular level entails
usually considered to be a group of organs that serve
relatingthatleveltotheoneimmediatelyaboveitandthe
some well-defined function of the body. The parts of
oneimmediatelybelowit.Forexample,scientistsstudying
these systems can be described separately, but they work
aparticularsubcellularorganellecanbesaidtohavemas-
together to produce the overall system behavior. That is,
tered it when they can explain how the function of the
the individual behavior of the parts is integrated to
organellederivesfromtheactivitiesofitsparts,themole-
produce overall behavior. The various organ systems
culesthatmakeitup,andhowtheorganelle’sfunctionis
and their functions in the body are summarized in
regulatedbyandcontributestothefunctionofthecell.
Table 1.1.1.
Each of these organ systems is essential to the survival REDUCTIONISM IS AN EXPERIMENTAL
of the organism, the living human being. It is possible PROCEDURE; RECONSTITUTION IS A
to survive with a single compromised system—such as
THEORETICAL PROCEDURE
persons with failed kidneys or failed immunological
systems—but these persons could not survive in natural The processes used in going “down” or “up” in this
ecosystems. hierarchy are not the same. We use reductionism to
3
©2012ElsevierInc.Allrightsreserved.
4 QUANTITATIVE HUMAN PHYSIOLOGY
Knowing the behavior of the individual parts and pay-
TABLE1.1.1 OrganSystemsoftheBody ing close attention to how these parts are connected, it
is possible to predict system behavior from the parts’
OrganSystem Function behavior using simulation or other techniques. Because
it is impossible, except in rare and limited cases, to reas-
Nervoussystem/endocrine Sensoryinputandintegration;
semble broken systems (we cannot unscramble the
system commandandcontrol
egg!), we must test our ideas of subcellular function
Musculoskeletalsystem Supportandmovement
theoretically.
Cardiovascularsystem Transportationbetweentissues
andenvironmentalinterfaces HOLISM PROPOSES THAT THE BEHAVIOR OF
THE PARTS IS ALTERED BY THEIR CONTEXT IN
Gastrointestinalsystem Digestionoffoodandabsorption
ofnutrients THE WHOLE
Respiratorysystem Regulationofbloodgasesand Holism conveys the idea that the parts of an organism
exchangeofgaswiththeair
are interconnected and that each part affects others. The
Renalsystem Regulationofvolumeand parts cannot be studied in isolation because important
compositionofbodyfluids aspects of their behavior depend solely on their interac-
Integumentarysystem(skin) Protectionfrommicrobial tion with other parts. Reductionism seems to imply that
invasionandwatervaporbarrier the whole is the sum of the parts, whereas holism sug-
gests that the whole is greater than the sum of the parts.
Reproductivesystem Passlifeontothenext
generation Emergent properties of systems arise from complex
interactions among the parts. Examples of emergent
Immunesystem Removalofmicrobesandother
properties include self-replication. The ability of cells
foreignmaterials
to form daughter cells is a system property that does
not belong to any one part, but belongs to the entire
system. Consciousness is also an emergent property that
Level Discipline arises from neuronal function, but at a much higher
level of organization.
Universe Cosmology
PHYSIOLOGICAL SYSTEMS OPERATE AT
Society Sociology MULTIPLE LEVELS OF ORGANIZATION
SIMULTANEOUSLY
Body
Explanation Function
It should be clear from Figure 1.1.1 that all the levels
Physiological systems Physiology
of organization simultaneously operate in the living
Organs human being. Processes occur at the molecular, subcel-
lular, cellular, organ and system level simultaneously
Cells and cell products Cell physiology
and dynamically.
Subcellular organelles
Biochemistry CELLS ARE THE ORGANIZATIONAL
Molecules
UNIT OF LIFE
Chemistry
Atoms
THE CELL THEORY IS A UNIFYING PRINCIPLE
Subatomic particles High-energy physics OF BIOLOGY
The cell theory states that all biological organisms are
FIGURE 1.1.1 Hierarchical description of physical reality as applied to
physiologicalsystems.Weattemptto“explain”somethingintermsofits composed of cells; cells are the unit of life and all life
component partsand describea function fora part in terms of its role comes from preexisting life. The cell theory is so estab-
inthe“higher”organizationalentity. lished today that it forms one of the unifying principles
ofbiology.
explain the function of the whole in terms of its parts,
The word cell was first used by Robert Hooke
by going “down” in the levels of organization. We
(1635(cid:1)1703) when he looked at cork with a simple
describe the function of the parts at one level by show-
microscope and found what appeared to be blocks of
ing how they contribute to the behavior of the larger
materialmakingupthe cork. The termtodaydescribesa
level of organization, going “up” in Figure 1.1.1. These
microscopic unit of life that separates itself from its sur-
processes are fundamentally different. Reductionism
roundingsby athin partition, the cell membrane.
involves actually breaking the system into its parts and
studying the parts’ behavior in isolation under con- Thestatement“alllifecomesfrompreexistinglife”means
trolled conditions. For example, we can take a sample thatthereisnospontaneousgenerationoflifefrominan-
of tissue and disrupt its cells so that the cell membranes imatematerials.Mostbiologistsbelievethatlifedidarise
are ruptured. We can then isolate various subcellular spontaneously, but over a very long period of time. This
organelles and study their behavior. This procedure statement was made by Virchow (1821(cid:1)1902) when
characterizes the behavior of the subcellular organelle. he wrote “omnis cellula e cellula”—all cells come from
The Core Principles of Physiology 5
othercells.Lifedoesnotspontaneouslygenerateoverour cells derives from their expression of different parts
lifetimes. of the genome. Here expression means using DNA to
produceproteins.
CELLS WITHIN THE BODY SHOW A MULTITUDE
OF FORMS THE CONCEPT OF HOMEOSTASIS IS A
CENTRAL THEME OF PHYSIOLOGY
Large, multicellular organisms such as ourselves consist
of a vast number of different cells that share some fea- EXTRACELLULAR FLUID SURROUNDS ALL
tures but vary in size, structure, biochemical makeup, SOMATIC CELLS
and functions. A sampling of the spectrum of cells that
make up the body is illustrated in Figure 1.1.2. Almost As described above, each cell in our body is surrounded
all cells in the body have a cell membrane, also called by a cell membrane that defines the limits of the cell
the plasma membrane, and most contain a nucleus. and separates the interior of the cell from its exterior.
The simplest cell in the human is probably the erythro- The interior consists of a number of subcellular orga-
cyte, which is the only cell in the body that lacks a nelles suspended in a fluid, the intracellular fluid. The
nucleus. exterior consists of an extracellular matrix that holds
things in place and an extracellular fluid. Nearly all
THE DIVERSITY OF CELLS IN THE BODY cells of the body come in intimate contact with the
DERIVES FROM DIFFERENTIAL EXPRESSION extracellular fluid. The last step in delivery of nutrients
OF THE GENOME and the first step in removal of wastes is achieved
through the extracellular fluid (Figure 1.1.3). The extra-
The outward appearance and behavior of an organism cellular fluid was called the milieu interieur, or the inter-
define its phenotype, which is related to but not iden- nal environment, by the great French physiologist,
tical to the organism’s genetic material, its genotype. Claude Bernard (1813(cid:1)1878). Survival of the cells
The genotype consists of the set of alternate forms of depends on the maintenance of a constant internal
genes, called alleles, that the organism has, and these environment. The maintenance of a constant internal
alternate forms of genes are further defined by the environment is called homeostasis, which is literally
sequence of nucleotides in their DNA. DNA is the translated as same standing.
geneticmaterialbecauseitispassedonthroughthegen-
erations, it determines the kind of proteins that cells THE BODY CONSISTS OF CAUSAL
can produce, and these materials make up the pheno- MECHANISMS THAT OBEY THE LAWS
type. The genome is the entirety of the hereditary infor-
mation, including all of the genes and regions of the OF PHYSICS AND CHEMISTRY
DNA that are not involved in producing proteins. ARISTOTLE (384(cid:1)322 ) POSITED FOUR
BC
Nearly all cells in the body contain the entire genome.
DIFFERENT KINDS OF CAUSALITY
The exceptions include the erythrocytes and the repro-
ductive cells. Those cells that are not reproductive cells 1. Material cause
are called somatic cells (from the Greek soma, meaning A house is a house because of the boards, nails,
body). Thus, the great majority of body cells are somatic shingles, and so on that make it up. We are what
cells, and they all contain the same amount and kind of we are because of the cells and the cell products
DNA. The astounding diversity of the types of human that make us up.
FIGURE 1.1.2 Examples of the
differentcellsthatpopulatethehuman
body.Motorneuronssuchastheone
Erythrocyte Leukocyte Eosinophil
illustrated are found in the ventral
Inner hair cell horn of the spinal cord. The inner
hair cells are found in the cochlea
and form part of our response to
sound. Erythrocytes, leukocytes, and
eosinophilsareallfoundintheblood.
Cellstypicallyarenotcolored,butmay
beseenincolorbytheiradsorptionof
histological stains. Hepatocytes in the
liverhelppackagenutrients,formbile,
and detoxify foreign chemicals. The
enterocyteslinethesmallintestineand
absorb nutrients from the food into
Hepatocyte Enterocyte Parietal cell the blood. The parietal cells secrete
HCl in the stomach. This is a small
Motor neuron
samplingofthediversityofcellforms
Cardiomyocyte inthehumanbody.