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TRANSCRIPT
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Introduction to Physiology
Chapter 1
Levels of Organization
• Physiology– Study of the functioning of a living organism and its
component parts – all chemical and physical processes
• Organization of life– Atoms, molecules, cells, tissues, organs, organ systems,
and organisms– The cell is the smallest unit of structure capable of
carrying out all life processes
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Figure 1.1 Levels of organization and the related fields of study
CHEMISTRY
Atoms Cells TissuesMolecules Organs
PHYSIOLOGY
CELL BIOLOGYMOLECULAR
BIOLOGY
ECOLOGY
Organsystems Organisms
Populations ofone species
Ecosystem ofdifferent species Biosphere
Organ Systems in Review
• Integumentary• Musculoskeletal• Respiratory• Digestive• Urinary• Reproductive• Circulatory • Nervous • Endocrine• Immune
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Table 1.1 Organ Systems of the Human Body and their Integration
Function Versus Process
• Function explains the “why”– Teleological approach: adaptive significance of an event
• Process or mechanism describes the “how”– Mechanistic approach
• Red blood cell example: “Why do red blood cells transport oxygen?”– “Because cells need oxygen and red blood cells bring it
to them.” -Explains the Why?– “Oxygen binds to hemoglobin molecules contained in the
red blood cells.” -Explains the How? (most of physiology)
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Themes in Physiology
• Structure and function • Molecular interactions
– Compartmentation
• Energy/Metabolism• Information flow coordinates body function• Homeostasis = stability
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Homeostasis
• External or internal change• Loss of homeostasis
– Sensed by organism
• Physiological attempt to correct• Dynamic steady state (not the same as equilibrium)• Successful compensation=Homeostasis reestablished• Failure to compensate results in disease
(pathophysiology)
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Figure 1.3 Homeostasis
Compensation fails
Internal changeresults in loss
of homeostasis
Organism inhomeostasis
Organism attemptsto compensate
Externalchange
Internalchange
Compensation succeeds
WellnessIllness or disease
Figure 1.5 Mass balance in an open system
Input
To maintainconstant level,output mustequal input.
Output
Mass balance in an open system Mass balance in the body
Mass balance
Law of Mass Balance
Existingbody load
Excretion ormetabolicremoval
Intake ormetabolicproduction
=
Input Output
Intake throughintestine,lungs, skin
+ −
Metabolicproduction
Excretion bykidneys, liver,lungs, skinBODY
LOADMetabolismto a newsubstance
Control Systems and Homeostasis
• Regulated variables are kept within normal range by control mechanisms– Keeps near set point, or optimum value
• Control systems – local and reflex– Input signal– Integrating center– Output signal
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Figure 1.8 A comparison of local and reflex control
Brainevaluates the change and initiates a response.
Systemicchange in blood pressure sensed
here.
Brain
LOCALCHANGE
LOCALRESPONSE
Blood vessels
REFLEXRESPONSE
is initiated by cellsat a distant site.
In local control, cellsin the vicinity of thechange initiate theresponse.
In reflex control, cells at a distantsite control theresponse.
Response
Stimulus
Integrating center
KEY
Control Systems and Homeostasis
• Local control• Reflex control
– Long-distance pathway– Uses nervous and/or endocrine systems– Response loop
– Stimulus, sensor, input signal, integrating center, output signal, target, response
– Feedback loop– Negative feedback stabilizes variable (body temperature, blood
pressure, etc.)– Positive feedback reinforces stimulus (childbirth, blood clotting)– Feedforward control anticipates change (salivation reflex)
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Figure 1.9 Steps in the response loop of a reflex control pathway
RESPONSEWater temperatureincreases.
TARGET
OUTPUTSIGNAL
Signal passesthrough wire toheater.
Heater turns on.
INTEGRATINGCENTER
Control box isprogrammedto respond totemperature below29 degrees.
INPUTSIGNAL
Signal passes fromsensor to controlbox through the wire.
STIMULUSWater temperature isbelow the setpoint.
SENSORThermometersenses temperaturedecrease.
Feedbackloop
Reflex steps
Feedback loop
Thermometer
Water temperatureis 25° C
Watertemperatureincreases
Controlbox
Wire
Wire to heater Heater
Figure 1.10 Oscillation around the setpoint
Time
Response loopturns on
Setpoint of function
Normalrange offunction
Negative feedback turnsresponse loop off
Tem
pera
ture
(°C
)
28
29
30
31
32
Figure 1.11 Negative and positive feedback
Response
Initialstimulus
Stimulus
Response
Initialstimulus
Stimulus
Response loopshuts off
Negative feedback: the response counteractsthe stimulus, shutting off the response loop.
Positive feedback: the response reinforces the stimulus, sending the variable farther from the setpoint.
Feedback cycle+An outside factor isrequired to shut offfeedback cycle.
+
Figure 1.12 A positive feedback loop Baby drops
lower in uterus to initiate labor
Push baby against cervix
Cervicalstretch
causing stimulates
Uterine contractions
Oxytocinrelease
causes
Positive feedback loop
Delivery of baby stops the cycle
Laboratory
Experimental Design
• Hypothesis• Independent and dependent variables• Experimental controls• Data collection and replications• Difference between models and theories
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Interpretation of Human Experiments
• Difficult to interpret results– Genetic and environmental variability
– Crossover studies– Placebo effect and nocebo effect
– Blind, double-blind studies, and double-blind crossover studies
– Ethics of humans as test subjects
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Experimental Design Formats
• Longitudinal studies versus cross-sectional studies• Prospective versus retrospective studies• Meta-analysis
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Figure 1.14a FOCUS ON . . . Graphs (1 of 5)
The standard features of a graphinclude units and labels on theaxes, a key, and a figure legend.
(Describes the information represented by the graph)
Independent variables(units)
Legend
1 unit
x-axis
KeyGroup AGroup B
y-axis
1 unitD
ependent
vari
able
(unit
s)
Figure 1.14b FOCUS ON . . . Graphs (2 of 5)
Bar graph. Each bar shows a distinct variable. The bars are lined upside by side along one axis so that they can be easily compared withone another. Scientific bar graphs traditionally have the bars runningvertically.
Diet
Food inta
ke (
g/d
ay)
4
A
2
3
1
B C
8
6
7
5
GRAPH QUESTION
Which food did thecanaries prefer?
Canaries were fedone of the three dietsand their food intakewas monitoredfor three weeks.
Figure 1.14c FOCUS ON . . . Graphs (3 of 5)
Histogram. A histogram quantifies the distribution of one variableover a range of values.
Num
ber
of
students
4
0
2
3
1
86 7
5
GRAPH QUESTION
How many studentstook the quiz?
The distribution ofstudent scores ona 10-point quizis plotted on a histogram.
42 31 5 9 10
Quiz score
Figure 1.14d FOCUS ON . . . Graphs (4 of 5)
Line graph. The x-axis frequently represents time; the pointsrepresent average observations. The points may be connected bylines, in which case the slope of the line between two points showsthe rate at which the variable changes.
Bod
y w
eig
ht
(g)
40
0
20
30
10
6 7
60
GRAPH QUESTION
When did male mice increasetheir body weight the fastest?
Male and female mice were fed a standard dietand weighed daily.
42 31 5Day
KEY
Males
Females
50
Figure 1.14e FOCUS ON . . . Graphs (5 of 5)
Exam
sco
re (
%)
40
20
30
10
10 12
60
GRAPH QUESTION
For graphs (d) and (e),answer the following:
Student scores were directly related to the amountof time they spent studying.
62 4 8Time spent studying (hours)
Scatted plot. Each point represents one member of a test population.The individual points of a scatter plot are never connected by lines, but abest fit line may be estimated to show a trend in the date, or better yet,the line may be calculated by a mathematical equation.
50
80
70
100
90
•What was the investigator trying to determine?
•What are the independent and dependent variables?•What are the results or trends indicated by the data?
About This Chapter
• Physiology is an integrative science• Function and mechanism• Themes in physiology• Homeostasis• Control systems and homeostasis• The science of physiology
© 2013 Pearson Education, Inc.