Chapter 1 Physiology: Introduction To Physiology

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Physiology is the study of

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the normal functioning of a living organism and its component parts.

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Many complex functions are

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emergent properties that cannot be predicted from the properties of the individual component parts

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Physiologists study the many levels

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of organization in living organisms, from molecules to populations of one species.

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The cell is

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the smallest unit of structure capable of carrying out all life processes.

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Collections of cells that carry out related functions make up

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tissues and organs.

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The human body has 10 physiological organ systems:

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integumentary,musculoskeletal, respiratory, digestive, urinary, immune, circulatory, nervous,endocrine, and reproductive.

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The function of a physiological system or event is the

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“why” of the system.

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Themechanism by which events occur is the

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“how” of a system.

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The teleological approach to physiology explains

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why events happen.

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the mechanistic approach explains

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how they happen.

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Translational research applies

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the results of basic physiological research to medical problems.

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The four key themes in physiology are

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structure/function relationships, such as molecular interactions and compartmentation; biological energy use; information flow within the body; and homeostasis.

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Homeostasis is

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the maintenance of a relatively constant internal environment. Variables that are regulated to maintain homeostasis include temperature, pH, ion concentrations, oxygen, and water.

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Failure to maintain homeostasis may result in

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illness or disease.

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The body’s internal environment is the

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extracellular fluid.

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The human body as a whole is adapted to cope with

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a variable external environment.

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Most cells of the body

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can tolerate much less change.

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The law of mass balance says that

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if the amount of a substance in the body is to remain constant, any input must be offset by an equal loss.

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Input of a substance into the body comes from

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metabolism or from the outside environment.

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Output occurs through

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metabolism or excretion.

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The rate of intake, production, or output of a substance x is expressed as

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mass flow, where mass flow = concentration × volume flow.

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Clearance is the rate at which

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a material is removed from the blood by excretion, metabolism, or both. The liver, kidneys, lungs, and skin all clear substances from the blood.

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Cells and the extracellular fluid both maintain homeostasis, but they are not

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identical in composition. Their stable condition is a dynamic steady state.

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Most solutes are concentrated in either one compartment or the other, creating a state of

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disequilibrium.

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Regulated variables have a

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setpoint and a normal range.

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The simplest homeostatic control takes place at the

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tissue or cell level and is known as local control.

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Control systems have three components:

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an input signal, an integrating center,and an output signal.

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Reflex pathways can be broken down into

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response loops and feedback loops.

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A response loop begins when

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a stimulus is sensed by a sensor.

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The sensor is linked by the input signal to

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the integrating center that decides what action to take.

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The output signal travels from the integrating center to a

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target that carries out the appropriate response.

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In negative feedback, the response

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opposes or removes the original stimulus, which in turn stops the response loop.

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In positive feedback loops, the response reinforces

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the stimulus rather than decreasing or removing it. This destabilizes the system until some intervention or event outside the loop stops the response.

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Feedforward control allows

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the body to predict that a change is about to occur and start the response loop in anticipation of the change.

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Regulated variables that change in a predictable manner are

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are called biological rhythms. Those that coincide with light–dark cycles are called circadian rhythms.

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Observation and experimentation are the key elements of

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scientific inquiry.

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Ahypothesis is

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a logical guess about how an event takes place.

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In scientific experimentation, the factor manipulated by the investigator is the

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independent variable.

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In scientific experimentation, the observed factor is the

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dependent variable.

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All well-designed experiments have

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controls to ensure that observed changes are due to the experimental manipulation and not to some outside factor.

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Data, the information collected during an experiment, are

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analyzed and presented, often as a graph.

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A scientific theory is

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a hypothesis supported by data from multiple sources.

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When new evidence does not support a theory or a model, the theory or model must be

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revised.

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Animal experimentation is important because of

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the tremendous variability within human populations and because it is difficult to control human experiments. In addition, ethical questions may arise when using humans as experimental subjects.

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To control many experiments, some subjects take an inactive substance known as a

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placebo. Placebo and nocebo effects, in which changes take place even if the treatment is inactive, may affect experimental outcomes.

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In a blind study, the subjects

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do not know whether they are receiving the experimental treatment or a placebo.

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In a double-blind study, a

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third party removed from the experiment is the only one who knows which group is the experimental group and which is the control.

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In a crossover study, the

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control group in the first half of the experiment becomes the experimental group in the second half, and vice versa.

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Meta-analysis of data

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combines data from many studies to look for trends.