Chapter 1 -_the_study_of_body_function - αντιγραφή

Chapter 1 - The Study of Body Function

• Physiology – Study of biological function.– Our emphasis is on cellular mechanisms, i.e.

how the structure accomplishes its tasks.

• [read about the development of pharma-ceutical drugs]..

Homeostasis• All the regulatory mechanisms of the

body work in concert to maintain a constant internal environment despite changes in the external environment.

• Our focus will be how body organs contribute to homeostasis.• We define and “gauge sickness” in terms of deviations from the norm. If your internal environment can not be maintained at the constant level, you are sick..

• Homeostasis is most commonly regulated by Negative feedback.

• Negative feedback occurs when sensors are activated by changes in the internal environment, i.e. deviations from the set point.

• The sensors activate effectors (smooth muscle, cardiac muscle, or glands), which increase or decrease their activities.

• The altered functions of the effectors produce a change in the opposite direction from the sensor until the set point is again reached..

Negative Feedback

Homeostatic mechanism regulates body temperatureSlide number: 1

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Control centerThe brain detects thedeviation from the setpoint and signals effectororgans.

ReceptorsThermoreceptors sendsignals to the control center.

EffectorsSkin blood vessels dilateand sweat glands secrete.

StimulusBody temperature rises above normal.

ResponseBody heat is lost to surroundings,temperature drops toward normal.

too high

too low

Normal bodyTemperature37oC (98.6oF)

StimulusBody temperature drops below normal.

ResponseBody heat is conserved,temperature rises toward normal.


EffectorsSkin blood vessels constrict andsweat glands remain inactive.

Effectorsgenerates body heat.

Control centerThe brain detects thedeviation from the set pointand signals effector organs. If body temperature

continues to drop, controlcenter signals muscles tocontract involuntarily.




too high








ResponseBody heat is lost to surroundings,temperature drops toward normal.

too high


too low






too low





Control centerThe brain detects thedeviation from the set pointand signals effector organs.


too low









too low





EffectorsMuscle activitygenerates body heat.





too low





ResponseBody heat is conserved,temperature rises toward normal.

EffectorsMuscle activitygenerates body heat.



• Positive feedback also occurs, although less commonly.

• Positive feedback occurs when the action of the effector amplifies those changes that stimulated the sensors..

• Homeostasis is regulated by two general categories of regulatory mechanisms:– Intrinsic: “built-in” to organs under

regulation.• e.g. the presence or absence of gap

junctions in heart muscle regulates the speed of each cardiac cycle.

– Extrinsic: outside the organ.• e.g. regulation by the nervous and/or

endocrine systems..

Review Primary Tissues

Chapter 1 -_the_study_of_body_function - αντιγραφή

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