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 temperature Slide number: 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control center The brain detects the deviation from the set point and signals effector organs. Receptors Thermoreceptors send signals to the control center. Effectors Skin blood vessels dilate and sweat glands secrete. Stimulus Body temperature rises above normal. Response Body heat is lost to surroundings, temperature drops toward normal. too high too low Normal body Temperature 37 o C (98.6 o F) Stimulus Body temperature drops below normal. Response Body heat is conserved, temperature rises toward normal. Receptors Thermoreceptors send signals to the control center. Effectors Skin blood vessels constrict and sweat glands remain inactive. Effectors generates body heat. Control center The brain detects the deviation from the set point and signals effector organs. If body temperature continues to drop, control center signals muscles to contract involuntarily.

Homeostatic mechanism regulates body temperature Slide number: 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature rises above normal. too high Normal body Temperature 37 o C (98.6 o F)

Homeostatic mechanism regulates body temperature Slide number: 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Receptors Thermoreceptors send signals to the control center. Stimulus Body temperature rises above normal. too high Normal body Temperature 37 o C (98.6 o F)

Homeostatic mechanism regulates body temperature Slide number: 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control center The brain detects the deviation from the set point and signals effector organs. Receptors Thermoreceptors send signals to the control center. Stimulus Body temperature rises above normal. too high Normal body Temperature 37 o C (98.6 o F)

Homeostatic mechanism regulates body temperature Slide number: 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control center The brain detects the deviation from the set point and signals effector organs. Receptors Thermoreceptors send signals to the control center. Effectors Skin blood vessels dilate and sweat glands secrete. Stimulus Body temperature rises above normal. too high Normal body Temperature 37 o C (98.6 o F)

Homeostatic mechanism regulates body temperature Slide number: 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control center The brain detects the deviation from the set point and signals effector organs. Receptors Thermoreceptors send signals to the control center. Effectors Skin blood vessels dilate and sweat glands secrete. Stimulus Body temperature rises above normal. Response Body heat is lost to surroundings, temperature drops toward normal. too high Normal body Temperature 37 o C (98.6 o F)

too low Normal body Temperature 37 o C (98.6 o F) Homeostatic mechanism regulates body temperature Slide number: 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature drops below normal.

Receptors Thermoreceptors send signals to the control center. too low Normal body Temperature 37 o C (98.6 o F) Homeostatic mechanism regulates body temperature Slide number: 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature drops below normal.

Receptors Thermoreceptors send signals to the control center. too low Normal body Temperature 37 o C (98.6 o F) Homeostatic mechanism regulates body temperature Slide number: 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature drops below normal. Control center The brain detects the deviation from the set point and signals effector organs.

Receptors Thermoreceptors send signals to the control center. too low Normal body Temperature 37 o C (98.6 o F) Homeostatic mechanism regulates body temperature Slide number: 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature drops below normal. Control center The brain detects the deviation from the set point and signals effector organs. If body temperature continues to drop, control center signals muscles to contract involuntarily.

Effectors Skin blood vessels constrict and sweat glands remain inactive. Receptors Thermoreceptors send signals to the control center. too low Normal body Temperature 37 o C (98.6 o F) Homeostatic mechanism regulates body temperature Slide number: 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature drops below normal. Effectors Muscle activity generates body heat. Control center The brain detects the deviation from the set point and signals effector organs. If body temperature continues to drop, control center signals muscles to contract involuntarily.

Effectors Skin blood vessels constrict and sweat glands remain inactive. Receptors Thermoreceptors send signals to the control center. too low Normal body Temperature 37 o C (98.6 o F) Homeostatic mechanism regulates body temperature Slide number: 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stimulus Body temperature drops below normal. Response Body heat is conserved, temperature rises toward normal. Effectors Muscle activity generates body heat. Control center The brain detects the deviation from the set point and signals effector organs. If body temperature continues to drop, control center signals muscles to contract involuntarily.

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