Chapter 1 - An Introduction to the Human Body - Critical Thinking Questions - Page 26: 3

No. I don't agree. Homeostasis is not just about temperature; in the context of anatomy and physiology, it refers to balance and constancy of an internal environmental condition (the controlled condition)--body temperature, blood glucose, blood pressure, heart rate, blood oxygen concentration, hemoglobin etc. For example, the normal human blood pressure is usually accepted as 120mm Hg systolic over 90 mm Hg diastolic for normal healthy adults (120/80)- this varies with age, height, illness, and activity. But it is desirable to keep blood pressure within a healthy range. A person with a blood pressure of more than 140/90 is much more likely to have a heart attack than with a blood pressure of 118/70. So the body has mechanisms to monitor and adjust blood pressure to keep it within a healthy range. In other words, when blood pressure gets too high, the brain gets impulses that tell it that blood pressure has risen out of the safe zone; the brain sends back messages to the heart ( negative feedback) to keep the blood pressure ( a controlled condition) within the constant or homeostatic range. Homeostatic conditions vary, but adjustments are constantly being made by negative feedback to maintain the desired range of values of the controlled condition( body temperature, blood pressure, heart rate, respiratory rate etc.

Homeostasis, or constancy of a "controlled condition," is maintained by a physiologic arrangement that includes the controlled condition, a control center and afferent and efferent impulses to give warning of changes and to effect adjustments in the controlled condition. So if blood pressure falls below normal ranges baroreceptors in blood vessels will send impulses to the brain.The two most important set of receptors are the baroreceptors in the carotid sinus and the aortic arch. As blood pressures falls, these baroreceptors slow in their rates of firing. This change is picked up by the cardiovascular center in the medulla oblongata. Here in the control center, the ratio of sympathetic neural output is increased over the parasympathetic output which goes to effectors in heart and blood vessels; this results in constriction of blood vessels and increases in heart stroke volume, as well as in the heart rate. The end result is that the blood pressure rises back into the desired homeostatic range.This negation of the departure from the controlled condition (blood pressure) is achieved, in this case by a negative feedback mechanism.