### Homeostasis and Thermoregulation **Understanding the Control System** This diagram illustrates the biological control system responsible for maintaining homeostasis, specifically focusing on body temperature regulation. #### Components of the System 1. **Body Temperature** - This is the variable being regulated. The process starts with the current body temperature. 2. **Sensors** - These detect changes in body temperature and send this information to the integrating center. 3. **Integrating Center (Set Point)** - This is the control center which compares the detected body temperature with the set point, or the optimal body temperature. 4. **Effectors** - These are mechanisms (such as sweat glands, blood vessels, muscles) that can influence body temperature in response to signals from the integrating center. 5. **Responses** - These are the actions carried out by the effectors, such as sweating, shivering, vasodilation, or vasoconstriction, to return the body temperature to its set point. #### Flow of Information - The body temperature is sensed by sensors. - Sensors send information to the Integrating Center. - The Integrating Center processes the information, comparing it to the set point. - If the current body temperature deviates from the set point, the Integrating Center sends signals to the effectors. - Effectors act to correct the deviation by generating appropriate responses. - These responses, in turn, affect the body temperature, which is again monitored by the sensors. This feedback loop continues to ensure that the body's temperature remains within a narrow, optimal range, maintaining homeostasis. #### Diagram Explanation - The diagram has several components arranged vertically. - Arrows indicate the direction of information transfer, starting from the detection of body temperature and moving through sensors, to the Integrating Center, then to effectors, and finally to the resulting responses. - The cycle is depicted to show that responses lead back to changes in body temperature, which are once again monitored by sensors, illustrating a continuous feedback loop. **Lab 1: Homeostasis and Negative Feedback Systems** A healthy individual maintains homeostasis - a relatively constant internal environment. Homeostasis is maintained by cells, tissues, and organs that operate together as negative feedback systems. The negative feedback systems in the human body are parts of the nervous and endocrine systems. A graph of a controlled variable shows the variable fluctuating around a set point. External factors stress the system and cause the variable to increase or decrease. A normally functioning negative feedback system detects the change and causes a response that moves the variable back toward the set point. Much of medical diagnosis is based on tests that measure controlled variables. If any of these variables are outside normal range, a particular illness can be diagnosed. Inherited and environmental differences among individuals result in variations in physiological measurements. Therefore, two healthy individuals may have somewhat different body temperatures, resting heart rates, and other physiological values. Normal range of values is a range of measurements that includes most healthy people. Any value within this range is considered normal, while values outside the range may be the result of illness or injury causing a loss of homeostasis. [Keep in mind that the measurements of an individual will also vary over the course of time. These fluctuations are usually the result of external factors and negative feedback responses and are usually within the normal range of values.] ### A. Flow Diagram: Body Temperature Regulation A flow diagram is a useful way of organizing the information about a negative feedback system. The flow diagram can then be used to predict how external factors or damage to parts of the system will change the controlled variable. #### Procedure 1. Use the outline on the following page to construct a flow diagram of the body temperature regulating system. 2. Use the flow diagram to predict responses and changes in temperature. ### B. Resting Heart Rate The resting heart rate is regulated as a part of a larger and more complex negative feedback system that controls blood pressure. The sensors for this system are neurons called baroreceptors. When blood pressure increases, baroreceptors signal the cardiac center, which then sends a greater number of nerve impulses on parasympathetic nerves to slow the heart rate. When blood pressure decreases, the baroreceptors detect the change and signal the cardiac center, which then sends fewer parasympathetic impulses and may send more sympathetic nerve impulses, which increase heart rate.