Introduction to the human body Salivary gl. (smooth muscle tissue) Serosa Liver Small intestine Large intestine The human being Anus ers or sn level muscle tissue Organ level Figure 1.1 The levels of structural complexity. Homeostasis Homeostasis is maintained by control systems which detect and respond to changes in the internal environ- The composition of the internal environment is main- ment. A control system(Fig. 1. 3)has three basic compo tained within narrow limits, and this fairly constant state nents: detector, control centre and effector. The control is called homeostasis. Literally, this term means'unchang- centre determines the limits within which the variable g, but in practice it describes a dynamic, ever-changing factor should be maintained. It receives an input from the situation kept within narrow limits. When this balance is detector or sensor and integrates the incoming informa- threatened or lost, there is a serious risk to the well-being tion. When the incoming signal indicates that an adjust- of the individual. There are many factors in the intern ment is needed the control centre responds and its output environment which must be maintained within narrow to the effector is changed. This is a dynamic process that limits and some of these are maintains homeostasIntroduction to the human body 5_ Figure 1.1 The levels of structural complexity. Homeostasis The composition of the internal environment is main￾tained within narrow limits, and this fairly constant state is called homeostasis. Literally, this term means 'unchang￾ing', but in practice it describes a dynamic, ever-changing situation kept within narrow limits. When this balance is threatened or lost, there is a serious risk to the well-being of the individual. There are many factors in the internal environment which must be maintained within narrow limits and some of these are listed in Box 1.1. Homeostasis is maintained by control systems which detect and respond to changes in the internal environ￾ment. A control system (Fig. 1.3) has three basic compo￾nents: detector, control centre and effector. The control centre determines the limits within which the variable factor should be maintained. It receives an input from the detector or sensor, and integrates the incoming informa￾tion. When the incoming signal indicates that an adjust￾ment is needed the control centre responds and its output to the effector is changed. This is a dynamic process that maintains homeostasis