We focus considerable attention on disease and organ dysfunction, and yet the large majority of us find our body performs very well despite all of the stress and abuse we subject it to. In later chapters, the major organ systems and the common disorder s that affect them will be described in detail. While asleep, the major organ systems are already working in conce rt, albeit at a low, basal level. The circulatory and pulmonary systems are providing the oxygen and other nutrients needed by every cell to function. Together, the complex communications networks of the endocrine and nervous systems are regulating heart rate, blood pressure, body temperature, and other involuntary or autonomic processes.
Metabolism continues at a slowed pace, involving virtually every body organ.
As dawn approaches, the body begins to wake up. Finally, we awaken, sometimes prompted by an alarm clock but often without any external stimuli. Since it has been 8 or more hours since our last meal, one of the first things we feel is hunger. The appetite center, located in the hypothalamus area of the brain, works through an intricate feedback system involving hormones, nerves, and sensory org ans to ensure that we eat enough. It's also usual to awaken to a full bladder.