As you can imagine, cigarette smoke contains many impurities that are inhaled in great numbers directly into the lung. For this reason, the alveolar spaces of the smoker contain numerous scavenger cells (macrophages) that are filled with engulfed (phagocytized) particles of impurities and debris, as illustrated in Picture of scavenger cells in a smoker's alveolus Under the microscope, with this high magnification, you can actually see the black and brown engulfed particles in the alveolar scavenger cells. Indeed, smoker's lung may have so much of this particulate material that the lung looks gray-black to the naked eye. Most of the time, you don't need a microscope to tell if someone is or was a heavy smoker. A naked eye examination of a smoker's lung will usually reveal an enlarged gray-black lung with enlarged air spaces (the emphysema, as you saw in Figure 4 and will see again in Figure 8).
Exercise is extremely important to staying healthy both in body and mind. Being active can help a person continue to do things they enjoy and be independent as they age. Long term physical activity increases the benefits of long-term health. This is the reason many health experts advise individuals to be as active as possible and to set aside at least three days a week for some form of activity that keeps the heart beating at a steady pace. Physical exercise also has many mental benefits. For example, a person diagnosed with depression or anxiety is most often asked to conduct some form of physical activity apart from taking medication. This is because, the body produces hormones known as endorphins which improve mood and relieve stress. Depression can be alleviated by improving mood and anxiety can be relieved by reducing stress.