Bones provide a storehouse for minerals that can be withdrawn for emergencies.
Physical activity stimulates the bones to maintain their strength. Attached to the bones are ligaments that hold bones together and tendons which connect bones to 620 muscles. In addition to moving the body, they produce heat, squeeze blood into isolated tissues, maintain posture, and, when exercised, increase endorphin hormones which results in a feeling of well-being. Muscle tissue also surrounds arteries so that blood pressure can be increased where tissue nutrients are most needed. The skin is the largest organ of the body and the most exposed.