Tips. 1  If you want to focus on a particular muscle area, you can do so by changing the stride length. 2  For an elliptical with multiple users, use one whose stride length is adjustable to accommodate different heights. 3  Do not rely solely on guidelines.
3. Intercellular chemical signals secreted into the circulatory system; carried to organs they control, where they bind to receptors and produce a response. 4. Intercellular chemical signals, secreted by nerve cells; important in the function of the nervous system.
Most chemical digestion takes place in the duodenum by chemicals secreted by the liver, pancreas and small intestine. The other two sections of the small intestine, the jejunum and the ileum, absorb food molecules by way of the villi directly into the blood stream.