Hormones are chemical signals produced by glands that are transported to target organs to induce responses. They bind to receptors in cell membranes or nuclei to exert effects. Hormone levels and receptor function are controlled by feedback mechanisms to maintain homeostasis. The endocrine system regulates processes like growth, metabolism, and reproduction through the action of hormones, while the nervous system provides more rapid responses. Diseases can occur if hormone levels become abnormal or receptors are damaged.

6. Chemical signals and their modes of action most peptides, proteins and glycoproteins steroids and thyroid hormones

9. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

10. Table 45.1 (continued ) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

12. Hormones and the female reproductive cycle

13. Hormones control the reproductive cycle of human females

14. Performance-enhancing drugs