Veterinary Physiology-III

DEFINITION

• The term hormone means "to excite" or "arouse".
• Hormones are chemicals secreted at variable rates in response to external or internal stimuli by an endocrine gland or a group of cells in very low concentrations (nanomolar to picomolar – 10 ^-9 to 10 ^-12 M) directly into the blood for transport to some distant target organs/cells where they alter already existing reactions but cannot initiate new reactions.