Biology Ch. 17
Chemical Messengers
• Autocrine chemical messengers- released by cells and have a local effect on the same
cell type
• Paracrine chemical messengers- released by cells and affect other cell types locally
without being transported through the bloodstream
• Neurotransmitter- produced by neurons and secreted into extracellular spaces by
presynaptic nerve terminals; travels short distances
• Endocrine chemical messengers- type of intercellular signals; Produced by cells of
endocrine glands, enter circulatory system, and affect distant cells
Characteristics of hormones
• Produced in small quantities
• Secreted into intercellular space
• Transported some distance in circulatory system
• Acts on target tissues elsewhere in the body
• Response depends on hormone
