PHYSCI 107 Chapter Notes - Chapter 10: Triiodothyronine, Thymus, Autonomic Nervous System
Document Summary
A hormone released into the bloodstream is distributed throughout the body. Each hormone has target cells, specific cells that have the receptors that bind and read the hormonal message when it arrives. But hormones are really like e-mail spam cells throughout the body are exposed to them whether or not they have the necessary receptors. At any moment, each individual cell can respond to only a few of the hormones present: both systems rely on the release of chemicals that bind to specific receptors on target cells, both systems share various chemical messengers. The endocrine system includes all the endocrine cells and tissues of the body. Endocrine cells are glandular secretory cells that release their secretions into the extracellular fluid (as noted in chapter 4). We define hormones as chemical messengers that are released in one tissue and transported by the bloodstream to target cells in other tissues: amino acid derivatives. Peptide hormones consist of chains of amino acids.