26 - F HUMORAL COMMUNICATION Endocrinology, the study of...

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F HUMORAL COMMUNICATION Endocrinology, the study of the hormonal controls of bodily function, is a relatively new discipline within physiology. This description attempts to convey the principles of endocrinology and to expose the reader to some of the exciting developments presently occurring in this field. It has to be balanced, however, with a need to avoid excessive biochemical complexity for beginning students. This requirement presents a dilemma because hormones are chemicals and their properties depend totally on the physicochemical makeup of the diverse array of molecules that behave as hormones. The material is exceedingly important for the reader who is trying to understand how animals function. To help simplify portions of the description, much of the detail that is needed for completeness but that may detract the reader from easily obtaining an overview has been separated from the main text. 2007 version – page 199
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Chapter 26. INTRODUCTION TO ENDOCRINOLOGY Chemically mediated controls of physiologic function are extremely diverse. Specific chemicals mediate critical processes in nervous function such as synaptic transmission, which involves the triggered release of neurotransmitters responsible for initiating action potentials in the postsynaptic neuron. Neuromuscular transmission is mediated by acetylcholine or by norepinephrine, depending on the division of the nervous system involved. In both cases specific molecules carry information from one cell to another. The responses to these transmitters are rather simple compared to those of other chemical mediators, but the communication principles involved are quite similar. Somewhat related to the foregoing is the local exchange of information from one cell to different cells in close proximity (Figure 26-1) in tissues other than in the nervous system. Such chemical mediators are called paracrines, or local hormones. Autocrines are chemical mediators that appear to have controlling actions on the very cells (or neighboring cells of the same type) that produce them. Although autocrines and paracrines do not exhibit all of the characteristics of endocrines, the principles of information transfer applies equally well. The release of histamine from specialized cells with resultant local vasodilation or "reddening" in adjacent tissues is an Figure 26-1. Autocrines, paracrines and endocrines. This is a simple depiction of types of humoral communication involving soluble molecules that are secreted into the interstitium in order to act on cellular targets. The “tissue” at the top consists of intermixed cells. Autocrine action (blue) results from a molecule secreted from cell #1 acting upon itself or the very same cells nearby (e.g. #2). When the target cell is a distinct but close-by cell type (#4) from the cell (#2) secreting the molecule (green), the term paracrine is used. In the third scenario, endocrine (red), the molecule, from #5 diffuses through the interstitium, is picked up by blood and carried off to some distant tissue
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This note was uploaded on 03/23/2009 for the course ANSCI 1110 taught by Professor Brucecurrie during the Fall '08 term at Cornell University (Engineering School).

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26 - F HUMORAL COMMUNICATION Endocrinology, the study of...

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