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Animal Hormones 1 and 2 - Signaltypes Electric:...

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    Signal types Electric: nerve impulses are actually a  combination of chemical  ( neurotransmitters ) & electric events,  but influence only nerve cells in the  immediate vicinity (adjacent) Chemical: chemicals ( hormones released by a cell diffuse and can be  broadly distributed & influence activity of  many cell types
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    Speed of action Nerve impulses lead to immediate  responses (such as muscle contractions  needed to evade a predator) Hormone action involves secretion,  diffusion & circulation, thus slower  response but better suited to gradual  adjustments involved in homeostasis
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    Some terms Hormones secreted by  endocrine  cells Recipient of a hormone message is a  target cell Target cells must have the appropriate  receptor  to respond to the hormone Hormones with a ‘localized’ effect are  said to have  paracrine  functions (e.g.  histamine & growth factors)
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    More terms Autocrine  effects are when the  secreting cell responds to its own  hormones binding to receptors Neurotransmitters  are released in  response to electric impulses and bind  to receptors on adjacent cells
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    Chemical Signals:                     Endocrine functions Autocrine & paracrine functions          Neurotransmitter functions
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    Endocrine system in  humans: Nine major glands Cells of other organs  also release  hormones, so  endocrine functions  not limited to  endocrine glands!
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    Two types of glands Exocrine: release secretions that are  not hormones through ducts that lead  outside the body (e.g. sweat & salivary  glands) Endocrine: release secretions  (hormones) directly into extracellular  fluid (ductless)
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    The Giant Weta:   Larger than some small mammals, consider how  signals may be sent among cells in this large insect Insects have been valuable ‘models’ for studying hormones Physiological  processes in  invertebrates, such as  insects, are the same  as in vertebrate  animals: sensory &  nervous systems,  excretion, gas  exchange, locomotion,  and digestion, for  example. On a cellular  level, we are really not  that much different than  insects!
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    Invertebrate Hormones Sir Vincent Wigglesworth discovered  that a gland in the head of insects is  responsible for controlling the molting  process Decapitating a juvenile bug blocks  molting into adult; but if head left on for  1 week after final blood meal molting  still occurs after decapitation
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    Headless bugs, cont.
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