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Hypothalamic-Hypophysical Portal System

Discussion in 'MCAT Study Question Q&A' started by justadream, Sep 4, 2014.

  1. justadream

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    Is this associated with only the posterior pituitary (in which ADH and oxytocin are made by the hypothalamus and then transported to the PP)?

    How about for the anterior pituitary?
     
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  3. Cawolf

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    It is associated with the anterior pituitary - the adenohypophysis.

    The hypothalamus produces releasing hormones that travel to the adenohypophysis through the HH portal system.

    The posterior pituitary (neurohypophysis) is directly derived from neural tissue and is aglandular - secreting hormones produced by the hypothalamus (vasopressin/oxytocin). The tissue simply stores and releases hormones that are produced "upstream".
     
  4. justadream

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    @Cawolf
    The hormones secreted by the AP are actually PRODUCED in the AP too, correct? I know there's like a corresponding hormone from the hypothalamus that controls each of the hormones actually secreted by the AP.

    Also, are you saying that the HHP system is only associated with the AP and not the PP?
     
  5. Cawolf

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    Yes - the anterior pit. hormones are produced by epithelial derived cells in the glandular tissue.

    The hypothalamus creates and releases "releasing hormones" to tell the anterior pit. to release it's "stimulating" hormones - these travel through the HH portal system to reach the anterior pit.

    As far as I have learned yes - it is only with the anterior pit. The posterior pit. is technically contiguous with the hypothalamus by the infundibulum (or stalk) and vaso/oxy are carried directly by the nervous tissue.
     
  6. Czarcasm

    Czarcasm Hakuna matata, no worries.
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    Just an FYI, if you care: A portal system occurs when a capillary bed flows via a portal vein to another capillary bed first before flowing back through veins (this is one example of a portal system; another occurs from the small intestines to the liver). Hypothalamus produces tropic hormones, which is a fancy term for hormones that regulate other endocrine glands. These hormones pass through the first capillary bed (some travel systemically), which then travel to the AP to bind to specific receptors. Binding to the specific cell receptor activates a specific type of endocrine cell within the AP. The cell that responds to that stimulus releases a hormone which travels through the second capillary bed through rest of the body.
     
  7. justadream

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    @Czarcasm

    So the HHP is not associated with the PP then?
     
  8. Cawolf

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    It really doesn't, if you need confirmation, just look at any picture.

    I picked a random one.

    Note the blood flows through the median eminence prior to the adenohypophysis to form the portal system.

    [​IMG]
     
  9. justadream

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    @Cawolf
    So the PP hormones are essentially transported in vesicles through axons?

    If so, what's the reasoning behind this difference in transmission for AP hormones (regulated using tropic hormones via HHP system) and PP hormones (direct transmission via axons)?
     
  10. techfan

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    I believe it's due to the embryological origin of the tissue. The posterior pituitary is a downgrowth of diencephalon (I think it is pretty much a downgrowth of hypothalamus) and is nervous tissue and anterior pituitary is upgrowth of oral ectoderm (Rathke's pouch) and is endocrine or glandular tissue. Pretty much what Cawolf said in his first post
    Here's a separated picture.
    [​IMG]
     
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  11. Cawolf

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    Yup, due to tissue origin. The AP is glandular tissue and the PP is nervous tissue. Simply two different "things" that grow together to form the pituitary as a whole.
     
  12. fakedoctor123

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    My mnemonic I like to use is 'PP is an extension.' In other words, the posterior pituitary is an extension of the hypothalamus and is not actually a gland, that's why it's also called the 'neurohypophysis.' The hypothalamus' neuroendocrine cells make oxytocin and and the PP simply releases them. The axons of the neuroendocrine cell in the hypothalamus reach all the way into the posterior pituitary (there is no portal system here).

    In contrast, the anterior pituitary is actually a gland (that's why its called adenohypophysis, because adeno means gland). So the hypothalamus has a portal system (capillary bed in series) with the anterior pituitary and regulates the production of the FLATPiG hormones from the anterior pituitary. Cells in the anterior pituitary actually make and secret the FLATPiG hormones.
     
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  13. noroxytocin

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    If the system involving the anterior pituitary is the hypothalamic hypophyseal system, is there a name for the system involving the posterior pituitary, even though the pituitary stock connects them?
     

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