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by Anonymous on November 16th, 2007

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What would happen to hormone production, if the connection between the hypothalamus and the anterior pituitary gland was severed?

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  • by SomeSayMarryMoney on November 16th, 2007

    SomeSayMarryMoney

    You would still be able to utilize hormones sent to the adenohypophysis (the anterior pituitary) because they travel from the hypothalamus via a portal system of blood vessels. Oxytocin and antidiuretic hormone, however, travel through the stalk of the pituitary and wouldn't be able to communicate with their target cells in the neurohypophisis (posterior pituitary).

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  • by iwnit on November 16th, 2007

    iwnit

    1) "If all the neural connections between the hypothalamus and the pituitary gland were severed,
    the secretion of which pituitary hormones would be affected? Which pituitary hormones would
    not be affected ?"

    "The secretion of vasopressin and oxytocin, that is, major posterior pituitary hormones would be affected. The anterior pituitary hormones would not be affected because the influence of the hypothalamus on those hormones is excerted no by connecting nerves but via the hypohpysiotropic hormones in the portal vascular system."
    Source:
    http://instruct1.cit.cornell.edu/courses/bmep402/Quiz/BMEP%20402%20Prelim%202%20Answers.pdf


    2) "A key to understanding the endocrine relationship between hypothalamus and anterior pituitary is to appreciate the vascular connections between these organs. As will be emphasized in later sections, secretion of hormones from the anterior pituitary is under strict control by hypothalamic hormones. These hypothalamic hormones reach the anterior pituitary through the following route:

    - A branch of the hypophyseal artery ramifies into a capillary bed in the lower hypothalamus, and hypothalmic hormones destined for the anterior pituitary are secreted into that capillary blood.
    - Blood from those capillaries drains into hypothalamic-hypophyseal portal veins. Portal veins are defined as veins between two capillary beds; the hypothalamic-hypophyseal portal veins branch again into another series of capillaries within the anterior pituitary.
    - Capillaries within the anterior pituitary, which carry hormones secreted by that gland, coalesce into veins that drain into the systemic venous blood. Those veins also collect capillary blood from the posterior pituitary gland. "

    "The utility of this unconventional vascular system is that minute quantities of hypothalamic hormones are carried in a concentrated form directly to their target cells in the anterior pituitary, and are not diluted out in the systemic circulation. "
    Source and further information:
    http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/anatomy.html


    3) Some Effects of Transection of the Pituitary Stalk:
    "Transection of the pituitary stalk causes massive necrosis in the anterior lobe of the gland. This infarct represents the territory whose sole blood supply is derived from the long portal vessels which run down the stalk.
    A small part of the glandular tissue of the anterior lobe regularly survives because its blood supply (through the short portal vessels) is not interrupted when the stalk is cut.
    If a barrier is inserted between the cut ends of the stalk, to isolate the pituitary permanently from the hypothalamus, the surviving anterior-lobe cells become small and degranulated and lose most of their functional capacity.
    In animals, long-term effects of section of the pituitary stalk include retardation of growth; severe atrophy of the adrenals, the gonads, and the accessory sex organs ; and a less marked atrophy of the thyroid. In rats regression of some mammary tumours occurred."
    http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1816815


    4) Further information:
    Diabetes Insipidus as a Complication after Pituitary Surgery:
    http://www.medscape.com/viewarticle/558561_3

    Acquired growth hormone deficiency due to pituitary stalk transection:
    http://cat.inist.fr/?aModele=afficheN&cpsidt=4632322

    "the postnatal clinical course is more severe when growth hormone deficiency is associated with pituitary stalk interruption syndrome than when the pituitary is
    only reduced in height"
    http://www.eje-online.org/cgi/reprint/139/1/84.pdf

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  • by TheAnswerer on November 16th, 2007

    TheAnswerer

    You wouldn't produce anymore hormones, as the hypothalamus and pituitary gland are major hormone productors.

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