chapter 5 companion site for basic medical endocrinology, 4th edition author: dr. goodman

Chapter 5Companion site for Basic Medical Endocrinology, 4th Edition

Author: Dr. Goodman

Companion site for Basic Medical Endocrinology, 4th Edition. by Dr. Goodman Copyright © 2009 by Academic Press. All rights reserved.

2

Integration at the cellular level. A cell may receive inputs from hormones A, B, and C simultaneously. Hormone B acting through a G-protein coupled receptor activates adenylyl cyclase (AC) through the stimulatory subunit Gs. Hormone C binds to its G-protein coupled receptor, which inhibits adenylyl cyclase through the inhibitory subunit Gi, and activates phospholipase C through the Gq subunit, resulting in cleavage of phosphatidylinositol bis-phosphate (PIP2) and the release of diacylglycerol (DAG) and inositol trisphosphate (IP3). Hormone A, acting through a tyrosine kinase receptor, activates cyclic AMP phosphodiesterase (PDE), which degrades cAMP. The combined actions of the three hormones determines the concentration of cyclic AMP.

FIGURE 5.1


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Synergistic effects of human growth hormone (hGH) and the synthetic glucocorticoid dexamethasone (DEX) on lipolysis as measured by the increase in glycerol release from rat adipocytes. Both hGH and Dex were somewhat effective when added individually, but when added together the overall tissue response was greater than the sum of the responses produced by each hormone alone. (From Gorin, E., Tai, L.R, Honeyman, T.W, and Goodman, H.M. (1990) Evidence for a role of protein kinase C in the stimulation of lipolysis by growth hormone and isoproterenol. Endocrinology 126: 2973.)

FIGURE 5.2


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Determinants of the magnitude of a hormonal response.

FIGURE 5.3


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Determinants of the duration of a hormonal response.

FIGURE 5.4


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The relationship between concentration and response at three different levels of sensitivity. Arrows indicate the concentration of hormone that produces a half-maximal response for each level of sensitivity. Note that the abscissa is plotted on a logarithmic scale.

FIGURE 5.5


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Concentration response relationships showing different capacities to respond. Note that the concentration needed to produce the half maximal response is identical for all three response capacities. Note that the abscissa is plotted on a logarithmic scale.

FIGURE 5.6


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The effects of up or down regulation of receptor number on sensitivity to hormonal stimulation. Note that the abscissa is plotted on a logarithmic scale.

FIGURE 5.7


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Spare receptors. Note that the concentration of hormone needed to produce a half maximal response is considerably lower than that needed to occupy half of the receptors. Note that the abscissa is plotted on a logarithmic scale.

FIGURE 5.8


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Redundant mechanisms to stimulate hepatic glucose production. Hormonal and neural mechanisms are marshaled to combat potentially life-threatening low blood glucose concentrations.

FIGURE 5.9


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Redundant mechanisms to activate glycogen phosphorylase by a single hormone, epinephrine, acting through both 1 and receptors.

FIGURE 5.10


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Idealized representation of the effects of epinephrine and growth hormone on plasma concentrations of free fatty acids.

FIGURE 5.11


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Push–pull mechanism. Epinephrine inhibits insulin secretion while promoting glucagons secretion. This combination of effects on the liver stimulates glucose production while simultaneously relieving an inhibitory influence. (+) = increases; () = decreases

FIGURE 5.12


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Push–pull mechanism to activate glycogen phosphorylase while simultaneously inhibiting glycogen synthase.

FIGURE 5.13

chapter 5 companion site for basic medical endocrinology, 4th edition author: dr. goodman

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