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The Hypothalamo-Pituitary-Adrenal Axis. Table 10.1 Factors Influencing Evaluation of Endocrine Function in Aging. Physiologic Metabolism Body Composition Nutrition Exercise Stress. Inter-endocrine Relations Secretory Rate Transport to target site. Hormone Metabolism Activity
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Table 10.1 Factors Influencing Evaluation of Endocrine Function in Aging Physiologic Metabolism Body Composition Nutrition Exercise Stress Inter-endocrine Relations Secretory Rate Transport to target site Hormone Metabolism Activity T4 T3 T DHT Number & Affinity Of Receptors
Hypophysiotropic hormones CRH: corticotropic releasing hormone GHRH: growth hormone releasing hormone GHIH: growth hormone inhibitory hormone Somatostatin PRH: prolactin releasing hormone GnRH: gonadotropin releasing hormone TRH thyrotropin (TSH)-releasing hormone Pituitary Hormones ACTH: adrenocorticotropin hormone LH: lutenizing hormone FSH: follicle stimulating hormone PL: prolactin TSH: thyroid stimulating hormone GH: growth hormone **Please see Figures 10.7-10.9 in text** Figure 10.1
Figure 10.3 Diagram of a section of the adrenals illustrating the various zones and hormones
Figure 10.6 Reminder CRH: corticotropic releasing hormone ACTH: adrenocorticotropic hormone
Actions Of Glucocorticoids Actions of Adrenaline/Noradrenaline Target cellular
Figure 10.5 Schematic diagram of corticosteroid action in target cell
Gene expression & new protein synthesis • Relatively long latency of onset • Medium & long term cell program • Organization of cell networks for complex functions • Activation/repression of pre-existing cell proteins • Rapid onset of action • Rapid adaptation to changes in the milieu • Dynamic modifications of long term cell programs
Figure 10.7 Diagrammatic representation of the anterior pituitary
Figure 10.8 Diagrammatic representation of the posterior pituitary
Changes with Aging in the Hypothalamo-Pituitary-Adrenal Axis No significant changes in healthy, non-stressed, elderly The few changes that occur are rapidly compensated for (e.g. decreased secretion of GCs from the adrenal cortex) but also less rapid metabolism in the liver & less urine excretion Therefore the circulating levels remain constant Also, normal ACTH & cortisol responses to CRH administration Some alterations of the circadian rhythm
STRESS Cortisol, norepinephrine, and epinephrine
Figure 10.4 Corticosterone titers in young (3-5 mo) and aged (24-28 mo) rats Old rats Young rats
Exposure to Stress Generates: • Specific responses: vary with the stimulus (specialized responses) and generate different responses with each different stimulus. • Nonspecific responses: (also called non- specialized) are always the same • regardless of the stimulus • mediated through stimulation of neural, endocrine, and immune axis