Chapter 7 - The Endocrine System

Ie each hormone in the pathway feeds back to suppress

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i.e. each hormone in the pathway feeds back to suppress hormone secretion by the “upstream” endocrine centers (E.5.c) This is referred to as long-loop negative feedback (E.5.d) Long vs. Short-Loop Negative Feedback Cortisol Secretion: Long-Loop Feedback Growth Hormone: Complex Endocrine Pathway IV)Hormone Interactions A) Sometimes the combined effect of two or more hormones is greater than the sum of the effects of the hormones individually – this is the concept of synergism or potentiation. B) Characteristics of Hormone Interactions: B.1) Permissiveness B.2) Some hormones cannot fully exert their effects without the presence of a second hormone – this is the concept of permissiveness. (B.2.a) e.g. thyroid hormone has a permissive effect on sexual maturation B.3) Hormone Interactions: Antagonism B.4) Two hormones can cause opposite effects and diminish the effectiveness of each other – this is the concept of antagonism. B.5) Two hormones are considered functional agonists if they have opposing physiological actions. (B.5.a) e.g. the action of glucagon to increase blood glucose is antagonistic to the action of insulin to decrease blood glucose B.6) Antagonistic hormones don’t necessarily compete for membrane receptors, rather they may act by a different metabolic pathway or by down- regulating the receptor population for an another hormone. V) Endocrine Pathologies
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A) Three basic patterns of endocrine pathology A.1) Hormone excess A.2) Hormone deficiency A.3) Abnormal responsiveness of target tissues B) Hypersecretion exaggerates a hormones’s effect C) Hyposecretion diminishes or eliminates a hormone’s effects D) Receptor or second messenger problems cause abnormal tissue responsiveness E) Diagnosis of pathologies depends on the complexity of the reflex VI)Hormone Evolution A) Evolutionary conservation Endocrine System Summary I) Hormones II) The Classification of Hormones III) Control of Hormone Release IV)Hormone Interactions V) Endocrine Pathologies VI)Hormone Evolution
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