Chapter 45 Hormones & Endocrine System

Chapter 45 Hormones & Endocrine System - Chapter 45:...

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Chapter 45: Hormones & Endocrine System - Hormone = chemical signal secreted into extracellular fluid - Carried by circulatory system (blood or hemolymph) - Communicates regulatory messages within the body - May reach all parts of the body only target cells are equipped to respond ==> hormone traveling through the body elicits specific responses from target cells physiology - A. Nervous system - Conveys high-speed electrical signals along neurons - Control movement of body parts in response to environmental changes B. Endocrine system - all of an animal’s hormone secreting cells - hormones coordinate slower but longer acting responses to stimuli - (i.e. stress, dehydration, low blood glucose levels) - regulate long-term developmental processes - by informing different parts of body: - how fast to grow - when to develop characteristics that distinguish male from female or juvenile from adult - endocrine gland = ductless gland that secretes hormones directly into bloodstream Overlap Between Endocrine & Nervous Regulation - neurosecretory cells = specialized nerve cells that release hormones into the bloodstream - in response to signals from other nerve cells - located in hypothalamus & adrenal medulla - sometimes called neurohormones - distinct from “classic” hormones released by endocrine glands - hormones in endocrine system & as chemical signals in nervous system - epinephrine - “fight-or-flight” hormone - produced by adrenal medulla (endocrine gland) - neurotransmitter - local chemical signal that conveys messages in nervous system - nervous system plays role in sustained responses by increasing/decreasing secretion from endocrine glands - Control Pathways and Feedback Loops - biological control systems: 1. A receptor / sensor detects a stimulus 2. Sends information to control center 3. Compares incoming information to a set point / “desired” value 4. Control center sends out signal that directs an effector to respond - endocrine & neuroendocrine systems: - outgoing signal is efferent signal - hormone/neurohormone - acts on particular effector tissues - elicits specific physiological / developmental changes
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- 3 types of simple hormonal pathways - missing: complex neuroendocrine pathways in which a hormone secreted by one endocrine tissue acts on another endocrine tissue - controls its release of a different hormone then acts on target tissues - common feature of control pathways: feedback loop connecting response to the initial stimulus - negative feedback - effector response reduces initial stimulus ==> eventually response ceases - prevents: - overreaction by the system - wild fluctuations in variable being evaluated - operates in many endocrine & nervous pathways - esp. those involved in maintaining homeostasis - positive feedback - reinforces the stimulus ==> leads to greater response
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This note was uploaded on 05/09/2008 for the course BISC 220L taught by Professor Herrera,mcclure during the Spring '07 term at USC.

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Chapter 45 Hormones & Endocrine System - Chapter 45:...

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