Lecture Notes Chapter 45

Lecture Notes Chapter 45 - Chapter 45: Hormones and the...

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Chapter 45: Hormones and the Endocrine System Overview: The Body’s Long-Distance Regulators An animal hormone is a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the body Hormones may reach all parts of the body But only certain types of cells, target cells, are equipped to respond Examples: Insect metamorphosis is regulated by hormones – ecdyson is the universal molting hormone in arthropods (steroid) The endocrine system and the nervous system act individually and together in regulating an animal’s physiology The nervous system Conveys high-speed electrical signals along specialized cells called neurons The endocrine system (made up of endocrine glands) Secretes hormones that coordinate slower but longer-acting responses to stimuli Overlap Between Endocrine and Nervous Regulation The endocrine and nervous systems often function together in maintaining homeostasis, development, and reproduction Specialized nerve cells known as neurosecretory cells release neurohormones into the blood Both endocrine hormones and neurohormones function as long-distance regulators of many physiological processes Control Pathways and Feedback Loops There are three types of hormonal control pathways: A common feature of control pathways is a feedback loop connecting the response to the initial stimulus Negative feedback regulates many hormonal pathways involved in homeostasis Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses Hormones convey information via the bloodstream to target cells throughout the body Three major classes of molecules function as hormones in vertebrates: Proteins and peptides (e.g. insulin, growth hormone) Amines derived from amino acids (e.g. adrenalin) Steroids (testosterone, estrogen) 1
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Signaling by any of these molecules involves three key events: 1. Reception The possession of the appropriate receptor determines whether a cell can respond to the stimulus 2. Signal transduction Translation into the cellular “language” Often involves an amplification step 3. Response At the cellular level the response to a hormone usually involves changes in the expression of certain genes There is a principle difference in transduction of water-soluble and lipid-soluble hormones, since the latter can readily cross a lipid bilayer, whereas peptides cannot. Cell-Surface Receptors for Water-Soluble Hormones The receptors for most water-soluble hormones are embedded in the plasma membrane, projecting outward from the cell surface Binding of a hormone to its receptor initiates a signal transduction pathway leading to specific responses in the cytoplasm or a change in gene expression The same hormone may have different effects on target cells that have Different receptors for the hormone Different signal transduction pathways
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Lecture Notes Chapter 45 - Chapter 45: Hormones and the...

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