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

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Chapter 45 Notes: Hormones and the Endocrine System Hormone: a molecule that is secreted into the extracellular fluid, circulates in the blood (or hemolymph), and communicates regulatory messages throughout the body Although the circulatory system allows a hormone to reach all cells of the body, only its target cells have the receptors that enable a response A hormone elicits a specific response, such as a change in matabolism, from its target cells, whereas cells lacking a receptor for that particular hormone are unaffected Chemical signaling by hormones is the function of the endocrine system, one of two basic systems for communication and regulation throughout the body Hormones secreted by endocrine cells regulate reproduction, development, energy metabolism, growth, and behavior The stomach and kidney both contain endocrine cells Other organs are grouped in ductless organs (endocrine glands) Hormones serve a range of functions in the body: 1. Maintain homeostasis 2. Mediate responses to environmental stimuli 3. Regulate growth, development, reproduction 4. Coordinate body’s responses to stress, dehydration, or low blood glucose 5. Control appearances of characteristics that distinguish a juvenile animal from an adult Endocrine Glands: secrete hormones directly into the surrounding fluid; contrast with exocrine glands (salivary glands) which have ducts that carry secreted substances onto body surfaces or body cavities Nervous System: a network of specialized cells - neurons, that transmit signals along dedicated pathways These signals, in turn, regulate other cells, including neurons, muscle cells, and endocrine cells Because signaling by neurons can regulate the release of hormones, the nervous and endocrine systems often overlap in function Local regulators: secreted molecules that act over short distances and reach their target cells solely by diffusion, function in paracrine and autocrine signaling Paracrine signaling: target cells lie near the secreting cell Autocrine signaling: the secreted molecules act on the secreting cell itself Neurotransmitters: at many synapses, neurons secrete neurotransmitters that diffuse a very short distance to bind receptors on the target cells; central to sensation, memory, cognition, and movement
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Chemical classes of hormones Polypeptides (proteins and peptides)-insulin Amines-epinephrine and thyroxine Steroids-cortisol (lipid-soluble, can pass through cell membranes readily)
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