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CHAPTER 18 The Endocrine System Endocrine is NOT Exocrine • Exocrine glands secrete their products into ducts. – Sudoriferous (sweat) glands – Sebaceous (oil) glands – Mucous glands – Digestive glands None of these are hormones! Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. A Little Endocrine FYI: • Endocrinology is the study of ductless glands or tissues and their hormonal products • Endocrine gland – composed of a prominent parenchyma of secretory cells, connective tissue, blood vessels and nerves. • Endocrine glands are ductless and secrete their products directly into the blood. – Can include any group of cells that secrete a hormone. Endocrine Glands • Endocrine glands secrete hormones. – Do not have ducts – Secrete their hormones directly into the interstitial fluid that surrounds them. – The hormones then diffuse into the blood stream through capillaries and are carried to target cells throughout the body. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Endocrine Glands/Organs Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Endocrine Glands & Organs • Classic Glands – Pituitary – Thyroid – Parathyroid – Islets of Langerhans – Adrenal Glands – Gonads – Placenta • Organs w/ Endocrine Functions – Brain – Heart – Liver – GI Tract – Kidneys – Adipose (fat) Chemical Messenger Classifications • Chemical messenger is any substance produced by a cell that plays a physiological role in the control of the activity of a another cell. • Hormone is any substance elaborated by one cell to regulate another cell and may be delivered in an endocrine, paracrine, autocrine or pheromonal route. But what about all those neuro messengers? “Neuro Is As Neuro Does” • Neurotransmitters are released by neurons and travel only across the synaptic cleft/neuromuscular junction • Neuromodulators are released by neurons to affect other neurons but are not immediately taken up or metabolized like NTs • Neurohormones are hormones produced by a nerve cell and released into the blood to reach their target cells Control by the Nervous and Endocrine Systems • The nervous and endocrine systems act together to coordinate all systems of the body. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Credit: Dr. Michael Ormsbee, Florida State University Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Hormone Delivery Review • Endocrine where the messenger is bloodborne. • Neuroendocrine where the hormone released by a nerve is blood borne. • Paracrine where the released hormone diffuses to adjacent target cells through the immediate extracellular space. • Autocrine where the hormone may feedback to the cell of origin to regulate it’s own release. Continued • Neuromodulator is a hormone that modulates the response of a neuron to a neurotransmitter or other hormone. (all act as NM- feedback loops) • Pheromone is a chemical messenger released to the exterior of one animal to stimulate a response in another member of the same species. • Chalones (K-lone) are putative cellular mitotic inhibitors • Growth factors are mitogenic peptides which may later become known as hormones. Hormone Activity Hormones are either: • Lipid-soluble – Steroid hormones, thyroid hormones, nitric oxide (NO) • Water-soluble – Amine hormones, peptide and protein hormones, eicosanoid hormones • Water-soluble hormones circulate freely in the plasma; Lipid-soluble hormones circulate bound to transport proteins. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Credit: Dr. Michael Ormsbee, Florida State University Where Do Hormones Come From? Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Where Do Hormones Come From? Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Physiological Role of Hormones A.K.A. : What do hormones do? 1. Hormones affect cellular synthesis and secretion of other hormones within other endocrine glands and neurons. 2. Hormones affect anabolic and catabolic processes. 3. Hormones affect contraction, relaxation, and metabolism of muscle. Continued 4. Hormones control reproductive processes such as gondal differentiation, maturation, and gametogenesis. 5. Hormones stimulate and inhibit cellular proliferation, thus affecting growth. Hormones regulate cell division and differentiation of the fertilized egg. Continued Some More 6. Hormones regulate the excretion and reabsorption of inorganic cations and ions. 7. Hormones have a permissive action on other hormones 8. Hormones play an important part in animal behavior. How Do Hormones Exert Their Influence?? Short answer: RECEPTORS • Receptors (proteins or glycoproteins) provide specificity for hormone-cell interaction. • Receptors may be components of the cell membrane or they may by cytosolic or nuclear receptors. (steroid/thyroid/vitamin d) • Cells do not possess receptors for all hormones but rather have a limited number of receptor types. Hormone Activity • Hormones traveling throughout the body will only affect target cells that possess specific protein receptors. • Receptors are continually being synthesized and broken down. • Receptors may be down-regulated in the presence of high concentrations of hormone. • Receptors may be up-regulated in the presence of low concentrations of hormone. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Mechanisms of Hormone Action Lipid-soluble hormones bind to receptors within target cells. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Mechanisms of Hormone Action Water-soluble hormones bind to receptors on the exterior surface of the target cell. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Mechanisms of Hormone Action How a target cell responds to a hormone is based on: – The hormone’s concentration in the blood – The number of hormone receptors on the target cell – Influences exerted by other hormones – Some hormones work more effectively when a second hormone is present to assist them (synergistic effect). – Some hormones oppose the action of others (antagonistic effect). Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Control of Hormone Secretion Hormones are secreted in short bursts when needed. Secretion is regulated by: – Signals from the nervous system – Chemical changes in the blood – Other hormones Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Control of Hormone Secretion Most hormone regulation is achieved via negative feedback. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Control of Hormone Secretion A few hormones operate via positive feedback. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Control of Hormone Secretion Interactions Animation: Hormonal Cycles You must be connected to the Internet and in Slideshow Mode to run this animation. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Neurotransmitters (NT) • NT’s are chemical messengers released from neurons into the synapse between the nerve and its effector cells • Secretory cells, muscle cells, or other neurons. • Usually act in a paracrine fashion • Many peptide hormones that function in a classical sense are also synthesized in specific neurons and may function as NT’s. Neurohormones NT’s that diffuse beyond the synapse and enter the blood stream are termed Neurohormones. – i.e. Dopamine NT’s act very rapidly in comparison to neuromodulators which exert a more sustained response. Neuromodulatory hormones may originate from non-neuronal sources – i.e. corticosteroids, androgens, estrogens.