Endocrine System - 1 Endocrine System 2009 The coordination...

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1 Endocrine System 2009 The coordination of all organs and tissues in our bodies is very complex and is brought about by the nervous system and endocrine system. The nervous system controls the functions of cells, tissues, and organs by rather close contact, that is, nerves come to cells, tissues, organs and rather closely interact with them. On the other hand, the activity of cells, tissues, and organs are also directed by hormones that come to them from far distances. Endocrine glands secrete a large number of hormones into the bloodstream for distribution to specific target cells (really specific receptor sites on the cell membrane, cytoplasm, or nucleus of these target cells). Most hormones are proteins, peptides, steroids, or tyrosine derivatives. Or more simply, derived from amino acids (proteins, peptides, biogenic amines) or derived from cholesterol. Peptide and protein hormones are synthesized in RER, packaged in Golgi, and stored in granules. Biogenic amines (epinephrine, serotonin, etc.) are made from decarboxylated amino acids (tyrosine) and are stored in granules until they are released after the cell receives a stimulus. Peptide, protein, and amines attach to receptors in the cell membrane of their target. Steroid hormones (glucocortocoids, sex hormones, and aldosterone) have cholesteryl ester as their backbone. Steroids are synthesized on mitochondria and smooth ER. To make any steroid hormone, cholesterol must be converted to pregnenolone . This conversion takes place on the inner membrane of mitochondria and then pregnenolone is transferred back and forth between the SER and mitochondria for further transformation until the final steroid hormone is produced). Steroids are rapidly secreted from the cell. They are not stored. Steroid hormones enter cells by facilitated diffusion (they do not bind to a receptor in the target cell’s plasma membrane) and bind to intracellular receptors. Peptide and protein hormones are made in cells with an extensive RER and Golgi. Steroid hormones are made in cells with an extensive SER and abundant mitochondria. Thyroid hormones (derived from tyrosine) are unique in their synthesis and storage and, like steroids, they enter cells to bind with intracellular receptors . So, most hormones bind to receptors (transmembrane proteins) on the target cells surface. Steroids and thyroid hormones bind to receptors that are in the cytoplasm or nucleus of the target cells. Both steroids and thyroid hormones are lipophilic and it was once thought they both entered cells by diffusion. It now appears that both require a transporter protein to enter cells (facilitated diffusion).
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2 Pituitary Gland: Really two different glands, the neurohypophysis (or posterior pituitary) and the adenohypophysis (or anterior pituitary). Both of these are attached to median eminence at the base of hypothalamus. The attachment is by the pituitary stalk. See Blue Histology for animation of embryonic development of pituitary. The neurohypophysis is the exception that all
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This note was uploaded on 11/08/2011 for the course SCIENCE 3254 taught by Professor Dr.shoupe during the Spring '11 term at Fort Valley State University .

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Endocrine System - 1 Endocrine System 2009 The coordination...

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