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Animal Endocrine Systems

Animal Endocrine Systems. Biology 2: Form and Function. Hormones regulate. Together with nervous system, responsible for regulation of body organs Secreted by ductless glands into surrounding capillary network

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Animal Endocrine Systems

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  1. Animal Endocrine Systems Biology 2: Form and Function

  2. Hormones regulate... • Together with nervous system, responsible for regulation of body organs • Secreted by ductless glands into surrounding capillary network • Long-term, narrow-to-broad impact mediated by contact of hormone with receptor molecules at target site • Receptor molecules may be internal or external to cell • Endocrine system is distinct to organ self-regulation, or autocrine/paracrine system

  3. There are four classes of hormone • Polypeptides - short chains < 100 amino acids in sequence, e.g., ADH • Glycoproteins - long chains (100+) of amino acids connected to carbohydrate, e.g., FSH • Amines - derivatives of tyrosine and tryptophan, e.g., epinephrine, thyroxine • Steroids - lipid derived • sex steroids, e.g., testosterone • corticosteroids, e.g., aldosterone

  4. In mammals, there is a close association between the endocrine and neural systems... • Nervous system-controlled endocrine glands include: • Adrenal medulla • Posterior and anterior pituitary (via Hypothalamus) • Pineal gland • Examples of non-nervous system controlled endocrine secretion include pancreas (insulin), and adrenal cortex (aldosterone)

  5. Hormones that enter cells • Includes all lipophilic (lipid-soluble) hormones (e.g., steroids, thyroxine) • Bind to specific receptors in cytoplasm, which then moves to the nucleus, or binds directly to receptor proteins in nucleus • Receptor molecule, once activated, binds to portions of DNA and stimulates transcription, ultimately effecting protein production and cell metabolism

  6. Hormones that do not enter cells... • Water soluble hormones that bind to the outside of cell membranes, requiring a secondary messenger inside cell to complete message • Secondary messengers include • Cyclic AMP • IP3/Ca2+

  7. Cyclic AMP • e.g., effects of epinephrine on b-adrenergic centers • Binding of epinephrine to G-protein receptor causes G-protein sub-unit to disassociate • G-protein sub-unit binds with membrane enzyme adenlyl cyclase • Adenlyl cyclase, now activated, catalyzes formation of cAMP from ATP • cAMP binds to and activates protein kinase-A, responsible for phosphorylation of certain proteins specific to tissue/cell • in liver, stimulates conversion of glycogen to glucose • In cardiac muscle, increases speed and force of heart beat

  8. Inositol triphosphate/Ca2+ • e.g., effects of epinephrine on a-adrenergic centers • Binding of epinephrine to G-protein receptor causes G-protein sub-unit to disassociate • G-protein sub-unit binds with, and activates membrane enzyme phospholipase C • Phospholipase C cleaves certain phospholipids to produce IP3 • IP3 binds with receptors on endoplasmic reticulum, stimulates release of Ca2+ • Ca2+ binds to calmodulin, which activates different types of protein kinases, causing phosphorylation of different cellular proteins

  9. The Posterior Pituitary • neurally derived: hormones are part of neuroendocrine reflex. • Secretes Antidiuretic hormone (ADH) and Oxytocin (although both are made in the hypothalamus) • ADH stimulates water retention by the kidneys (alcohol inhibits ADH, causing dehydration) • Oxytocin stimulates uterine contractions and milk-ejection reflex

  10. Anterior pituitary • Epithelially-derived tissue, produces • GH, growth hormone (somatotropin) • ACTH, adrenocorticotropic hormone (corticotropin) • TSH, thyroid stimulating hormone (thyrotropin) • Gonadotropins LH (luteinizing hormone) and FSH (follicle stimulating hormone) • Prolactin (PRL) • MSH, Melanocyte-stimulating hormone

  11. Control of the Anterior Pituitary by the Hypothalamus is still hormone-mediated • Releasing and inhibitory hormones are secreted by the hypothalamus and carried via a c apillary network connected to a second caillary network - the hypothalamo-hypophyseal portal system • for example, gonadotropin releasing hormone (GnRH) stimulates the release of FSH and LH • In turn, hypothalamus is controlled by negative feedback inhibition

  12. Other endocrine glands • Adrenal glands • The adrenal medulla secrets epinephrine and norepinephrine, triggering alarm responses across the body at various targets, preparing the body for ‘fight or flight’ • The adrenal cortex secretes cortisol and other glucocorticoids, an aid in glucose homeostasis, as well as aldosterone, responsible for salt balance

  13. The pancreas has both exocrine and endocrine functions

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