Introduction to Endocrine System Other organs tissues that contain endocrine cells Endocrine Gland o Pituitary o Thyroid o Parathyroid o Adrenal o Pineal o Hypothalamus o Thymus o Pancreas o Ovaries testes o Kidneys Liver o Stomach Heart Skin o Adipose tissue Endocrine vs Exocrine body other parts of the body o Endocrine secrete products into interstitial fluid and diffuse into blood o Exocrine secrete products into ducts or lumens or to the outer surface of the Hormones Mediator molecules released in one part of the body that regulate activity in o Local hormones Act locally on neighboring cells paracrine or on the same cell that secreted them autocrine without first entering the blood stream Ex IL 2 released from helper T cells stimulates proliferation of helper T cells and activation of cytotoxic T cells Ex Histamine released by mast cells stimulates HCl secretion from parietal cells in stomach o Circulating hormones Enter interstitial fluid and then the bloodstream Lipid soluble bound to transport proteins Steroid Hormones o Derived from cholesterol o Chemical groups attached to the core of the structure makes o Ex cortisol testosterone estrogens progesterone it unique aldosterone Thyroid Hormones o Tyrosine ring with attached iodines o Very lipid soluble Nitric Oxide o Hormone and neurotransmitter Water soluble free Peptide and Protein Hormones o chains of amino acids o hypothalamic releasing and inhibiting hormones o ADH oxytocin hGH TSH ACTH o Insulin glucagon EPO Biogenic amines o Modified amino acids o Catecholamines NE epinephrine dopamine o Serotonin melatonin and histamine Eicosanoids o Derived from arachidonic acid 20 carbon fatty acid o Prostaglandins and Leukotrienes o Local Hormones Functions of Hormones o Help Regulate Extracellular fluid Metabolism Biological clock Contraction of cardiac and smooth muscle Glandular secretion Some immune functions Growth and development Reproduction o Hormones only affect target cells with specific membrane or intracellular protein receptors o General mechanism of action Bind to cell surface or receptor inside target cell Cell responds via Synthesis of new molecules Change in membrane permeability Altered rates of reaction Different target cells may respond to the same hormone differently Hepatocytes insulin stimulates glycogen synthesis Adipocytes insulin stimulates triglyceride synthesis o Steroid Hormone Action Receptors typically intracellular Work by changing the level of specific gene expression o Peptide Hormone Action peptide hormones bind to cell surface receptors peptide hormones evoke changes in the activity of existing proteins through a second messenger e g cyclic AMP second messengers alter the phosphorylation state of existing proteins Second messengers o Water soluble peptide hormones bind to cell surface receptors production intracellular second messenger o Hormones first messengers may increase or decrease the level of second messengers o Ex cAMP calcium ions cGMP o Same hormone may use different second messengers in different target cells Ex Norepenephrine o Second messengers initiate a cascade of biochemical reactions often involving phosphorylation or dephosphorylation within the target cell