Lesson 3 Check Off List Describe the differences between direct paracrine endocrine and synaptic communication o The Endocrine System Regulates long term processes Growth Development Reproduction o Direct Communication Use Chemical messengers to relay information and instructions between cells Exchange of ions and molecules between adjacent cells across gap junctions links cytoplasm of two cells Occurs between two cells of same type Highly specialized and relatively rare Ex Cardiac muscle cells Uses chemical signals to transfer information from cell to cell within single o Paracrine Communication tissue Most common form of intercellular communication Communication is between close cells short distance o Endocrine Communication Endocrine cells release chemicals hormones into bloodstream Communicates to cells far away Alters metabolic activities of many tissues and organs simultaneously Note paracrine factors can also enter the bloodstream however their concentrations are usually too low to affect distant cells tissues Target Cells are specific cells that possess receptors needed to bind and read hormonal messages Hormones chemical messengers that are transported through blood to distant targets Stimulate synthesis of enzymes or structural proteins Increase of decrease rate of synthesis Turn existing enzyme or membrane channel on or off o Synaptic Communication Chemical message is neurotransmitter Ideal for crisis management Occurs across synaptic clefts Travels a very short distance across synaptic cleft to reach the target cell Limited to a very specific area Response usually not long lasting Nervous system response faster than endocrine system Ex Email vs postal mail Describe the different classes of hormones and their properties Classes of Hormones o Hormones can be divided into 3 groups 1 Amino Acid Derivatives also known as Biogenic Amines Are small molecules structurally related to amino acids 2 Peptide hormones o Derivatives of tyrosine Thyroid hormones Catecholamines Epinephrine norepinephrine from adrenal medullae of adrenal glands dopamine o Derivatives of tryptophan Dopamine serotonin melatonin Melatonin produced from pineal gland Are chains of amino acids Most are synthesized as prohormones pro inactive form o Inactive molecules converted to active hormones before or after they are secreted Glycoproteins o Proteins are more than 200 amino acids long and have carbohydrate side chains Examples Thyroid stimulating hormone TSH Luteinizing hormone LH Follicle stimulating hormone FSH Short polypeptides small proteins o Short chain polypeptides Antidiuretic hormone ADH and oxytocin OXT each 9 amino acids long o Small proteins Growth hormone GH 191 amino acids and prolactin PRL 198 amino acids o Includes all hormones secreted by Hypothalamus heart thymus digestive tract pancreas and posterior lobe of the pituitary gland as well as several hormones produced in other organs Eicosanoids derived from arachidonic acid a 20 carbon fatty acid o Paracrine factors that coordinate cellular activities and affect enzymatic processes such as blood clotting in extracellular fluids 3 Lipid derivatives o Some eicosanoids such as leukotrienes have secondary roles as hormones leukotrienes can cause inflammation during allergic reactions o A second group of eicosanoids prostaglandins involved primarily in coordinating local cellular activities In some tissues prostaglandins are converted to thromboxanes vasoconstrictor and prostacyclins vasodilator which also have strong paracrine effects Steroid hormones derived from cholesterol o Released by The reproductive organs androgens by the testes in males estrogens and progestins by the ovaries in females The cortex of the adrenal glands corticosteroids The kidneys calcitriol o Because circulating steroid hormones are bound to specific transport proteins in the plasma They remain in circulation longer than secreted peptide hormones o Secretion and Distribution of Hormones Hormones circulate freely or travel bound to special carrier proteins Lipid soluble hormones require special carriers for transport in blood why Lipid derivatives derive from fat which doesn t mix well with water So it won t dissolve well in blood Makes it more soluble and allows it to dissolve better Free hormones unbound Remain functional for less than 1 hour o Diffuse out of bloodstream and bind to receptors on o Are broken down and absorbed by cells of liver or o Are broken down by enzymes in plasma or interstitial target cells kidneys fluids Thyroid and Steroid hormones Remain in circulation much longer because most are bound Enter bloodstream o More than 99 percent become attached to special transport proteins o Bloodstream contains substantial reserve of bound hormones Which bind to receptors on the cell surface Which bind to receptors inside the cell What are the different types of second messengers and how do they amply the signal Mechanisms of Hormone Action o Hormone Receptor Is a protein molecule to which a particular molecule binds strongly Responds to several different hormones requires different hormone receptor for each hormone Different tissues have different combinations of receptors Presence or absence of specific receptor determines hormonal sensitivity A cell may respond to multiple hormones as long as that cell has the receptors for those hormones o Hormones and Plasma Membrane Receptors Catecholamines and Peptide Hormones Are not lipid soluble o Unable to penetrate plasma membrane Bind to receptor proteins at outer surface of plasma membrane extracellular receptors Eicosanoids Are lipid soluble Diffuse across plasma membrane to reach receptor proteins on inner surface of plasma membrane intracellular receptors First and Second Messengers The hormone is the first messenger it must activate a second messenger inside the cell to cause a change in the cell For instance o Water soluble hormone binds to receptors in plasma membrane Cannot have direct effect on activities inside target cell o Therefore uses intracellular intermediary to exert effects First Messenger o Leads to second messenger o May act as enzyme activator inhibitor or cofactor o Results in change in rates of metabolic reactions Important Second Messengers o Cyclic AMP cAMP derivative of ATP Explain how hormones travel through the body o Cyclic GMP cGMP derivative of GTP o Calcium ions The Process of Amplification the binding of a small number of hormone molecules to membrane receptors leads to
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