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HormoneOutline• Classification of hormone• Properties and function of hormone• Mechanism
IntroductionHormone- a molecule produced by specific cells that influences thefunction of distant target cells. Only a small amount ofhormone is required to alter cell metabolism- all multicellular organisms produce hormones; planthormones are also called phytohormones- hormones in animals are often transported in the blood.- endocrine hormone molecules are secreted (released) directlyinto the bloodstream, while exocrine hormones (orectohormones) are secreted directly into a duct, and from theduct they either flow into the bloodstream or they flow fromcell to cell by diffusion
Introduction- hormone secretion can be stimulated and inhibited by: other hormones (stimulating- or releasing-hormones) plasma concentrations of ions or nutrients neurons and mental activity environmental changes, e.g., of light or temperature- hormones have the following effects on the body: stimulation or inhibition of growth mood swings activation or inhibition of the immune system regulation of metabolism
Introduction preparation of the body for fighting, fleeing, mating, andother activity preparation of the body for a new phase of life, such aspuberty, parenting, and menopause control of the reproductive cycle hunger cravings a hormone may also regulate the production and releaseof other hormones. Hormone signals control the internalenvironment of the body through homeostasis
Hormones Classification- vertebrate hormones fall into three chemical classes:i. Amine-derived hormonesderivatives of the amino acids tyrosine and tryptophan.Examples are catecholamines and thyroxineii. Peptide hormonesconsist of chains of amino acids. Examples of smallpeptide hormones are TRH and vasopressin. Examples ofprotein hormones include insulin and growth hormone.More complex protein hormones bear carbohydrate sidechains and are called glycoprotein hormones. Luteinizinghormone, follicle-stimulating hormone and thyroid-stimulating hormone are glycoprotein hormones.
Hormones Classificationiii. Lipid and phospholipid derived hormonesderive from lipids such as linoleic acid and arachidonicacid and phospholipids. The main classes are the steroidhormones that derive from cholesterol and theeicosanoids. Examples of steroid hormones aretestosterone and cortisol. The adrenal cortex and thegonads are primary sources of steroid hormones.Examples of eicosanoids are the widely studiedprostaglandins
Hormone FunctionsSource Hormone FunctionsHypothalamus Gonadotropin-releasinghormone (GnRH) *Corticotropin-releasinghormone (CRH)*Growth hormone-releasinghormone (GHRH)*Somatostatin*Thyrotropin-releasinghormone (TRH)*Stimulates LH and FSH secretionStimulates ACTH secretionStimulates GH secretionInhibits GH and TSH secretionStimulates TSH and prolactin secretionPituitary Luteinizing hormone (LH)*Follicle-stimulatinghormone (FSH)*Corticotropin (ACTH)*(adrenocorticotropic hormone)Stimulates cell development andsynthesis of sex hormones in ovariesand testesPromotes ovulation and estrogensynthesis in ovaries and spermdevelopment in testesStimulates steroid synthesis in adrenalcortex
Hormone FunctionsSource Hormone FunctionsGrowth hormone (GH)*Thyrotropin (TSH)*(thyroid-stimulating hormone)Prolactin*Oxytocin*Vasopressin*Metabolic effects in many tissuesStimulates thyroid hormone synthesisStimulates milk production in mammaryglands and assist in the regulation ofthe male reproductive systemUterine contraction and milk ejectionBlood pressure and water balanceGonads Estrogen ^(estradiol)Progestins ^(progesterone)Androgens ^(testosterone)Maturation and function ofreproductive system in femalesImplantation of fertilized eggs andmaintenance of pregnancyMaturation and function ofreproductive system in malesThyroid Triiodothyronine (T3)#Thyroxine (T4)#(after conversion to T3)General stimulation of many cellularreactions
Hormone FunctionsSource Hormone FunctionsAdrenal cortex Glucocorticoids^(cortisol, corticosterone)Mineralcorticoids^(aldosterone)Diverse metabolic effects as well asinhibiting the inflammatory responseMineral metabolismGastrointestinal tract Gastrin*Secretin*Cholecystokinin*Somatostatin*Stimulates secretion of stomach acidand pancreatic enzymesRegulates pancreatic exocrinesecretionsStimulates secretion of digestiveenzymes and bileInhibits secretion of gastrin andglucagonPancreas Insulin*Glucagon*Somatostatin*General anabolic effects includingglucose uptake and lipogenesisGlycogenolysis and lipolysisInhibits the secretion of glucagon* peptide or polypeptide ^ steroid # amino acid derivative
Hormone Action MechanismSteroid hormone- steroid hormone is not water soluble. They travel in bloodattached to protein carriers- when they arrive at the target cells, they dissociate from theirprotein carriers and pass through the plasma membrane ofthe cell- some steroid hormone bind to a specific receptor proteins inthe cytoplasm and then move as a hormone-receptorcomplex into the nucleus- other steroid travel directly into the nucleus beforeencountering their receptor protein
Hormone Action Mechanism- the hormone receptor protein, activated by binding to thehormone is now able to bind to specific regions of the DNA.- these DNA region is known as the hormone responseelements- the binding of hormone-receptor complex has a direct effecton the level of transcription at that site.- messenger RNA (mRNA) is produced, which then codes forthe synthesis of specific proteins
Hormone Action MechanismNon-steroid hormone(1) Peptide hormones are transported in theblood.(2) They combine with receptors in theplasma membrane of a target cell.(3) The hormone-receptor combination iscoupled by G-protein to activateadenylate cyclase.(4) Cyclic AMP then activates one or moreenzymes which(5) Phosphorylates specific cellular proteinsthat(6) alter the activity of the cell in some way.
Hormone Action MechanismNon-steroid hormone- non-steroid hormones (water soluble) do not enter the cellbut bind to plasma membrane receptors (1st messenger)
Hormone Action Mechanism- binding activates G- protein in the membrane that activates orinhibits adenylate cyclase on the inner surface of membrane
Hormone Action Mechanism- adenylate cyclase converts ATP to cAMP (2nd messenger). Ca+2,cGMP, IP3, & DAG are also 2nd messenger types- activation of a cAMP-dependent protein kinase called proteinkinase A- protein kinase A is normally in an catalytically-inactive state,but becomes active when it binds cAMP.- upon activation, protein kinase A phosphorylates a number ofother proteins, such as enzymes that are either activated orsuppressed by being phosphorylated.- such changes in enzymatic activity within the cell clearly alterits state- phosphodiesterase inactivates cAMP
Hormone Action MechanismNon-steroid hormone (eg. glucagon)- glucagon binds its receptor in the plasma membrane of targetcells (e.g. hepatocytes).- bound receptor interacts with and, through a set of Gproteins, turns on adenylate cyclase, which is also an integralmembrane protein.- activated adenylate cyclase begins to convert ATP to cyclicAMP, resulting in an elevated intracellular concentration ofcAMP.- high levels of cAMP in the cytosol make it probable thatprotein kinase A will be bound by cAMP and thereforecatalytically active.
Hormone Action Mechanism- active protein kinase A "runs around the cell" addingphosphates to other enzymes, thereby changing theirconformation and modulating their catalytic activity- levels of cAMP decrease due to destruction by cAMP-phosphodiesterase and the inactivation of adenylate cyclase.