Bài giảng Biology 25: Human Biology - Chapter 15

Chapter 15Biology 25: Human BiologyProf. GonsalvesLos Angeles City CollegeBased on Mader’s Human Biology,7th edition and Fox’s 8th ed PowerpointsHormonesRegulatory molecules secreted into the blood or lymph by endocrine glands.Lack ducts.Carry hormone to target tissue where it produces its effects.Chemical Classification of HormonesAminesPolypeptidesGlycoproteinsSteroidsAminesHormones derived from tyrosine and tryptophan.Include hormones secreted by adrenal medulla, thyroid, and pineal glands.PolypeptidesChains of amino acids (100) bound to one or more carbohydrate (CHO) groups.FSHLHSteroidsLipids derived from cholesterol.Are lipophilic hormones.TestosteroneEstradiolCortisolProgesteroneThyroid HormonesTyrosine derivatives bound together.Contain 4 iodine atoms (T4).Contain 3 iodine atoms (T3).Small, non-polar molecules.Soluble in plasma membranes.Hormone PrecursorsProhormone:Precursor is a longer chained chemical that is cut and spliced to make the hormone.Preprohormone:Prohormone derived from larger precursor molecule.Prehormone:Molecules secreted by endocrine glands that are inactive until changed to hormones by target cells.Anterior and posterior pituitary glands.Also called the neurohypophysis.Formed by downgrowth of the brain during fetal development.Is in contact with the infundibulum.Nerve fibers extend through the infundibulum.Posterior PituitaryHypothalamic Control of Posterior PituitaryHypothalamus produces:ADH: supraoptic nuclei.Oxytocin: paraventricular nuclei.Hormones transported along the hypothalamo-hypophyseal tract. Stored in posterior pituitary.Release controlled by neuroendocrine reflexes.Master gland (also called adenohypophysis).Derived from a pouch of epithelial tissue that migrates upward from the mouth.Consists of 2 parts:Pars distalis: anterior pituitary.Pars tuberalis: thin extension in contact with the infundibulum.Anterior PituitaryTrophic effects:Health of the target glands, depends upon stimulation by anterior pituitary for growth.High plasma hormone concentration causes target organ to hypertrophy.Low plasma hormone concentration causes target organ to atrophy.Anterior PituitaryHormonal control rather than neural.Hypothalamus synthesizes releasing hormones and inhibiting hormones.Hormones are transported to axon endings of median eminence.Delivers blood and hormones to anterior pituitary via portal system.Hypothalamic Control of the Anterior PituitaryHypothalamic Control of the Anterior PituitaryHormones secreted into the hypothalamo-hypophyseal portal system regulate the secretions of the anterior pituitary.Anterior pituitary and hypothalamic secretions are controlled by the target organs they regulate.Negative feedback inhibition by target gland hormones.Feedback Control of the Anterior PituitaryFeedback Control of the Anterior PituitaryNegative feedback at 2 levels:The target gland hormone can act on the hypothalamus and inhibit releasing hormones.The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone.Growth Hormone (GH) - Somatotrophic Hormone (STH) Increases Growth and Maintenance of Organs by:stimulating protein anabolismpromotes fat catabolism (use of fat rather than sugars for energy) Abnormal Secretions of STHGiantism -- hypersecretion during childhood (before epiphyseal plates close)Acromegaly -- hypersecretion during adulthoodDwarfism -- hyposecretion during childhoodCachexia (Simmond's Disease) - hyposecretion during adulthood causes premature aging and atrophy of organs Thyroid HormonesThyroid gland located just below the larynx.Thyroid is the largest of the pure endocrine glands.Follicular cells secrete thyroxine.Parafollicular cells secrete calcitonin.Production of Thyroid HormonesI- (iodide) actively transported into the follicle and secreted into the colloid.Oxidized to (Io) iodine.Iodine attached to tyrosine.Attachment of 1 iodine produces monoiodotyrosine (MIT).Attachment of 2 iodines produces diiodotyrosine (DIT).MIT and DIT or 2 DIT molecules coupled. Production of Thyroid HormonesT3 and T4 produced.TSH stimulates pinocytosis into the follicular cell.Enzymes hydrolyze to T3 and T4 from thyroglobulin.Attached to thyroid-binding protein and released into blood.T3 Effects Stimulates cellular respiration by:Production of uncoupling proteins.Stimulate active transport Na+/ K+ pumps.Lower cellular [ATP].Increases metabolic heat.Increases metabolic rate.Stimulates increased consumption of glucose, fatty acids and other molecules.Parathyroid HormoneParathyroid glands embedded in the lateral lobes of the thyroid gland.Only hormone secreted by the parathyroid glands.Single most important hormone in the control of plasma Ca++ concentration.Stimulated by decreased plasma Ca++ concentration.Disorders of the ThyroidHyperthyroidism (Grave's disease)elevated PBIincreases nervousness and irritabilityelevated BMRexophthalmos - results in edema behind the eyes HypothyroidismCretinism - occurs if the hyposecretion is during fetal or early developmental life.results in reduced metabolismresults in reduced growthresults in mental retardationMyxedema - occurs if the hyposecretion is during adult liferesults in reduced metabolismresults in reduced mental & physical activityresults in increased blood pressureresults in accumulation of subcutaneous fluids Adrenal GlandsPaired organs that cap the kidneys.Each gland consists of an outer cortex and inner medulla.Adrenal medulla:Derived from embryonic neural crest ectoderm (sympathetic ganglia).Synthesizes and secretes:Catecholamines (mainly epinephrine but some norepinephrine).Adrenal GlandsAdrenal cortex:Does not receive neural innervation.Must be stimulated hormonally.Consists of 3 zones: Zona glomerulosa: Aldosterone: regulate Na+ and K+ balance.Zona fasciculata: Cortisol: regulate glucose metabolism.Zona reticularis:Androstenedione and DHEA: supplement sex steroids.Adrenal MedullaInnervated by sympathetic nerve fibers.Increase respiratory rate. Increase heart rate, cardiac output; and vasoconstrict blood vessels, thus increasing venous return.Stimulate glycogenolysis.Stimulate lipolysis.General Adaptation Syndrome (GAS)Stress stimulates pituitary-adrenal axisAlarm phase:Adrenal glands activated.Stage of resistance:Stage of readjustment.Stage of exhaustion:Sickness and/or death if readjustment does not occur.Abnormal Adrenal Cortical Function: Addison's Disease - caused by Hyposecretion of Cortical hormonesresults in increased blood potassium levelsresults decreased sodium retention and dehydrationresults decreased blood glucose levelsresults decreased blood pressureresults decreased stress resistanceresults increased risk of kidney failure Cushing's syndrome - causes by Hypersecretion of Cortical Hormonesresults in shifts of the body fat to the face and shouldersresults in general body weaknessresults in altered carbohydrate & electrolyte metabolism Adrenogenital Syndrome - caused by Hypersecretion of Gonadotropinsresults in premature sexual development in both males and femalesresults in masculinization of females PancreasEndocrine portion consists of islets of Langerhans.Alpha cells secrete glucagon.Stimulus is decrease in plasma glucose concentrations.Stimulates lipolysis.Beta cells secrete insulin.Stimulus is increase in plasma glucose concentrations.Promotes entry of glucose into cells.Diabetes MellitusType I (insulin-dependent) diabetesPancreas does not produce insulinT cells destroy pancreatic isletsNeeds daily insulin injectionsType II (noninsulin-dependent) diabetesMost common type of diabetesObesity and inactivity are risk factorsInsulin is produced, but there is decreased response to the insulin perhaps because of a lack or deficiency in insulin receptors.Consequences:May lead to blindness, kidney disease, & circulatory disorders like atherosclerosis, heart disease, and stroke. Lack of circulation may also cause gangrene. Diabetic coma may also result and there is an increased risk of having a stillborn child. Gonads and PlacentaGonads (testes and ovaries):Secrete sex hormones.Testosterone.Estradiol.Progesterone.Placenta:Secretes large amounts of estrogen and progesterone.ThymusSite of production of T cells (thymus-dependent cells), which are lymphocytes.Pineal GlandMelatonin:Production stimulated by the suparchiasmatic nucleus (SCN) in hypothalamus.SCN is primary center for circadian rhythms.May inhibit GnRH.Autocrine and Paracrine RegulationAutocrine:Produced and act within the same tissue of an organ.Paracrine:Are produced within one tissue and regulate a different tissue of the same organ.Synergism:Two hormones work together to produce a result.Additive:Each hormone separately produces response, together at same concentrations stimulate even greater effect.Epinephrine and norepinephrine.Complementary:Each hormone stimulates different step in the process.FSH and testosterone.Hormonal InteractionsHormonal InteractionsPermissive effects:Hormone enhances the responsiveness of a target organ to second hormone.Increases the activity of a second hormone.Prior exposure of uterus to estrogen induces formation of receptors for progesterone.Hormonal InteractionsAntagonistic effects:Action of one hormone antagonizes the effects of another.Insulin and glucagon.ProstaglandinsMost diverse group of autocrine regulators.Produced in almost every organ.Wide variety of functions.Immune system:Promote inflammatory process.Reproductive system:Play role in ovulation.Digestive system:Inhibit gastric secretion.ProstaglandinsRespiratory system:May bronchoconstrict or bronchodilate.Circulatory system:Vasoconstrictors or vasodilators.Urinary system:Vasodilation.Effects of Hormone ConcentrationConcentration of hormones in blood reflects the rate of secretion.Half-life: Time required for the plasma concentration is reduced to ½ reference level.Physiological range of concentration produces normal tissue response.Effects of Hormone ConcentrationVarying hormone concentration within normal, physiological range can affect the responsiveness of target cells.Priming effects (upregulation)Increase number of receptors formed on target cells. Greater response by the target cell.Effects of Hormone ConcentrationDesensitization (downregulation):Decrease in number of receptors on target cells.Produces less of a target cell response.Insulin in adipose cells.Pulsatile secretion may prevent downregulation.GnRH and LH.Mechanisms of Hormone ActionHormones of same chemical class have similar mechanisms of action.Location of cellular receptor proteins.Target cell must have specific receptors for that hormone (specificity).Hormones bind to receptors with high bond strength (affinity).Low capacity of receptors (saturation).Hormones That Bind to Nuclear Receptor ProteinsLipophilic steroid and thyroid hormones bound to plasma carrier proteins.Hormones dissociate from carrier proteins to pass through lipid component of the target cell membrane.Receptors for the lipophilic hormones are known as nuclear hormone receptors.Nuclear Hormone ReceptorsFunction within cell to activate genetic transcription.mRNA directs synthesis of specific enzyme proteins that change metabolism.Receptor must be activated by binding to hormone before binding to specific region of DNA called HRE (hormone responsive element).Located adjacent to gene that will be transcribed.Hormones That Use 2nd MessengersCannot pass through plasma membrane.Catecholamines, polypeptides, and glycoproteins bind to receptor proteins on the target cell membrane.Actions are mediated by 2nd messengers (signal-transduction mechanisms).Extracellular hormones are transduced into intracellular second messengers.Hormones That Use 2nd Messengers3 classes of 2nd messenger systems:Adenylate cyclase.Phospholipase C.Tyrosine kinase.Hormone binds to receptor protein.Dissociation of a subunit of G-protein.G-protein binds and activates adenylate cyclase.ATP cAMP + PPi cAMP attaches to inhibitory subunit of protein kinase.Adenylate Cyclase-cAMPActivates protein kinase.Phosphorylates enzymes within the cell to produce hormone’s effects.Modulates activity of enzymes present in the cell.Alters metabolism of the cell.cAMP inactivated by phosphodiesterase.Hydrolyzes cAMP to inactive fragments.Adenylate Cyclase-cAMP