1HormonesChapter 12Endocrine System Function• Major control and communication system• Controls activities that require long duration– digestion and energy metabolism– osmoregulation, water balance, ion balance and excretion– growth and development– reproductionEndocrine Systems• Invertebrates– Most hormones arise from neurosecretorycells in CNS– Hormones typically released directly to target tissues– Principally involved in regeneration, growth, development, and reproduction– Little homeostatic functionEndocrine Systems• Vertebrates– Much greater prevalence of non-neural endocrine glands– More complex control pathways • One hormone stimulates the release of another.– Greater involvement in homeostasisHormones• Chemical signals broadcast to other cells• Endocrine– signals circulated throughout the body• Paracrine– signals broadcast locally within tissues• Autocrine– Signals act directly on the cell that releases itHormone Classes• Amines– hormones derived from tyrosine and tryptophan– adrenal medulla hormones, thyroid hormones, pineal gland hormones• Peptide Hormones – made from polypeptide chains– most hormones (insulin, FSH)• Steroids– derivatives of cholesterol– adrenal cortex hormones, gonadal hormones2Mechanism of Action:Steroids & Thyroid Hormones• nonpolar– pass directly through the cell membrane • bind to protein receptor in cytoplasm or in nucleus • protein binds to gene on DNA in the nucleus • stimulates expression of that gene (protein production)Mechanism of Action:Peptides and Most Amines• Polar– cannot pass through hydrophobic lipid bilayer• bind to receptor proteins on cell surface – activation of membrane-bound enzymes • production of a second messenger inside the cell – e.g. cAMP, DAG-IP3, •2ndmessenger activates or deactivates various enzymesHormonal Regulatory Mechanisms• Regulating hormone levels– e.g. Negative feedback• Change causes change in opposite direction• e.g. thyroxine/TSH• Regulating tissue response– e.g. down regulation• Decrease # of receptors on target cell with chronically elevated hormone levelsVertebrate EndocrinologyHypothalamus-Pituitary Axis• Hypothalamus (brain region)– controls release of pituitary hormones• Neural control of endocrine function• Pituitary gland– Two distinctive lobes (posterior and anterior)– Linked to hypothalamus by infidiubulumPosterior Pituitary (Neurohypophysis)• Composed of neurosecretory cells• Hormones released when neurons undergo action potentialsPosterior Pituitary Hormones• ADH (Anti-Diuretic Hormone)– Arginine vasopressin (mammals) or arginine vasotocin (other verts)– increases reabsorption of H2O by kidneys – induces vasoconstriction in arterioles - ↑ BP– Sexual behavior (amphibians) and oviposition (reptiles and birds)– Skin permeability (amphibians)• Oxytocin– Uterine contraction during childbirth – milk letdown during breast feeding – male function unclear (↑ occurs in both sexes during sexual arousal)3Anterior Pituitary (Adenohypophysis)• Composed of epithelial cells• Different cell types secrete various peptide hormones• Secretion controlled by hormonal release from hypothalamus into hypothalamal-hypophysealportal systemAnterior Pituitary Hormones• TSH (Thyroid Stimulating Hormone, Thyrotropin)– Stimulates thyroid gland• Release thyroid hormones• Stimulates thyroid growth• ACTH (Adrenocorticotropin)– Stimulates adrenal cortex to release glucocorticoidsAnterior Pituitary Hormones• PRL (Prolactin)– Breast development and milk production during pregnancy– Development and maintenance of corpus lutea (non-primate mammals)– Crop milk secretion in pigeons, brood patch development in birds– Controls sensitivity of testes to LH– Enhances uptake / inhibits secretion of ions in fish and amphibians– Lots of other modulatory functionsAnterior Pituitary Hormones• MSH (Melanocyte Stimulating Hormone)– Integument pigmentation• GH (Growth Hormone, Somatotropin)– Stimulates growth, protein synthesis, fat breakdown and ↑blood glucose levels– Functions indirectly through somatomedins(e.g., insulin-like growth factors)Anterior Pituitary Hormones• FSH (Follicle Stimulating Hormone, Follitropin)– regulates female sex hormones, egg development – Stimulates Sertoli cells to release local mediators that induce spermatozoa development• LH (Luteinizing Hormone, Lutropin)– ovulation, regulation of female sex hormones– induces corpus luteum formation after ovulation – Induces secretion of androgens by Leydig cells of testes“Adrenal” Glands• Releases hormones in response to stress – glucocorticoids (e.g. cortisol)• Elevate blood glucose• Anti-inflammatory and Immunosuppression– mineralocorticoids (e.g. aldosterone)•Na+/K+balance, blood pressure regulation– androgens (e.g., DHEA)• sexual characteristics– epinephrine (“flight vs. fight”)• ↑ blood glucose, lipolysis• ↑ thermogenesis (shivering and non-)• ↑ cardiovascular / respiratory activity4Thyroid Gland (Tetrapods)• Thyroid hormones (TH)– Thyroxine (T4) and triiodothyronine (T3)• Increase metabolic rate and body heat production (endotherms)• Metamorphosis in amphibians• Growth and developmentPancreas• Endocrine cells located in Islets of Langerhans• Contain two cell types– α cells - secrete glucagon– β cells - secrete insulin• Important in regulating glucose levels of the bloodInsulin• Induces glucose uptake and utilization by cells (esp. muscle and liver) • Lowers blood glucose levels– promotes removal of glucose from blood• Promotes formation of glycogen– polymer of glucose for storage• Promotes conversion of glucose into fat in adipose tissue• Stimulates amino acid uptake by cells and protein formationGlucagon• Increase in blood glucose:– Activates liver enzymes to convert glycogen into glucose• Stimulates breakdown of stored fat and release of fatty acids into blood – used as secondary energy sourceGonads (Testes and Ovaries)• Produce steroid hormones– androgens (e.g., testosterone)• sperm development• reproductive tract maturation• secondary sex characteristics• sexual behavior (M and F)– estrogens and progesterone• oocytic development• reproductive tract development• secondary sex characteristicsComparative Endocrinology:Insect Molting / Metamorphosis• Development patterns in