April 28, 2014 – Chemical signals and hormones II Announcements: Lab this week will meet in the computer labs Final Exam: May 15 ICES evaluation 1. Pre-lecture quiz 2. Review of cell-to-cell signaling & thyroid hormones (T3 & T4) 3. Specificity 1. Lipid soluble hormones – Steroids 2. G-coupled protein receptors – 3. Tyrosine kinase receptors 4. Hormone-mediated physiological tradeoffs Endocrine systems are regulated by negative feedback Endocrine pathway Neuroendocrine pathway Stimulus Neuroendocrine-to-endocrine pathway Stimulus Stimulus Endocrine cell Endocrine signal Effector cell Response Sensor cell Sensor cell Neural signal Neural signal CNS CNS Neuroendocrine signal Effector cell Response Neuroendocrine signal Endocrine cell Endocrine signal Effector cell Response Chemical characteristics of hormones – major classes Peptides and Polypeptides Secretin Amino Acid Derivatives Steroids Cortisol Epinephrine Receptor Receptor Not lipid soluble; bind to receptors on surface of target cell Target cell Most not lipid soluble; bind to receptors on surface of target cell Lipid soluble; bind to receptors inside target cell Receptor Hormone Transport and Action on Target Hydrophobic messengers pass into cell where they bind with transcription factors which affect gene expression. Hydrophilic hormones bind to a receptor on the cell membrane which causes several reactions known as a signal transduction pathway. This can affect the properties of enzymes/proteins, etc. or it may affect gene expression. Thyroid Hormone Thyroid hormone: - Actually two hormones (T3/T4) Mammals mainly secrete T4 - but some T4 is converted under certain circumstances - Same receptor binds both, but ↑affinity for T3 T3/T4 are membrane soluble - ↑metabolism in muscles, heart, liver & kidney T4 T3 Figure 47-8 T3 T3 Juvenile frog (tadpole) Adult frog Locomotion Swim via movements of muscular tail Locomotion Tailless; walk or hop Respiration Gas exchange occurs in gills, across skin, and in lungs Respiration Gas exchange occurs across skin, and in lungs Nutrition Most are herbivorous; have a long gut specialized for digesting algae and plants Nutrition Excretion Most nitrogenous wastes excreted as ammonia Most are carnivorous; have a large mouth or long tongue for catching prey; short gut specialized for digesting proteins Excretion Most nitrogenous wastes excreted as urea Thyroid hormone levels go up as flat fish go through this metamorphosis. Anadromous versus Resident Stream Sticklebacks Higher metabolic rates Lower metabolic rates Migrate from ocean to freshwater to breed Permanent residents in freshwater Bigger Smaller Take home message: The same hormone can have multiple physiological effects How do we explain this? Altering individual behaviors by altering overall thyroid levels seems like a pretty blunt way to go about changing specific phenotypes. How could this system be fine-tuned to optimize specific traits under different contexts? A.) changes in TRH expression B.) changes in TSH expression C.) alterations of TSH receptors D.) alteration of T3/T4 receptors in specific cell types. Hormonal specificity: G-protein coupled receptors Hormonal specificity: G-protein coupled receptors Hormonal specificity: Tyrosine kinase receptors Hormonal specificity: Steroids and gene transcription STEROID HORMONE ACTION Nucleus Hormone receptor Steroid hormone mRNA Proteins DNA Hormonereceptor complex 1. Steroid 2. Hormone binds hormone enters target cell. to receptor, induces conformational change. Hormoneresponse element RNA polymerase 3. Hormone-receptor 4. Many mRNA complex enters nucleus and binds to DNA, induces start of transcription. transcripts are produced, amplifying the signal. Ribosome 5. Each transcript is translated many times, further amplifying the signal. Hormone-mediated Tradeoffs: Interactions between stress, reproduction and immune function Extraordinary ordinary Junco: http://juncoproject.org/videos/chapter-2/ Hormone-mediated Tradeoffs Interactions between stress, reproduction and immune function Stress Short-Term Stress Response “Fight or flight” response is stimulated by epinephrine Figure 47-7a-hypothesis Figure 47-7b-setup Some additional effects of the “fight or flight response 1.) Redirection of blood flow from the skin and digestive system toward heart, brain, and muscles. 2.) Relaxation vascular smooth muscle to aid in vasodilation Take home message: 1.) Short term stress responses are EXTREMELY beneficial over the short term. 2.) Prolonged stress responses can be harmful. *Radio Lab episode on stress: http://www.radiolab.org/story/91580-stress/ Long term stress responses Feedback inhibition by cortisol on ACTH Hypothalamus Pituitary gland Adrenal gland Results of injecting ACTH into human volunteers This graph shows the . . . a. Positive influence ACTH has on cortisol release b. Inhibitory feedback of cortisol on ACTH release Results of injecting cortisol into human volunteers This graph shows the . . . a. Positive influence ACTH has on cortisol release b. Inhibitory feedback of cortisol on ACTH release ure 47-15 Stressed individual Unstressed individual ACTH also stimulates the release of aldosterone. Why should this be a part of the stress response?