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Intro to Endocrinology The Endocrine System • With the nervous system, coordinates and directs the activity of the body’s cells • Widespread effects, but controls major processes: – Reproduction – Growth & development – Mobilizing body defenses against stressors – Maintaining blood electrolyte, nutrients, and water levels – Regulates cellular metabolism and energy balance A comparison: Endocrine System • Regulates the body • Uses chemical signals called hormones • Slow to kick in and effects are long-lasting Nervous System • Regulates the body • Uses nerve impulses/neurotransmitters • Very fast- muscles and glands into immediate action Quick brainstorm! You are walking barefoot and step on a piece of broken glass (ouch!). You immediately pull your foot back. Why is it a good thing that the nervous system was in charge of responding to this stimulus rather than the endocrine? Hormones • Chemical substances secreted by endocrine cells into the extracellular fluids • Regulate metabolic activity of other cells Turn & briefly discuss with your neighbor: All hormones circulate in the bloodstream at the same time, so how do tissues “know” which hormones to “listen” to? Hormones • Each hormone ONLY acts on one type of cell (a target cell) or tissue (target tissue) • Each target cell has a receptor for that hormone ONLY. Lock and key! • Locations of receptors: – Plasma membrane – Interior of cell When a hormone binds to its receptor… • Causes one or more of the following changes: 1. Changes permeability of the plasma membrane 2. Synthesis of proteins or certain regulatory molecules (like enzymes) 3. Activation or inactivation of enzymes 4. Stimulation of mitosis 5. Promotion of secretory activity Talk at your table and be ready to share: 1. What does this mean? 2. What does “synthesis” refer to? 3. What are enzymes for? 4. What’s the result of this? 5. What does this mean? Hormone chemistry • Peptide (protein)-derived • Amino acid-derived • Lipid-derived Oxytocin Polypeptide-Derived Hormones • Made by the process of translation – – – – Gene on DNA is copied by mRNA mRNA is “read” by a ribosome The ribosome + tRNA make a protein The protein folds and does its job • Not lipid soluble; bind to receptors on cell surface • Ex: insulin Growth hormone Amino Acid-Derived Hormones • Amino acids are the building blocks of proteins • These hormones are modified amino acids – Mainly tyrosine and tryptophan • Not lipid soluble; bind to surface receptors • End in “-ine” (ex: epinephrine, thyroxine) Tryosine Thyroxine Lipid-Derived Hormones • Most are steroid hormones (cholesterol derived) • Unlike protein hormonesthese are not stored in large amounts • Lipid soluble; act on intracelluar receptors (in cytoplasm or nucleus) • End in –ol or –one (ex: testosterone, cortisol) Cholesterol Testosterone Be ready to answer! • Describe the relative speed of the nervous system compared to the endocrine system. • How does the endocrine system relate to the digestive system? • At some given time, there are 5 hormones in the blood. How does the target cell know which one to “listen” to? • Which class of hormone acts on intracellular receptors of a cell? Feedback loops • Most work by negative feedback to maintain homeostasis • Rate of the process decreases as the concentration of the product increases • Avoids accumulation of a product • Thyroid hormone Hypothalamus TRH Anterior pituitary TSH Thyroid gland Thyroid hormones Target cells Feedback loops • A few work by positive feedback • Original stimulus is promoted • Rate of the process increases as the concentration of the product increases • Continues until stimulus ends or product consumed • Childbirth Oxytocin causes uterus to contract/push baby towards cervix Baby pushes against cervix Brain stimulates pituitary to release oxytocin Stretching sends nerve impulses to brain Stimulating Endocrine Glands • Hormonal stimuli – Most common stimulus – Endocrine organs prodded into action by other hormones – Ex) Hypothalamus pituitary another endo organ Stimulating Endocrine Glands • Humoral Stimuli – Changing levels of something in the blood (ions, nutrients) stimulates hormone release – Example: PTH released when blood calcium drops Stimulating Endocrine Glands • Neural Stimuli – Rarest – Nerve fibers stimulate hormone release – EX: Sympathetic stimulates release of adrenaline and noradrenaline from adrenal glands Crash Crouse: Great Glands- Your Endocrine System • During the video, take notes on the general job of each gland. It’s a good preview for what’s coming up! • https://www.youtube.com/watch?v=WVrlHH14q3o