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) TryosineThyroxine

Lipid-Derived Hormones Most are steroid hormones (cholesterol derived) Unlike protein hormones- these 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 Anterior pituitary Thyroid gland Target cells TRH TSH Thyroid hormones

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 Baby pushes against cervix Stretching sends nerve impulses to brain Brain stimulates pituitary to release oxytocin Oxytocin causes uterus to contract/push baby towards cervix

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!