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Endocrine
| Question | Answer |
|---|---|
| Endocrinology | Study of hormones – what they are, what they do, where they come from, and how they work |
| Crine | means secretion |
| Endo | means to happen inside the body |
| Endocrine system | Uses chemical messengers to relay information between cells, often over long distances |
| How many different hormones do humans have | About 30 |
| Functions of the Endocrine System | 1. Regulates long-term processes – Growth – Development – Reproduction 2.Uses chemical messengers to relay information and instructions between cells 3. Works with the nervous system to maintain homeostasis |
| Exocrine cells | Secrete products onto epithelial surfaces via ducts – Ex: sudoriferous and sebaceous glands, salivary glands, goblet cells (mucous) |
| Endocrine cells | – Glandular secretory cells without ducts (ductless) – Products released directly into the blood – Products are called hormones – Hormones circulate until they reach a specific target tissue – Ex: thyroid releasing hormone (TRH), thyroid stimulating h |
| Inter | means BETWEEN |
| 4 types of intercellular communication | 1) Direct 2) Paracrine 3) Endocrine 4) Synaptic |
| Direct | 2 cells function as one unit) – Exchange of ions and molecules between adjacent cells across gap junctions – Occurs between 2 cells of same type – Highly specialized and relatively rare: heart and cilia |
| Paracrine | (cells in the same tissue talking) – Local hormones – Uses chemical signals to transfer information from cell to cell within single tissue, autocrine communication to same cells |
| Endocrine | (message usually from far away) – Endocrine cells release chemicals (hormones) into bloodstream – Alters metabolic activities of many tissues and organs simultaneously |
| Target Cells | Are specific cells that possess receptors needed to bind and “read” hormonal messages |
| Synaptic Communication | (nerve to: nerve, muscle, or gland) – Ideal for crisis management! – Occurs across synaptic clefts – Chemical message is neurotransmitter – Limited to a very specific, small area (across the synaptic cleft, only) – Short-lived, broken down fast |
| Hormones = | the Keys |
| Target cell receptors = | he Locks |
| Hormone ‘key’ | released from secretory cell • Circulates in blood until reaches target cell ‘lock’ |
| Target cell | has a receptor specifically for the hormone |
| Hormone bypasses cells with | the wrong receptors ( Key does not fit these locks) |
| Hormone binds to | receptor of target cell, ‘unlocking’ the chemical message |
| Physiological response begins in | target cell |
| 4 Common Responses of the Target Cell | After hormone binds, a response occurs in the target cell: a) Produces new hormone b) Makes new enzyme (protein) c) Increase or decrease the rate at which an enzyme or protein is manufactured in the cell d) Open or close a gate or channel in the mem |
| Free hormones | (usually peptide hormones) – Remain functional for < 1 hour • Diffuse out of bloodstream and bind to receptors on target cells • Broken down and absorbed by cells of liver or kidneys • Broken down by enzymes in plasma or interstitial fluids |
| Bound hormones | (usually thyroid and lipid hormones) – Remain in circulation much longer because > 99% are bound to special transport proteins (albumins) – Bloodstream contains substantial reserve of bound hormones |
| 3 Classes of Hormones | A. Amino acid derivatives • Small molecules related to amino acids (protein building blocks) B. Peptide hormones • Chains of amino acids, mostly stored as prohormones (inactive) until secreted C. Lipid derivatives • Eicosanoids made from arachidon |
| Amino Acid Derivatives | Small molecules structurally related to amino acids Amino acids are the building blocks of proteins |
| Tyrosine makes: (DENT) | • Dopamine made from levodopa in brain and kidney • Epinephrine, Norepinephrine made in adrenal medulla • Dopamine, Epinephrine, and Norepinephrine are catecholamines • Thyroid hormone made by thyroid gland |
| Tryptophan makes: (Phan of being happy and sleepy) | • Melatonin made by pineal gland • Serotonin made by brain and gut |
| Tyrosine | – Dopamine – Epinephrine – Norepinephrine – Thyroid hormone (T4 – thyroxine) |
| Tryptophan | – Melatonin – Serotonin |
| Peptide Hormones | Made as prohormones (inactive), then converted to active |
| Glycoproteins | – More than 200 aa long with CHO sidechains – TSH, FSH, LH – all from lobe of anterior pituitary gland |
| Short polypeptides/small proteins | – Includes all from hypothalamus, thymus, heart, GI, pancreas, and posterior lobe of pituitary gland – Short: 9 aa’s long are short chain polypeptides like ADH and OXT – Small: longer chains of protein like insulin (51 aa), GH (191 aa), and PRL |
| Lipid Derivatives | Eicosanoids, Steroid Hormones, |
| Eicosanoids | – Derived from arachidonic acid, a 20-carbon fatty acid – 4 types (see next slide) |
| Steroid Hormones | – Derived from lipids similar to cholesterol – Bound to carrier proteins so stay in circulation much longer – Released by reproductive organs of males and females, by cortex of adrenal glands, and by kidneys, and created as vitamin D (see next slide |
| Lipid-derived Eicosanoids | Leukotrienes, Prostaglandins, Thromboxane, Prostacyclin |
| Leukotrienes | – Pro-allergic response (asthma and rhinitis) – Singulair |
| Prostaglandins | – Pain, uterine contractions which cause menstrual cramps – Suppressed by COX-1 and COX-2 inhibitors |
| Thromboxane | – Vasoconstriction and blood clot formation (thrombosis) – Raises blood pressure |
| Prostacyclin | – Opposite of thromboxane – Prevents formation of platelet plug (clot) and is a vasodilator |
| Lipid-derived Steroids | • Made from cholesterol • Bound to specific transport proteins in blood plasma • Ex: albumin protein • Circulate longer than peptide hormones, longer lasting effects • Reproductive organs • Ovaries release estrogen and progesterone • Testes release |
| Upregulation vs. Downregulation | Cells change the number of receptors in their membranes in order to deal with lack of or too much of a hormone |
| Receptor Locations in a Cell + the HRC | 1. Intracellular Receptors 2. Cell Surface Receptors |
| Intracellular Receptors are located in | cytoplasm or on DNA of target cell |
| Cell Surface Receptors are located on | plasma membrane of target cell |
| What happens when a hormone binds to a receptor? | it forms a Hormone Receptor Complex (HRC) |
| Up-regulation | – Absence of a specific hormone (low levels compared to normal) – Triggers increase in number of hormone receptors for that hormone |
| Down-regulation | – Overabundance of specific hormone (high levels compared to normal) – Triggers decrease in number of receptors for that hormone |
| REMINDER: The cell plasma membrane is an | amphipathic phospholipid bilayer |
| Water soluble, non-steroid hormones | – Are first messengers – Cannot enter cell and must bind outside, relying on a second messenger to relay the instructions to the cell – Causes a second messenger (like cAMP or calcium) to activate |
| Lipid soluble hormones | – Can enter cell cytoplasm or through nuclear envelope to DNA and create change |
| Amplification | – When a small number of first messengers causes thousands of second messengers to be made in the cell |
| Receptor cascade | – When a single hormone causes the release of more than one type of second messenger in a series of linked reactions |
| Types of Receptor Systems | • Direct gene activation • Second messenger system |
| Direct gene activation | – Intracellular receptors – Hormones are lipid soluble steroids and can enter lipid bilayer directly to DNA |
| Second messenger system | – Plasma membrane receptors – Water-soluble non-steroid hormones which are not made of lipids and therefore cannot dissolve through the lipid bilayer – Two groups: 1. G-protein linked receptors (ex: glucagon receptor) 2. Non-G linked receptors (ex: |
| Lipid-soluble Steroid Hormones | Use Direct Gene Activation |
| Lipid-soluble Steroid Hormone (SH) | • Made from cholesterol • Will dissolve through lipids, like the plasma lipid bilayer • Direct Gene Activation – Enters nucleus, binds to intracellular receptor on DNA directly • Slower action – hours to days after initial binding of receptor • D |
| Lipid-soluble Steroid Hormone List | 1. Aldosterone -Adrenal gland (CORTEX making corticosteroids) 2. Cortisol-Adrenal gland (CORTEX making corticosteroids) 3. Androgens-Adrenal gland (CORTEX making corticosteroids) 4. Testosterone-Testes 5. Estrogens-Ovaries 6. Progesterone- Ovaries 7 |
| Direct Gene Activation | 1. Travels in blood, bound to ‘taxi’ protein carrier like albumin. Passes through lipid bilayer 2. Enters nucleus through pore and binds to hormone receptor to form a Hormone Receptor Complex (HRC) 3. Docks on shape-specific receptor on DNA (or mitocho |
| Water-soluble Non-steroid Hormones | Use 2nd Messenger Systems |
| Water-soluble Non-Steroid Hormone (NSH) | • Will dissolve in blood and easily be transported by plasma (liquid) • 2nd Messenger System • Once bound, cascade of events triggered inside the cell leads to cellular change (signal transduction) • Receptors for catecholamines, peptides, and some |
| Second (2nd) Messenger System Players | • First messengers • Hormone Receptor Complex • G protein • Adenylate Cyclase • 3 Second messengers • Protein kinase |
| First messengers | – All are water soluble and must bind to an extracellular receptor – Catecholamines, peptide hormones, eicosanoids |
| Hormone Receptor Complex | – Where the first messenger (hormone) binds to the extracellular receptor |
| G protein | – Attached inside cell to bottom of extracellular receptor – Interprets first messenger instructions – Tells adenylate cyclase to make cAMP or uses Ca2+ to open Ca2+ channel |
| Adenylate Cyclase | – Gets the first message from G protein – If excited, converts ATP to cAMP (the 2nd messenger) inside the cell |
| 3 Second messengers | 1. Cyclic Adenosine Monophosphate (cAMP) 2. Cyclic Guanine Monophosphate (cGMP) 3. Calcium (Ca2+) |
| Protein kinase | – Understands the second messenger is cAMP – Phosphorylates a protein that is either in the cytoplasm already or is part of a membrane channel – Causes changes to happen in the cell, for example: • Epinephrine causes heart muscles to contract faster |
| 2nd Messenger System | 1. Water soluble hormone is first messenger 2. Seeks and binds to specific hormone receptor on plasma membrane surface. Forms Hormone Receptor Complex HRC. 3. Activates G-protein 4. G-protein activates Adenylate Cyclase AC, which converts ATP t |
| Breaking cAMP: Phosphodiesterase (PDE) | • Remember: cAMP is the second messenger! • As long as it exists, the cell continues to phosphorylate a protein and cause an effect to occur • cAMP levels usually short-lived because phosphodiesterase, an enzyme in the cytoplasm, will inactivate cA |
| **Note: (About Effectors) | an effector is a thing which causes change. In 2nd messenger systems, there are several effectors (like G-protein) moving the message forward, and one effector (PK) which performs the final step to bring about change! |
| G-proteins can do 2 things with calcium | • Open calcium channels in the plasma membrane • Release calcium ions stored inside the cell (i.e., terminal cisternae near actin/myosin/tropomyosin) |
| Catecholamines, ADH, and OXT use | calcium as 2nd messenger |
| G-proteins and Calcium players | • Calcium • G-protein • Phospholipase C (PLC) • Diacylglycerol (DAG) • Inositol triphosphate (IP3) • Protein kinase C (PKC) • Calmodulin (CaM) |
| Endocrine Reflexes | 1. Humoral stimuli 2. Hormonal stimuli 3. Neural stimuli |
| Humoral stimuli | • Changes in composition of extracellular fluid • Heart, pancreas, parathyroid glands, and digestive tract |
| Hormonal stimuli | • Changes in levels of circulating hormones • Arrival or removal of specific hormone |
| Neural stimuli | Arrival of neurotransmitters at neuroglandular junctions |
| Simple endocrine reflex | • Involves only 1 hormone • Controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract |
| Complex endocrine reflex | • One or more intermediary steps • 2 or more hormones • Often involve the hypothalamus • Hypothalamus: the portion of the brain that links the nervous system to the endocrine system via the pituitary gland |
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tarich5z
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