BSC2086 Anatomy & Physiology II Exam #1 Study Guide 1 Lesson 3: Endocrine System Part I Endocrine System • Regulates long-term processes o Growth o Development o Reproduction • Uses chemical messengers to relay information and instructions between cells Homeostasis and Intercellular Communication • Direct Communication: Exchange of ions and molecules between adjacent cells across gap junctions o Occurs between two cells of same typeBSC2086 Anatomy & Physiology II Exam #1 Study Guide 2 o Highly specialized & relatively rare o Ex) Cardiac muscle • Paracrine Communication: Uses chemical signals to transfer information from cell to cell within a single tissue o Communication between close cells (short distance) of the same type o Most common form of intercellular communication • Endocrine Communication: Endocrine cells release chemicals (hormones) into bloodstream o Long distance communication of cells o Alters metabolic activities of many tissues & organs simultaneously • Paracrine factors can enter bloodstream, but their concentrations are usually too low to affect distant cells/tissues • Target Cells: Specific cells that possess receptors needed to bind and “read” hormonal messages • Hormones: Chemical messengers transported through blood o Stimulate synthesis of enzymes or structural proteins o Increase OR decrease rate of synthesis Turn existing enzyme or membrane channel “on” or “off” o Long-lasting effects • Synaptic Communication: Occurs across synaptic clefts o Travels very short distance to reach target cell o Ideal for crisis management (fast reaction) o Chemical message = neurotransmitter o Limited to very specific area o Response usually not long-lasting o Nervous system faster than endocrine system Ex) E-mail vs. postal “snail” mailBSC2086 Anatomy & Physiology II Exam #1 Study Guide 3 Hormones • Hormones can be divided into three (3) groups: o Amino acid derivatives o Peptide hormones o Lipid derivatives • Hormones circulate freely or travel bound to special carrier proteins o Lipid soluble hormones require special carriers for transport in blood • Amino Acid Derivatives: Small molecules structurally related to amino acids o Derivatives of Tyrosine: Thyroid hormones Catecholamines • Epinephrine & norepinephrine – produced by adrenal medulla of adrenal glands • Dopamine o Derivatives of Tryptophan: Serotonin Melatonin – produced in pineal gland • Peptide Hormones: Chains of amino acids o Most synthesized as prohormones – inactive molecules converted to active hormones before or after they are secreted o Glycoproteins: Proteins more than 200 amino acids long with carbohydrate side chains Thyroid-Stimulating Hormone (TSH) Luteinizing Hormone (LH) Follicle-Stimulating Hormone (FSH) o Short Chain Polypeptides Antidiuretic Hormone (ADH) Oxytocin (OXT) • Each nine (9) amino acids long o Small Proteins Growth Hormone (GH): 191 amino acids Prolactin (PRL): 198 amino acids o Short polypeptides/small proteins includes all hormones secreted by: Hypothalamus Heart Thymus Digestive tract Pancreas Posterior lobe of pituitary gland Several hormones produced in other organs • Lipid Derivatives o Eicosanoids: Derived from arachidonic acid – a 20-carbon fatty acid Paracrine factors that coordinate cellular activities & affect enzymatic processes (like blood-clotting) in extracellular fluids Prostaglandins: Involved primarily in coordinating local cellular activitiesBSC2086 Anatomy & Physiology II Exam #1 Study Guide 4 • Converted to thromboxanes (vasoconstrictor) & prostacyclins (vasodilator) in some tissues o Also have strong paracrine effects o Steroid Hormones: Derived from cholesterol Released by: • Reproductive organs o Males – testes androgens o Females – ovaries estrogens & progestins • Cortex of adrenal glands corticosteroids • Kidneys calcitriol Remain in circulation longer than secreted peptide hormones because they are bound to specific transport proteins in the plasma • Free Hormones: Remain functional for less than 1 hour & are inactivated when they: o Diffuse out of bloodstream & bind to receptors on target cells o Are broken down & absorbed by cells of liver or kidneys o Are broken down by enzymes in plasma or interstitial fluids • Thyroid & steroid proteins… o Remain in circulation longer because most are bound to carrier proteins o Enter the bloodstream More than 99% attach to special transport proteins Bloodstream contains substantial reserve of bound hormones • Catecholamines & peptide hormones… o Are NOT lipid soluble – unable to penetrate plasma membrane o Bind to receptor proteins at outer surface of plasma membrane (extracellular receptors) • Eicosanoids o Are lipid soluble o Diffuse across plasma membrane to reach receptor proteins on inner surface of plasma membrane (intracellular receptors) Mechanisms of Hormone Action • Hormone Receptor: Protein molecule to which a particular molecule binds strongly o Responds to several different hormones Presence or absence of specific receptor determines a cell’s hormonal sensitivity o Different tissues have different combinations of receptors A cell can respond to multiple hormones as long as that cell has receptors for that hormone • First Messenger: Hormone o Must trigger a second messenger inside the cell to cause a change within the cell o Bind to receptors in plasma membrane o Can’t have direct effect on activities inside target cell o Use intracellular intermediary to exert effects o May act as enzyme activator, inhibitor, or cofactor o Results in change in rates of metabolic reactions • Important second messengers: o Cyclic-AMP (cAMP) – derivative of ATPBSC2086 Anatomy & Physiology II Exam #1 Study Guide 5 o Cyclic-GMP (cGMP) – derivative of GTP o Calcium ions • Amplification: The binding of a small number of hormone molecules to membrane receptors that leads to thousands of second messengers in the cell o Magnifies effect of hormone on target cell o Ex) Cue ball (hormone) strikes many billiard balls (second messenger) but can then hit many more billiard balls • Down-Regulation: Presence of a hormone triggers decrease in number of hormone receptors o When levels of
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