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Lecture 6

by: Kelly Wetmore

Lecture 6 Bio 242

Kelly Wetmore

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Lecture 6
Intro Human Physiology
Barbara Van Sciver
Class Notes
BIO 242, University of Rhode Island, Lecture, Physiology, Biology, notes
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This 4 page Class Notes was uploaded by Kelly Wetmore on Tuesday March 1, 2016. The Class Notes belongs to Bio 242 at University of Rhode Island taught by Barbara Van Sciver in Winter 2016. Since its upload, it has received 16 views.

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Date Created: 03/01/16
Thursday, May 19, y Lecture 6 Intercellular Chemical Messengers ­ Paracrine • Binds to receptor • Secretory ———> target cell • Can only act upon nearby cells • EX: Histamine­ causes blood vessels to dilate • Short distance signals ­ Neurotransmitters • Pre­ and post­ synaptic neuron • Electricity ­ Hormones • Released into blood • Secretory cells find target cells ­ Neurohormones Membrane Transport ­ Solubility • ECF and ICF • Polar and Nonpolar ­ Size • Small polar molecules can get through protein channels 1 Thursday, May 19, y • Large polar molecules in a carrier ­ Active transport • Uphill (low concentration to high concentration) • Requires ATP • Against the concentration gradient ­ Passive transport Carrier Mediated Transport ­ Facilitated diffusion • Downhill (Higher to lower concentration) • With aid Na+/K+ Pump- Active Transport ­ Pumps sodium and potassium ­ Sodium is being pumped uphill ­ Dephosphorated ­ Potassium is released ­ 3 Na+ for every 2 K+ ­ Pump requires energy ­ Against the concentration gradient = Uphill pump Membrane Channels ­ Leaky • Always open 2 Thursday, May 19, y • Not regulated ­ Ligand • Chemical messenger gated • Channels open only when it receives a receptor ­ Voltage gated • Depends on the voltage of the channel (open or closed depending) Electrical Properties of the Membrane ­ Anions are negative and are non­diffusible (can’t get out of the cell) in ICF ­ Actions of the sodium/potassium pump • 2 K+ <———> Na_3 • More permeable to potassium than sodium • It requires energy to move potassium into the cell but it doesn’t require energy to  get it out of the cell • Pump’s concentration gradient favors potassium movement into the cell ­  Resting membrane potential = ­70 mV • No potential energy Membrane Potential ­ The difference in electrical voltage (potential) that exists across the membrane of  most cells ­ ———> Membrane is polarized Current ­ Flow of electricity 3 Thursday, May 19, y ­ Movement of Ions Excitable Tissues ­ Neurons and muscles can undergo changes of action potentials ICF and ECF ­ ICF • Negative charges are trapped • Potassium pumped out —> • Negative ­ ECF • Sodium pumped in <— • Positive ­ Charges line up at membrane Graded Potentials ­ Short distance signals (die out very quickly) ­ Decremental (keeps getting stronger) ­ Strength is proportional to stimulus strength Action Potentials ­ Long distance signals (released at axon terminal) ­ Non­decremental ­ Strength is not proportional to stimulus 4


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