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Lecture 6

Lecture 6






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    Lecture 6 Lecture 6 Presentation Transcript

    • Diffusion Summary
      • Diffusion is the movement of molecule from one location to another by random thermal motion
      • The net flux between the two compartments always proceed from higher to lower concentration
      • Diffusion equilibirum is reached when the two concentration become equal
    • Osmosis Summary
      • Water crosses membranes by diffusing through protein channels in the membrane
      • Osmosis is the diffusion of water from higher water concentration to lower water concentration. Osmolarity total solute concentration in the solution. The higher osmolarity of a solution the lower the water concentration.
      • Osmosis across membrane permeable to water but impermeable to solute leads to increase volume in the compartment that initially had higher osmolarity.
      • Application to a solution of sufficient pressure will prevent the osmotic flow of water into the solution from the compartment of pure water. This pressure is osmotic pressure.
      • The greater the osmolarity of a solution the greater the osmotic pressure
      Osmosis Summary
      • The osmolarity of the extracellular fluid is about 300 mOsm. Intracellular fluid has osmolarity equal to that of extracellular fluid
      • Na and Cl ions are major effectively nonpenetrating solutes in the extracellular fluids. K ions and various organic solute are nonpenetrating solute in the intracellular fluid
      Osmosis Summary
    • Endocytosis and Exocytosis
      • During endocytosis vesicles will be formed that enclose a small volume of extracellular material
      • Three classes of endocytosis (1) fluid endocytosis (2) adsorptive endocytosis and (3) phagocytosis
      • Vesicles content digested by lysosome enzyme
      • Exocytosis provide a means of adding components to the plasma membrane and a route to release impermeable molecules into extracellular fluid
    • Mediated Transport System
      • Involve binding of the transported solute to transporter protein in the membrane. Changes in the conformation of the transporter move the binding site to the opposite side of the membrane
      • The binding sites exhibit chemical specificity and saturation
      • Facilitated diffusion move molecule from higher to lower concentration across the membrane by means of transporter. Metabolic energy is not required.
      • Active transport moves molecules against an electrochemical gradient across a membrane by means of transporter and require energy
      Mediated Transport System
      • Primary active transport uses the phosphorylation of the transporter by ATP to drive the transport process
      • Secondary active transport uses the binding of ions (often Na) to the transporter to drive the transport process
      • In secondary active transport the downhill flow of an ion is linked to the uphill movement of a second solute either in the same direction as the ion (cotransport) or opposite direction of the ion (countertransport)
      Mediated Transport System
    • Epithelial Transport
      • Molecules can cross epithelial layer by (1) through the extracellular spaces between the cells (paracellular pathway) and (2) through the cell across both luminal and basolateral membrane
      • The permeability and transport characteristics of the luminal and basolateral plasma membrane differ, resulting in the ability of the cells to actively transport a substance between the fluid on one side of the cell and the fluid on the opposite side of the cell
      • Major chemical substance in extracellular fluid are Na and Cl. Intracellular contain high K and negatively charged proteins and phosphate compound
      • Electrical resulting from this distribution have a significant role in cell integration and communication
      Membrane Potentials
      • Potential difference determine the difference in the amount of charge between two points.
      • The movement of electric charge is called current
      • The current depends on the potential difference between the charges
      Membrane Potentials
    • Terms describing the membrane potential
      • Potential – Potential difference: The difference between two points
      • Membrane potential: The voltage between inside and outside the cell
      • Resting potential: The steady membrane potential of a cell that is not producing an electric signal
    • Ion Distribution
      • Particles / molecules
        • electrically charged
      • Anions
        • negatively charged
      • Cations
        • positively charged
      • Anions (-)
        • Large intracellular proteins
        • Chloride ions Cl-
      • Cations (+)
        • Sodium Na+
        • Potassium K+
      Ion Distribution
    • The resting Membrane Potential
      • All cells have potential difference, inside negatively charged with respect to the outside. This potential is the resting membrane potential
    • Role of Electric Forces on Ion Movement
      • Separation of electric charge across plasma membranes known as Membrane Potential
      • Membrane Potential provides an electric force that influences the movement of ions across the membrane.
    • Resting Membrane Potential
      • The magnitude of the resting membrane potential determined by two factors:
      • Differences in specific ion concentration in the intracellular and extracellular fluids
      • Differences in the membrane permeabilities to the different ions
      • Plasma membrane Na, K- ATPase pumps maintain intracellular Na concentration low and K high
      • In almost all resting cells, the plasma membrane is much more permeable to K than to Na
      Resting Membrane Potential
    • Electrochemical Gradient
      • The Direction and Magnitude of ion fluxes across membranes depend on both the concentration difference and the electrical difference.
      • These two forces are collectively known as the electrochemical gradient .
    • Graded Potentials and Action Potentials
      • Changes in the membrane potential from its resting level produce electric signals
      • These signals occur in two forms: graded potentials and action potentials
      • Graded signaling over short distance while action potentials are long distance signals of nerve and muscle membrane