Cellular Transport and Tonicity

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Cellular Transport and Tonicity

• Biology 2121

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Selective Permeability of the Plasma Membrane

• Which substances can move freely through the
  phospholipid bilayer?
• Water, gases (oxygen, carbon dioxide) fats
• Small- polar nonpolar molecules
• Which substances are blocked?
• Glucose ions
• Larger substances (polar)
• Processes
• Passive (no ATP)
• High to lower concentration gradients
• Driving Force? KE of the substances
• Active (requires ATP)
• Low to higher concentration gradients

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Passive Processes

• 1. Diffusion vs. Osmosis
• 2. Simple Diffusion
• Gases nonpolar lipid soluble substances
  (fat-soluble vitamins)
• 3. Facilitated Diffusion
• Sugars (glucose amino acids ions)
• Integral or Transmembrane proteins
• Channel or carrier proteins
• 4. Osmosis
• Movement of water dependent on solute
  concentration (extracellular/intracellular)

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Tonicity

• Measure of the ability of a solution to cause a
  change in cell shape or tone caused by osmotic
  flow of water
• Why does osmosis occur?
• Water concentration differences
• Solute concentration affects water concentration
• Dependent on the number (concentration)
• Osmolarity
• Permeability of solute molecules
• Permeable to all solute molecules equilibrium
• If membrane is impermeable (see U-tube)

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Water Movement and Solute Concentration
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Tonicity Conditions

• Isotonic
• Cells have same concentrations of non-penetrating
  solutes as found in cells
• Our cellular fluids and IVs
• Hypertonic
• Solutions have higher concentration of
  non-penetrating solutes
• Salty or high saline conditions
• Hypotonic
• Solutions containing a lower concentration of
  non-penetrating solutes
• dilute

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Active Transport

• Driving Force? ATP
• Solute pumps (ions- K, Na, etc.)
• Sodium-Potassium Pump
• primary active transport
• Neurons, cardiac and skeletal tissue
• Vesicular Transport
• Fluids contain large particles and macromolecules
  
• Vesicles

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Vesicular Transport

• Exocytosis
• ejects substances from cells
• Hormone and mucous secretion
• Endocytosis
• Substance moves into cell and vesicle formed
• transcytosis, vesicular trafficking
• Phagocytosis
• Pinocytosis