GEN PHYSIOLOGY PRELIM

• Forces producing movements of water and other molecules across membranes or barriers:
• Diffusion is affected by electrical charge and permeability of the barrier
• Diffusion:

  • Gas or substance in solution expands due to particle motion to fill available volume
  • Particles move randomly from regions of high concentration to low concentration until uniform
• Donnan Effect:

  • Ion on one side of a membrane affects distribution of other ions
  • Diffusible ions distribute themselves to have equal concentration ratios at equilibrium
• Solvent Drag:

  • Solvent moving drags along some solute molecules
• Filtration:

  • Fluid forced through a membrane due to hydrostatic pressure difference
  • Smaller molecules pass through pores, larger molecules are retained
• Osmosis:

  • Movement of solvent molecules across a membrane to higher solute concentration
  • Effective osmotic pressure prevents solvent migration
• Tonicity:

  • Describes effective osmotic pressure relative to plasma
  • Isotonic solutions have the same EOP as plasma
  • Hypertonic solutions have greater pressure
  • Hypotonic solutions have lesser pressure
• Active Transport:

  • Ions and larger molecules transported by carrier molecules
  • Facilitated diffusion: no energy required from greater to lesser concentration
  • Active transport: energy required from lesser to greater concentration, carried out by pumps with ATP
• Endocytosis/Exocytosis:

  • Hormones and large polypeptides enter cell by endocytosis, secreted by exocytosis
  • Exocytosis: proteins move from endoplasmic reticulum to Golgi complex, then to cell membrane for secretion
• Cell membrane and resting membrane potential:

  • Resting membrane potential has negative intracellular and positive extracellular charge
  • Cell membrane properties: impermeable to intracellular proteins, moderately permeable to Na+, freely permeable to Cl- and K+
• Factors affecting movement of particles across the membrane:

  • Particle size: hydrated ions affect size
  • Ion channels: separate channels for Na+, K+, Cl-
  • Voltage: control ease of ion passage
  • Neurotransmitters: agents that control ion channel passage
• Forces acting on ions:

  • Concentration gradient: ions move from high to low concentration
  • Electrical gradient: ions move based on charge difference
  • Equilibrium reached when influx equals efflux
• Ionic basis of resting membrane potential:

  • Na+ actively transported out, K+ actively transported in
  • K+ diffuses out due to concentration gradient, Na+ diffuses in
  • Membrane permeability to K+ greater than Na+ at rest, leading to polarized state
• Na+ is actively transported out of the cell and K+ is actively transported in
• K+ diffuses back out of the cell due to its concentration gradient, while Na+ diffuses back into the cell
• At rest, the permeability of the membrane to K+ is much greater than to Na+, resulting in a greater passive K+ efflux compared to the passive Na+ influx
• The membrane is impermeable to most anions in the cell, so the K+ efflux is not accompanied by an equal flux of anions
• This imbalance maintains the membrane in a polarized state, with the interior of the cell negatively charged and the exterior positively charged