Ch. 6: Interactions with Extracellular Environ.

• Extracellular Environment:

  • matrix of proteins and polysaccharides
  • cells receive nourishment from and release wastes into
  • cells secrete chemical regulators to communicate
• Body Fluids:

  • Intracellular Compartment: 67% of our water.
  • Extracellular Compartment: 33% of our water.
  • 20% is blood plasma, and 80% is interstitial fluid.
• Interstitial fluid is what connects the intracellular compartment to the blood plasma.
• Extracellular Matrix: A network of fibers and proteins that surrounds and supports cells.

  • contains collagen and elastin
  • Integrin: glycoproteins that extend from cytoskeleton to ECM.
• Functions of ECM:

  • relay signals
  • impact a polarity
  • affects both adhesion and motility
  • affects proliferation
• Non-Carrier Mediated Transport:

  • simple diffusion: down concentration gradient
  • Ex: lipid-soluble molecules
• Carrier Mediated Transport:

  • Facilitated diffusion: down concentration gradient, must use carrier protein.
  • Active Transport: against concentration gradient, must use ATP.
• Passive Transport: high to low concen , no energy

  • Simple Diffusion
  • Facilitated Diffusion
• Active Transport: low to high concen, uses energy like ATP

  • Pumps
• Solution: solvent (typically water) and solute (molecules dissolved)
• Gas Exchange: net diffusion of O2 into cells and CO2 out of cells due to concentration gradient.
• Mean Diffusion Time: the average time it takes for a solute to diffuse.

  • increases with SA
  • everything in the body is w/in 100um of a blood capillary
• Rate of Diffusion: # of diffusing particles / unit time.

  • magnitude of concentration difference
  • permeability of the membrane to molecules
  • temperature of the solution
  • surface area
• Water Molecules:

  • no overall charge, can pass through plasma membrane, but slowly
• Aquaporins: water channels.

  • many are located in the brain, kidneys, eyes, lungs.
• Tonicity: the effect of a solution on the osmosis of water.
• Hypotonic: solutions with a lower solute concentration than cell.

  • water goes into the cell.
  • cell expands
• Hypertonic: solutions with a higher solute concentration than cell.

  • water goes out of the cell.
  • cell shrinks
• Osmoreceptors: neurons in the hypothalamus
• Dehydrated -> blood becomes more concentrated -> blood volume decreases -> increases plasma osmolality -> increased ECF osmality -> osmoreceptor sitting in ECF -> water leaves osmoreceptor -> shrinks
• Carrier Proteins:

  molecule specific : only one or multiple related

  competition b/t similar molecules
• Transport Maximum: the max rate at which a substance can be moved across the membrane.

  Carriers are Saturated -> all in use

  the point at which increasing concen. of molecules does not increase movement of the substance
• Glucose is moved across the membrane via facilitated diffusion, which does not require energy.
• GLUT1: CNS

  GLUT2: insulin and hepatocytes

  GLUT3: neurons

  GLUT4: adipocytes and skeletal muscle fibers

  GLUT14: testes
• GLUT4: found in adipocytes and skeletal muscle fibers.

  Activated by insulin or exercise.

  important for muscle physiology and glucose homeostasis
• Calcium Pumps.

  all cells of the body pump into EE

  ER of striated muscle cells pump into cisternae of ER
• Primary Active Transport:

  hydrolysis of ATP -> ADP + Phosphate

  the pump is an ATPase enzyme.

  conformation change of protein due to phosphorylation
• Primary Active Transport Examples:

  Proton Pump

  Calcium Pump

  Na+/K+ Pump
• Na+/K+ Pump:

  3 Na binds to pump, activates ATPase, phosphate group binds

  3 Na EXIT the cell

  2 K bind and release the phosphate group

  2 K ENTER the cell
• Secondary Active Transport:

  A single carrier transports an ion down its concentration gradient while transporting a second molecule against its concentration gradient. 

  Indirect need for ATP
• Na/ Glucose Pump:

  secondary AT

  Na+ and glucose both bind to carrier

  causes a confirmation change

  both are transported into the cell
• Cotransport: both molecules move in the same direction
• Countertransport: molecules more in opposite directions.
• Absorption: transport of digestion products across the epithelium into the blood.

  Ex: cotransport of sodium and glucose
• Reabsorption: transport of molecules out of the urinary filtrate back into the blood.
• Transcellular Transport: materials move through the cytoplasm of the epithelial cell.
• Paracellular Transport: in the very tiny spaces between epithelial cells.
• Junctional Complexes: bind epithelial cells together.
• Exocytosis: exiting the cell

  Endocytosis: entering the cell
• Why is there a charge difference in the cell?

  -The membrane is permeable

  -Na/K pumps

  -Negatively charged molecules inside the cell