Physiology Ch. 6

Located outside the cell

• 33% of the body's water located in extracellular environment
• of this 20% is the blood plasma, 80% is the interstitial fluid

The cells of the organs are suspended with the extracellular material (matrix) of connective tissues that contain protein fibers of collagen and elastin

Plasma (cell )membrane is semi-permeable or selectively permeable

• Carrier-mediated
• Non carrier-mediated

• Passive transport
• Active transport

Transport of molecules across cell membrane that is mediated by protein carriers within the membrane

• Active net movement against (up) a concentration gradient
• Requires metabolic energy (ie: from lower to higher concentration)

• Primary active transport
• Sodium-potassium pump
• Secondary active transport

Use of exocytosis and endocytosis

• Random molecular motion
• Net diffusion of an ion/molecule always occurs in the direction of lower concentration

• Magnitude of concentration difference across membrane
• Permeability of the membrane to the molecule/substance
• Temperature of the solution
• Surface area of the membrane
• Presence of ion channels/gates (ex: Na+, K+)

Passive net movement down a concentration gradient (high to low) ex: transport of glucose from the blood across plasma membrane

The net diffusion of solvent (water) across a membrane (high to low)

• Concentration difference present on the 2 sides of a selectively permeable membrane
• Membrane must be relatively impermeable to the solute

Amount of pressure/force that would be required to prevent osmosis from occuring

• As a result of the permeability properties across the cell membrane a membrane potential can be present
• The membrane potential is the difference in charge across the cell membrane (outside vs inside)
• Unequal distribution of charges between the inside and outside of the cell, causes each cell to act as a tiny battery

• Cellular proteins and phosphate groups are negatively charged
• K+ is positively charged

• Na+ is positively charged
• Cl is negatively charged

• The membrane potential that would exactly balance the diffusion gradient and prevent the net movement of a particular ion is known as the equilibrium potential
• Magnitude of difference in charge on the 2 sides of the membrane

• -90mV
• No k+ movement within or outside the cell

• 60 mV
• no movement

• Resting membrane potential is less than equilibrium potential (Ek) because some Na+ can also enter the cell
• The slow rate of Na+ efflux is accompanied by slow rate of K+ influx

• Ratio of the concentrations of each ion on the 2 sides of the plasma membrane
• Specific permeability of membrane to each different ion

-65 to -85 mV

-70mV