Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 6 Interactions Between Cells and the Extracellular Environment 6-1

Extracellular Environment 6-3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extracellular Environment  Includes all constituents of body outside cells  67% of total body H 2 O is inside cells (=intracellular compartment); 33% is outside cells (=extracellular compartment-ECF)  20% of ECF is blood plasma  80% of ECF is interstitial fluid contained in gel-like matrix- where we want H 2 O to go. 6-4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Body-Fluid Compartments  Body has intracellular and extracellular compartments  Intracellular is inside cells  Extracellular is outside cells  Separated by cell’s outer membrane  Extracellular is composed of blood plasma and interstitial fluid 1-45

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extracellular Matrix  Is a meshwork of collagen and elastin fibers linked to molecules of gel-like ground substance and to plasma membrane integrins  = glycoprotein adhesion molecules that link intracellular and extracellular compartments  Interstitial fluid resides in hydrated gel of ground substance 6-5

Movement Across Plasma Membrane 6-6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transport Across Plasma Membrane  Plasma membrane is selectively permeable--allows only certain kinds of molecules to pass  Many important molecules have transporters and channels  Carrier-mediated transport involves specific protein transporters  Non-carrier mediated transport occurs by diffusion 6-7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transport Across Plasma Membrane continued  Passive transport moves compounds down concentration gradient; requires no energy  Active transport moves compounds against a concentration gradient; requires energy and transporters 6-8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diffusion  Is random motion of molecules  Net movement is from region of high to low concentration 6-9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Non-polar compounds readily diffuse thru cell membrane  Also some small molecules such as CO 2 and H 2 O  Gas exchange occurs this way Diffusion continued 6-10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Cell membranes are impermeable to charged and most polar compounds  Charged molecules must have an ion channel or transporter to move across membrane Diffusion continued 6-11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diffusion continued  Rate of diffusion of a compound depends on:  Magnitude of its concentration gradient  Permeability of membrane to it  Temperature  Surface area of membrane  H 2 O levels 6-12

Osmosis 6-13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Osmosis  Is net diffusion of H 2 O across a selectively permeable membrane  H 2 O diffuses down its concentration gradient  H 2 O is less concentrated where there are more solutes  Solutes have to be osmotically active  i.e., cannot freely move across membrane 6-14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  H 2 O diffuses down its concentration gradient until its concentration is equal on both sides of a membrane  Some cells have water channels (aquaporins) to facilitate osmosis Osmosis continued 6-15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Is the force that would have to be exerted to stop osmosis  Indicates how strongly H 2 O wants to diffuse  Is proportional to solute concentration Osmotic Pressure 6-16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tonicity  Is the effect of a solution on osmotic movement of H 2 O  Isotonic solutions have same osmotic pressure  Hypertonic solutions have higher osmotic pressure and are osmotically active  Hypotonics have lower osmotic pressure  Isosmotic solutions have same osmolality as plasma  Hypo-osmotic solutions have lower osmotic pressure than plasma  Hyperosmotics have higher pressure than plasma 6-19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-20

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Regulation of Blood Osmolality  Blood osmolality is maintained in narrow range around 300mOsm  If dehydration occurs, osmoreceptors in hypothalamus stimulate:  ADH release  Which causes kidney to conserve H 2 O and thirst 6-21

Membrane Transport Systems 6-22

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Facilitated Diffusion  Is passive transport down concentration gradient by carrier proteins 6-25

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Active Transport  Is transport of molecules against a concentration gradient  ATP is required 6-26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Na + /K + Pump  Uses ATP to move 3 Na + out and 2 K + in  Against their gradients 6-27

Membrane Potential 6-35

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Membrane Potential  Is difference in charge across membranes  Results in part from presence of large anions being trapped inside cell  Diffusable cations such as K + are attracted into cell by anions  Na + is not permeable and is actively transported out 6-36

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Equilibrium Potential  Describes voltage across cell membrane if only 1 ion could diffuse  If membrane permeable only to K +, it would diffuse until it reaches its equilibrium potential (E k )  K+ is attracted inside by trapped anions but also driven out by its concentration gradient  At K+ equilibrium, electrical and diffusion forces are = and opposite  Inside of cell has a negative charge of about -90mV 6-37

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Resting Membrane Potential (RMP)  Is membrane voltage of cell not producing impulses  RMP of most cells is –65 to –85 mV  RMP depends on concentrations of ions inside and out  And on permeability of each ion  Affected most by K + because it is most permeable 6-41

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Some Na + diffuses in so RMP is less negative than E K+ Resting Membrane Potential (RMP) continued 6-42

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Role of Na+/K+ Pumps in RMP  Because 3 Na+ are pumped out for every 2 K+ taken in, pump is electrogenic  It adds about –3mV to RMP 6-43

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Summary of Processes that Affect the Resting Membrane Potential 6-44