Chapter 6 Interaction Between Cells & Extra-cellular Environment

1. Chapter 6Interaction Between Cells & Extra-cellular Environment Remon Wahba, MD

2. Chapter 6 Outline • Extra-Cellular Environment • Movement Across Plasma Membrane • Osmosis • Membrane Transport Systems • Membrane Potential • Cell Signaling 6-2

3. Cells & The Extra-Cellular Environmentr • Water, Ions and other molecules are present in our body in TWO Compartments: • Intracellular = inside the cells • Extracellular = outside the cells • There is always interaction between the two compartments (movement of Ions and Molecules)

4. Body Water • Water in our body is distributed between: • The Intracellular Compartment • 67% of total body H20 • The Extracellular Compartment (ECF) • 33% of total body water is outside cells • 20% of ECF is Blood Plasma • 80% of ECF is Interstitial Fluid • Present in between the cells • Contained in gel-like matrix 6-4

5. Extracellular Matrix • Is a meshwork of Collagen & Elastin fibers linked to molecules of gel-like ground substance & to plasma membrane integrins • Glycoprotein adhesion molecules that link Intracellular & Extracellular compartments Fig 6.1 6-5

6. A Simplified Body Plan

7. Movement Across Plasma Membrane 6-6

8. Transport Across Plasma Membrane • Plasma membrane is Selectively Permeable--allows only certain kinds of molecules to pass • Two main types of transport: • Passive transport • Moves compounds down concentration gradient • Requires No Energy • Includes Diffusion, Osmosis, Facilitated Diffusion • Active transport • Moves compounds against concentration gradient • Requires Energy & transporters

9. Transport Across Plasma Membrane • Two major categories: • Non-carrier mediated transport • Occurs by Diffusion, Osmosis • Carrier-Mediated transport • Requires specific protein transporters & Channels • Includes Facilitated Diffusion & Active Transport

10. Diffusion • Is caused by random motion of molecules • Net movement is from regions of High Concentration to regions of Low Concentration OR • Movement down the concentration gradient

11. Diffusion

12. Diffusion • Concentration • Number of molecules in a given unit of volume • Gradient • Physical difference between two regions

13. Non-polar compounds diffuse readily through the cell membrane Also some small polar molecules including C02 & H20 Gas exchange occurs by Diffusion Diffusion(continued) 6-10

14. Diffusion(continued) • Cell membrane is Impermeable to charged & most polar compounds • Charged molecules must have: • Ion Channels OR • Protein Transporters to move across the membrane

15. Diffusion(continued) Rate of diffusion depends on: Magnitude of the concentration gradient Permeability of the membrane Temperature Surface area of the membrane 6-11

16. Diffusion(continued) • Diffusion of H20 Molecules is called Osmosis

17. Osmosis • Is net diffusion of H20 across a selectively permeable membrane • H20 diffuses down its concentration gradient • H20 is less concentrated where there are more solutes • Solutes have to be Osmotically Active • i.e. cannot move freely across the membrane

18. Osmosis

19. H20 diffuses Down its Concentration Gradient until its concentration isequal on both sides of membrane Osmosiscontinued 6-14

20. Is the Force that would have to be exerted to stop osmosis Indicates how strongly H20 wants to diffuse Is proportional to Solute Concentration The more concentration of the solute, the more is the Osmotic Pressure Osmotic Pressure 6-15

21. Molarity & Molality

22. Molarity & Molality • The Molecular weight of a molecule is the sum of the Atomic Weights of its atoms

23. Molecular Weights • NaCl: • Na = 23.0 • Cl = 35.5 = 58.5 • Glucose: • C6 = 12x6 = 72 • H12 = 1x12 =12 • O6 = 16x6 = 96 =180

24. mole • An amount of any compound equal to its molecular weight in gramsis called mole and it contains a fixed number of molecules. • Avogadro’s number: • Number of molecules present in a mole • It is equal to 6.02 X 1023

25. mole • So one mole of Naclcontains the same number of molecules as one mole of Glucose • (They are different in weight but they contain the same number of molecules). • = Avogadro’s number

26. Molarity & Molality One molar solution (1.0M) = One mole of solute dissolved in water to make 1L of solution Doesn't specify exact amount of H20 One molal solution (1.0m) = One mole of solute dissolved in 1 L (1KG) of H2o Measurement of concentration of solutes (number of molecules) in solutions 6-16

27. Molarity & Molality

28. Molarity & Molality • Osmolality (Osm) • is total Molality of a solution • Depends on number of molecules or particles • NaCl dissociates into Na+ & Cl- • So1.0 molal solution of NaCl yields a 2 Osm solution ( has double the osmolality of 1 molal solution of glucose

29. Molarity & Molality

30. Tonicity • Is the effect of a Solution on the Osmotic Movement of H20

31. Tonicity • Isotonic solutions • Have Same osmotic pressure as Plasma • E.g. 5% Dextrose & 0.9% NaCl • Hypertonic solutions • Have Higher osmotic pressure than Plasma • Water moves to the outside of Cells • Hypotonic solutions • Have Lower osmotic pressure than Plasma • Water moves to the inside of Cells

32. Effects of tonicity on RBCs Fig 6.11 shrink 6-19

33. Regulation of Blood Osmolality • Blood Osmolality is maintained in a narrow range around 300m Osm • In cases of dehydration, Osmoreceptors in Hypothalamus are stimulated leading to: • ADH Release • Which causes kidney to conserve H20 • Thirst • To increase water intake

34. Regulation of Blood Osmolality

35. Membrane Transport Systems 6-21

36. Carrier-Mediated Transport • Molecules, Too Large to diffuse are transported across the cell membrane by • Protein Carriers 6-22

37. Carrier-Mediated Transportcontinued • Protein Carriers exhibit: • Specificity for single molecule • Competition among substrates for transport • Saturation when all carriers are occupied • This is called Tm(transport maximum) 6-23

38. Facilitated Diffusion • Is Passive Transport down concentration gradient by: carrier proteins 6-24

39. Active Transport • Is Transport of molecules Against a Concentration Gradient • Requires Energy (ATP) 6-25

40. Na+/K+ Pump • Uses ATP to move • 3 Na+ out & • 2 K+ in Against their gradients Fig 6.17 6-26

41. Secondary Active Transport • Uses energy from “downhill” transport of Na+to drive “uphill” movement of another molecule • Also called Coupled Transport • ATP required to maintain Na+ gradient • Important for Oral Rehydration • Glucose helps the absorption of Na+ then water follows by osmosis 6-27

42. Transport Across Epithelial Membranes • Absorption is transport of digestion products across intestinal epithelium into blood • Reabsorption transports compounds out of urinary filtrate back into blood Fig 6.19 6-29

43. Transport Across Epithelial Membranescontinued • Transcellular Transport • Moves material from 1 side of Epithelial Cells to the other (Through the Cell) • Paracellular Transport • Moves material through tiny spaces between Epithelial Cells 6-30

44. Bulk Transport • Movement of Large Molecules & Particles across plasma membrane • Occurs by Endocytosis & Exocytosis (Ch 3) 6-31

45. Membrane Potential 6-32

46. Membrane Potential Fig 6.22 • Is difference in Electric charge across the Plasma Membrane • The inside of the cell is Negatively charged compared to the outside 6-33

47. Resting Membrane Potential (RMP) • Is membrane voltage of cell in unstimulated state (undisturbed) • RMP of most cells is -65 to –85 mV • RMP depends on: • Concentrations of ions inside & outside • Permeability of each ion • Affected most by K+ because it is more permeable 6-38

48. Resting Membrane Potential (RMP) • Results from: • LARGE NEGATIVELY CHARGED organic molecules inside the cell • Na+ / K+ pump • Three Na+ are pumped out • Two K+ are pumped in • The Plasma Membrane is more permeable to K+ than Na+

49. Resting Membrane Potential (RMP)continued • Some Na+ diffuses in so RMP is less negative than EK+ Fig 6.25 6-39

50. 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 Fig 6.26 6-40