IVMS-Interactions Between Cells and the Extracellular Environment

Interactions Between Cells and the
Extracellular Environment
Compiled and Presented by
Marc Imhotep Cray, M.D.
Basic Medical Sciences Professor

Companion Notes
http://www.slideshare.net/drimhotep/ivmsoverview-of-cell-biology

Extracellular Environment

 Includes all constituents of the body located
outside the cell.
 Body fluids are divided into 2 compartments:
 Intracellular compartment:
 67% of total body H20.
 Extracellular compartment:
 33% total body H20.
 20% of ECF is blood plasma.
 80% is interstitial fluid contained in gel-like matrix.

2

Extracellular Matrix

 Consists of collagen, elastin and gel-like ground
substance.
 Interstitial fluid exists in the hydrated gel of the ground
substance.
 Ground substance:
 Complex organization of molecules chemically linked to
extracellular protein fibers of collagen and elastin, and
carbohydrates that cover the outside of the plasma membrane.
 Collagen and elastin:
 Provide structural strength to connective tissue.
 Gel:
 Composed of glycoproteins and proteoglycans which have a high
content of bound H20 molecules.
 Integrins are glycoproteins that serve as adhesion molecules
between cells and the extracellular matrix.

3

Categories of Transport Across
the Plasma Membrane
 Cell membrane is selectively  May also be categorized
permeable to some
molecules and ions. by their energy
 Not permeable to proteins, requirements:
nucleic acids, and other  Passive transport:
molecules.
 Net movement down a
 Mechanisms to transport concentration gradient.
molecules and ions through
Does not require
the cell membrane:


metabolic energy
 Carrier mediated transport: (ATP).
Facilitated diffusion and
Active transport:


active transport.
 Non-carrier mediated  Net movement against a
transport. concentration gradient.
 Diffusion and osmosis.  Requires ATP.

4

Diffusion

 Molecules/ions are in constant state of
random motion due to their thermal
energy.
 Eliminates a concentration gradient and distributes
the molecules uniformly.
 Physical process that occurs whenever there is
a concentration difference across the
membrane and the membrane is permeable to
the diffusing substance.

5

Diffusion Through Plasma
Membrane

 Cell membrane is permeable to:
 Non-polar molecules (02).
 Lipid soluble molecules (steroids).
 Small polar covalent bonds (C02).
 H20 (small size, lack charge).
 Cell membrane impermeable to:
 Large polar molecules (glucose).
 Charged inorganic ions (Na+).

6

Rate of Diffusion
 Speed at which diffusion occurs.
 Dependent upon:
 The magnitude of concentration gradient.

 Driving force of diffusion.

 Permeability of the membrane.

 Neuronal plasma membrane 20 x more
permeable to K+ than Na+.
 Temperature.

 Higher temperature, faster diffusion rate.

 Surface area of the membrane.

 Microvilli increase surface area.

7

Osmosis

 Net diffusion of H20 across a
selectively permeable membrane.
 Movement of H20 from a high[H20]
to lower [H20] until equilibrium is
reached.
 2 requirements for osmosis:
 Must be difference in [solute] on the
2 sides of the membrane.
 Membrane must be impermeable to
the solute.
 Osmotically active solutes:
 Solutes that cannot pass freely
through the membrane.

8

Effects of Osmosis

 H20 moves by osmosis into the lower [H20]
until equilibrium is reached (270 g/l glucose).
 Osmosis ceases when concentrations are
equal on both sides of the membrane.

9

Osmotic Pressure

 The force that would have to be exerted to prevent
osmosis.
 The greater the [solute] of solution, the > the osmotic
pressure.
 Indicates how strongly the solution “draws” H20 into it by
osmosis.

10

Molarity and Molality
 One-molar solution:
 1 mole of solute dissolved in H20 to = 1 liter.
 Exact amount of H20 is not specified.
 Ratio of solute to H20 critical to osmosis.
 More desirable to use molality (1.0 m).
 One-molal solution:
 1 mole of solute is dissolved in 1 kg H20.
 Osmolality (Osm):
 Total molality of a solution.
 Freezing point depression:
 Measure of the osmolality.
 1 mole of solute depresses freezing point of H20 by –1.86oC.
 Plasma freezes at –0.56oC = 0.3 Osm or 300 mOsm.

11

Effects of Ionization on Osmotic
Pressure

 NaCl ionizes when
dissolved in H20.
Forms 1 mole of Na+
and 1 mole of Cl-, thus
has a concentration of
2 Osm.
 Glucose when
dissolved in H20 forms
1 mole, thus has a
concentration of 1
Osm.
12

Tonicity

 The effect of a solution  Hypotonic:
on the osmotic  Osmotically active solutes
movement of H20. in a lower osmolality and
 Isotonic: osmotic pressure than
 Equal tension to plasma. plasma.
 RBCs will not gain or  RBC will hemolyse.
lose H20.
 Hypertonic:
 .  Osmotically active solutes
 RBC will crenate. in a higher osmolality
and osmotic pressure
than plasma

13

Regulation of Blood Osmolality

 Maintained in narrow
range by regulatory
mechanisms.
 If a person is
dehydrated:
 Osmoreceptors stimulate
hypothalamus:
 ADH released.
 Thirst increased.
 Negative feedback loop.

14

Carrier-Mediated Transport
 Molecules that are too large
and polar to diffuse are
transported across plasma
membrane by protein
carriers.
 Characteristics of protein
carriers:
 Specificity:
 Interact with specific
molecule only.
 Competition:
 Molecules with similar
chemical structures
compete for carrier site.
 Saturation:
 Tm (transport maximum):
 Carrier sites have
become saturated.

15

Facilitated Diffusion

 Passive:
 ATP not needed.
 Powered by thermal
energy of diffusing
molecules.
 Involves transport of
substance through
plasma membrane down
concentration gradient by
carrier proteins.
 Transport carriers for
glucose designated as
GLUT.

16

Primary Active Transport

 Hydrolysis of ATP directly
required for the function of
the carriers.
 Molecule or ion binds to
“recognition site” on one
side of carrier protein.
 Binding stimulates
phosphorylation (breakdown
of ATP) of carrier protein.
 Carrier protein undergoes
conformational change.
 Hinge-like motion releases
transported molecules to
opposite side of membrane.

17

Na+/K+ Pump

 Carrier protein is also an ATP
enzyme that converts ATP to
ADP and Pi.
 Actively extrudes 3 Na+ and
transports 2 K+ inward
against concentration
gradient.
 Steep gradient serves 4
functions:
 Provides energy for
“coupled transport” of other
molecules.
 Regulates resting calorie
expenditure and BMR.
 Involvement in
electrochemical impulses.
 Promotes osmotic flow.
18

Secondary Active Transport

 Coupled transport.
 Energy needed for “uphill” movement obtained
from “downhill” transport of Na+.
 Hydrolysis of ATP by Na+/K+ pump required
indirectly to maintain [Na+] gradient.

19

Secondary Active Transport

 Cotransport (symport):
 Molecule or ion moving in the
same direction as Na+.
 Countertransport (antiport):
 Molecule or ion moving in the
opposite direction of Na+.
 Glucose transport is an
example of:
 Cotransport.
 Primary active transport.
 Facilitated diffusion.

20

Transport Across Epithelial
Membranes

 Absorption:
Transport of digestion
In order for a

 products across the
molecule or ion to intestinal epithelium into
the blood.
move from the  Reabsorption:
external  Transport of molecules out
of the urinary filtrate back
environment into into the blood.
Transcellular transport:
the blood, it must 

Moves material through the
first pass through an


cytoplasm of the epithelial
cells.
epithelial  Paracellular transport:
membrane.  Diffusion and osmosis
through the tiny spaces
between epithelial cells.

21

Bulk Transport

 Movement of many large molecules, that cannot be
transported by carriers, at the same time.
 Exocytosis:
 Fusion of the membrane-bound vesicles that contains
cellular products with the plasma membrane.
 Endocytosis:
 Exocytosis in reverse.
 Specific molecules can be taken into the cell because of the
interaction of the molecule and protein receptor.

22

Membrane Potential

 Difference in charge
across the membrane.
 Cellular proteins and
phosphate groups are
negatively charged at
cytoplasmic pH.
 These anions attract
positively charged cations
from ECF that can diffuse
through the membrane
pores.

23

Membrane Potential (continued)

 Membrane more permeable
to K+ than Na+.
 Concentration gradients for
Na+ and K+.
 K+ accumulates within cell
also due to electrical
attraction.
 Na+/ K+ATPase pump 3 Na+
out for 2 K+ in.
 Unequal distribution of
charges between the inside
and outside of the cell,
causes each cell to act as a
tiny battery.
24

Equilibrium Potentials
 Theoretical voltage produced across
the membrane if only 1 ion could
diffuse through the membrane.
 If membrane only permeable to K+,
K+ diffuses until [K+] is at
equilibrium.
 Force of electrical attraction and
diffusion are = and opposite.
 At equilibrium, inside of the cell
membrane would have a higher
[negative charges] than the
outside.
 Potential difference:
 Magnitude of difference in charge
on the 2 sides of the membrane.

25

Nernst Equation
 Allows theoretical membrane potential to be
calculated for particular ion.
 Membrane potential that would exactly balance the
diffusion gradient and prevent the net movement
of a particular ion.
 Value depends on the ratio of [ion] on the 2 sides
of the membrane.
 Ex = 61 log [Xo]
z [Xi]
 Equilibrium potential for K+ = - 90 mV.
 Equilibrium potential for Na+ = + 60 mV.

26

Resting Membrane Potential

 Resting membrane potential is less than Ek
because some Na+ can also enter the cell.
 The slow rate of Na+ efflux is accompanied
by slow rate of K+ influx.
 Depends upon 2 factors:
 Ratio of the concentrations of each ion on the 2
sides of the plasma membrane.
 Specific permeability of membrane to each
different ion.
 Resting membrane potential of most cells
ranges from - 65 to – 85 mV.
27

Cell Signaling
 How cells communicate with each other.
 Gap junctions:
 Signal can directly travel from 1 cell to the next through
fused membrane channels.
 Paracrine signaling:
 Cells within an organ secrete regulatory molecules that
diffuse through the extracellular matrix to nearby target
cells.
 Synaptic signaling:
 Means by which neurons regulate their target cells.
 Endocrine signaling:
 Cells of endocrine glands secrete hormones into ECF.
 For a target cell to respond to a hormone, NT, or
paracrine regulator; it must have specific receptor
proteins for these molecules.
28

Cellular Transport
 Diffusion, Dialysis and Osmosis Tutorial by RM Chute
 Osmosis - Examples Colorada State University
 Osmosis by Terry Brown
 Interactive Cellular Transport by Rodney F. Boyer
 Hypotonic, Isotonic, Hypertonic by June B. Steinberg
 Osmosis McGraw-Hill Companies, inc
 Symport, Anitport, Uniport by University of Wisconsin
 Facilitated Diffusion by University of Wisconsin
 Passive and Active Transport from Northland Community and
Technical College
 The Plasma Membrane Dr JA Miyan at Department of
Biomolecular Sciences, UMIST, UK
 Endocytosis of an LDL EarthLink
 Osmosis (thistle tube)

29

Cellular Structure and Function
 Comparison of Prokaryote, Animal and Plant Cells by Rodney F.
Boyer
 Flash animations of Biological Processes by John L. Giannini
 Organize It by Leif Saul
 Stem Cells Sumanas Inc.
 Membrane Structure Tutorial
 Various Cellular Animations University of Alberta
 Cellular Receptor Animations University of Oklahoma
 Cell Tutorial from "Cells Alive!"
 Simple cell by Terry Brown
 Kinesin - Molecular Motor Sinauer Associates Inc., W. H. Freeman
Co. and Sumanas Inc.
 Kinesin Movie RPI
 Cellular Animations by Donald F. Slish
 Flagella and Cilia from Northland Community and Technical College

30

IVMS-Interactions Between Cells and the Extracellular Environment

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