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Interactions Between Cells & the Extracellular Environment Chapter 6
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Transcript of Interactions Between Cells & the Extracellular Environment Chapter 6
Interactions Between Cells & the Extracellular Environment
Chapter 6
CHEMICAL REGULATORS extracellular environment represents all
constituents outside the cell Mechanism of chemical regulators.
obtain nourishment, release secretions, eliminate wastes
impact/interact neighboring (1) cells,(2) different tissues&/or
(3) different organs Body Fluids Divided into compartments:
extracellular 33% bld plasma & interstitial fluid intracellular
67% fluids serve as communication link cells tissues organs One big
communication network connective tissue of a tissue/organ
Extracellular Matrix complex network of proteins specific for any
given tissue EC fluid interspersed within functions: scaffolding
for cellular attachment transmits information to regulate activity,
migration, growth & differentiation ECM Outside of the cell
connective tissue of a tissue/organ An Example ECM composed of
fibrous proteins but also ground substance, analogous to a hydrated
gel & location of IF comprised of glycoproteins &
proteoglycans gel binds water highly functional, complex
organization of molecules chemically linked to EC protein fibers
& glycoproteins of glycocalyx Location of interstitial fluid
Glycocalyx == carbohydrate (sugary) region outside of the ECM Binds
water (water loving) forms gel Integrin class of glycoproteins that
extend from the cytoskeleton within the cell. Connect intracellular
and various elements of the ECM. Links ECM and ICM components.
Allows for info to be exchanged between block integrin - binding
site on platelets, slows bld clotting integrins - adhesion molecule
between cell & ECM, physically joining EC & IC compartments
serve to relay signals or integrate them Transport Across the
Plasma Membrane
serves as a barrier to movement - EC & IC compartments
selectively permeable membrane transport processes E requirements
passive transport active transport carrier-mediated transport
versus transport without a carrier Selective only certain things
can pass through can change according to the needs of cells. Can
either diffuse across or need a carrier molecule Diffusion &
Osmosis molecules of a solution are in constant motion
solvent solute mean diffusion time conc gradient exists, motion
tends to eliminate the difference, with the random motion of
molecules is diffusion will move in both directions but a net
movement from higher to lower until equilibrium is reached Net flux
of invt depending upon concentration gradient 100 micrometers is
the magic number, this distance or less. PM is 10 nanometers
Diffusion times (10^-7 seconds) Time it takes from start to end of
diffusion- mean diffusion times Compartment one has higher solute
concentration, if membrane is permeable to solute it is going to
flow along conc. Gradient Most cells are going to be within 100 um
to a capillary, Why in regards to a capillary? site of exchange,
blood in capillary, and nutrients and oxygen and etc in blood.
Epithelial tissue is not vascularized so needs to be in this
distance in order to obtain the nutrients they need to grow and to
get rid of waste. increases with distance; distances kept within
100 m for effective exchange will follow concentration gradient
between compartments
Diffusion through a PM nonpolar molecules O2 & steroids, or
small polar covalent molecules without charge CO2, ethanol &
urea, can easily cross the PM will follow concentration gradient
between compartments Within the cell, O2 is low but outside of the
cell it is high, so O2 will diffuse into the cell, because cell is
metabolically active and contains CO2, the CO2 goes out and is
later picked up. Membrane Channels charged inorganic ions, Na+
& K+, utilize channels
Why? Gives you a mechanism for control, REGULATOR. Can be open by
particular physiological stimuli. channels may be OPEN or GATED for
large, polar molecules, carrier proteins are needed in the PM for
movement particular physiological stimuli opens/closes gate Rate of
Diffusion J = PA (Co Ci) magnitude of conc gradient
speed of diffusion per unit time J = PA (Co Ci) net flow (J) is
directly proportional to the conc gradient (Co-Ci), the surface
area (A) and the membrane permeability coefficient (P) magnitude of
conc gradient diffusing substances permeability to PM temperature
SA available distance Larger conc gradient => FASTER movement
More permeable = faster movement across PM Higher temp = faster
diffusion More SA = can move more molecules across that space,
increases diffusion Distance, need to watch parameter (100 um)
Permeability is very important in how things move across a plasma
membrane ** greater P, larger the J across the PM for any given
conc difference & A magnitude of conc gradient driving force
for diffusion BUT will not move if PM not permeable to that
molecule Osmosis net diffusion of water requirements:
follows waters conc gradient requirements: conc difference of
solute between sides of membrane membrane selectively impermeable
to solute nonpenetrating solute osmotically active creates osmotic
pressure pull of water aquaporins water channels facilitate
movement of water present in some cell types or can be inserted in
response to regulatory molecules Example : solute cant make it
across (non-penetrating solute) In order for water to move its
going to follow its concentration gradient, which depends on how
much solute is there More water on outside so flows into where most
solute is and makes the inner circle expand. Water can also diffuse
through PM without using an aquaporin but depends on pm of the cell
Osmotic Pressure (OP) Inside cell SWELLS Osmotic Pressure- how much
pressure do I need to apply so that water does not flow? Higher
pressure with 360g/L sucrose more solutes, greater conc difference,
so need to apply more pressure so water does not flow. OP of a soln
represents the pressure that must be applied to a solution to
prevent the net flow of water indicates how strongly a
solndrawswater water drawn more rapidly with greater solute conc
ratio of solute to solvent not completely specified
amt of water changes due to MW of substance MOLARITY Molarity vs
Molality better measurement of concentration when discussing
osmosis weigh one mole of substance and place in 1Kg water thus can
compare between solutes since both in same amt of water Molarity:
1.0 mole of solute and bring it up to 1L. 1 mole of glucose = 180 g
Molality: 1.0 mole of molecultes, but put into 1kg of H2O, so you
end up with slightly different volumes Molarity(M): ratio of solute
to solvent, the amount of water changes due to MW of substance
Molality (m): both solutes are in the same amount of water.
MOLALITY Osmolality OP depends on ratio of solute to solvent, not
chemical characteristics of solute osmolality Osm total molality of
a solution what about electrolytes? ionize plasma & other
biological fluids have a complex osmolality due to the presence of
organic molecules & electrolytes cell activity leads to
constant change Electrolytes dissociate/ ionize -going to have
osmosis occurring bc two conc are different Complex bc have organic
molecules and cells are constantly changing so needs to be
addressed by the organism Isotonic when have same inside and out
Cells are dynamic, making and using things-> environment inside
and outside cell is constantly changing Tonicity describes effect
of solution on osmotic movement of water, thus cell shape &
volume solute load 300 mOsm solutions described by how they change
cell volume (& thus shape) by causing water movement take into
account both solute conc & solute permeability for each solute
crossing the PM Standard is 300 mOsm -isotonic have no exchange
-hypotonic when water moves into cell and becomes lg and round
-hypertonic when cell shrinks, loses water If 200 then hypotonic
and if 400 then hypertonic Osmolality vs Tonicity
Can a solution be iso-osmotic but not isotonic? YES, if solute is
permeable to membrane, ie is a penetrating molecule, thus can
freely cross the PM Urea is going to move into the cell and cause
fluid flow but have a penetrating molecule * Look if it is
penetrating and can or cannot move Question When a cell comes in
contact with a soln, hypertonic or hypotonic, the initial conc of
solutes determines the degree of change - impermeant If a cell were
placed in a solution containing 100 mOsm impermeant solutes, how
would its final volume compare to its initial volume? answer on
notecard It would increase by 3 times Homeostasis of Plasma
Concentration
variety of mechanisms exist to keep blood plasma osmolality
maintained within very narrow limits In kidneys is going to open up
water channels and allow us to have water intake Carrier-Mediated
Transport
cellular metabolism relies on the cells ability to uptake molecules
it needs from the EC fluid many of these molecules cannot be
attained by simple diffusion, require protein carriers specificity,
saturation & competition Comparison Need protein carriers->
and display characteristic of saturation- are carrier mediated If
only have 25 carriers then completely saturated at 25 * With
diffusion it will continue to move as long as there is a conc
gradient carrier proteins display the characteristic of saturation
if carrier can transport more one molecule type, then they will
compete for transport becomes saturated Facilitated Diffusion
passive transport Display specificity, competition, and saturation
depending on carrier We can add transporters to pm or also take
them away ** about meeting needs of cell cell stimulated, insert
carriers into PM to meet cell needs display specificity,
competition & saturation Active Transport Primary
energy required for carrier function typically, molecules/ions
moved against their conc gradient process: binding of molecule to
be transported to recognition site binding stimulates ATP
hydrolysis phosphorylation causes carrier protein to undergo
conformational change hingelike motion of carrier protein releases
transported molecule to other side often referred to as pumps ATP
hydrolysis-> energy Pumps- active transport mech (pump utilizing
energy) Na-K Pump creates steep ion gradient functions:
provides E for coupled transport of other molecules used to
generate electrochemical events (impulse) innervous & muscle
tissue Na movement impt for osmotic reasons stops, observe Nai,
cause osmotic influx of water (damage cell) Move Na out and K in
Active Transport Secondary
sets up gradient X driven indirectly by passive ion gradients
created by operation of primary active pump symport Na wants to
move into cell and K wants to move out Symport- when glucose and Na
move in same position If molecules moving in opposite direction
then anti symport Stop pumping Na-K which means that we are going
to lose the concen gradient-> will be able to move for a little
while but will eventually stop what happens if the Na-K pump is
poisoned? Movement of solutes across a typical PM involving
membrane proteins
Many of these membrane proteins can be modulated by various
signals, resulting in controlled rise or fall in specific solute
fluxes across PM Can move many things like amino acids, NaCl
Specialized cells may contain additional transporters and channels
Transport Across Epithelial Membranes
Since epithelial cells line the bodys surface as well as cavities
of hollow organs, molecules entering the body must pass through an
epithelial cell layer absorption reabsorption transcellular
transport, transepithelial transport, transcytosis paracellular
transport Junctional complex that seal off epith but are NOT
absolute * directionality* NOTICE polarity, or definite direction
of transport in epithelial cells apical-basolateral Movement of
Glucose presence & number dependent on location
Junctional Complex physically join presence & number dependent
on location glued together velcroed together Bulk Transport
endocytotic events for secretion, use exocytosis
exocytosis can use pinocytosis, phagocytosis, bringing elements/
food into cell or can be very specific through a receptor
endocytotic events for secretion, use exocytosis movement of
molecules too large to be transport through PM