chapter 6 interaction between cells & extra-cellular environment
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Chapter 6 Interaction Between Cells & Extra-cellular Environment. Remon Wahba, MD. Chapter 6 Outline Extra-Cellular Environment Movement Across Plasma Membrane Osmosis Membrane Transport Systems Membrane Potential Cell Signaling. 6-2. Cells & The Extra-Cellular Environmentr. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 6 Outline
Extra-Cellular Environment Movement Across Plasma MembraneOsmosisMembrane Transport SystemsMembrane PotentialCell Signaling
6-2
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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)
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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
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Extracellular Matrix Is a meshwork of Collagen & Elastin fibers
linked to molecules of gel-like ground substance & to plasma membrane integrinsGlycoprotein adhesion molecules that link
Intracellular & Extracellular compartments
Fig 6.16-5
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A Simplified Body Plan
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
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
gradientRequires Energy & transporters
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.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
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Diffusion
Is caused by random motion of moleculesNet movement is from regions of High
Concentration to regions of Low Concentration
OR
Movement down the concentration gradient
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Diffusion
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Diffusion
Concentration Number of molecules in a given unit of volume
Gradient Physical difference between two regions
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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
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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
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Diffusion (continued)
Rate of diffusion depends on:Magnitude of the concentration
gradient
Permeability of the membrane
Temperature
Surface area of the membrane6-11
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Diffusion (continued)
Diffusion of H20 Molecules is called Osmosis
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Osmosis
Is net diffusion of H20 across a selectively permeable membraneH20 diffuses down its concentration
gradientH20 is less concentrated where there are more solutesSolutes have to be Osmotically Active
i.e. cannot move freely across the membrane
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Osmosis
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H20 diffuses Down its
Concentration
Gradient until its
concentration is equal
on both sides of
membrane
Osmosis continued
6-14
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Is the Force that would have to be exerted to stop osmosis Indicates how strongly H20 wants to diffuse
Is proportional to Solute ConcentrationSolute ConcentrationThe more concentration of the solute, the more is the Osmotic Pressure
Osmotic Pressure
6-15
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Molarity & Molality
The Molecular weight of a molecule is
the sum of the Atomic Weights of its
atoms
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Molecular Weights NaCl:
Na = 23.0Cl = 35.5
= 58.5 Glucose:
C6 = 12x6 = 72H12 = 1x12 =12O6 = 16x6 = 96
=180
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mole An amount of any compound equal to its
molecular weight in grams is called molemole 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
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mole So one mole of Nacl contains 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
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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 H2oMeasurement of concentration of solutes
(number of molecules) in solutions
6-16
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Molarity & Molality
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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
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Molarity & Molality
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Tonicity
Is the effect of a Solution on
the Osmotic Movement of
H20
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Tonicity Isotonic solutions
Have Same osmotic pressure as PlasmaE.g. 5% Dextrose & 0.9% NaCl
Hypertonic solutions Have Higher osmotic pressure than PlasmaWater moves to the outside of Cells
Hypotonic solutionsHave Lower osmotic pressure than PlasmaWater moves to the inside of Cells
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Effects of tonicity on RBCs
Fig 6.11
shrink
6-19
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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 H20Thirst
To increase water intake
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Regulation of Blood Osmolality
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Carrier-Mediated Transport
Molecules, Too Large to diffuse are transported across the cell membrane by
Protein Carriers
6-22
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Carrier-Mediated Transport continued
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
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Facilitated Diffusion Is Passive Transport down concentration gradient by:
carrier proteins
6-24
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Active Transport
Is Transport of molecules Against a Concentration Gradient
Requires Energy (ATP)
6-25
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Na+/K+ Pump
Uses ATP to move 3 Na+ out &
2 K+ inAgainst their gradients
Fig 6.176-26
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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
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Absorption is transport of digestion products across intestinal epithelium into blood
Reabsorption transports compounds out of urinary filtrate back into blood
Fig 6.19
Transport Across Epithelial Membranes
6-29
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Transport Across Epithelial Membranes continued
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
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Bulk Transport Movement of Large Molecules & Particles across
plasma membrane Occurs by Endocytosis & Exocytosis (Ch 3)
6-31
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Membrane Potential Is difference in
Electric charge across the Plasma Membrane
The inside of the cell is Negatively charged compared to the outside
Fig 6.22
6-33
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Resting Membrane Potential (RMP)
Is membrane voltage of cell in unstimulated state (undisturbed)
RMP of most cells is -65 to –85 mVRMP depends on:
Concentrations of ions inside & outside
Permeability of each ionAffected most by K+ because it is
more permeable6-38
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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+
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Some Na+ diffuses in so RMP is less negative than EK+
Fig 6.25
Resting Membrane Potential (RMP) continued
6-39
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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 6.266-40
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Resting Membrane Potential (RMP)
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Cell Signaling Cells communicate with each other Two main ways:
Chemical messengers: To respond to a chemical signal, the target cell must have a Receptor protein specific for chemical messenger ParacrineHormones (Endocrine)Neurotransmitters
Electric communication:Gap Junctions
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Cell Signaling
In Paracrine signaling, cells secrete regulatory molecules that diffuse to nearby target cells
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Cell Signaling
In Endocrine signaling, cells secrete chemical regulators that move through Blood Stream to distant target cells
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Cell Signaling
In Synaptic signaling, A neuron sends messages using Neurotransmitter to another cell via synapses