chapter 6 interaction between cells & extra-cellular environment remon wahba, md

Chapter 6Interaction Between Cells

& Extra-cellular Environment

Remon Wahba, MD

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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

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

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

Molarity & Molality

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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

Membrane Transport Systems

6-21

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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

Membrane Potential

6-32

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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)

Cell Signaling

6-41

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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

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Cell Signaling continued

Some use Gap Junctions through which signals pass directly from one cell to the next