Chapter 6
Interaction Between Cells
&
Extra-cellular Environment
Remon Wahba, MD
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 6 Outline
Extra-Cellular
Environment
Movement Across Plasma Membrane
Osmosis
Membrane Transport Systems
Membrane Potential
Cell Signaling
6-2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cells & The Extra-Cellular Environmentr
Water,
Ions and other molecules are present in our
body in TWO Compartments:
Intracellular = inside the cells
Extracellular
There
= outside the cells
is always interaction between the two
compartments (movement of Ions and Molecules)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Active
Diffusion, Osmosis, Facilitated Diffusion
transport
Moves compounds against concentration gradient
Requires 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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diffusion
Is
caused by random motion of molecules
Net movement is from regions of High
Concentration to regions of Low Concentration
OR
Movement
gradient
down the concentration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diffusion
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diffusion
Concentration
Number
of molecules in a given unit
of volume
Gradient
Physical
regions
difference between two
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diffusion (continued)
Non-polar
compounds diffuse readily through the cell
membrane
Also some small polar molecules including C02 & H20
Gas exchange occurs by Diffusion
6-10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diffusion (continued)
Rate
of diffusion depends on:
Magnitude of the concentration gradient
Permeability
of the membrane
Temperature
Surface
area of the membrane
6-11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diffusion (continued)
Diffusion
of H20 Molecules
is called Osmosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osmosis
Is
net diffusion of H20 across a selectively permeable
membrane
 H 20
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osmosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osmosis continued
H20
diffuses Down its
Concentration Gradient
until its concentration is
equal on both sides of
membrane
6-14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osmotic Pressure
 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
6-15
Molarity & Molality
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Molarity & Molality
The
Molecular weight of a molecule is the sum
of the Atomic Weights of its atoms
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Molecular Weights
NaCl:
Na
= 23.0
Cl = 35.5
= 58.5
Glucose:
C6 = 12x6 = 72
H12 = 1x12 =12
O6 = 16x6 = 96
=180
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
mole
An
amount of any compound equal to its
molecular weight in grams is 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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Molarity & Molality
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Molarity & Molality
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tonicity
Is
the effect of a Solution on the
Osmotic Movement of H20
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Effects of
tonicity on
RBCs
Fig 6.11
shrink
6-19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Regulation of Blood Osmolality
Membrane Transport Systems
6-21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Facilitated Diffusion
 Is
Passive Transport down concentration gradient by:
carrier proteins
6-24
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Active Transport
Is
Transport of molecules
Against a Concentration
Gradient
Requires
Energy (ATP)
6-25
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Na+/K+ Pump
Uses
ATP to move
Na+ out
3
&
 2 K+ in

Against their
gradients
Fig 6.17
6-26
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Secondary Active Transport
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
 Uses
6-27
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bulk Transport
Movement
of Large Molecules & Particles across
plasma membrane
Occurs by Endocytosis & Exocytosis (Ch 3)
6-31
Membrane Potential
6-32
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Membrane Potential
Is
difference in
Electric charge
across the Plasma
Membrane
Fig 6.22
The
inside of the cell
is Negatively
charged compared
to the outside
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 mV
RMP depends on:
Concentrations of ions inside & outside
Permeability
of each ion
Affected most by K+ because it is more
permeable
6-38
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Resting Membrane Potential (RMP) continued
Na+
diffuses in so
RMP is less
negative than
EK+
Some
Fig 6.25
6-39
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Resting Membrane Potential (RMP)
Cell Signaling
6-41
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
Paracrine
Hormones (Endocrine)
Neurotransmitters
Electric communication:
Gap Junctions
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell Signaling
In
Paracrine signaling, cells secrete regulatory
molecules that diffuse to nearby target cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell Signaling
In
Endocrine signaling, cells secrete chemical
regulators that move through Blood Stream to
distant target cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell Signaling
In
Synaptic signaling, A neuron sends messages
using Neurotransmitter to another cell via synapses
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell Signaling
Some
continued
use Gap Junctions through which signals
pass directly from one cell to the next