Transcript Cell Physiology BDS lecture

Dr Pradeep Kumar
Professor in Physiology
KGMU, Lko
 60%
Water
 7% Minerals
 18% Proteins and related
substances
 15% Fats (Females have 10 % less body
water – relatively greater amount of adipose
tissue)
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
Extra cellular fluid ( ECF) 1/3 of body fluid
Intra cellular fluid (ICF) 2/3 of body fluid
Blood plasma

ECF
Interstitial fluid
Lymph fluid
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Body fluid compartments have different
sizes and volumes, and different
compositions.
If you manipulate one body fluid
compartment, it has an effect on another
compartment.
in all the compartments you should get the
same number of particles: 300 million
particles per liter,
Different compositions (different amounts of individual
particles)
 Different volumes,


Same osmolalities (total number of particles)
0.3 Osmolal = 300 mOsmolal (actually closer to 280mOsmolal)
Plasma
Interstitial
Intracellular
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If the numbers of particles are always the same, how can we
have higher numbers of potassium ions inside of the cell
compared to the outside of the cell?
Won’t the potassium ions want to move down their
concentration gradient towards equilibrium? Yes, they will
want to, but the cell membranes are semi-permeable and will
prevent the potassium (and other particles) from crossing.
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
If you have a cell containing 300 mOsm of potassium
(K+) immersed in pure water, will it shrink or burst?
The potassium cannot flow out of the cell to equalize
its numbers inside and outside of the cell because it is
blocked in by the cell membrane. The particles in the
cell will suck water into the cell until the cell bursts.
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What particles can cross the cell membrane?
Gases (O2, CO2)
Lipids and lipid-loving (hydrophobic or
lipophylic) substances, such as alcohol
Selectively permeableallows some substances
to pass
 Only small uncharged
molecules or fat soluble
molecules can pass
through membrane
without help- diffusion
(passive transport)

http://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swf
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Two ways:
Osmosis
Hydrostatic pressure
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
Osmosis
◦ a chemical potential energy difference dependent on the
water concentration on two sides of the membrane
◦ Driving force for water movement across cell membranes

Hydrostatic pressure
◦ The pressure of the fluid exerted on the vessels, or container
(change in energy/mole)
◦ Animal cell membranes are “flexible” so it is not a driving
force across cell membranes
◦ IT IS a driving force for moving plasma water across walls
of capillaries

Osmotic pressure is the amount of hydrostatic pressure
required to stop osmosis from moving water from low to high
concentration across a cell membrane. Osmotic pressure is
attributed to the osmolarity of a solution. The solution with
the highest number of particles will have the highest
hydrostatic pressure.
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the amount of hydrostatic pressure (force of fluid exerted on
the vessel wall) required to counter osmosis
Osmotic pressure is
attributed to the
osmolarity
of a solution
Isosmotic - has same
osmolarity as body fluids
Hyperosmotic - higher
osmolarity than body fluids
Hyposmotic- lower
osmolarity than body fluids
Figure 4-10;
Guyton & Hall
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 What
will happen to a cell placed in the
following solutions?
 Isosmotic (300 mOsm): no net gain or loss of
water.
 Hyperosmotic (600 mOsm): particles suck, so
solution will suck the water from the cell,
which will shrink.
 Hyposmotic (100 mOsm): particles suck, so cell
will suck water from the solution and burst.
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Membrane Potential
Active Electrical Properties of the Neuron
Synaptic Transmission
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Neuron as the functional units of nervous system
Structure of a neuron
1x Neuron: carrying signals
50x Supporting cells: protect, insulate, reinforce, assist neurons
Multiple sclerosis (MS): immune system-myelin
sheath
loss of signal conduction, muscle control, brain
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Ion channels have three important
properties
1. They conduct ions
2. They recognize and select specific ions
3. They open and close in response to
specific electrical, mechanical, or chemical
signals.
Gates: voltage-gated channels, ligandgated channels, mechanically gated
channels, non-gated channels
Several types of stimuli control the opening
and closing of ion channels
Voltage-gated channel
[Ca++]i

Only a very thin shell of charge difference
is needed to establish a membrane potential.
Resting potential: the voltage across the plasma membrane of a resting
neuron
A nerve signal originates as a change in the resting potential: The action po
Any + ion
Vg Na+ channel open
Vg K+ channel open
Thank You