Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st Year, 2nd Year, 3rd Year and Final year Physiology 62 Membrane Transport PPT-Powerpoint Presentations and lecture notes
Substances transported for
chemical reactions
Elimination from
the cells
electrical
potentials at the
membrane
Cell Membrane
? surrounds entire cell and cell organelles
? Fluid in nature ? movement of molecules
? Phospholipid bilayer ? head ? polar/hydrophilic
tail ? nonpolar/hydrophobic
? Proteins
Integral ?carrier & channel
Peripheral-receptors & antigen
Peripheral protein
Intrigal protein
(ankyrin)
Band 3
cytoskelatal protein
spectrin
Extrinsic protein
Glycolipid
Head
ECF
(hydrophilic)
Glycoprotein
r
l
a
ye
d bi
L
i
pi
Tail
(hydrophobic)
cholesterol
Integral proteins
Intrinsic protein
ICF
Functions of cell membrane
? Acts as semi permeable barrier ?(selective)
oMaintains difference in composition of
ICF & ECF & fluid in various organelles
oProtects cell from toxic substances
oExcretion of waste products
oTransport of nutrients
? Receives signals from the outside
?Chemical signals
?Electrical signals
?Site for attachment to the neighboring cells
Transport across cell membrane
Transport Mechanisms
Passive
Active
?Simple diffusion
?Primary active transport
?Facilitated diffusion ?Secondary active transport
?Filtration
?Endo/Exocytosis
?Osmosis
?dialysis
Methods of transport
Passive
Active
Diffusion
Osmosis Filtration
Dialysis
Simple
facilitated
?Lipid bilayer
?Protein
Leaky channels
voltage gated
channels
Gated channels
Ligand gated
Simple diffusion -
Movement of molecules from higher
concentration to lower concentration till
equilibrium is reached
.Diffusion can takes place through:
a) Lipid bilayer
i) Lipid soluble substances-
O2,Co2,alcohol, steriods etc
ii) Lipid insoluble ? water (through
spaces bet lipid mol) urea, sugar
(less or no permeability)
iii) Electrolytes ? impermeable
? charge on fatty acid chain
- Hydrated forms are larger
.
b) Protein Channels Open/leaky ? Na+ channels,
K+ channels
Gated ?channels open under specific conditions
Ligand gated Voltage gated
Na+
Na+,
K+
K+
Ca++,
Mutation of ionic channels produce channelopathies ?affecting
muscle and brain ? paralysis or convulsions
Factors affecting rate of diffusion
? Lipid solubility
? Molecular size & wt.
Molecular
? Temperature
? Thickness of membrane
Membrane related
? Surface area
? Concentration gradient
? Pressure gradient
Gradients
? Electrical gradient
Fick's law of diffusion ?
Imp.
Q
CPA
MW X
Q = net rate of diffusion
C = conc. gradient of a substance
P = permeability of membrane to the sub.
A = surface area of a membrane
MW = molecular wt. of sub.
X = thickness or distance
II. Facilitated diffusion :
- for larger water soluble mols.
- type of passive transport
- along the conc. Gradient
- carrier mediated transport
Me - re
chanism
ceptor site on one side
- Rate of transport ? Vmax
i
t
y
Vmax
Simple diffusion
l
oc
Facilitated diffusion
ve
Conc. gradient
Initially, rate is directly proportional to conc. gradient
Till it reaches ( l
Vmax
imitation because of no. of
carrier mols. & rate of conformational change)
Hormonal regulation by changing #of carriers.
- Peculiarities of carrier mediated transport ?
?
specificity,
? competitive or noncompetitive inhibition ?
phloridzin for glucose
? saturation,
? blocking of receptor
V
? max
-Examples ? transport of glucose, amino acids,
galactose, etc. in the peripheral cells or counter
transport of Ci and HCO3 in renal tubules
III. Osmosis & osmotic pressure?
when two solutions of different concentrations are
separated by a semi permeable membrane (
impermeable to solute and permeable to water ) water
mols. diffuse from solution having less conc. To the
sol. having higher conc.
Osmotic pressure is the minimum pressure
applied on the solution with high conc. which
prevents osmosis.
- depends upon total no. of particles of dissolved
solutes rather than type of the particles
Osmols or mOsmols ? expresses conc. of
osmotically active particles
1 osmol = total no. of particles in gram molecular
wt. of non diffusible substance per kg. of water
Applied -
Isotonic, hypotonic & hypertonic solutions
Isotonic solution ? fluids having osmolarity
same as that of plasma ( 290 mOsmols ) . Red
cells suspended in such solution do not shrink
or swell. ( 0.9 % NaCl, 5% glucose )
In Hypotonic soln. RBCs swell and hemolysis
may occur.
In hypertonic solution RBCs shrink because
water moves out.
Gibbs ? Donnan Equilibrium
Explains difference in the conc. of
diffusible ions in two compartments separated by
semi permeable membrane, when one
compartment contains non diffusible ions
Na +
Na +
Proteins are non
Cl -
Cl -
diffusible anions in A
Pr -
Conc. Of Na + is more
in A as compared to B
A
B
A
B
Na+ 30
Na+ 30
conc. Gradient for Cl -
Pr - 30
Cl -30
Na+ 30
Na+ 30
Cl - 15
Cl - 15
More ?vity in A
Pr - 30
electrical gradient
Na+ 45
Na+ 15
Conc. gradient
Cl - 15
Cl - 15
electrical gradient
Pr - 30
Na+ 40
Na+ 20
Cl - 10
Cl - 20
Pr - 30
Explaination ?
1) All the solutions are electrically neutral.
( total no. of anions = total no. of cations )
2) Product of diffusible cations and an
anions in both the compartment is equal.
( Na+A x Cl-A = Na+B x Cl-B )
Applied ?
In ICF conc. of diffusible K+ is more because of
presence of non diffusible Pr - and PO4 -
Diffusion potential or Equilibrium potential - E
Potential generated across the cell membrane in
the presence of non diffusible ions in one
compartment.
Magnitude of potential developed can be
calculated by Nernst equation.
Nernst equation -
Equilibrium potential or diffusion potential (E)
= + 61 log ------------
Conc. inside
Conc. outside
EK = - 94 mV
ENa = + 61 mV
ECl = - 90 mV
Goldmann-Hodgkin's equation =
C
- 61 log --------------------------------------
Nai.PNa + CKi.PNa + CClo.PClo
CNao.PNa + CKo.PNa + CClo.PCli
IV. Filtration
Filtration is a process in which fluid along
with solutes passes through a membrane due to
difference in pressures on both sides.
e.g. Filtration at capillary
Capillary hydrostatic pressure ? 28mm Hg
Interstitial fluid hydrostatic pressure - -2mm Hg
Colloidal osmotic pressure - 25mm Hg
Net Filtration pressure = 28 - (- 2 + 25) = 5 mm Hg
V. Dialysis ?
separation of larger dissolved particles from
smaller particles
It is used for elimination of waste products in the
blood in case of renal failure.
Active transport
? Primary active transport
? Secondary active transport
? Endocytosis
? Pinocytosis
? Phagocytosis
? Exocytosis
Peculiarities of active transport
1) Carrier mediated transport
2) Rapid rate of transport
3) Transport takes place against electrochemical
gradient ( uphill )
4) Expenditure of energy by transport protein
which incorporates ATPase activity
5) Carrier protein shows specificity, saturation
competitive inhibition, blocking
6) Substances transported ? Na+ , K+, H+, Cl -, I - ,
Glucose, Amino acids
I. Primary active transport ?
Examples - Na+ - K+ pump, Ca++ pump
H+-K+ pump
- Inner surface of carrier mol. has ATPase
which is activated by attachment of specific
ions and causes hydrolysis of ATP molecule
- Energy released from ATP causes
conformational change in the carrier which
transports ions to the opposite side.
a) Na+ -K + pump- electrogenic pump
- Attachment of 2K+ on outer side & 3 Na+ on inner side
Activation of ATPase
3Na+
Conformational change
Efflux of 3 Na+ & influx of 2K+
ATP 2K+
aes
Creates high K+ conc. & - vity inside the cell
Helps in maintaining cell volume
Na-K pump is one of the major energy using
process in the body & accounts for a large part
of basal metabolism.
Regulators of Na-K pump ?
- Incraesed amount of cellular Na conc.
- Thyroid hormones increase pump activity by more # of Na-K
ATPase mol
- Aldosterone also increases # of pumps
- DOPamine inhibits pump
- Insulin increases pump activity
- Oubain or Digitalis inhibits ATPase (used when weakness of
cardiac muscle ?maintains Ca conc. In ICF of cardiac muscle
- Ca++ pump ?
present in the membrane of ER,
mitochondria and cell membrane
- involves uniport carrier
- helps to maintain low Ca++conc. in ICF
II. Secondary active transport
Active transport depending upon conc.
gradient of Na+ from ECF to ICF created by
utilization of energy
_ carrier does not have ATPase activity
Substance is transported along with Na+
(Na increases affinity of carrier for gl.)
Na+ is transported only when glucose mol. is
attached
Examples ? a) Reabsorption of glucose & amino
acids in PCT & Intestinal mucosa ? Co-transport
mechanism
b) H+ secretion by tubular epithelium
? counter transport mechanism
c)In heart Na-K ATPase indirectly affects Ca transport. ?antiport
in the membrane of cardiac muscle exchanges intracellular Ca
for extracellular Na
basal
lumen
Na+
K+
Glucose
? Na + ? K + pump on basal side
? Electrochemical gradient for Na + on luminal side
? Carrier mediated transport (SGLT-1)of Na+ along
with glucose ( or amino acid ) through the apical
membrane
? Transport of glucose by facilitated diffusion
( GLUT-2 ) through basal side
Types of transporters
Uniport
Synport
Antiport
Extracellular material to be tackled by
lysosomes is brought into the cell by
endocytosis
3 types
pinocytosis
phagocytosis
Specialised
All cells
Receptor
cells
mediated
endocytosis
Requires ATPase, Ca, microfilaments
Pinocytosis
ECF
ECF
dynamin
Membrane deforming
coat protein
Endocytic
vesicle
B. Receptor mediated endocytosis ? highly
selective process to import imp. specific large
molecules. Requires energy & Ca++.
e.g. endocytosis of low density
lipoproteins
Coated pit Clathrin, actin, e.g. endocytosis of viruses such as
myosin
hepatitis, AIDS viruses & excess iron
C. Phagocytosis
? Internalization of large multimolecular
particles, bacteria, dead tissues by
specialized cells e.g. certain types of
w.b.c.s ( Professional phagocytes)
? The material makes contact with the
cell membrane which then invaginates.
bacterium
Pseudopodia
internalization
Phagoso-
some
Fusion
Residual
body
absorption
digestion
Phagocytosis
Passive transport Active transport
? No expenditure of
? Expenditure of energy
energy molecules
mol. ( ATP )
? Takes place along
? Can take place against
conc., electrical, &
conc. Gradient
pressure gradient
? Carrier may or may
? Carrier is always
not be required
required
? Rate is proportional to
? Rate is proportional to
conc. difference
availability of carrier
& energy. (Vmax)
Simple Diffusion Facilitated Diffusion
? Passive transport
? Passive transport
? For small molecules
? For large molecules
? No carrier required
? Carrier mediated
? Rate of transport is
? Initially rate is
directly proportional to
proportional to conc.
conc. gradient
gradient till Vmax
? Examples ?
( saturation of carriers)
Lipid soluble ?
? Examples ?
O2, CO2, alcohol glucose, amino acids
Lipid insoluble ?
urea, Na+, K+
This post was last modified on 08 April 2022