Download MBBS Physiology Presentations 62 Membrane Transport Lecture Notes

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