This presentation is about various types of cell transport mechanism which occurs at cellular level within the body. This is a basic presentation, intended for first year students of Medical and Health science courses .

1. BIOPHYSICAL LAWS
MOVEMENTS OF
MATERIALS ACROSS
PLASMA MEMBRANE
Dr. Aniket A Shilwant
BAMS, MD

2. MOVEMENTS OF MATERIALS ACROSS PLASMA MEMBRANE
The plasma membrane mediates the movements of materials essential
electrolytes, nutrients, enzymes, etc. across the cell.
The processes involved in these movements may be classified mainly into 2types-
 Passive Processes
 Active Processes
Passive Processes:-
Substances move across the cell membranes without any assistance of the
cell.
It is done due to Kinetic energy of each individual molecule
It moves along the concentration gradient from an area of greater
concentration to an area of lower concentration.
The substances may also be forced across plasma membranes by pressure
from an area of higher pressure to an area where it is less.

3. Active Processes:-
In this the cell contributes energy in moving the substances across the
membrane since the substances moves against concentration gradient.

4. PASSIVE PROCESSES
1) Diffusion
2) Facilitated diffusion
3) Osmosis
4) Filtration
5) Dialysis

5. DIFFUSION
 Movement of molecules or ions from a region of higher concentration to a region of
low concentration is -Diffusion.
 This movement from higher concentration to lower concentration continues until
molecules are evenly distributed. This state is called as Sate of Equilibrium.
 The difference between high and low concentration is called as Concentration
Gradient.
 So in this particular mechanism movement of molecules is said to be along the
concentration gradient.
e.g. 1) Dye Pellet
2) Dispersible Tablet

6. FACILITATED DIFFUSION
 This process is accomplished with the assistance of integral proteins in the
membranes which serves as carriers.
 Some chemical substances even though insoluble in liquid can cross the plasma
membranes double lipid layer.
 The rate of facilitated diffusion depends upon –
a) The difference in the concentration of substances on either side of the
membrane.
b) Amount of carrier available to transport the substances.
c) How quickly the carrier and the substances combines.
e.g. Glucose molecule - Movement of glucose molecule is greatly accelerated by
Insulin.

9. OSMOSIS
 It is nothing but the net movement of fluid (specially water
molecules) through a selective permeable membrane from an
area of higher concentration of water to an area of lower
water concentration.
 This water molecule pass through the channels made up in
the integrated proteins in the membranes.
e.g. A beaker containing pure water on one side and a
sodium chloride solution on the other both of which are
separated by a semipermeable membrane.

10. OSMOTIC PRESSURE
 The amount of pressure required exactly to stop the
process of osmosis is called the Osmotic pressure.
 To express the concentration of a solution in terms of
number of particles, the unit called is Osmole which is
used in place of grams. 1 Osmole is equivalent to 1 gram
molecular of undissociated solute.
OSMOLARITY
 The osmolar concentration expressed as osmoles per litre
of solution and not osmoles per kilogram of water.

11. TONICITY OF SOLUTIONS
Isotonic solution:-
A solution in which the total concentration of water molecules and solute molecules
are same on both the sides of the semipermeable membrane.
Ex. 0.85% NaCl sol. Is isotonic for RBC.
Hypotonic solution:-
If ever RBCs are placed in a solution having lower concentration of solutes and higher
concentration of water, it is called as –Hypotonic solution.
In this condition water enters cells faster than it leaves, which causes the RBCs to
swell and eventually burst. This rupture of RBCs is called as- Hemolysis or Laking
of RBC.

12. TONICITY OF SOLUTIONS
Hypertonic Solution:-
This type of solution contains higher concentration of solute and lower concentration
of water rather than RBCs.
Ex. 10% NaCl sol. In this condition water molecules move out of the cell at a faster rate
than they enter. This causes the cell to shrink. The shrinkage of RBCs in this manner is
called as – Crenation of RBCs.

14. FILTRATION
Movement of water and solutes across a
selectively permeable membrane from an area of
high hydrostatic pressure to an area of low
hydrostatic pressure is called as- Filtration.
This is seen at the arterial ends of the
capillaries where movement of fluid occurs along
with the dissolved substances from blood into the
interstitial fluid.
Ex. Glomeruli of kidneys

15. DIALYSIS
It is the diffusion of solute particles across a selectively permeable
membrane and involves separation of molecules from larger ones.
The patient’s blood is passed across a Dialysis machine outside the body. It
contains a selectively permeable membrane through which the patient’s blood is
passed through. The renal failure patient has enormous protein molecules and waste
products in his blood. As the blood passes through the membrane of dialysis
machine, small particles and waste products pass from the blood into a solution
surrounding the dialysis membrane and the filtered blood is then returned to the
patient’s body.

16. HEMODIALYSIS PERITONEAL DIALYSIS

17. ACTIVE PROCESSES
1) Primary Active Transport:-
In primary active transport, the energy is derived directly by breakdown of ATP or
any other high energy phosphate compound.
2) Secondary Active Transport :-
In secondary active transport, the energy is derived secondarily from energy that
has been stored in the form of ionic concentration (common carrier protein).
In both above processes transport depends upon the carrier proteins that penetrate
through the membranes as like for the facilitated diffusion.
3) Special type of Active Transport

18. PRIMARY ACTIVE TRANSPORT:-
SODIUM-POTASSIUM PUMP
 In this transport process sodium ions are actively transported outside the cell while potassium ions are
transported from outside to the inside.
 This pump is responsible for maintaining sodium-potassium concentration.
 Establishes the negative potential (electrical voltage) inside the cells.
 Carrier protein:-
1) 2separate globular proteins
2) One larger subunit (100000) and a smaller subunit (55000).
 It has 3receptor sites for binding sodium ions on the portion of the protein that protrudes to the
interior of the cell.
 It has similar 2receptor sites for potassium ions on the outside.
 The inside portion of this protein near to the sodium binding site has ATPase activity.
 When 2 potassium ions bind on the outer side of the carrier protein and 3 sodium ions get bind on the
interior side of the carrier protein, the ATPase function of the protein becomes activated.
 ATP ADP phosphate bond of energy.
 This energy is then utilised to make a conformational change in the protein carrier molecule, 3sodium
ions 2potassium ions.

19. PRIMARY ACTIVE TRANSPORT
 SODIUM – POTASSIUM PUMPS
 CALCIUM PUMPS
 HYDROGEN PUMPS

20. SECONDARY ACTIVE TRANSPORT:-
CO-TRANSPORT
Sodium ions are transported out of the cells by primary active transport, a large
concentration gradient of sodium usually develops.
Diffusion energy of sodium literally can pull other substances along with the sodium
through the cell membrane. This phenomenon is called as-Co-Transport.
Ex. Glucose and many Amino Acids.

21. COUNTER TRANSPORT
Transport mechanisms where transport of ions takes place in a direction opposite to the
primary ion.
Ex. Sodium-Hydrogen counter transport occurs in proximal tubules of nephrons in
kidneys.
 SODIUM – HYDROGEN
 SODIUM – CALCIUM
 CALCIUM – MAGNESIUM
 CALCIUM – POTASSIUM

23. SPECIALACTIVE TRANSPORTS
ENDOCYTOSIS
EXOCYTOSIS
TRANSCYTOSIS

24. ENDOCYTOSIS
Transport mechanisms where macromolecules enter the cell. Macro molecules
cannot pass through the cell membranes either by active or passive process. Such
substances are transported into the cell by endocytosis.
Endocytosis is of 3types:-
Pinocytosis
Phagocytosis
Receptor mediated endocytosis

25. PINOCYTOSIS
Macromolecules in the form of droplets of fluids
enter inside the cell. It is also called as Cell-
Drinking.
Macromolecules bind the outer surface of cell
membrane.
Cell membrane evaginates around the droplets.
Droplets are engulfed by the membrane.
Engulfed droplets converts into- vesicles-vacoules
also called as-Endosomes.
Endosome travels inside the cell and fuses with the
Lysosome.
It is then digested and degraded by the hydrolytic
enzymes present inside the lysosome.

26. PHAGOCYTOSIS
 Larger macromolecules enter inside the cell. It is also
called as Cell-Eating.
 When bacteria or foreign body enters the body, the
phagocytic cell projects towards it with the help of
pseudopodium.
 The particles are then engulfed and converted into
vacuole called as- Phagosome.
 Phagosome travels inside the cell and fuses with the
Lysosome.
 It is then digested and degraded by the hydrolytic
enzymes present inside the lysosome.

27. RECEPTOR MEDIATED ENDOCYTOSIS
It is the transport of macromolecules inside the cell with the help of a receptor
protein.
Receptor protein – Clathrin, Caveolin
Ex. Hormonal action, Vitamin

28. RECEPTOR MEDIATED ENDOCYTOSIS

29. STAGES OR MECHANISM OF ENDOCYTOSIS
1. Chemical attraction – Chemotaxis
2. Evagination – Pseudopods
3. Engulfing – Eating / Drinking
4. Vacoule formation – Endosomes
5. Presentation to Lysozyme
6. Hydrolysis & Disintegration

30. EXOCYTOSIS
It is the process in which the
substances are expelled outside the cell and
that too without any assistance of cell
membrane.
Mechanism:-
Calcium plays an important role in
release of some neurotransmitters causing
desired effects.

31. TRANSCYTOSIS
 Invagination of extracellular substance
 Vesicle formation
 Moving of vesicle across the cell and expelled out through opposite direction
 Involves receptor-coated pits
 Receptor protein is caveolin and not clathrin
 Also called – vesicle trafficking or cytopempsis
Ex. Human Immunodeficiency Virus

32. REFERENCES
 Textbook of Medical Physiology – Guyton & Hall
 Pearson education, Published as – Benjamin Cummings
 Textbook of Medical Physiology – Prema Sembulingam
 Image sources – Textbooks of medical physiology & e-source

33. Thank you all…
Dr. Aniket A Shilwant
Associate Professor
Dept. of Sharir Kriya
G. J. Patel Institute of Ayurvedic Studies & Research
New Vidyanagar, Anand, Gujarat