Greetings to everyone. I'm so glad that you all are responding great to my posts and videos. Thank you for the love and support which you all are giving me these days and today we are going to discuss about our fourth topic i.e. "Transportation of substances across cell membrane". In this blog i'm posting only the slides which would help you to revise and understand the topic better.
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CHANNEL LINK:
https://www.youtube.com/channel/UCZrabu-CtMa5AEexu1j2GNw
ENGLISH VIDEO:
TAMIL VIDEO:
TRANSPORTATION OF SUBSTANCES ACROSS CELL MEMBRANE:
The structure of plasma membrane provides it with a property of selective permeability which means it allows only selective materials to pass through it.
PASSIVE TRANPORT occurs when substances can cross the semipermeable plasma and organelle membranes and move down the concentration gradient (down hill) without using energy. They are DIFFUSION ,FACILITATED DIFFUSION, OSMOSIS.
DIFFUSION:
Diffusion refers to the movement of molecules from an area of higher concentration to an area of lower concentration ,and occurs mainly in gases ,liquids and solutions.
Diffusion can also occur across a semipermeable membrane such as the plasma membrane or the capillary wall.
Only small molecules or soluble enough to cross the membrane can diffuse through.
For example oxygen diffuses freely through the walls of alveoli (where the oxygen concentration is high) into the blood stream ,(where the oxygen concentration are low).
However blood cells and large protein molecules in the plasma are too large to cross and so they remain in the blood.
OSMOSIS:
OSMOSIS refers specifically to diffusion of water down its concentration gradient .the force In which it occurs is called OSMOTIC PRESSURE.
Osmosis proceeds until the equilibrium is reached , at which point the solutions on each side of the membrane are of same concentration . It is said to be ISOTONIC.
Plasma osmolarity is maintained within a very narrow range because if the plasma water concentration rises i.e. the plasma becomes more dilute than the intracellular fluid within the red blood cells , then the water will move down its concentration gradient across the membranes and into the red blood cells .this may cause the red blood cells to swell and burst. In this situation plasma is said to be HYPOTONIC.
When the plasma water concentration falls the plasma becomes more concentrated than the intracellular fluid within the red blood cells ,And the plasma becomes HYPERTONIC .water passively moves by osmosis from the blood cells into the plasma and the blood cells shrink.
SOLUTE (A particle , usually a salt).
SOLVENT (liquid usually water).
HYPOTONIC (low solute and high solvent) eg:0.45% NS .
ISOTONIC (equal solute and solvent ratio) eg:0.9% NS.
HYPERTONIC (high solute and low solvent) eg.5%DNS.
OSMOSIS WITH EXMAPLE:
A patient is having +3 pitting edema so they have bunch of solvents in their tissues which should be get back to their veins and then excreted out .you do this by giving a HYPERTONIC solutions in their vein .Because the concentration of solute is higher in the vein and solvent is higher outside the vein .by giving a HYPERTONIC solution which contains high solute and low solvent it creates a osmotic pressure it pulls out the water from the tissues into the veins and it creates an equal ratio of the solute and the solvent.
For dehydrated patients we give them isotonic solutions because we want to expand the volume of the blood but don’t want the solvent to move out of the vein or to the tissue.
HYPOTONIC solution has lower concentration of electrolytes than plasma.
For example in patient with diabetic ketoacidosis the intracellular space become dehydrated and the cells will be shrunk. By administering hypotonic solution the water moves from the higher concentration to lower and the cells will be rehydrated.
FACILITATED DIFFUSION:
This passive process is used by some substances that are unable to diffuse through semipermeable membrane unaided (eg : glucose , amino acids ).
Specialized protein carrier molecules in the membrane have a specific sites that will attract and bind to the substances to be transferred, And this will look like a lock and key mechanism.
The carrier then change its shape and deposits the substance on the other side of the membrane.
The carrier sites are specific and can be used by only one substances.
As a result there are finite number of carriers, there is a limit to the amount of a substance which can be transported at any time .this is known as transport maximum.
BULK TRANSPORT:
Transfer of particles too large to cross the membrane occurs by pinocytosis (cell drinking) or phagocytosis (cell eating).
These particles are engulfed by extensions of the cytoplasm which enclose them forming a membrane bound vacuole.
Pinocytosis allows the cells to bring in fluid. In phagocytosis larger particles (eg: cell fragments ,microbes)are taken into the cell.
Lysosomes release the vacuole membrane releasing the enzymes which digest the content.
EXOCYTOSIS:
Extrusion of waste materials by reverse process through the plasma membrane is called exocytosis.
Vesicles formed by Golgi apparatus usually leave the cell in this way ,as do any indigestible residues of phagocytosis.
these are the slides which i have used
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