DIFFUSION & CELL TRANSPORT

MRS. PAEZ

ANATOMY & PHYSIOLOGY

DIFFUSION Click icon to add picture• DEFINITION: THE NET MOVEMENT OF

MOLECULES FROM AN AREA OF RELATIVELY HIGH CONCENTRATION TO AN

AREA OF RELATIVELY LOW CONCENTRATION.

• THE DIFFERENCE BETWEEN HIGH AND LOW CONCENTRATIONS IS THE CONCENTRATION GRADIENT.

• DIFFUSION PROCEEDS “ DOWN THE CONCENTRATION GRADIENT” OR

“DOWNHILL”

• A PASSIVE PROCESS: DOES NOT REQUIRE THE CELL TO EXPEND ENERGY

DIFFUSION IN THE BODY Click icon to add picture

INTRACELLULAR CONCENTRATION OF CARBON DIOXIDE IS HIGH, BECAUSE IT IS GENERATED INSIDE THE CELL

BY RESPIRATION.

THE CONCENTRATION OF CO2 IS MUCH LOWER OUTSIDE THE CELL.

THE CELL MEMBRANE IS FREELY PERMEABLE TO CO2 AND

THEREFORE IT DIFFUSES INTO THE EXTRACELLULAR FLUID- DOWN ITS CONCENTRATION GRADIENT-AND

THEN INTO BLOODSTREAM.

DIFFUSION ACROSS THE CELL MEMBRANE

•SUBSTANCES DIFFUSE:

1)EITHER THROUGH THE PHOSPHOLIPID PORTION : ALCOHOL, FATTY ACIDS, STEROIDS, OXYGEN, CARBON DIOXIDE.

2)OR THROUGH PROTEINS IN THE MEMBRANE: WATER & IONS ( SODIUM, POTASSIUM, CALCIUM)

OSMOSIS

•OSMOSIS: DIFFUSION OF WATER ACROSS A MEMBRANE

• SOLUTES: DISSOLVED MATERIALS

•WATER WILL FLOW ACROSS A MEMBRANE TOWARD THE SOLUTION CONTAINING THE HIGHER SOLUTE CONCENTRATION ( BECAUSE THAT’S WHERE THE CONCENTRATION OF WATER IS LOWER )

• AS OSMOSIS OCCURS, WATER MOLECULES CROSS THE MEMBRANE UNTIL THE SOLUTE CONCENTRATIONS IN THE TWO SOLUTIONS ARE IDENTICAL.

HYPOTONIC SOLUTION

• SOLUTION THAT CONTAINS LESS SOLUTE THAN THE CELL. WATER WILL FLOW INTO THE CELL CAUSING IT TO SWELL.

• IN RED BLOOD CELLS ( RBC’S) THIS CAUSES THE CELL TO BURST- CALLED HEMOLYSIS

ISOTONIC SOLUTION Click icon to add pictureA SOLUTION THAT CONTAINS AN EQUAL AMOUNT OF SOLUTE AS

THE CELL.

EQUILIBRIUM EXISTS BECAUSE FOR EVERY WATER MOLECULE THAT

MOVES OUT OF THE CELL, ANOTHER MOVES IN TO REPLACE

IT.

SALINE IS GIVEN TO PATIENTS BECAUSE IT IS ISOTONIC TO THE EXTRACELLULAR FLUIDS OF THE

BODY.

HYPERTONIC SOLUTION Click icon to add picture

•A SOLUTION THAT CONTAINS MORE SOLUTE THAN THE

CELL. WATER WILL FLOW OUT THE CELL CAUSING IT TO

SHRIVEL AND DEHYDRATE.

•IN RED BLOOD CELLS ( RBC’S) THIS CAUSES THE CELL TO

SHRIVEL AND SHRINK- CALLED CRENATION.

FILTRATION

KIDNEYS

• WHERE OSMOTIC PRESSURE FORCES WATER ACROSS A MEMBRANE. IF SOLUTE MOLECULES ARE SMALL ENOUGH TO FIT THROUGH MEMBRANE PORES, THEY WILL BE

CARRIED ALONG

• OCCURS ALONG THE WALLS OF SMALL BLOOD VESSELS-PUSHING WATER

AND DISSOLVED NUTRIENTS INTO TISSUES.

CARRIER- MEDIATED TRANSPORT•DEFINITION: MEMBRANE PROTEINS BIND SPECIFIC IONS OR ORGANIC SUBSTRATES AND CARRY THEM ACROSS THE CELL MEMBRANE

•THESE PROTEINS ARE SUBSTRATE-SPECIFIC-THEY ONLY BIND TO SPECIFIC MOLECULES

•PASSIVE OR ACTIVE PROCESS

FACILITATED DIFFUSION

• A PASSIVE PROCESS

• DEFINITION: A TYPE OF CARRIER-MEDIATED TRANSPORT WHERE COMPOUNDS ARE TRANSPORTED ACROSS THE MEMBRANE BY CARRIER PROTEINS

• THE SUBSTANCE BINDS TO A RECEPTOR SITE ON THE CARRIER PROTEIN, CAUSING THE SHAPE OF THE PROTEIN TO CHANGE. THIS MOVES THE MOLECULE TO THE INSIDE OF THE CELL.

• RATE OF DIFFUSION IS LIMITED BY AVAILABILITY OF CARRIER PROTEINS IN MEMBRANE.

ACTIVE TRANSPORT

• MOLECULES MOVED “UPHILL” OR AGAINST THE CONCENTRATION GRADRIENT ( FROM LOW TO HIGH CONCENTRATION)

• ATP IS REQUIRED

• EXAMPLE: ION PUMPS- MOVE SPECIFIC IONS IN OR OUT OF THE CELL

ION EXCHANGE PUMPS• SODIUM-POTASSIUM PUMP

• MAINTAINS THE LEVEL OF NA+ HIGH IN EXTRACELLULAR FLUIDS

• KEEPS LEVEL OF K+ HIGH IN THE INTERIOR OF THE CELL ( CYTOPLASM)

• MAINTAINS HOMEOSTASIS OF CELLS- USES 40% OF ATP PRODUCED BY CELLS