Moving forward into the bulk transport.
We've covered primary active transport,
secondary active transport during the active
transport section here. And now we'll move in to
bulk transport. This means not just moving one
thing. It's just like it sounds. Lots of stuff
all at once. There are a few different mechanisms.
We've kind of covered them already when we
discussed the endomembrane system. We have
endocytosis which is where we bring in food
or water. Specifically we can have phagocytosis.
We break that word down. Phag- means to eat,
cytosis, so it's cellular eating. And then
pinocytosis which is cellular drinking.
They pull in a lot of fluid and electrolytes
and such to balance the inside of the cell.
The opposite of that, that we also explored with
the export of things from the endomembrane system
whether it was the glucose that we produced inside
the cell that was for transport out of the cell,
would be exocytosis. So we exocytose stuff out
of the cell. The vesicle comes along
binds with the cell membrane, pops open and
drops all the materials to the external environment.
We could get rid of wastes in this manner also.
So after we have a lysosome bind with things
and break things down then those waste could
also be exocytosed. A similar mechanism
that is a little bit more complicated is the
receptor mediated endocytosis. So endocytosis,
yes. We are going to pull some things into the
cell. But in this case we want to pull in
some very specific things. So the cell actually
produces some receptors. Puts the receptors
out in the membrane. Once its put the receptors
out in the membrane then the molecule of intent
can bind to them. Let's use cholesterol as an
example. This is how LDLs work in order to
move cholesterol into cells. So we can have
cholesterol floating around in the blood.
We want cholesterol. We'll throw out some receptors
for cholesterol. Once cholesterol shows up
and binds to receptors in these, they're called
clathrin coated pits. Clathrin is just a kind of
protein that these receptors exist amongst. And
the molecule of interest here, cholesterol jumps
on to those receptors and then the cell will
endocytose, capture those and draw them inside
the cell to eventually have cholesterol hidden
out of the blood inside the cell.
Now, in hypercholesterolemia, the condition
where people are not taking in cholesterol
as well, results from having some problems with
the actual docking of the little receptors
into the clathrin coated pits. So the cells
are making receptors for cholesterol
however they are not able to actually pick up
the cholesterol and bring it into the cell
because they don't bind into the pits properly.
So what that results in is an individual
having much more cholesterol in their blood than
you would normally have. And that leads to
heart disease and all of those other associated
problems. So, receptor mediated endocytosis
is different from regular endocytosis because
it requires or it's asking for very specific
molecules. We just used cholesterol as an example
whereas general endocytosis is consuming
whatever happens to be there. So in this lesson
we have certainly covered some different means
of moving things. Passive transport where we
require no energy and moving things across
the cell membrane. We can move down the cell
concentration gradient. So if it's high
concentration outside to inside, we move things
down. That's passive. If we have to go
in the opposite direction, we are having active
transport. So you should now be able to describe
primary active transport in terms of the sodium
potassium pump as well as diagram secondary
active transport. Recall that it is dependent
on the energy invested in the primary mechanism.
So, the sodium potassium pump in this case. And
then we spent a moment here with bulk transport.
So now you should be able to distinguish
the three types of bulk transport.
I hope this cleared things up for you. Thanks for
joining me. I look forward to seing you again shortly.