So along with bringing things into
the cell, active transport also involves
bringing things out of the
cell and across the cell.
So in exocytosis, vesicles are going
to fuse with the plasma membrane
and spit out their contents
into the extracellular fluid.
And in transcytosis, vesicles are gonna
move across the cell from one side to the other
and sometimes fuse with neighbouring cells.
So we've discussed the plasma
membrane extensively, now let's switch gears
and move to the inside or the
internal environment of the cell.
The inside of the cell
consist of the cytoplasm
and in the cytoplasm, you have the cytosol or
the intracellular fluid that's found in the cell,
and you have organelles which are the
specialised structures that are gonna perform
different functions inside of the cell.
So before we talk about
all of the different structures,
let's talk about the cell skeleton
also referred to as the cytoskeleton.
The cytoskeleton are different types of
filaments and tubules found throughout the cell.
They give the cell a
structural integrity or its shape
And they also allow for movement of
substances across the cell as sometimes
they are intracellular highways
and surface streets on your cell.
So there's three main cytoskeletal elements.
The smallest of them are the
microfilaments also known as actin
and the medium size is going
to be your intermediate filaments
and the largest of them is
going to be your microtubules.
Each of these cytoskeletal elements
plays an important role in the cell.
Your actin microfilaments are very important for maintenance of shape of the cell and they
also allow for some movement of substances through the cell especially at the cell surface
The intermediate filaments are usually
surrounding the nucleus of the cell
and help to create their nuclear
lamina or the area around the cell
so that the nucleus is in
the right place of the cell.
And then the microtubules which extend from
near the nucleus toward the periphery of the cell
is also very important for structure
as well as transport of cargo
throughout the cell using
the vesicles in the cell
so the vesicles are going to
basically travel along this microtubules.
So the microtubules extend from a
specific structure known as the centrosome.
And the centrosome is made up of two
centrioles which are at 90 degrees to each other
and are located just next to the nucleus.
And so from the centrosome, these microtubules are
going to grow or radiate from this area of the cell.
This is especially important
when we're talking about mitosis
as the centrosomes play a central role in
the production of spindle fibers in mitosis
Another structure that is derived from the
microtubules of the cell are the cilia and the flagella.
These both involve movement, either movement
of particles or movement of the cell themselves.
For example, in the respiratory
system, you have cilia that allow you
to cough up substances that you don't want getting
down into the lower respiratory area of your body.
And when you think of flagella,
think of sperm and their ability to swim
toward an oocyte in order
for reproduction to occur.
So the cilia and the flagella in our bodies
are going to move in different ways.
The flagella are usually going to
move in a propeller-like or a round motion
whereas the cilia in our body
are going to beat back and forth
so the analogy that I like to use is a boat.
If you have the opportunity
to have a motorboat,
the propeller on the back of the
boat is gonna propel you forward
whereas if for whatever
reason your motor doesn't work,
you always can use the oars and move
back and forth in order to get where you're going.