- [Voiceover] I think we have a pretty good idea
of how the liver works.
One of the things I
kinda touched on when we talking about our hepatic lobule
is that we have bile that's produced in the liver
and flows out through the common hepatic duct.
Now bile is composed of two things.
One are just bile pigments.
Bile pigments are just sort of
things that make the color
or are not necessarily important for the function
of bile.
And the other thing that we have are bile salts.
Now this is the most important part.
This is what actually helps us emulsify,
remember that term,
emulsify which just means to organize
to eventually absorb our fat.
So bile salts help us emulsify fat.
They allow us to turn fat into micelles,
which can then be absorbed in the ileum.
So let's take a step back
and get a better idea of how our biliary tree really works.
Remember the liver synthesizes bile
but it doesn't necessarily store it.
The bile that's made here
actually goes through
what's called the
common hepatic duct.
So this is the common hepatic duct
that comes out of the liver.
So bile that leaves
from the liver after it's produced
has to go somewhere to be stored.
Where is it stored?
One of the first places that it's going to go
is this duct right here.
And this guy is called the cystic duct.
This is the cystic duct.
And this is the next place that we see bile flow
after the common hepatic duct.
The cystic duct
will then lead our bile
to be stored momentarily
in an organ that sorta sits as a blind pouch.
This guy is our gallbladder.
The gallbladder has one and one purpose only.
This is the dude that stores our bile.
This is where our bile hangs out
until it's time to be released.
So when bile just comes into our gallbladder
and is just sitting there,
what causes it to suddenly
decide to leave and go somewhere else?
As I'll mention in detail in a separate video
the hormone that causes
bile to be released from the gallbladder
is called
sort of a mouthful
cholecystokinin.
Cholecystokinin.
Which is often abbreviated just CCK.
Now this term might be a little crazy but if you ever heard
of the surgical procedure called a
cholecystectomy.
Cholecystectomy,
that's just the removal of the gallbladder.
So cholecystokinin
will cause our gallbladder
to contract.
And when the gallbladder contracts,
remember it's a blind pouch,
so this is just going to squeeze
all the bile that's just sitting here
right back out
to flow through the cystic duct
and now go somewhere else.
The next place you're gonna have bile flow through
is going to be another duct altogether.
Now this guy
is called the common bile duct.
The common bile duct.
And this is sorta the last
part of the biliary tree we're talking about here.
The last part of the biliary tree
that conducts our bile
until it finally reaches
the GI tract.
And the part of the GI tract that bile is released into
is the duodenum.
The duodenum or the first part of the small intestine.
In the duodenum
the bile is finally going to get to see some fat
and start doing its job by emulsifying or making the fat
easier to absorb.
Now the fat isn't absorbed in the duodenum.
In fact the bile salts
with our new emulsified fat from our food
will travel along to the ileum.
Now you remember the ileum's the last part
of our small intestine.
And this is where we're going to have our
bile salts and our
fats that were just emulsified
absorbed.
So this is where the absorption process occurs.
The ileum is where absorption of
our bile salts and our fats occur.
The duodenum is where bile is secreted into the GI tract.
So bile is secreted
into the GI tract.
Now we talked about what happens
to fats once they're absorbed in the ileum
when we talked about the small intestine.
But what happens to our bile salts?
Well the bile salts,
after they've been absorbed in the ileum,
are actually gonna circulate right on back to the liver
to undergo this process all over again.
So if we were to review all the different pit stops that our
bile takes in this process.
Number one
is that bile is made in the liver.
Then once it's made number two it's going to go
through the common hepatic duct
and then flow to
the cystic duct
to be stored in the gallbladder
until we receive cholecystokinin
as a signal to tell the gallbladder to contract
and then from there
bile is squeezed out of the gallbladder,
re-enters the cystic duct.
I guess you can say this is the fifth place it would go.
Re-enters the cystic duct
and goes into the common bile duct.
The common bile duct is the last part of the biliary tree
which will then
release its contents into the duodenum.
And so finally our bile has reached the GI tract.
The bile salts will then do their job
to emulsify the fats that we've eaten.
And then we'll have our bile salts
get re-absorbed in the ileum
before it heads back to the liver
where it gets reused.
So we reuse some of the existing bile salts
in the liver.
And that's
how our biliary tree works.