In this image, we can see the liver as seen from
the side, and it’s growing eventually, that’s
down from the gut, but it also grows in part
towards the head. So it’s growing towards
the head end. And this process begins about
the third week after fertilization.
As it grows, it begins to fork into a left and right
liver lobe. And these lobes grow forwards
towards the head, and as they go, they gradually
form cords. So I’m representing these cords
with my fingers and they grow forward towards
the head until they reach the margin of the
pericardial cavity. There’s a band of
tissue which separates
the pericardial cavity from the liver, and
this is known as transverse septum.
Later in life, this will contribute to the diaphragm.
So the liver is relatively large and well
developed in the embryo. It is probably about
twice the relative size in the embryo than
it is in the adult, and this has to do with
the function that the liver carries out in
the embryo. As it grows forward, as we can
see in this diagram, the liver is pressed
against the diaphragm at the bare area. And
on the other side of the bare area of the
diaphragm will be the pericardial cavity.
The liver is important because it’s a major
site of blood cell development, early in development,
and relatively, therefore, much more significant
than it is in the baby. It will actually diminish
significantly in size even during the course
of development. Now, let’s look at the development
of the gall bladder. This grows out as a bud,
a diverticulum growing out from the original
liver bud. We can see it here in association
with the cords of the liver formed in the original
endoderm of the liver as it grows forward.
The gall bladder is a system which will transport
and concentrate bile and prepare
it for release into the duodenum subsequently.
The bile cells tend to be green in colour.
So it’s an important storage organ in the
development of the intestinal system.
Bile is actually produced in the liver from week
12, stored in the gall bladder that will make
its way into the intestine from there. When
the baby is born, the first stool that it
passes, known as meconium, are often therefore
glossy green in colour as a result of the
bile salts and bile pigments present in the
intestine having been produced from the liver
and stored in the gall bladder.