The last aspect is now that you’ve
reabsorbed these particular molecules,
whether it be a water, whether it be ions,
whether it be things like fats, proteins,
carbohydrates, where do they go?
Most of this is going to be picked
up in the hepatic circulation,
but to talk about the hepatic circulation,
we need to diagram out a little
bit where the blood flow goes.
So from the heart, you would have
places like the celiac artery
that delivers blood flow to places like
the spleen, the stomach, and the liver.
The superior mesenteric
artery delivers blood flow
to the pancreas and parts
of the small intestine,
and then the inferior
mesenteric artery delivers
to some of the intestines
as well as the colon.
But it’s interesting that all of
these molecules are also linked
to the liver via the
So, you are actually passing
through multiple capillary beds
as you go from the celiac
artery through the stomach,
and then it goes
back to the liver.
Why is this so important for
digestion and absorption?
Is once you absorb something through say
some place like the small intestine,
what you’ve absorbed is going
to travel back to the liver.
If you’ve absorbed water form the colon,
that’s also going to travel back to
the liver via the portal circulation.
Individual components of the circulation
involve different amounts of blood flow to it.
The majority of the blood flow
goes to the mucosal layer
and less of the blood flow
goes to the muscular layer.
The other item to consider
especially in the small intestine
is that there are differences in the
amount of blood flow based upon
the villi and microvilli
in those regions.
So if we have a microvilli over here,
you can see that there is a change
in the partial pressure of oxygen
as you move towards the
tip of the microvilli.
And that’s because of less and less circulation
as you move towards those microvilli.
Why this becomes important,
is that there are already low amounts
of oxygen in the microvilli themselves
and what can happen is
these can become ischemic
if there’s a pronounced vasoconstriction
for prolonged periods of time.
And that can then change
intestinal barrier properties
and cause problems with allowing
certain bacteria across the GI wall,
making it a little bit leakier.