Download Chapter 24

Digestion & Absorption
This illustration is
designed to show
you the “tunnels”
that nutrients must
pass through to get
to the blood. The
empty space labeled
“extracellular fluid”
is where the food
passes through in
the small intestine.
The pink area is the
inside of a cell. You
only see a small
portion of the cell.
On the other side of
the cell (out of our
view, towards the
bottom) is the blood
capillary, ready to pick
up nutrients from the
cell. Note that fatty
acids and cholesterol
do not need to travel
through tunnels!
• Amylose is a form of starch. Note that it is composed of
many glucoses linked together in a chain. The chain is too
big to be absorbed into the blood, so it needs to be cleaved
into individual glucoses.
• AmylASE is a digestive enzyme that will hydrolyze starch
into disaccharides of 2 glucose (we’ll talk about how those
get split up later!)
• Example of enzymatic carbohydrate digestion:
• The enzyme sucrASE splits the disaccharide sucrOSE into
its component monosaccharides
• Glucose and fructose are both small enough to be absorbed
• We’ll talk about sucrase in ch. 4. I used it as an example
here because it is difficult to find good pictures of amylase!
• This is how the enzyme lipase works: it
splits up triglycerides, which are chains of
fatty acids. The fatty acids are now small
enough to be absorbed.
Proteases cleave
proteins into
smaller pieces,
including
amino acids.
Now they are
small enough to
be absorbed.
We’ll talk about
peptidases in
later chapters!
Here is a view of the small intestine. Note how furry
it looks. The tiny folds are villi. You cannot see
microvilli in this picture.
Here is another view of the small intestine. Now, when you look at a close-up of each
villus (b), you can barely make out microvilli of each cell. An even closer up view
(c), shows a little more detail of the microvilli. Note that they are part of each
individual cell, while a villus includes many cells.
Here is a close-up of a
single villus. Here,
the illustrator has
included the
microvilli, you can see
them as tiny hairs on
each cell. Note the
blood vessels and
lymphatic vessels
right under the cells.
This is where nutrients
will go, after they pass
through the cells.
• One last picture
of villi and
microvilli!
• I lied! This is a real picture, a Scanning
Electron Micrograph of villi. You cannot
make out the microvilli.
• I like this picture, it’s the juncture between the
esophagus and stomach. Notice how completely
different the linings are!
• Denaturation (unraveling) of
proteins by hydrochloric acid
(HCl) increases the surface
area available to proteases
• This is an
overview of
the effects
of CCK
This one looks
at CCK and
secretin
An illustration of emulsification by bile
This illustrates the relationship of the pancreas and small intestine. Cells of the
pancreas make bicarbonate and enzymes. They put those products into the
pancreatic duct, which empties into the duodenum, right after the pyloric sphincter.
Picture (a) shows where the pancreatic duct empties into the duodenum.
Picture (b) shows how the pancreatic duct is formed, and how the
cells are arranged. Picture (c) is an actual photomicrograph of
pancreatic cells.
This shows how the liver sends bile to the gall bladder, and
how the gall bladder then sends it to the small intestine;
through the same duct (b) the pancreas uses!
Another illustration of pancreatic cells
sending products into the duct