B Fruitfull

Acid Reflux causes and Treatment

Digesting Food

Digesting Food


Voiceover: One of the keys to
understanding child nutrition is understanding what happens
to the food our children eat once it’s entered their mouths. Let’s start by drawing a very
basic model of digestion. Now the food our children eat can be
broken down into three catergories and their categories of what
we call macro nutrients. All of these macro nutrients are
digested in slightly different ways, so I’m going to color code them
so that we can sort of follow what happens to each of these
categories of macro nutrients. The major macro nutrients are
carbohydrates, I’ll write carbs for short, fats and proteins. When we use the term micro nutrients, we’re talking about things
like vitamins and minerals, and the other important components
in the food that we eat. Now the digestive tract is
actually just a long tube that extends from the mouth
all the way down to the anus. We’re going to follow that
tube and trace the path of food after it enters the mouth and
as it passes down this long tube that leads all the way
through the digestive system. Digestion actually begins in the
mouth with the active chewing that’s an important part of
digestion that we sometimes overlook because it makes big pieces
of food, it breaks them down into smaller, more manageable
pieces that can be attacked by the different enzymes. Some of those actually are secreted
directly into the oral cavity or the mouth by accessory
glands called salivary glands. The salivary glands secrete
saliva, surprisingly. In that saliva are a
couple of different enzymes and I’m going to color
code the enzymes as well. The first enzyme that’s in
the saliva is called amylase. Amylase works to begin the
digestion of carbohydrates that’s why I’ve done it in purple,
we call that salivary amylase because there’s also another kind of
amylase that comes into play later on in the digestive tract. The other enzyme found in
saliva is called lipase. We also call that salivary lipase because
there’s a different kind of lipase that comes into the picture later on. Lipase begins the digestion of fats,
that’s why I’ve drawn it in yellow. Food is chewed in the mouth
and then swallowed down in the form of what we call a bolus. That bolus has been mixed up
with these salivary juices or the salivary enzymes and it passes down a tube
called the esophagus. This is the esophagus. The esophagus leads down into
a dilated part of this tube that we call the stomach,
so this is the stomach. There’s actually a sphincter
here or it’s kind of like a valve that we call the lower
esophageal sphincter that guards the entry way to the stomach. If that valve becomes leaky
then food can actually leak up from the stomach and give us heartburn,
that’s where heartburn happens. Once food enters the stomach, it gets
mixed with a bunch of other things that are secreted by the stomach. Things like hydrochloric
acid or stomach acid and I’ll just write HCl because
that’s the chemical abbreviation for hydrochloric acid. The stomach also secretes a
digestive chemical called pepsin. Pepsin I’ll write in green because pepsin,
you guessed it, it digests proteins. The other thing that the stomach
secretes is a chemical called lipase. This is gastric lipase, gastric
means it comes from the stomach and just like the salivary lipase,
the gastric lipase continues the work of digesting the fats that
have entered the stomach. Now the stomach is really muscular, so
it kinds of churns all this food around. The food that’s come down
the esophagus as a bolus and what ends up leaving the
stomach is more of a liquid. We call that liquid, chyme,
that’s what leaves the stomach. It leaves the stomach through
another valve or sphincter that’s the pyloric sphincter. That’s a good word for a spelling bee. Once the chyme has passed
through the pyloric sphincter it enters into the first
part of the small intestine and that part of the small
intestine is called the duodenum. I’ll just write that in, duodenum. Some really important things
happen in the duodenum or the duodenum as it’s sometimes called. What happens there is that the liver
secretes a chemical called bile. That bile is stored sometimes
when it’s not needed immediately. It’s stored, so it’s created in the liver. I’ll just draw it kind of
coming out of the liver. It actually is stored in a small
organ called the gallbladder. That’s over here so the
gallbladder’s going to store the bile and I’m just going to write that
in for you, that’s our gallbladder. This is our liver, and then
when the bile is needed and I’ll just write the
bile in here in yellow, so you can probably guess what
the bile is used to digest. When the bile is needed it’s
secreted out of the gallbladder and it enters the
duodenum, right about here. There’s another accessory organ that
also sort of dumps it’s products into the duodenum, right
about there at the same spot. I’ll draw that one in blue and this
accessory organ is called the pancreas. The pancreas, and the
pancreas is really important. It secretes probably the most
important digestive enzymes into the small intestine and
those enzymes are amylase, and this is now pancreatic amylase. It also secretes pancreatic lipase,
another way of digesting fat. Then it secretes two enzymes that
are used in the digestion of protein. One is called trypsin and
it’s cousin chymotrypsin. All of that exciting stuff
happens in the duodenum and after that, the
small intestine continues and it continues on for anywhere
from about 15 to 30 feet. It’s really long and coiled up on itself. I’m drawing it kind of spread out, these coils of small intestine
are actually all curled
up on top of each other. The second part of the small intestine and I’ll just try and give you a sense
of how long this part of the tube is. The second part of the small
intestine is called the jejunum. Jejunum. Then the last part of the small
intestine is called the ileum. Basically the small intestine
is where big particles of food are broken down into
their absorbable units and absorbed in this
tube the small intestine. What happens next is that the small
intestine joins the large intestine. The large intestine is sort of like a
storage and drying unit, if you will. It kind of curls around and there’s an
ascending portion, a transverse portion, and the one I’m drawing now, the
descending portion of the large intestine. It ends in an S shape part
that we call the sigmoid colon. This would be your ascending portion
of the large intestine, the transverse, and the descending here, I’ll
just write des for lack of space. Now what’s absorbed in the large
intestine are things like excess water, so the longer feces because this
is ultimately going to be feces that’s secreted out once it
passes through the sigmoid colon. This is our end product of digestion and feces is going to
pass out through the anus. The longer the feces sits in the large
intestine, the drier it’s going to get because water is being absorbed and some solutes are also
being absorbed in that tube. The food we eat is going to
be chewed up in the mouth and swallowed in the form of a bolus. The bolus is going to
pass down the esophagus and through the lower esophageal
sphincter into the stomach where it’s going to be
mixed with stomach acid and things like pepsin and
lipase and turned into chyme. That chyme is going to pass
through the pyloric sphincter and it’s going to head
down into the duodenum. In the duodenum, bile from
the liver and the gallbladder is going to be secreted into this part, as well as the pancreatic
digestive enzymes like amylase, lipase,
trypsin, and chymotrypsin. While this food is digesting into
it’s smaller absorbable parts it’s also being absorbed as it
passes through this long tube and you can see how
much time there is here to absorb all of the nutrients because
we don’t want food to pass through here without enough time for those
important nutrients to be absorbed. Then it gets here to the large intestine
and this valve I didn’t put this in but this is called the ileocecal valve because it’s between
the ileum and the cecum. Interestingly in case you’re interested
here, this is where the appendix is. It’s a little kind of pocket
extension of the cecum and if for example, you eat a grape
and you swallow all of the seeds, and you have pretty bad luck then one
of those seeds might get stuck in here. This appendix might get
clogged and fill up with pus and then you’ve got
yourself an appendicitis. If you’re lucky and that doesn’t happen, then the food that couldn’t
be either digested or absorbed passes into this ascending
colon and slowly moves up through the transverse colon
and down the descending colon. As it’s kind of progressively
dried and stored. Then once it enters the sigmoid colon
then a bowel movement is triggered and feces are secreted through the anus. That is sort of the big
picture of how digestion works. Now, I just want you to
have just kind of a window into what it looks like if we
took, let’s say a cross section through this small intestine. Let’s say I took a slice, like
this, out of the small intestine. What you would see, would be
a muscular tube like this. Let’s say this is the
chunk we’ve just cut out. That tube on the inside is going to have
this kind of finger-like projections and this finger-like projections are
called villi, so this is a villus. I’ll write the plural term which is villi and I’ll just make this
arrow pointed two of them so you understand that
that’s the plural term. The villi, what they do is
they increase the surface area for absorption of all of
those important nutrients that are going to be found in the lumen. The proteins, the fats,
and the carbohydrates that are going to be
passing through this lumen. Better yet to further
increase the surface area there are this kind of small, they
look like hairlike projections, projecting off of the villi and this
is what we call the brush border. These are called micro
villi or smaller villi. The micro villi make up the brush border. What that does is it further
increases the surface area for absorption in the small intestine. Now just to give you another view of
what the small intestine looks like, what happens if I were to give you another
cross section that looks like this. Through the wall of the small intestine. What if we were to kind of slice it open. What you would see, you
have your muscular wall here and here are your finger-like
projections called villi. Because we’ve zoomed in a bit, you can actually see that the
brush border or the micro villi are actually made up of
cells called enterosites. Each of these cells has their own nucleus and they’re actually selective
cells that can aid in the absorption of all of the important
nutrients in the small intestine. These guys are called enterosites. Now inside each of this villi,
this finger-like projections is something called a central lacteal. The central lacteal is actually sort of
a projection of the lymphatic system. The central lacteals are continuous
with the lymphatic system. Because I’m drawing them in yellow,
you might guess that the fats that are going to be in this lumen and they’ve been emulsified by the bile. They’ve been broken down into
smaller pieces by the gastric lipase and the salivary lipase
and the pancreatic lipase. All of this small units of fat are going
to be absorbed into the central lacteal and passed into the lymphatic system. Now there’s also in each of this villi there is a little capillary network. Each of this villi, each
of this central lacteals is surrounded by a network of capillaries
that bring blood toward the villus, and then also take blood away. As capillary networks do, they
carry blood away from an area. The proteins and carbohydrates,
so these are our carbohydrates and these are our proteins, and
these guys are going to be absorbed directly into the bloodstream,
into the capillary networks that sort of surround
these central lacteals. There are carbohydrates
going in, so you can see that this is how the small broken
down particles of the food that we eat actually get into our bodies,
get into our bloodstream. Next we’re going to be looking at how
are body uses those building blocks for either energy, for growth,
or for storage in the human body.

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