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>> So how do we get digestion?
We certainly have to have teeth, we have to have muscles,
we also need a contribution of enzymes.
So in the mouth we have saliva
and in saliva we have salivary amylase.
Amylase is looking for amylose-- that's the name I gave it.
It's a fancy name but it is you might call starch.
The mouth is all about the physical mastication chewing
of any of our big nutrients.
Then we swallow, it goes into the esophagus,
and now that material is now a bolus and it moves
to the stomach from the mouth via the esophagus;
from the esophagus through the low esophageal sphincter
into the stomach.
The stomach then produces hydrochloric acid.
This hydrochloric acid will begin protein denaturation.
Denaturation is just uncoiling.
It is not digestion; it is uncoiling,
making that complicated mess of proteins unfold.
Then we also have pepsin.
Pepsin is a result
of hydrochloric acid working on pepsinogen.
Pepsinogen is an inactive protein.
Once it gets turned on by the acid it becomes pepsin
and pepsin will try to digest the denaturated proteins.
Remember the stomach has those three layers of muscles
so we're going to get a lot of mastication, squeezing,
pummeling, starch and fats will get that.
Then from the pyloric sphincter
into the small intestine we have the contribution
from the gallbladder.
The gallbladder will hold bile.
That bile is made by the liver,
but the bile what it does is it emulsify fats; which is just
like if you have a greasy plate
at home you put some dishwashing detergent on it;
that's emulsifying the grease so that's what the bile does.
It takes those large fat globules and makes them smaller.
The pancreas will also secrete a variety of enzymes.
Those enzymes are for amylose
so that would be pancreatic amylase.
It also secretes pancreatic protease which would be
for polypeptides, and pancreas will secrete pancreatic lipase
which will be for those emulsified fats.
But there's one little problem
and that problem is the chyme that's
in the duodenum is highly acidic and we don't want our duodenum
to become Swiss cheese; so what we have
to do is cool off the acid
so the pancreas makes sodium bicarbonate
and sodium bicarbonate will make the pH of the duodenum neutral.
But the duodenum will also secrete a variety
of intestinal enzymes that we continue with proteases,
we'll have carbohydrates splitting enzymes,
we'll have things like maltase, sucrase and lactase
in the duodenum and into the jejunum.
If the chyme has gone in with these macronutrients,
by the time it's at the duodenum stage it has pretty much got
them to their smallest parts so if it was a starch
or an amylose, it is now glucose units.
If it was a protein it is now individual amino acids
and with fat it's become fatty acids or monoglycerides.
If the material goes from the ileum into the large intestine,
it is basically fiber and bile and cholesterol,
but mixed in there could be some water and some salts
and the body says hey I could use those
so let's try to reabsorb them.
But by in large any material
in the large intestine is pretty much roughage and it's going
to form fecal material.
Once we have absorbed our vitamins and minerals and water
and sugars and amino acids and fats,
we now have a little problem.
How do we get them from the small intestine
to the rest of the body?
And it's like parting of the seas.
We have any of the nutrients that are water soluble are going
to go through the portal blood system
to via a vein to the liver.
Anything that will go to the liver
from the small intestine has got to be water soluble.
So that means water soluble vitamins, water, minerals,
amino acids, the sugars, the glucose, fructose, galactose,
they are all water soluble.
Now what isn't water soluble would be fat soluble
so what's fat soluble?
The long chain fatty acids, the monoglycerides,
the fat soluble vitamins.
So they go off into the lactile, into the lymph system
and away they go to the heart.
Our water soluble though our water, water soluble vitamins,
minerals, amino acids and the sugars, fructose, glucose,
galactose, they go to the liver
and the liver says thank you very much
for this fresh supply of good nutrients.
How does all of this get controlled?
Well we rely on nerves when we stretch the stomach
that sends a message to the brain to say hey we're full,
stop eating but we also rely on hormones.
There are three that really stand up--
gastrin, secretin, and cholecystokinin.
Can you say that, can you spell that?
Sometimes it's just easier to call it CCK.
So gastrin is the hormone that when food gets
into the stomach it is secreted from the stomach wall
and it's stimulates the stomach glands
to secrete hydrochloric acid.
So that's what makes our stomach acidic; well it has to be
because protein needs to be denaturated.
What about secretin?
Secretin is going to respond
to this acidic chyme coming into the duodenum.
It will then go to the pancreas and it says pancreas save us
and so the pancreas responds with sending
out sodium bicarbonate and all is well in the duodenum.
Now CCK is involved in fat and protein digestion.
So what do we need for fat?
We need bile.
Where is bile?
It's in the gallbladder so CCK, when we have chyme
in the small intestine, CCK will be secreted;
it goes to the gallbladder,
the gallbladder then releases the bile.
Also CCK will go to the pancreas
and it will tell the pancreas hey give me some pancreatic
proteases, I've got the big guys, the protein,
the big guys really take a long time
to digest so I need some help.
You could think of it-- you've got this chart or table
in your textbook, you might want to see what happens
when you eat a peanut butter sandwich.
What happens at all at the mouth, at the stomach,
at the small intestine and the large intestine?
And lastly if you want to have a visual idea
of what the digestive system is about, then please go
to the link that's in this lesson for a You Tube video
that shows you the stages of the digestive system.
Well, good eating.