00:01
So when we are processing food
during the digestive process,
there are six
essential activities
that are going to take place.
00:09
First we have
ingestion or eating.
00:12
This is where we're going to
take the food into the mouth.
00:16
From there we're going
to have propulsion.
00:19
We need to be able to move
the food from the mouth
through the alimentary canal.
00:24
This is going to involve
the process of swallowing
as well as a process
known as peristalsis.
00:30
Which is our major
means of propelling food
and involves alternating
waves of contraction
and relaxation in one direction.
00:41
Also,
we have mechanical breakdown
which we sometimes refer
to as mechanical digestion.
00:48
And this is going to
include things like chewing,
mixing food with saliva,
the churning of
food in the stomach
and segmentation.
00:57
Segmentation is a process
that is going to take place
in the intestines
and involves local
constriction of the intestine
and the mixing of food
with digestive juices.
01:10
A fourth process in the
digestive process is digestion.
01:14
This is going to be a
series of catabolic steps
that are going to
involve the enzymes
that break down
our complex food molecules
into chemical building blocks
that we can use
for other metabolic
activities in the body.
01:28
After we digest or
break down the food.
01:31
We then absorb it,
this involves the passage
of the digested fragments
from the lumen of the GI tract
into the blood or lymph.
01:41
Finally,
We must get rid of
whatever was not digested.
01:45
This is referred
to as defecation
or the elimination of our
indigestible substances
by way of the anus
in the form of feces.
01:55
Two processes that involve
the movement of food
through the GI tract are
peristalsis and segmentation.
02:02
While they have
some similarities,
they also have some differences
In peristalsis adjacent
segments of the alimentary canal
are going to alternately
contract and relax.
02:15
This causes food to be moved
distallyalong the tract
and it's the primary
propulsion mechanism
of the digestive system.
02:25
While it is going to
mainly be propelling food
through the GI tract,
there is also some mixing
that does take place.
02:33
Segmentation on the other hand
is when non adjacent segments
of the alimentary canal are
going to contract and relax.
02:42
Food does move forward but
it also moves backward.
02:46
The primary function
of segmentation
is going to be mixing food
and breaking it
down mechanically,
although some
propulsion may occur.
02:56
So as you can see,
peristalsis is mainly
for propelling food forward
and segmentation is
mainly for mixing food
through mechanical digestion.
03:09
So now let's look at the
journey that food takes
through our digestive system.
03:15
Starting with ingestion
or eating of food,
food is going to be
taken into the mouth.
03:21
From there,
we're going to propel the
food through the GI tract
through multiple
different processes.
03:28
First,
in the oropharynx at the back
of the mouth and in the throat,
we have swallowing.
03:35
Following swallowing
we have peristalsis
where we're going
to prepell the food
through the remainder
of the GI tract
by way of the esophagus,
the stomach, the small intestine
and the large intestine.
03:50
Once we get into the lower parts
of the GI tract mainly
the the stomach,
although some of this does
take place in the mouth.
03:58
We're going to have
mechanical breakdown.
04:01
So starting in the mouth.
04:02
We're going to chew the food
which is going to start breaking
it down into smaller parts.
04:07
Once we get to the stomach,
We're going to turn the food
and then once we get
to the small intestine,
we're going to mechanically
break down the food
using segmentation.
04:19
Along with mechanical breakdown,
we also have a chemical
breakdown of our food
from the larger biomolecules
to the smaller biomolecules.
04:31
After we break the food down,
we have absorption.
04:35
Absorption is
going to take place
mostly in our small intestine
and our large intestine.
04:42
In this process,
nutrients and water are
going to be absorbed
into the blood vessels
or the lymph vessels.
04:50
Water is also going to go
into the blood vessels mainly
in the large intestine.
04:56
Finally, we have defecation
of any substances that were
not digested or absorbed.
05:03
This is in the form of feces
that is going to exit the
body by way of the anus.