(Narrator) This is Armando.
This video was created as part of the Hungry Microbiome Project,
which I made at CSIRO.
Throughout most of human history we have felt at war with microbes,
however the human body is colonised by a vast number of microbial population
known as the human microbiome.
Trillions of bacteria colonise our bodies.
We can find them in various locations,
such as our throat, our gut, and even our skin.
In a healthy adult human body
there are approximately ten times more bacteria than there are human cells.
Humans and their microbiota, which is bacteria,
have a symbiotic and mutualistic relationship,
which means that us humans and the bacteria work together,
work with each other, benefit off each other,
and depend on each other for survival.
There is a growing number of research
into the field of the human microbiota,
for example the association between the gut microbiota and our health.
It’s an ongoing research, and new insight on the
mutualistic symbiotic relationship are emerging rapidly.
Most of these studies and research are based on in vitro studies,
as well as animal studies.
Another important terminology we should learn is the microbiome,
which essentially means a community of bacteria.
So for example if I say the human oral microbiome,
it means the community of microbes
or bacteria that live within our oral cavity.
In this video we will investigate and focus
on the bacterias that lives in our gut.
When we talk about the community of bacteria that reside in our gut,
we can refer to them as the human gut microbiome.
We will first learn about what they are and what’s...
and some interesting facts about them,
and then we will look into the effects they have on the human body,
which is, as I mentioned, an exciting and relatively new field of research.
So we begin here with the digestive tract.
Looking at the digestive tract,
which is made up of the oesophagus, stomach, small intestine
and large intestine,
these microorganisms are mostly found in the large intestine,
though it is important to understand that we do find these bacteria
but also in the small intestine, just not as much.
So let us recap the regions of the large intestine.
Here is a small intestine that joins with the large intestine.
The large intestine is made up of the caecum,
the ascending colon, the transverse colon,
the descending colon, sigmoid colon, and rectum.
We also have the appendix that joins with the caecum.
You might be thinking though if bacteria are inside our body,
wouldn’t it initiate some form of immune response?
Well that is true, but the digestive tract,
as well as other tracts, are special, in that it contains mucus for example.
So if we zoom into the large intestine here
we have the lumen of the large intestine,
and here are the colon cells.
Above the colon cells we have mucus,
which acts as a barrier between
the microbe community within the lumen and the human cells.
The highly dense microbial community
and the host intestinal cell linings
are separated by a thick layer of mucus in the large intestine.
Interestingly if we compare this to the small intestine,
the small intestine and the microbes
are only separated by a thin layer of mucus,
much thinner compared to the mucus layer of the large intestine.
Therefore we can see
how that mucus helps keep these bacteria from causing any harm.
Also the antibodies that are a part of the mucosal system,
as well as the tight junctions between the intestinal cells,
help in this respect.
So there is a lot of barrier here allowing these bacteria
to live within us in a symbiotic mutalistic relationship.
So why do we have it?
Why do we have these bacteria living in our gut?
Well the gut microbiota become established at birth
and continue to change in composition throughout development.
In fact many factors influence the amount
of microbes we have inside our body,
such as taking medications, diet and lifestyle.
All are factors that influence the composition,
the amount and the different types of microbes we have.
And therefore each individual is unique,
in that each individual has a unique amount, composition of microbes.
In the large intestine
the bacteria are mainly found in the proximal colon,
because this is where substrate availability is highest.
But there are still so much bacteria everywhere else,
such as the transverse colon, as well as the descending colon.
And so we can say
that the bacterial density will increase
from the duodenum of the small intestine to the large intestine.
We find especially a lot of bacteria in the proximal colon.
As well with this increase in density,
there is also an increase in bacterial diversity,
so there are more bacterial species as we move towards the end of the colon.
With the increase in bacterial diversity and density
there is also an increase in mucus thickness.
Now the normal gut microbiota is dominated by anaerobic bacteria,
but there are some aerobic and facultative
anaerobic bacteria that are found in the intestine.
In total there are up to 1,000 species of bacteria living in our gut
that interestingly only belong to a few known bacterial species.
The most abundant bacteria come from the phyla,
firmictues and bacteroidetes.
Our gut microbiota play many fundamental roles in our body.
Let us learn a bit about the effects
the gut bacteria have on the host physiology.
The main impact gut microbes have on host physiology is on metabolism.
The gut microbiota has been shown to help absorb nutrients,
but the main effect on metabolism is that the gut microbiota
have a big role in fermentation.
You see, foods that are not digested and absorbed in the small intestine,
such as non-digestible carbohydrates, will reach the large intestine,
and here the carbohydrate will undergo fermentation by the bacteria.
So let us have a closer look at this process.
So here we have the colonocytes with mucus on top,
and here is the blood supply.
Within the lumen of the colon we find the bacteria communities,
waiting for food to come.
The non-digestible carbohydrate particles will reach the colon
and will be then fermented by the bacteria.
Through this fermentation process the bacteria will produce a by product,
a substance known as short chain fatty-acids.
Some of these short chain fatty-acids, such as butyrate,
are used as energy by the colon cells.
Up to 70% of the energy used by colon cells
come from short chain fatty-acids.
Short chain fatty-acids that are absorbed into the blood
can have other effects around the body.
There is some in evidence that
short chain fatty-acids will influence adiposity,
by increasing lipogenesis, the synthesis of fat.
Short chain fatty-acids have also shown to influence
the immune system in many ways, as well as
they’ve been shown to play a key role in the health of colon cells.
Another fundamental effect the gut microbiota play in our body
is its effect on gut morphology, so gut structure.
These effects include
increasing the amount of mucus in the intestinal tract,
decreasing intestinal cell permeability,
deepening the crypts of the intestine, increased vascular flow,
and stimulate tissue repair and renewal, particularly the villi.
All of these effects essentially will promote barrier integrity,
as well as the function of the digestive system.
The reason as to how the gut microbiota modulate most of
these activities remains elusive,
but most of the research suggests that it is attributed
to the production of the short chain fatty-acids
following fermentation of non-digestible foods.
The gut microbiota has also shown to have effect on the immune system.
For example it has shown to influence the maturation and development of
lymphoid tissues, such as Peyer’s patches and mucosal system,
as well as the lymph nodes.
The gut microbes are also able to regulate production
of some immune mediators,
including increasing concentration of secretory IgA antibodies.
Recently it has been found that the bacteria
are able to influence the composition of t-cells in the lamina propria.
The gut microbiome also has effects on the nervous system.
Most of these effects are based on animal studies,
and include decreasing synaptic connectivity
and promoting anxiety like behaviours, as well as pain perception.
There is also suggestions that the gut microbiota
influences bone homeostasis by regulating bone density,
as well as increasing the re-absorption of calcium from the gut.
Now we’re still only scratching the surface of our
understanding of gut microbes and how they affect our health.
It is an ongoing and exciting field of research.
I hope you enjoyed this video. Thank you for watching.
[Music playing]