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2. Frontiers of Biomedical Engineering: What Is Biomedical Engineering? (cont.)
Poziom:
Temat: Edukacja
Professor Mark
Saltzman: What I'm going to
talk about today is to continue
our discussion about what is
Biomedical Engineering and go a
little bit further and we'll
spend about half the class doing
that,
and then I want to spend the
last half of the class talking
about some biological structures
that are very important and that
you might not be familiar with.
I'll talk about biological
membranes and lipids and how
they're assembled.
But first, I want to start with
the assignment I gave you last
time, and I asked you all to
think about these two questions
and write some things down.
Let's start with the first,
with A on this list here.
What products of Biomedical
Engineering have you
encountered?
We talked about a few of these
last time but I'm sure there's
others, so what things did you
come up with as you were
thinking, anybody?
Student:
[inaudible]
Professor Mark
Saltzman: Okay,
so in the category of already
available: drug delivery
patches.
These are now available for a
variety of drugs,
Scopolamine for motion sickness
was one of the first that was
available and nitroglycerin for
treating heart disease is
already available and these are
really like band-aids but
they're band-aids that are
loaded with drugs and they're
designed in such a way that if
you apply this band-aid with
adhesive to your skin,
drug will enter your
bloodstream from the band-aid
through the skin,
and that's been,
I think, a good example.
Others?
Student:
[inaudible]
Professor Mark
Saltzman: Dissolvable
stitches or sutures,
now what needs to be engineered
in those?
So they have to be engineered
to be inert so that they can be
safely inside a system and
there's not every material you
could pick would have that
property.
It's - a suture or a stitch has
to hold the wound closed so it
has to have certain mechanical
strength and imagine the problem
of making something that's
dissolvable so it disappears but
also is strong enough to hold a
wound closed reliably for a
length of time.
Others?
Student:
[inaudible]
Professor Mark
Saltzman: Arthroscopic
surgery - what are you thinking
about there?
Student:
[inaudible]
Professor Mark
Saltzman: Yeah,
so you're thinking about the
instruments that they use in
arthroscopic surgery,
arthro means 'joint',
scopic means 'looking',
so it's looking into a joint
and these are instruments that
have very fine sort of needles
on the end,
but also cameras in them,
and you can put them inside a
joint and then look around and
see what's happening inside.
And not just a camera but there
are also tools on the end of
these things so you can cut and
you can do manipulations through
this instrument,
so that's a great example also.
Yeah?
Student:
Hearing
aidsProfessor Mark
Saltzman: Hearing aids -
that's a good one,
others?
Student:
[inaudible]
Professor Mark
Saltzman: Cochlear implants,
so that's the same kind of
function as a hearing aid,
to improve hearing,
but using a different
mechanism.
Not just an amplification
system that you put in your ear,
but actually an implant that
replaces the function of an
organ inside your ear.
That's a good example, others?
Must be a couple of others -
yeah--Student:
[inaudible]
Professor Mark
Saltzman: contact lenses.
Student: Lasik
surgeryProfessor
Mark Saltzman:
Lasik surgery - now why
that one, what makes you think
of that as an example?
Student:
[inaudible]Professor
Mark Saltzman:
Instruments,
it involves lasers and learning
how to make lasers that can do
the right amount of damage to
tissue,
right?
Because that's what the laser
is doing in the surgery is
cutting like a knife would do,
but doing the right amount of
damage and controlling it with
light is an advance there.
Others?
Student:
[inaudible]Professor
Mark Saltzman: Tissue
culturing - now what has to be
engineered in tissue culturing?
Student:
[inaudible]Professor
Mark Saltzman: I beg your
pardon?
Student:
[inaudible]Professor
Mark Saltzman: So what
kinds of engineering do you
think goes on behind that?
Student:
[inaudible]Professor
Mark Saltzman: The
technology that they use and
really there's quite a lot of
technology here starting from
the plates that you grow them in
turn out to be engineered so
they have the right properties.
And we're going to talk about
this more when we talk about
cell culturing later,
and we'll talk about lots of
potential applications of that
as well.
Student:
[inaudible]Professor
Mark Saltzman: Dialysis -
and this is a method to replace
or augment the function of your
kidneys,
to remove waste products really
from the blood,
which is something the kidney
does continuously.
Student:
[inaudible]Professor
Mark Saltzman: Cosmetic
surgery - you gave two examples,
one was Botox and the other was
liposuction.
So two different kinds of
strategies, one is a surgical
strategy, actually removing
tissue and we talked a little
bit about the engineering of
surgical instruments and things
like - so there's a lot of
Biomedical Engineering that goes
into everything that happens in
the operating room.
Botox is an injection of a
molecule, or a complex molecule
but a molecule,
so in what ways would that be
Biomedical Engineering?
Student:
[inaudible]Professor
Mark Saltzman:
Right and I think all of
those are good,
so there's lots of different
ways.
One is in terms of how you
deliver the molecule so it goes
where you want it to go and not
where else you want it to go.
And that's an engineering
problem that we're going to talk
a lot about, how to deliver
drugs so that you get the action
that you want,
at the site that you want and
not the toxicity.
If you delivered Botox all over
your body that wouldn't be a
good thing, it might not even be
a good thing if you delivered it
one place in your body,
but it's definitely not good if
you deliver it everywhere.
So controlling the dose is
really important and that's
going to turn out to be very
important in cancer therapy
because these are very potent
drugs that will have bad effects
in other sites and you want to
localize them where they want,
so we're going to talk about
that.
I think this is as good
list so let's go and think about
what might be a little bit more
challenging.
So in the future what things do
you think Biomedical Engineering
is going to produce in the
future?
Student:
[inaudible]Professor
Mark Saltzman:
An AIDS
vaccineStudent:
[inaudible]Professor
Mark Saltzman:
robotic
surgeryStudent:
[inaudible]Professor
Mark Saltzman:
artificial hearts that can
be used long term and that is a
- there's probably several
elements to that.
One is long term,
making them compatible with the
body so that you could tolerate
it for long term.
And the other thing means if
it's going to be long term,
than probably it has to be
implantable and that means all
of the heart has to be
implantable.
This is where we don't have
something that satisfies both of
those categories right now.
Imagine how much power it takes
to drive an artificial heart,
so you've got to have a battery
or some way of generating power
continuously to operate that and
that makes it difficult to think
about implantable and so that's
a really good example of
Biomedical Engineering.
Student:
[inaudible]Professor
Mark Saltzman:
Food supplies - food from
cloned animals.
We're going to talk about
cloning next week,
but why would cloning be an
advantage in producing food?
Student:
[inaudible]Professor
Mark Saltzman:
Controlling quality because
cloned animals are all
genetically identical and so you
wouldn't have variability that
way,
and so potentially you could
have - pick an individual that
has a really good quality meat
and always reproduce that same
thing.
Student:
[inaudible]Professor
Mark Saltzman:
Genetic scans for disease
predictions,
and we talked about one way you
might do that using gene chips.
Last time we talked very little
about that and so we'll talk
more about that next week,
but certainly technology is
going to be available,
but there's going to need to be
ways developed to put this
technology together.
If we looked at all 30,000
genes that were important in
each individual how do you pick
out which ones are important for
a particular disease?
Or what - and often it's not
going to be just one gene,
it's going to be combinations
of genes,
and how do you predict the fate
of the individual based on all
of the genes that you know to be
involved in progression of a
certain disease.
So it's not just knowing what
genes or figuring out ways to
look at gene expression,
it's figuring out how this
expression of key genes affects
the fate of the individual.
That's really a complex systems
problem, the kind of problems
that engineers are very good at
dealing with.
Others?
Student:
[inaudible]Professor
Mark Saltzman: So I'm
going to call that chips
implanted in the brain to
control prosthetics,
but I'm going to make it a
little bit more general and call
a brain-machine interface.
So it's some way of interfacing
activity in your brain with the
outside world,
and we'll talk about this as we
go along, but there's lots of
reasons to think that we're
going to have this in the not
too distant future.
Student:
[inaudible]Professor
Mark Saltzman:
Spinal cord regeneration -
that's a good one.
Student: Organs that
can be cultivated
…[inaudible]
Professor Mark
Saltzman: Organs grown from
single cells.
Student:
[inaudible]Professor
Mark Saltzman:
I didn't hear the last
partStudent:
[inaudible]Professor
Mark Saltzman:
Imaging of moving parts
like the - like a joint or
another moving part that might
be interesting to look at in
motion is the heart.
If you could image how the
heart is moving,
you would know a lot about its
function.
You could potentially learn a
lot about its function by
looking at how it moves,
not just a static picture of
it.
There's lots of parts of our
bodies that move,
the lungs for example,
and so yeah that's a good one.
Two
more--yeah--Student:
[inaudible]Professor
Mark Saltzman:
artificial pancreas - now
how are you thinking that might
work?
Student:
[inaudible]Professor
Mark Saltzman:
So maybe - and here
thinking about the pancreas has
many functions but one of its
important functions is to
secrete insulin.
So diabetics have lost that
normal function.
What if you could take just a
pump that's capable of
continuously administering
insulin at various rates and
connect it to a sensor that's
able to continuously measure the
sugar level in your blood?
Insulin is important for
regulating levels of sugar in
your blood.
Well if you can continuously
measure and then give the amount
of insulin you need to
compensate for that amount of
blood,
those things could work
together to be a totally
artificial pancreas,
make it totally out of
synthetic parts.
Now another approach would
be to take pieces of the
pancreas that already have all
that capability within them.
Individual cells of the
pancreas are capable of - of a
healthy pancreas are capable of
both sensing glucose and
secreting insulin.
So what if you could take cells
from a healthy individual and
put them into a diabetic
individual?
Then maybe those new cells you
put in would function as a
totally natural artificial
pancreas.
Now why isn't that done?
Why doesn't that already work,
do you think?
What are the engineering
problems to overcome to get that
to work?
Student:
[inaudible]Professor
Mark Saltzman:
The same problem is with
organ transplantation is that
the recipient has to be matched
to the donor and so that's a
problem.
That's a big problem and so can
you protect these cells that you
give to the recipient from
attack by the recipient's immune
system?
That's one challenge and we'll
talk about ways to think about
engineering approaches to solve
that problem.
One
more--Student:
control of angiogenesis
within…
[inaudible]Professor
Mark Saltzman:
control of angiogenesis,
and angiogenesis - angio
means 'blood' and genesis
means 'new' and so angiogenesis
is a development of new blood
vessels.
Many people believe that
tumors, most tumors require
blood vessels in order to grow.
If a tumor starts to grow and
it doesn't develop a vascular
supply it doesn't develop blood
vessels in it,
then it can't get bigger than a
certain size and there's lots of
evidence from many cancers
showing that this is true.
So if you could stop a tumor
from being able to develop blood
vessels you might be able to
stop its growth at a stage where
it's not harmful.
In fact, I don't know if in the
news the pioneer in this is a
man named Judah Folkman,
who is a surgeon who first
speculated that this was
important, and sadly he died on
Monday,
but had a dramatic impact on
our understanding of how cancers
develop in people and new
approaches.
So there already are some
approaches like this that are
working, but there's more that
needs to be done.
So of these things that are
up here, are any that seem
controversial to you or that you
would have said wasn't on my
list and I wouldn't say that
that's Biomedical Engineering?
Student:
[inaudible]Professor
Mark Saltzman:
Controversial in what
sense?
Student:
[inaudible]Professor
Mark Saltzman:
Controversial in the sense
that maybe it's not a good thing
to do,
or there might be some limits
on what we want to do there in
terms of integrating machines
with people's brains.
I think that's probably right,
and there might be some others
here where there might be some
concerns, or others that have
kind of concerns like that.
Student:
[inaudible]Professor
Mark Saltzman:
So there's some issues
about how these technologies
might be applied,
right?
If you had genetic scans that
were available for disease
prediction, do you want to know
everything that's going to
happen to you in terms of
susceptibility to disease?
Well, probably you want to know
some of it but you might not
want to know all of it right?
You might not want to know all
of it and that's a really
complicated question for an
individual to figure out and a
complicated question for society
to figure out,
what you want to make of
available in the regard.
Student:
[inaudible]Professor
Mark Saltzman:
If you can start to predict
you're going to have heart
disease that starts to develop
when you're 45 and you're
looking to buy insurance when
you're 30,
or you're looking for a job
when you're 30 and that
information is available to your
insurance company or your
employer,
that could have dramatic
effects on the choices that you
get to make.
So that's really - these are
really difficult questions to
answer.
We'll talk about - we'll raise
these issues as they come up.
We'll try to raise them with
all the technologies,
we won't try to answer them,
there are probably better
people at Yale to answer those
kinds of questions than I am.
We'll talk about the technology
and the questions that it brings
up, but I hope some of you get
interested and these will be
good topics to think about for
term papers as well for those
you that have that kind of
inclination.
But any that seem like
controversial or like,
‘I don't think that's
Biomedical Engineering' or
‘that's not what I want to
learn about in this course'.
Let me put it that way;
I hope we don't spend a week
talking about that one because
that's not what I thought
Biomedical Engineering was.
Any of these or do they all
seem on the mark?
Yeah?
Student: Food from
cloned animals
Professor Mark
Saltzman: Food from cloned
animals - you didn't expect that
to be Biomedical Engineering?
So why?
Student:
[inaudible]Professor
Mark Saltzman:
I think - I see where you
wouldn't see - I see where you
would put it in that category
and how you would be surprised
to put it in that category.
It should be in the category
because it's engineering to be
able to do this,
right?
It's a biological system that
you've engineered from taking
cells from one organism and
cloning them and developing a
whole other organism.
And it's also engineering that
helps humans,
right?
Because nutrition is going to
be one of the big problems of
your generation;
how to have enough nutritious
food for the population as it
grows.
Even to understand what
individuals should eat,
what should I be eating?
That's a really complicated
question that we have gotten
very confused about.
In large part because our
government has confused us about
it, but it's a confusing
question to know.
I think engineers have a role
to play in that,
but it's not sort of classical
Biomedical Engineering in the
way that developing an
artificial heart is where you
can see that.
But I think it's a good example
of a place where biomedical
engineers of the future are
going to contribute.
So I want to try to put
this together into a form that
I've come to understand what
Biomedical Engineering is and
present it to you.
Not only am I not an ethicist
and I'm not good at those kinds
of problems, I'm not much of an
artist either.
So this is a person - you can
recognize it as a person,
but let's say it was a person a
long,
long time ago and there was a
point when one person decided to
take instruments that were
around them and use them to
improve their life.
Somebody thought about a wheel,
or some group of people
discovered how to use a wheel,
some a knife,
and some levers and these were
very useful things in improving
the quality of their life and
that was - that's who you would
call the first engineer.
Then some - it couldn't have
been too long after those
instruments became available,
but somebody,
let's call them the first
biomedical engineer,
decided to use those
instruments to look at either
themselves or probably more
likely,
their neighbor.
Take a knife and open up the
skin and let's see what's
inside.
How do these fascinating things
around me work?
So people started turning these
machines they developed on
themselves to try to understand
how they worked.
This is one aspect of
Biomedical Engineering,
developing tools that allow you
to understand how human's
function and what's wrong when
they have disease and so some of
the things we've talked about
have that category.
Arthroscopic surgery in one
sense is a fancy example of
that, a way of looking inside a
joint to see what's happening
inside while the person is alive
and without hurting them.
Imaging of moving parts that
same way is sort of advance in
that.
As these tools became applied
more and more widely,
we learned more about how human
physiology worked.
As we learned about how humans
operate we could start to design
machines that would help humans
when they weren't functioning
properly.
I think the simplest example
was that once we learned that
there were bones or hard
elements inside the leg,
and that those bones were
important in keeping the leg
straight so that you could stand
up,
then somebody could invent an
artificial bone,
a splint that would be wrapped
around - that would be secured
to the outside of the leg to
give you mechanical support even
after you fell out of a tree and
you broke you leg.
So this is another kind of
engineering, an engineering not
to look more closely at how
humans work but an engineering
to improve their function when
it's failing.
As time goes on,
we've developed ever more
complex machines to study people
and we've talked about some of
these already:
EKG machines,
so an example of an electrical
device that can be used to
monitor a very elaborate
function deep inside your body,
the beating of your heart and
the rhythm of your heart.
We talked about modern imaging
methods and this is an example
of an fMRI, a functional MRI;
a map of the brain that not
only shows you the anatomy of
the brain but shows you
something about the chemistry of
what's going on inside.
You can put somebody in an MRI
machine now and have them read a
book and look at what parts of
their brain become activated
when they're reading and what
parts stop activating when they
stop reading,
so you can learn where in their
brain is reading done.
You can ask them to read French
and to read Spanish and you can
find different locations in the
brain that are involved in
processing of those different
languages.
These are really incredible
tools for understanding deep
inside the body what's
happening.
We can even understand it on a
molecular or cellular level now.
This is a picture of patch
clamp, it's a device that
engineers built to fasten onto
individual cells in order to
look at how molecules in the
membrane of the cell are
working,
and I'll talk a little bit
about that as we go along.
We can understand down to a
very fine level now because of
machines that we've built.
As our understanding is
improved and we've been able to
build more complicated
approaches to replacing
function.
We talked about the artificial
hip which is a modern precursor
of the splint I talked about
before.
Much more sophisticated in
terms of the materials that are
required and the design thinking
that goes behind it.
So now somebody can get an
artificial hip and they can live
for many decades with it and
have almost full function of
that hip over that period of
time.
This is an example of a
rudimentary brain machine
interface.
It's a device called a deep
brain stimulator,
developed by a company called
Medtronic,
and it looks like a pacemaker
that's implanted inside your
body.
Here is as pacemaker and this
pacemaker does the same thing
that a heart pacemaker does,
it generates periodic
electrical signals.
But instead of those signals
going to your heart they go into
the brain.
They go through these wires and
into these electrodes that are
deep in your brain,
and they stimulate tissue
inside the brain.
We've found that stimulation,
electrical stimulation deep in
the brain can help patients that
have Parkinson's Disease and can
reduce the tremors and loss of
muscle control that many
patients with Parkinson's
Disease use.
Now these are electrodes that
are only sending out signals.
They're producing electrical
signals in the brain--they're
not recording from the brain,
but it's not that big of a
difference.
It won't be long before we're
using these same kind of devices
to both record--to test what's
going on--and to act in the
right way and response.
This is a beginning of real
interface between machines and
brains.
Dialysis,
this is an example of a
membrane dialysis unit.
Dialysis is done millions of
times per day in this country
and around the world,
and keeps people alive when
their kidneys have failed and
they wouldn't survive for even a
week without dialysis.
You can keep people alive for
many decades with periodic
dialysis to remove waste
products from the blood.
We'll talk about these examples.
What I want to leave you with
is my picture,
not a very elaborate picture,
of what Biomedical Engineering
is to me, and two parts of it.
One, developing ways to
understand how humans work
better, how human physiology
operates,
and second, developing new
approaches for replacing
function in people when they're
sick.
I want to talk about - move
on and talk a little bit about
some general concepts from
physiology that are really
important and here is a table
that gives characteristics of an
average person.
This would be an average adult
male, 30 years old,
the average height and weight,
and surface area and
temperature, and lots of
characteristics of an average
person.
Let's think about some of these
like weight.
We think a lot about weight in
this country,
but weight is a remarkably
carefully controlled parameter
of a person,
that is, you have to work
pretty hard to gain weight or to
lose weight.
We take in a lot of food and
water everyday,
every year, and yet most of us
our weight stays remarkably
stable over that period of time
for adults despite how much we
eat and how much we drink.
Your body is able to regulate
your weight fairly well without
you really thinking about it.
Anybody - you're all too young
to have tried to lose weight
yet, but when you get to be
older and you start to think
about as your metabolism
changes,
trying to control your weight,
you realize how hard it is to
do, and you know this because
people spend a lot of energy
thinking about it.
Weight is remarkably well
controlled if you let your body
do its business.
Also, temperature,
you could measure your
temperature and you'd find
variations throughout the day or
maybe some throughout the year,
but within a remarkably narrow
range your temperature is
controlled.
When you go from here to going
outside, to going to a much
hotter room, your temperature
stays the same and your body is
able to control this on your
own,
you don't have to think about
it.
In fact, temperature is such a
carefully controlled parameter
that when it changes just a
little bit by a couple of
degrees,
we know that something's wrong.
You measure your temperature is
a little up, you've got a fever,
'something's wrong,
I better find out what that is'
because temperature is a very
highly controlled variable.
You could go through a lot
of these parameters and think
about it in the same way that
these things are really very
highly controlled.
Well that process of control to
maintain a constant environment
inside our body,
whether it's an environment of
constant mass or constant
composition, or constant
temperature,
is called homeostasis.
Your body has elaborate
mechanisms for maintaining this
state of homeostasis,
that is, things staying the
same;
the body stays the same,
homeostasis.
This, in spite of the fact that
we take a variety of chemicals
into our bodies in different
ways and we have to do that to
stay alive,
but we have mechanisms to
control this very well.
So homeostasis is enabled by
sometimes complex,
sometimes very simple control
mechanisms.
These are mechanisms that
can be described not too
differently from mechanisms that
you're familiar with for
maintaining homeostasis.
For example,
the thermostat in your dorm
room.
Maybe you don't control
thermostats in your dorm room,
some of you do and some of you
don't probably,
and maybe it doesn't work very
well so it might not be a good
example, but imagine a perfect
thermostat that you set for a
temperature and then the
temperature stays the same
inside the room no matter what
the temperature is outside.
Well how does that work?
It works by a control mechanism
called negative feedback,
and the thermostat is measuring
the temperature and then sending
a signal to a heater somewhere.
If the temperature drops below
a certain level it sends a
signal, 'turn on the heat',
and that signal stays on until
it gets a negative signal to
turn off.
When does that negative signal
happen?
When the temperature gets above
the level you want it to be.
So that's a negative feedback
control system.
The heater is on,
it's producing heat until a
negative signal is registered,
'oh we've gone too high',
and then it turns off.
Our bodies have mechanisms
like that, that mainly use the
principle of negative feedback
in order to control the
parameters that are important
for life within a certain range.
So why is temperature,
for example,
such an important thing to
control?
Why are all of us in this room
within plus or minus a few
tenths of a degrees at 37°
Centigrade, or 98.6°
Fahrenheit, why is that such an
important thing?
Student:
[inaudible]Professor
Mark Saltzman:
Because that's the
temperature at which many of the
molecules in our bodies operate
at their most efficient,
and enzymes is the best example
of that.
Enzymes work best,
enzymes are proteins that
catalyze chemical reactions and
our bodies operate by elaborate
networks of chemical reactions,
and our enzymes are optimized
to work at 37°.
When we're off from that
temperature then they don't work
properly.
And there are other examples as
well, but that's why it's
important.
So we're going to think
about - in the next few weeks -
we're going to think about the
human organism at different
levels of magnification and I've
shown those levels here.
The whole human organism is
made up of a collection of
organs, and organ systems,
you know this.
The cardiovascular system,
which is the heart and the
blood vessels which are
responsible for - and the blood
and so this is responsible for
moving blood around the body and
the blood brings oxygen and
nutrients to every part of the
body,
you know that.
Organs, organ systems like
the cardiovascular system are
made up of tissues and tissues
are collections of cells that
are working in synchrony for
some function.
The heart, for example,
has a muscular tissue.
It has a very well-developed
muscular tissue and its function
is to contract and relax,
contract and relax.
As it does that it changes the
volume of the heart and gives
the - creates the pressure that
moves blood around your body,
so it has that muscular system.
It also has a blood vessel
system in it.
The muscles of the heart have
to give blood themselves so they
have blood vessels inside.
Your stomach is a very complex
organ that has a muscle layer,
it has an epithelial layer
which is the interface with food
that comes in,
and it also has a nervous
system, so does the heart.
So organs are made up of
combinations of tissues where
all the tissues are collections
of cells that are doing some
function,
nervous tissue,
muscular tissue,
epithelial tissue,
those are examples of tissues
that form organs.
Here I just show tissues at
two levels of magnification and
when we think about tissues
we're going to be interested in
a couple of different
characteristics.
One, at the first level,
what are the cells that make up
that tissue?
Because the cells are the
fundamental component of our
bodies;
very interesting because all of
our cells in our body share many
characteristics and some of
those characteristics are shown
on this picture.
They have a nucleus,
they have a cell membrane,
they have organelles throughout
them, they have the same DNA.
All of your cells have the same
DNA, so the same genetic
information, and yet cells in
your brain,
and cells in your heart,
and cells in your kidney do
very different things.
So how can cells,
which have the same sort of
master information DNA,
in your brain,
and your heart,
and your kidney be so
different?
That's a question and it's one
that we'll talk about in weeks
to come.
How do those differences
between cells contribute to the
properties of the tissues,
which contribute to the
properties of the organs,
which contribute to the
properties of a person and this
maintenance of homeostasis?
The main function of all your
cells, and all your tissues,
and all your organs is to
maintain this homeostasis,
which allows you to live in a
changing environment.
We're going to spend the
first few weeks of the course
talking about first DNA and
genes.
We'll talk about how they work
and we'll go over that quickly
because I know most of you know
something about how DNA - what
DNA is and how it works.
Then we'll talk about
engineering of DNA and why this
has been such - not only a
rapidly growing and advancing
area but one that's so important
for Biomedical Engineering.
We'll talk about cells and how
they work, how cells in
different parts of the body are
different,
why, and how they contribute to
tissues at a very sort of simple
level so that you can understand
this as we start thinking about
using cells for engineering
purposes.
I want to just highlight
what's in Chapter 2,
because I told you we're not
going to cover the details in
Chapter 2 in the course,
but I give it to you as a
resource so that you - you might
have other books which describe
this which you like,
and you've read already and so
- but I'm going to assume that
you understand this information
to some extent.
And again if you don't,
and you feel like you'd like a
review session on this please
send me an email and I'll set
one up next week.
I do want to talk about one
important subject which you
might not have thought too much
about and that's lipids,
because lipids are so important
to the structure of the body
because they make up the
membranes that form the cells
that are the fundamental units.
Lipids are really complex
molecules on their own right,
but because of their particular
kind of complexity they allow
certain biological structures to
form.
So most of the lipids,
which make up cell membranes in
your body are of this category
of phospholipids.
They're derived from a
precursor called
triacylglyceride,
which is as glycerol molecule
with three fatty acid chains
dangling off of it.
Fatty acid chains are fat
molecules, they behave,
if you have a lot of them in
solution like oil.
That's what triglycerides are
like, they're just like oil.
So if you had a jar full of
triglycerides it would behave
like an oil, many would be
liquid at room temperature.
What happens if you add them to
water?
You get salad dressing, right?
You get glob- if you mix it you
get globlets of oil,
or globlets of triglycerides,
they're floating around in the
fluid if you mix it.
If you let it sit they settle
out into two phases again,
that's how triglycerides
behave.
Now if you've gone to the
doctor, often they'll measure
your triaglyceride level as a
measure of how healthy your
liver is and how healthy your
diet is.
Having too much triaglyceride
or fat in your blood,
the wrong kind of fat in
particular, is not considered a
good thing.
You need some of it because
some of it gets converted into
molecules called phospholipids,
and phospholipids are
different.
They have two fatty acid chains
and so these are the oily like
parts of the molecule,
the molecules that behave like
oil.
And then linked to the glycerol
instead of a third fatty acid
chain is a water soluble
molecule, like a salt.
Often it's a salt called
phosphocholine and so you get a
phospholipid that's made of
choline and two lipid chains.
Now this behaves very
differently in water because
part of it is water soluble,
this part is,
it's a molecule that would like
to dissolve in water and part of
it is like oil,
it doesn't want to dissolve in
water.
So what happens when you put
these molecules in water?
Well instead of forming
droplets like fat they arrange
in a very particular way,
they form these structures that
are called self-assembled
structures because they occur
naturally,
because of properties of the
lipids.
The lipids will form a bi-layer
where the water soluble part of
the lipid points out of this
layer and the oily part points
in.
The fascinating part about this
layer is that it solves the
problem for phospholipids about
how to exist in water when half
of you wants to be in oil,
and that the water soluble part
of the top leaflet here,
of the top points up into the
water,
and the fatty acid chains point
down.
The opposite leaflet does the
other thing, the water soluble
part points down and the fat
points up,
so now you have thin region of
fat which is surrounded on both
sides by water.
This is a really
interesting system because it
also solves a problem for the
cell.
The problem it solves for the
cell is how to do I make a
barrier around myself to define
what's in me and what's outside
of me when most of what's around
me and what's in me is water.
So inside the cell mostly
water, outside the cell mostly
water, but I need to separate my
water from the water outside.
We'll see why they have to
separate that in a minute,
but they do that - these lipid
bi-layers solve that problem for
them and they're self-assembled
structures from these molecules
called phospholipids.
Now that's not the only
thing in cell membranes,
there are also proteins in cell
membranes,
and these proteins are special
proteins that can exist within
membranes like this,
and they exist because these
proteins also have different
segments with different
properties.
Some of the segments dissolve
in water, the gray segments
here, and the lightly colored
segments don't dissolve in
water, they dissolve in fat.
So they like to be in the
membrane and they're stable
there and they won't come out
because their structure allows
them to exist in these unique
spaces.
I'm going to stop there and
we'll pick up on this topic,
not next week,
but the week after when we
start talking about cell
structure.
I wanted to introduce it to you
so that if you don't - haven't
heard about this before you
might want to read a little bit
about this before we get to
Chapter 5.
Next week we're going to talk
about genes and genetic
engineering, that's Chapter 3.
