Stenosis, ischemia and heart failure | Miscellaneous | Heatlh & Medicine | Khan Academy

As someone who’s married to a
doctor, in the medical field, I think it’s pretty important
to have a precise understanding of what the words mean, just
so that you can understand what people are talking about if
either you are a health care professional or if some health
care professional is talking to you, as my wife does
when, well, sometimes does, when she comes home from work. So let’s get a little bit more
precise with some of the words we’ve been talking about,
especially relative to heart disease and heart failure
and all of the rest. So let’s say this is an artery. The blood is flowing
in that direction. I’ll show the artery
branching off. It thins as it goes
farther and farther along. So this right here is an artery. And let me draw a
plaque in that artery. And we’ve been
studying these plaques in arteries since the
video on heart attacks. So let’s say that this is a
bunch of white blood cells and lipid material. So it’s cholesterol and
fats and all the rest. Now a word that you might hear
in kind of a medical context is stenosis. And the word “stenosis” just
refers to the narrowing, usually of a blood vessel. So this right here, this blood
vessel has been narrowed. So this right over
here is stenosis. It’s been narrowed
by this plaque. It can also refer
to the narrowing of kind of any type
of tubular structure. So if you have any type of kind
of pipe in a biological system and it gets narrow, they
might refer to stenosis there. But usually they’re talking
about a blood vessel. In this example that I’ve
drawn here it’s an artery. So the stenosis is
just the narrowing. Now once the blood
vessel is narrowed, that restricts the blood supply. So you aren’t able to get
as much blood through it. So the blood supply
is restricted. So restricted blood supply. Put the I there. Restricted blood supply. This restriction
of a blood supply that usually leads
to some type of loss of function, that’s called– so
this restricted blood supply– this is called ischemia. Another fancy word,
but it literally just means restricted blood supply. Ischemia. Now if you have stenosis in one
of your blood vessels, in one of your arteries, and it
restricts your blood supply. So it leads to ischemia. Let’s say let me draw a
muscle cell farther over here. Let’s say this is a coronary
artery that we’re dealing with. The muscle cells over here
are going to get less oxygen. So this guy– let me draw
this cell right over here. And I’m just drawing an
oversimplified diagram. I’m not going to imply
that muscle cells really look like that. And actually, they
won’t be– well, I won’t go into
the details here. But this guy’s not going
to get not enough oxygen. So you can imagine
that if we’re really zoomed in on the
surface of the heart, we’re looking at the heart
muscle tissue right here. If whoever’s heart this was,
if they started to go jogging or whatever, and this
cell needed more oxygen, probably wouldn’t be able
to get that oxygen because of the stenosis which
caused ischemia. And because of that, it
doesn’t have enough oxygen so it won’t be able to
help the heart pump. Remember, this is just one of
the muscles in the heart that’s going to help it pump
the blood properly. So it’s going to lead
to heart failure. And once again, the
word heart failure sounds more dramatic
than maybe it really is. It sounds like cardiac
arrest, where the heart stops. But heart failure is not saying
that the heart is completely failed. It’s just saying that the
heart is failing its ability to kind of properly
do its function. So when this guy goes
jogging, because he has a restricted blood
supply, because the heart is experiencing ischemia
downstream from this stenosis, that’s why there’s
heart failure. So not able to deliver. Now this heart failure, which
is due to the ischemia which is due to the stenosis, you
would call this heart failure due to coronary artery disease. Let me write it. We talked about
that two videos ago. Coronary artery disease. Which is really just kind of
an impairing of the heart’s function because of
reduced blood supply, because of a narrowing
in a blood vessel restricts the blood
supply ischemia, that is coronary artery disease. And because of coronary
artery disease, when this muscle
cell in the heart really needs to pump hard–
maybe because someone’s going up a hill or
climbing stairs– it’s not able to do it because
it’s not getting enough oxygen. And that inability to
properly, for the heart, not just the cell, but for the
whole heart, this is just one of many cells that maybe won’t
be able to pump properly, for the entire heart to not do
its job, that is heart failure. Now you’ve also probably
heard the term coronary heart disease. Or maybe just heart disease. These three things are
all the same thing. These are all the same. They all imply some type
of narrowing or stenosis of arteries that leads to
ischemia, reduced blood flow, so that the heart can’t function
as well as it otherwise could. Now the last thing
I want to focus on, and I talked a little bit
about it in the last video, is the idea of an
infarct or an infarction. These are kind of
funny words to say. I’ll write it over here. So infarct or infarction. So in the example I’ve drawn
so far, this cell, for example, maybe does not
get enough oxygen, especially once the
person is going upstairs and all of that, to properly
contract and help the heart actually pump. But it’s not dead. It’s still getting
some base level oxygen. Less because of the
stenosis and the ischemia, but it still gets some oxygen. And we saw in the video
on myocardial infarction or the video on heart
attacks that sometimes one of these plaques might become
unstable and they break off and then you have
a complete blocking of a vessel, a complete blocking
of an artery right here. And we saw in the
last video, we call this blocking what’s
called an embolism. And an embolism is the
general term for something that floated around and then
eventually blocks a vessel. And if it was due to kind of
a released plaque that also had clotting factors around
it after it got released, then we would call
this a thromboembolism. This would reduce the
blood flow so much, maybe a little bit might
be able to leak around, but it reduces it so much that
the cells downstream from this actually die. So you actually have
the cell right over here and this cell will die. It might get very little
blood or no blood at all, so it’s not getting enough
oxygen to actually survive. And when you have dead tissue
that’s due to a loss of oxygen, this is an infarct, dead
tissue due to a loss of oxygen. The process of it becoming dead
tissue due a loss of oxygen is an infarction. And this infarction, this
dead tissue due to loss of oxygen, in the myocardium, in
the muscle tissue of the heart. So now all of a sudden
you have muscle tissue in the heart that’s
beginning to die. This is a heart attack. This is a myocardial infarction. So hopefully that clarifies
things a little bit.


  1. Hehe we have a very normal stenosis of our trachea.
    Without knowing the real meaning of it i would think it is a bad condition. 🙂
    Thank you.

  2. A lot of your video is clear and accurate. In simplifying the explanation of ischemia, you misled your audience. Damaged heart muscle with sufficient injury can lead to ht failure, but it would be at the end of a much longer process. The example of jogging with a coronary artery stenosis would lead to "angina" NOT heart failure. Ht failure occurs when the heart fails to pump sufficient to the body's needs. It would be rare to develop heart failure while jogging, but common to suffer angina.

  3. Intersting and important information, which should have been mentioned:
    Blood doesn't only suply oxygen, but also blood supplies glusose and takes away lactic acid from the cell. When lactic acid accumulates very much, it causes the pain.

  4. Amazing work Sal. Quick bit for some of the commenters…

    1. Heart Failure is by definition the inability of the heart to maintain an adequate Cardiac Output (CO). This is the amount of blood pumped out per minute. If it's too low your body systems cannot oxygenate adequately of course.

    2. CAD/CHD is NOT the same thing as Heart Failure. These are conditions which can LEAD to heart failure (in other words, your heart gets damaged, the pump becomes weak, and THEN you end up with heart failure).

  5. Does anyone know what exactly is the difference between pulmonary vein and coronary artery? Thanks 😀

  6. The pulmonary vein takes the newly oxygenated blood from the lungs and brings it to the Left Ventricle of the Heart. The Coronary Artery are arteries that break off of the Aorta and feed the Heart oxygenated blood so it can keep doing its job.

  7. You have such a way to explain things so much simpler. Thanks alot it was a great video! You should do more on stuff like this. Now i understand it 100% thanks again!

  8. Heart failure can cause angina but that does not necessarily mean it is heart failure. Angina can be caused by cardio, pulmonary, or even problems like acid reflux because angina is just pain, discomfort, or tightness in the chest. Only about 30% of chest pain is even related to the heart.

  9. Pulmonary vein brings oxygenated blood from the lungs back to the heart. The coronary arteries "feed" the heart with blood so that it can respire. They actually are the first arteries leading away from the aorta, so the blood they give to the heart is really oxygenated.

  10. Atherosclerosis is the build up of fatty deposits within the arterial walls. LDL cholesterol is deposited and is ingested by macrophages, resulting in a fatty streak. Stenosis is the result the condition of narrowing of the lumen.

  11. So how come Ischemic Heart Disease is the most common cause of death in the world if it supposedly causes heart failure so rarely?

  12. Is ischemia defined as " restriction in blood supply" as per your explanation in video

    or it is strictly defined as "a restriction of blood supply in tissue"

    for theoretical or exact use

    [without doubting the common sense]

  13. Reply to Perry Wiseman
    Pulmonary vein returns blood from the lungs to the left atrium mate. From Left atrium, it does to left ventricle via the Mitral valve. 
    On a side story, good presentation. I liked.

  14.  Nobody wants simple cures from ancient wisdom!

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