…and more specifically, cardiac muscles. Why don’t they get tired? I don’t understand it. I mean, I know they get tired as you reach old age and shit, but why isn’t it ever tired before that?!
Sorry, just being bugging me.
Perhaps they are getting tired, but we don’t have nerves to feel it? Damn! Now i’m all curious too.
According to my ex-girlfriend, I don’t actually have a heart.
Go figure.
hears Sinistral clear his throat
kidnaps Sin and takes his place
The cardiac muscles contain a much, much higher concentration of mitochondria within its cell walls than skeletal or smooth muscle cells do. This heightened concentration gradient of mitochondria makes the cells generate more energy than a regular cell operating on 1-2% mitochondria do, so they never need rest. Of course, this also means that they use up oxygen and pyruvate at a much faster rate than normal muscles do, which is why under conditions which threaten the livelihood of an organism (such as extreme cold), the well-being of parts of the body such as the arms, legs, etc. are affected the most, whereas the body works hard to keep the chest area functioning normally.
So that also explains why the other muscles aren’t like that.
Awesome.
But uh…mithochondria? What?
Your cell isn’t just a nucles and a membrane with water in it. There are a lot of little things opearting in it, with various shapes and functions. Mythocondrias are the ones which catch some substances that resulted from your digestion and turn them into a substance that your body can use for energy. In the process, they use up oxygen, which is why you must breathe.
Yeah, Klez is right in saying that the heart has more mitochondria and that this is why it doesn’t get tired.
The reason for that is as follows:
When glucose (sugar, the main energy source your body uses) is broken down it undergoes glycolysis to split in 2, and that generates a little bit of energy and from here 2 things can happen: the end product can be converted to lactic acid to recycle NAD+, or it can toss the end product, pyruvic acid, into the mitochondria to release about 8x more energy from it. Thus mitochondria are the parts of cells that are responsible for supplying the cell with the energy it needs to perform whatever functions it is it needs to perform.
Here’s what happens when you do exercise: you either a)run out of glucose or b)the mitochondria get overwhelmed and can’t churn out all the energy you need as you need it. B) is the more common scenario and when that happens, instead of being tossed into mitochondria, pyruvate gets turned to lactic acid so NAD+ can be recycled and used to break down more glucose for the little energy glycolysis provides.
So you see, the problem when your muscles get tired is that the mitochondria can’t cope with the demands. So since heart muscle has more mitochondria, it can deal with the long term exercise as the mitochondria don’t get overwhelemed, so the energy supply doesn’t run out. A good marathon runner will have a lot of mitochondria in some muscles and in turn this will give him the ability to endure long exercises. Same with the heart.
If the heart gets “tired”, meaning it can’t cope because for example it doesn’t have all the oxygen it needs (oxygen is used by mitochodria), that’s a heart attack.
And Klez, you’re in bio at UT right?
Yeah, life science, actually!
Anaerobic respiration gets you 2 ATP molecules for every glucose molecule you consume through pyruvate cleavage (lololol), whereas aerobic respiration gets you about 34 to 36 ATP, practically. (ATP is adenosine triphosphate, your basic energy carrier). That’s why breathing is important 
This is also why blood doping works; you get a higher concentration of red blood cells in your system so that there are more oxygen carriers to be delivered to the mitochondria. That way, they don’t have to resort to anaerobic respiration, can net you 12-13 times more energy, and won’t harm your body through excess lactic acid buildup.
YES! More people in the sciences! FINALLY!
Blood doping has other ways of adversely affecting your body. While it provides extra oxygen for your muscles, it creates extra strain for your heart and people have died from this. I don’t know its true, but I remember hearing something along the lines that some athlete’s blood had the consistency of honey when he died of a heart attack.
Lactic acid has the advantage of creating a mild painful feeling to get you to stop doing whatever it is you’re doing that’s tiring you out.
My understanding is that muscles cramp because of a lack of ATP to uncouple the myosin heads from the actin. Actually nevermind, there’s a lot more to it.
sits down and takes notes of what Sin says Just because I tend to learn more from you in a few minutes than I do in about 4-5 months in class.
Cramming your blood to 100%+ viscosity is never good in any case 
That’s… really weird - I’m learning all of this at the moment! In fact my exam is tomorrow!
This has been a real help from you guys, study-wise! Thanks heaps!
Ninten:cool:
Deja vuuuuue x_X
…you all rock.
This is awesome, thanks a million!
The sad thing about this, is that I’m just doing this out of interest, it isn’t even on my course. >>;
My heart will never tire as long as Sinistral lives!
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It’s interesting what you learn from people online more than in classrooms.