Another NBME5 question

[cattyjane]

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Pt develops chest pain 3 hours ago. She's dyspneic and diaphoretic & anxious. Her pulse is 110 and regular, respiration 35/min, bp is 190/110. ECG shows acute MI. what's the cause of pain?
-abnormalities of ion transport in myocyte
-accumulation of metabolic products in heart tissue
-increased idastolic pressure
-increased systolic pressure

And why?

 

[knuckles]

MECHANISM OF ANGINA
The mechanisms responsible for the sensation of angina are complex and not clearly defined. An important feature is that ischemia reduces the formation of adenosine triphosphate (ATP), resulting in the development of acidosis, the loss of the normal ATP sodium-potassium pump, the loss of myocardial membrane integrity, and the release of chemical substances that stimulate chemosensitive and mechanoreceptive receptors innervated by unmyelinated nerve cells found within cardiac muscle fibers and around the coronary vessel [5]. The substances that are released include lactate, serotonin, bradykinin, histamine, reactive oxygen species, and adenosine [6-8]. In addition there are substances released from platelets, which often spontaneously aggregate in the area of a coronary artery stenosis, which may also be responsible for myocardial ischemia and angina. These include serotonin, thromboxane A2, and 5-hydroxytyrptamine [9,10].


http://www.uptodate.com/patients/content/topic.do?topicKey=~GSM9MBDcFS

 

[Vikingwizardguy]

or if you're not accustomed to uptodate, work with what you know. It's a safe rule of thumb to think that ischemia will lead to lactic acidosis. Last I checked, acid is bad for most life forms. An accumulation of acidic substances in a confined area which is not being properly perfused will likely activate some pain fibers and lead to the sensation of pain.

Another approach to pain is just thinking that the body must be made aware of when it is hurt. The body does this through metabolites. Almost every thing we sense is due to a change in the metabolic or ionic composition of the surroundings. Of those choices, choices one and two make sense. Ion composition in the myocyte is only important to physiology, not so much biochemistry and cell bio (which is what activates pain).

That's how i approach it, not sure if it's safe, and if the cell bio makes you comfortable, Knuckles's post is perfect.