Stem Cells: A Very Short Introduction (Very Short Introductions) by Slack Jonathan

Author:Slack, Jonathan [Slack, Jonathan]
Language: eng
Format: mobi, epub
Publisher: Oxford University Press
Published: 2012-02-22T23:00:00+00:00

So, although the technological problems of cell therapy for Parkinson’s disease are largely solved, the risk-benefit ratio in favour of this treatment as compared to others is not overwhelming at present.

Heart disease

The heart is an organ of which people are generally much more conscious than they are of their pancreatic islets or of the motor circuits in their brainstem. Everyone knows that the heart pumps the blood round the body and that if the heart stops you will die in a few minutes from lack of oxygen to the brain. In order to keep beating every minute of every day for 80 years or so, the heart has to be very robust. Most of the heart is composed of a specialized type of muscle cell called the cardiomyocyte. Unlike skeletal muscle, cardiomyocytes contract spontaneously but in the heart they do so in a concerted manner in response to electrical signals from special pacemaker regions. The pacemakers, in turn, are controlled by various hormonal, metabolic and neuronal inputs that affect the heart rate. The continued contraction of the cardiomyocytes of the heart depends on an abundant blood supply that brings oxygen and nutrients to the cells via the coronary arteries. The most common form of sudden death in modern developed societies is the heart attack (myocardial infarction), in which one or more coronary arteries becomes blocked and the sector of heart muscle that it normally supplies becomes deprived of oxygen. Unless the blockage resolves spontaneously, or as a result of emergency treatment, the affected region of heart muscle will die in about one hour. If the damage is extensive enough to abolish most cardiac function, the individual will also die. If the affected region is more limited, the patient will survive but with a permanently damaged heart. There is some dispute about whether cardiomyocytes are normally replaced during life, but if they are replaced it is at a very slow rate, and there does not appear to be any significant regeneration in areas of damage. Instead the damaged areas fill up with cardiac fibroblasts which secrete extracellular matrix material, and so the region of dead muscle will become replaced by a scar. This has mechanical integrity but is inactive when it comes to contraction, and so the heart function is correspondingly diminished. If the heart is subjected to a lot of excess stress then surviving cardiomyocytes will become enlarged and less mechanically competent, leading eventually to heart failure. The loss of function due to heart attacks is the most common cause for this, although there are other causes such as high blood pressure or valve disease. By definition, heart failure means an inability to supply the rest of the body with enough blood. It leads to numerous problems and is likely to prove fatal in a shorter or longer period, depending on severity.

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