Stem cells
One of the human body’s master cells, with the ability to grow into any one of the body’s more than 200 cell types.
All stem cells are unspecialized (undifferentiated) cells that are characteristically of the same family type (lineage). They retain the ability to divide throughout life and give rise to cells that can become highly specialized and take the place of cells that die or are lost.
Stem cells contribute to the body’s ability to renew and repair its tissues. Unlike mature cells, which are permanently committed to their fate, stem cells can both renew themselves as well as create new cells of whatever tissue they belong to (and other tissues).
Bone marrow stem cells, for example, are the most primitive cells in the marrow. From them all the various types of blood cells are descended. Bone marrow stem-cell transfusions (or transplants) were originally given to replace various types of blood cells.
Stem cells from bone marrow can also, quite remarkably, give rise to non-marrow cells. In a 1999 report in the journal Nature, scientists from Boston led by Dr. Louis M. Kunkel reported that they gave bone marrow transplants from normal mice to dystrophic mice. Some 12 weeks later about 10% of the muscle fibers in the diseased animals were making the correct form of dystrophin, the protein that is defective in Duchenne muscular dystrophy. This work suggests that bone marrow stem cells may offer new ways of treating muscular dystrophy (and other non-blood diseases).
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- Stenosis
A narrowing. For example, aortic stenosis is a narrowing of the aortic valve in the heart.
- Stenosis, aortic
Narrowing (stenosis) of the heart valve between the left ventricle of the heart and the aorta. This narrowing impedes the delivery of blood through the aorta to the body and makes it tough for the heart to carry out this Herculean task. A normal aortic valve has three leaflets or cusps, but a stenotic valve […]
- Stenosis, pulmonary
A condition in which the pulmonary valve is too tight, so that the flow of blood from the right ventricle of the heart into the pulmonary artery is impeded. This means that the right ventricle must pump harder than normal to overcome the obstruction. Treatment is necessary if the pressure in the right ventricle is […]
- Stenosis, subaortic
Narrowing of the left ventricle of the heart just below the aortic valve through which blood must pass on its way up into the aorta. The narrowing cuts the flow of blood. Subaortic stenosis may be congenital (present at birth) or acquired as part of a particular form of heart disease known as “idiopathic hypertrophic […]
- Stenotic
Narrowed, as in a stenotic artery. From the Greek “stenos” meaning narrow.