siRNA
Abbreviation for small inhibitory RNA, a short sequence of RNA which can be used to silence gene expression.
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- Sirolimus
A naturally occurring substance discovered in a soil sample from Easter Island. Sirolimus was initially thought to hold promise as an antifungal antibiotic but this idea was dropped when sirolimus was unexpectedly found to have immunosuppressive activity. The US Food and Drug Administration in 1999 approved the use of sirolimus as an immunosuppressant agent. But […]
- Situational syncope
The temporary loss of consciousness in a particular kind of situation. The situations that trigger this reaction are diverse, and include having blood drawn, straining while urinating or defecating, and coughing. It can also be due to the emotional stress, fear, or pain. When experiencing the trigger condition, the person often becomes pale and feels […]
- Situs inversus totalis
This condition (medically called situs inversus totalis) involves complete transposition (right to left reversal) of the thoracic and abdominal organs. The heart is not in its usual position in the left chest, but is on the right. Specifically related to the heart, this is referred to as dextrocardia (literally, right-hearted).The stomach, which is normally in […]
- Six fingers or toes
on either side of the extremity or somewhere in between. With the hand for example, the extra finger can be out beyond the little finger (which is called ulnar hexadactyly) or out beyond the thumb (radial hexadactyly) or, finally, between two of the normally expected fingers (intercalary hexadactyly). Far and away the most frequent form […]
- Sixth cranial nerve
to supply a muscle called the lateral rectus muscle that moves the eye outward. Paralysis of the abducent nerve may cause inward turning of the eye (esotropia) leading to double vision. All 12 cranial nerves, the abducent nerve included, emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge […]