Medical Dictionary Definitions A-Z List
Medical Dictionary Definitions A - Z - «S»:
Sinus headache: A headache caused by pressure within the sinus
cavities of the head, usually in connection with infection of the sinuses. Signs
and symptoms of sinus headache include pain and tenderness in the sinus area,
discharge from the nose, and sometimes swelling of the face.
Sinus node: The sinus node is one of the major elements in the cardiac conduction system, the system that controls the heart rate. This stunningly designed system generates electrical impulses and conducts them throughout the muscle of the heart, stimulating the heart to contract and pump blood.
Sinus rhythm: The normal regular rhythm of the heart set by the natural pacemaker of the heart called the sinoatrial (or sinus) node. It is located in the wall of the right atrium (the right upper chamber of the heart). Normal cardiac impulses start there and are transmitted to the atria and down to...
Sinus tachycardia: A fast heartbeat (tachycardia) because
of rapid firing of the sinoatrial (sinus) node.
The sinoatrial (or sinus) node is the natural pacemaker of the
heart. It is located in the wall of the right atrium (the right upper
chamber of the heart). Normal cardiac impulses start there...
Sinus, cavernous: A large channel of venous blood creating a "sinus" cavity bordered by the sphenoid bone and the temporal bone of the skull. The cavernous sinus is an important structure because of its location and its contents which include the third cranial (oculomotor) nerve, the fourth cranial ...
Sinus, ethmoid: See: Ethmoid sinus....
Sinusitis: Sinusitis is inflammation of the lining membrane of
any of the hollow areas (sinuses) of the bone of the skull around the nose. The sinuses
are directly connected to the nasal cavities.
Picture of the anatomy of the sinuses
Picture of the detail of the sinuses
Sinusitis headache: Headache that occurs in association with infection or
inflammation of the paranasal sinuses, the air cavities within the passages of
the nose. Common symptoms of sinus infection are
headache, facial tenderness or
pain, and fever. Other possible symptoms include cloudy, discol...
Sir Charles Bell
Sir Charles Bell: See: Bell, Charles....
siRNA: Abbreviation for small inhibitory RNA, a short sequence of RNA which can be used to silence gene expression....
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 Administrat...
Sitophilus granarius: See: Granary weevil....
Sitosterolemia: A genetic disease involving lipids (fats) in which there is excessive intestinal absorption of dietary sterols and impaired clearance of these sterols from the liver into the bile. These sterols include cholesterol and the plant sterol sitosterol (from which comes the name of the di...
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. Wh...
Situs inversus totalis
Situs inversus totalis: A condition in which there is
complete right to left reversal (transposition) of the thoracic and
abdominal organs. For example, the
heart is not in its usual position in the left chest but is in the
right chest. (This is position of the heart is referred to as