Dictionary

skeletal Pertaining to the skeleton, the bones of the body that collectively provide the frame for the body.

Sjogren’s syndrome An autoimmune disease that classically combines dry eyes, dry mouth, and another disease of the connective tissues, commonly rheumatoid arthritis, but sometimes lupus, scleroderma, polymyositis, or another autoimmune condition. Sjogren’s syndrome is an inflammatory disease of glands and other tissues of the body. Inflammation of the glands that produce tears (lacrimal glands) leads…

sixth disease See measles.

sixth cranial nerve See abducens nerve.

situs inversus totalis See reversal of organs, total.

sinusitis Inflammation of the lining membrane in any of the hollow areas (sinuses) of the skull around the nose. Sinusitis may be caused by anything that interferes with air flow into the sinuses and the drainage of mucous out of the sinuses. The sinus openings, called ostia, may be obstructed by swelling of the tissue…

sinus tachycardia Fast heartbeat (tachycardia) that occurs because of overly rapid firing by the sinoatrial node. Sinus tachycardia is usually a rapid contraction of a normal heart in response to a condition, drug, or disease, such as pain, fever, excessive thyroid hormone, exertion, excitement, low blood oxygen level (hypoxia), or stimulant drugs, such as caffeine,…

sinus rhythm The normal regular rhythm of the heart that is set by the sinoatrial (or sinus) node, which is located in the wall of the right atrium (the right upper chamber of the heart). Normal electrical impulses of the heart start there and are transmitted to the atria and down to the ventricles (the…

sinus node See sinoatrial node.

sinus barotrauma See aerosinusitis.

sinus 1 An air-filled cavity in a dense portion of a skull bone. The sinuses decrease the weight of the skull. The sinuses are formed in four right-left pairs. The frontal sinuses are positioned behind the forehead, while the maxillary sinuses are behind the cheeks. The sphenoid and ethmoid sinuses are deeper in the skull…

sinoatrial node The heart’s natural pacemaker, one of the major elements in the cardiac conduction system, the system that controls the heart rate. Abbreviated SA node. The SA node consists of a cluster of cells that are situated in the upper part of the wall of the heart’s right atrium, where the electrical impulses are…