Dictionary

Body systems

Anatomy and the conditions of each body system, from the heart and lungs to the skin.

StreptococcusA group of round bacteria that grow in chains, some of which cause infections in people.

stress managementWays of reducing stress or coping with it in healthy ways.

strictureA narrowed section of a hollow body passage, such as the urethra, esophagus or bowel, that is tighter than normal.

stridorA high-pitched, harsh sound made while breathing, usually heard when breathing in.

strokeSudden damage to part of the brain because its blood supply is blocked or a blood vessel in it bursts.

stroke volumeThe amount of blood the left ventricle pumps out with each heartbeat.

subarachnoid hemorrhageBleeding into the fluid-filled space between the two inner layers of tissue that cover the brain.

subarachnoid spaceThe space between two of the thin membranes that cover the brain and spinal cord, filled with cerebrospinal fluid.

subcostalBelow the ribs.

subcutaneous tissueThe layer of fat and loose connective tissue under the skin that attaches the skin to muscle.

subduralLocated beneath the dura, the tough outer membrane covering the brain and spinal cord.

subdural hematomaA collection of blood between the brain's tough outer covering (the dura) and the brain.

substanceIn mental health and addiction, a drug or chemical that changes mood, thinking or behavior, such as alcohol, nicotine or opioids.

substance abuseAn older term for using alcohol or drugs in a harmful way; today it is usually called substance use disorder.

substance misuseUsing alcohol, drugs or medicines in a way that can cause harm, or using a medicine other than as prescribed.

substance useThe use of alcohol, tobacco, drugs or medicines not as prescribed; when it causes harm, it is called substance use disorder.

substance use disorderA condition in which a person keeps using alcohol or another drug even though it is causing them harm.

suctioningRemoving mucus, saliva or other secretions from the mouth, nose or airway with a tube connected to a suction source.

sudden infant death syndromeThe sudden, unexplained death of a baby under 1 year old, usually during sleep, where no cause is found after full investigation.

sunburnSkin damage and inflammation from too much ultraviolet (UV) light from the sun or a tanning bed.

superficialNear or on the surface of the body or of a structure.

superior vena cavaThe large vein that carries blood from the head, neck, arms and upper chest back to the right atrium of the heart.

supinationTurning the forearm so the palm faces up or forward; for the foot, rolling it so the weight is on the outer edge.

supplementationAdding something to the diet, such as a vitamin, mineral or extra food, to meet the body's needs.

supraventricular tachycardiaA fast, regular heart rhythm that starts above the ventricles, usually 150 to 250 beats a minute.

surfactantA fatty substance coating the inside of the lungs' air sacs that lowers surface tension so they stay open.

swallowTo move food, liquid or saliva from the mouth down the throat into the esophagus.

swallowingMoving food, liquid or saliva from the mouth through the throat and esophagus to the stomach.

sympathetic nervous systemThe branch of the autonomic nervous system that gets the body ready for stress or danger ("fight or flight").

symphysisA joint where two bones are joined firmly by a pad of cartilage that allows only a little movement.

symphysis pubisThe joint at the front of the pelvis where the left and right pubic bones meet.

synapseThe tiny gap where a nerve cell passes a signal to another nerve cell, a muscle or a gland.

syncopeFainting: a short loss of consciousness from a drop in blood flow to the brain.

syncytialRelating to a syncytium, a large cell-like mass with many nuclei formed when cells fuse together.

syndromeA group of signs and symptoms that tend to occur together and make up a recognized condition.

syndrome of inappropriate antidiuretic hormoneA condition in which the body releases more antidiuretic hormone than it needs, so the kidneys hold on to too much water.

synovial fluidThe thick, slippery fluid inside movable joints that lets the bones move smoothly.

synovial jointA freely movable joint in which the bone ends sit in a capsule filled with lubricating fluid.

synthesizeTo make something by combining simpler parts, or to combine pieces of information into a whole.

syphilisA bacterial infection, spread mainly through sex, caused by Treponema pallidum.

systemicAffecting the whole body rather than one part.

systemic vascular resistanceThe resistance to blood flow in the body's arteries that the left ventricle has to push against.

systemic veinA vein of the body's main circulation, carrying blood from the tissues back toward the right side of the heart.

systoleThe part of each heartbeat when the heart muscle squeezes and pumps blood out.

systolic pressureThe top number in a blood pressure reading: the pressure in the arteries while the heart pumps.