The sinoatrial node (SA node) is called the "pacemaker" of the heart. It is a microscopic area of cardiac muscle located in the heart. It is connected to the autonomic nervous system, and acts to speed up or slow down the heart rate when necessary.
Sabauraudís dextrose agar
Sabauraud's dextrose agar is a culture medium for fungi containing peptone agar and glucose that has the pH adjusted to 5.6; it is the standard, most universally used medium in the field of mycology and is the international reference.
A saccade is a rapid, jerky or quick eye movement.
The saccule is the smaller of the two membranous sacs within the vestibule of the ear.
SAF (sodium acetate-acetic acid-formalin) fixative is used to preserve fecal samples.
Saline means containing salt; a salt solution.
Saline, or salt loading, is a method used to protect astronauts from orthostatic intolerance (lightheadedness or fainting) when they return to Earth from stays in space, a near-weightless environment. Just before landing, astronauts consume several liters of water and take salt tablets to help their bodies retain the water. This is an attempt to try and counteract the normal adaptive water loss that occurs in microgravity which causes some astronauts to experience orthostatic intolerance when subject to gravity forces.
A sarcomere is one of the basic units of a striated muscle which causes it to contract.
The scapula is the bone known as the shoulder blade.
In nuclear medicine, scintillation describes the light emitted when an x-ray or gamma ray is absorbed by a crystal or liquid radiation detector.
Scintillation counting is a technique for measuring the quantity of a radioactive isotope present in a sample. In biology, liquid scintillation counting is mainly used for isotopes such as carbon 14, sulfur 35 and phosphorous 32 and particularly for the low energy emission of hydrogen 3. Gamma emissions are often measured by counting the scintillations that they cause in a crystal. Autoradiographic images can be enhanced by using a screen of scintillant behind the film.
A scintillation detector records the flash of light resulting from ionization of a chemical that transforms incident electromagnetic or radioactive energy into light.
Scopolamine is a drug that prevents muscle spasm by blocking the activity of the neurotransmitter acetylcholine. It is a central nervous system depressant used to prevent motion sickness.
Seborrheic dermatitis is a common, chronic, inflammatory skin disease characterized by dry or moist, greasy scales and yellowish crusts. Common sites are the scalp, eyelids, face, external surfaces, or the ears, axillae, breasts, groin, and gluteal folds.
Sediment is matter which subsides to the bottom, from water or any other liquid.
Sedimentation is the settling of a component of a mixture under natural or artificial gravitational fields so that the mixture separates into two or more phases or zones.
Semi-permeable means partially but not freely or wholly permeable, e.g. permeable to some usually small molecules but not to other usually larger particles.
Semicircular canals are the three bony tubes in the labyrinth of the ear and are associated with balance; they are known as the anterior, posterior and lateral semicircular canals.
A sensing system is one that provides automatic detection of a signal or action.
A sensor is a device, such as a photoelectric cell, that receives and responds to a signal or stimulus. Sensors can also refer to single cells or a group of specialized cells which detect a particular stimulus and initiate the transmission of impulses via the sensory nerves.
Sensorimotor controls are controls of the mixed nerves that contain both sensory and motor fibers (afferent and efferent fibers).
Sensorimotor reactions are reactions of the mixed nerves that contain both sensory and motor fibers (afferent and efferent fibers).
Sensory relates to the input into the nervous system from the nerve receptors of the body; it is any information carried from receptors throughout the body toward the brain and spinal cord.
Sensory-motor relates to a nerve possessing both sensory and motor functions.
The sensory-motor system refers to the interaction of the sensory nerves -- such as those that sense sight, smell and touch -- with the nerves that control muscular movement. Signals from the sensory nerves are sent to the brain where they can be processed to make a specific muscular response.
Septicemia is a systemic disease caused by the multiplication of microorganisms in the circulating blood.
Serological refers to serology, the study of blood serum and its constituents, particularly their contribution to the protection of the body against disease.
Serology is the branch of laboratory medicine that studies blood serum for evidence of infection by evaluating antigen-antibody reactions in vitro.
Serum is the fluid portion of the blood ; it is essentially similar in composition to plasma but lacks fibrinogen and other substances that are used in the coagulation (blood clotting) process.
Serum glutamic oxaloacetic transaminase (SGOT)
Serum glutamic oxaloacetic transaminase (SGOT) is a catalytic enzyme found in various parts of the body, especially the heart, liver and muscle tissue. Increased amounts of the enzyme occur in the serum as a result of myocardial infarction, acute liver disease, the actions of certain drugs, and any disease or condition in which cells are seriously damaged.
Serum glutamic pyruvic transaminase (SGPT)
Serum glutamic pyruvic transaminase (SGPT) is a catalytic enzyme normally found in high concentrations in the liver. Greater than normal amounts in the serum indicate liver damage.
A sextant is a navigational instrument used for measuring the altitudes of celestial bodies.
A sigmoidal curve is a curve in the shape of the letter S or of the Greek letter sigma.
Signal conditioning is the process of converting information or data into a form that is better perceived by human beings.
A silique is a seed pod of a plant.
Simethicone is an antiflatulent and is prescribed to decrease excess gas in the GI tract.
The sinoatrial node (SA node or sinus node) is called the "pacemaker" of the heart. It is a microscopic area of cardiac muscle located in the heart. It is connected to the autonomic nervous system and acts to speed up or slow down the heart rate when necessary.
Sintering means to heat a powdered substance without thoroughly melting it, causing it to fuse into a solid but porous mass.
The sinus node is also known as the sinoatrial node (SA node); it is called the "pacemaker" of the heart. It is a microscopic area of cardiac muscle located in the heart. It is connected to the autonomic nervous system and acts to speed up or slow down the heart rate when necessary.
Skeletal muscles are muscles that connect bones together.
The skeletal system is the system of interconnecting bones which form the rigid framework of the human body. The skeletal system not only provides the body with form, but also protects and supports its soft organs and tissues. It also provides attachments for muscles and serves as a system of levers essential for locomotion.
Skin conductance is a measure of the electrical conducting power of the skin surface.
Sleep is a physiologic state of relative unconsciousness and inaction of the voluntary muscles, the need for which recurs periodically. Sleep is divided into two distinct states known as non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). These two states occur in a roughly 90 minute cycle that is repeated 5 to 6 times a night and includes four stages of NREM sleep, and REM.
Sleep latency is a common measure of sleep quality. It is latency or, simply, the amount of time required to fall asleep after the beginning of the rest period.
Sleep is divided into two distinct states known as non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). These two states occur in a roughly 90 minute cycle that is repeated 5 to 6 times a night and includes four stages of NREM, and REM. NREM sleep is the sleep from which REM sleep emerges (except in special cases such as Narcolepsy). As we fall asleep, we enter the transition sleep called Stage 1 and begin our first "sleep cycle." Within a few minutes we evolve into our "baseline" sleep called Stage 2. It is from Stage 2 sleep that the other three Stages emerge. Stage 2 sleep occupies approximately 50-65% of our sleep time. Within 15-20 minutes we have slowly entered Stage 3 followed by Stage 4 sleep, often called delta sleep or slow wave sleep because of the very high voltage, slow brain waves. Delta sleep is similar to being in a coma. However, unlike a coma, it is reversible. As we transverse these first four Stages of sleep, our respiration and heart rate slow and the body is almost immobile. After 20-30 minutes of slow wave sleep, we lighten into Stage 2 and almost immediately change gears into a very active brain wave pattern known as paradoxical or REM sleep. Simultaneous with this dive into REM, our respiration and heart rate increases substantially, and we loose our ability to use our postural or skeletal muscles. Also, our brain becomes so activated that we start to hallucinate and experience what we call dreams. Our eyes move down to mid-line, just as in wakefulness, and they begin the move sporadically, many times in relation to what we are dreaming. In effect, we are a highly activated brain in a paralyzed body. This paradoxical state will last 10-20 minutes and then we return to Stage 2 again. This is the end of a sleep cycle. It all starts over again, except that we gradually loose our delta sleep and replace it with longer periods of alternating Stage 2 and REM sleep. By the final sleep cycle of the night, we will spend approximately half our time in Stage 2 and half in REM.
In MRI, a section or "slice" of the body is often imaged. The slices are put together to form a complete picture.
Slow-twitch muscle fiber
Slow muscle fibers are smaller than fast muscle fibers, and, unlike fast-twitch muscle fibers, they use oxygen, do not have much strength in contraction, but are very resistant to fatigue, thus they are used for prolonged, continuous activities such as distance running or endurance events. They are most active in resisting gravity and are important in maintaining posture.
The small intestine is divided into the duodenum, jejunum, and ileum. It is here that most of the processes of digestion and absorption of food take place.
Smallpox is an acute, highly infectious viral disease initially characterized by chills, high fever, and backache, with subsequent widespread eruption of pimples that eventually blister, produce pus, and form pockmarks.
Smooth pursuit tracking
Smooth pursuit tracking is the type of eye movement that occurs when the eyes follow and track a single distinct target that is in motion.
Sodium is a soft grayish metal in the alkaline metals group and is one of the most important elements in the human body. Sodium ions are involved in acid-base balance, water balance, the transmission of nerve impulses, and the contraction of muscles.
Sodium urate is a substance in crystal form found in the urine, blood, and some tissues in the body.
Solar inertial mode
Solar inertial mode is the mode of navigation whereby a spacecraft is directed towards the sun using inertial detectors, which automatically provide vehicle position, heading, and velocity.
Solar surface eruptions
Solar surface eruptions are caused by particles or objects colliding with the solar surface. The particles can sometimes cause solar flares, which consist of protons and alpha particles, to shoot into outer space.
The soleus is the broad, flat muscle located in the lower leg, beneath the calf muscle, that flexes the foot so that the toes point downward.
Solid Sorbent Air Sampler (SSAS)
The Solid Sorbent Air Sampler (SSAS) is a device used for capturing chemical contaminants which consists of 8 sorbent tubes and a pump assembly in a cylindrical outer case. The pump assembly is battery powered and helps draw air through a sample tube which absorbs the chemical contaminants.
Solid-phase radioimmune inhibition assay
The solid-phase radioimmune inhibition assay measures the concentration of a biomolecule by the degree of displacement of the radioactive form, preventing it from forming complexes with the solid-phase anti-immunoglobulin.
Solidification is the process of changing the state of matter from a liquid to a solid, such as water changing to ice.
Somatic refers to the non-productive parts of a body.
Somatoliberan, a decapeptide released by the hypothalamus, is a growth hormone-releasing factor that induces the release of human growth hormone (somatotropin).
The somatosensory cortex is the area of the cerebral cortex of the brain to which the sensory signals are sent. The somatic senses include vision, hearing, taste, smell and equilibrium.
Somatosensory receptors are single nerve endings which allow the brain to have superficial and deep body sensations.
Growth hormone (or somatotropin) is an anterior pituitary hormone that causes growth of almost all cells and tissues of the body.
Sorbent refers to the property of a substance that allows it to interact with another compound, usually making it bind.
South Atlantic Anomaly (SAA)
The South Atlantic Anomaly (SAA) is caused by part of the inner Van Allen Radiation Belts lying closest to the Earth's surface. The SAA arises primarily because the Earth's magnetic field is offset from its center. Over this region, the geomagnetic field draws particles closer to the Earth than in other regions of the belts, which causes the fogging of the detector windows of some satellites and results in the compromising of data. The charged particles in the zone can also build up static charges on satellites. The South Atlantic Anomaly is located over a large portion of South America, the South Atlantic and the Southern tip of Africa.
Space Adaptation Syndrome (SAS)
Space Adaptation Syndrome (SAS), also called space motion sickness, is a syndrome that afflicts about half of all space travelers. Symptoms, which resemble those of motion sickness on earth, range from minor (nausea and headaches) to severe (vomiting) and vary from person to person. Although, the exact cause is unknown, SAS is believed to be caused by conflicting sensory inputs from the eyes, inner ear (vestibular system) and the tactile senses (touch).
Space motion sickness
Space motion sickness, or space adaptation syndrome, is a syndrome experienced by space travelers that is similar to motion sickness on earth (air sickness, car sickness, sea sickness), causing nausea, dizziness and sometimes vomiting. It affects about 60% of the people who travel in space with varying degrees of severity. Also called space adaptation syndrome, or SAS.
Spacehab is a pressurized module designed to be attached to the Orbiter middeck. Smaller in size than the Spacelab, it provides approximately 1100 cubic feet of additional volume for support of crew and experiments. It is connected to the Space Shuttle by a modified tunnel adapter, and draws resources such as cooling, power, data and housekeeping systems from the Shuttle's cabin and cargo bay/payload support provisions. The Spacehab module can accommodate various quantities and sizes of equipment, hardware lockers, and racks.
Spacelab is a reusable laboratory that contains space flight hardware carried in the Space Shuttle's payload bay. Most life sciences experiments are conducted in the Spacelab. Equipment is mounted along the walls and floor of the pressurized cylindrical Spacelab module. Crewmembers float into the Spacelab through a tunnel adapter that transits from the airlock in the Shuttle middeck to the Spacelab.
Spacelab Middeck Experiments (SMIDEX)
The Spacelab Middeck Experiments (SMIDEX) facility flew for the first time on SLS-1. The rack contained five experiments originally designed to fly in the Shuttle middeck. An advantage of flying SMIDEX on SLS-1 was that it offered additional flight opportunities for the backlog of experiments waiting to fly in the Shuttle middeck.
Spatial is relating to space or a space.
Spatial orientation refers to the process of aligning or positioning in a three-dimensional space with respect to a specific direction or reference system.
A species is a fundamental category of taxonomic classification ranking after genus and consisting of organisms capable of interbreeding.
Specific gravity is the ratio of a solid or liquid to the mass of an equal volume of distilled water at 4 degrees Celsius or of a gas to an equal volume of air or hydrogen under prescribed conditions of temperature and pressure.
A spectrometer is any instrument used for measuring the intensity and wavelengths of visible or invisible electromagnetic radiation.
A spectrophotometer is an instrument for measuring the intensity of light of a definite wavelength transmitted by a substance or a solution, giving a quantitative measure of the amount of material in the solution absorbing the light; a colorimeter with a choice of wavelength and photometric measurement.
A spectroreflectometer is a type of light measuring device that measures the quantity and color of light reflected from a surface.
A spectrum analyzer is an instrument used to analyze the frequency content and characteristics of a signal.
Spinal bone marrow
Spinal bone marrow is the tissue that is inside the cavities of the bones of the spine.
The spinal cord is the portion of the central nervous system enclosed in the vertebral column, or back, consisting of nerve cells and bundles of nerves connecting all parts of the body with the brain.
Spinalis is a spinal muscle; the medial component of the erector spinae muscle; it is comprised of musculus spinalis capitis, m. spinalis cervicus and m. spinalis thoracis.
Spirometry is making pulmonary measurements with a spirometer, an instrument used for measuring respiratory gases.
The spleen is a lymphoid organ, the site of T-cell and B-cell responses to immunogens and foreign substances. It is situated on the left side of the body below and behind the stomach. In early life it is a blood-forming organ and a storage organ for red blood cells. It also acts as a blood filter.
Splenic trapping refers to the ability of the spleen to temporarily sequester red blood cells.
Spongy (cancellous) bone
Spongy bone consists of lamellae arranged in an irregular latticework of thin plates of bone called trabeculae. The spaces between the trabeculae of some bones are filled with red marrow, which produces blood cells. Spongy bone makes up most of the bone tissue of short, flat, irregularly shaped bones and most of the epiphyses of long bones. Spongy bone tissues in the hipbones, ribs, breastbone (sternum), backbones (vertebrae), skull, and the ends of some long bones are the only sites of red marrow storage and are the sites of the formation and development of blood cells in adults. The os calcis (heel bone) is primarily trabecular or spongy bone surrounded by compact bone.
A spore is a reproductive, usually unicellular body produced asexually by plants and some invertebrates.
A squall is a brief, sudden and violent windstorm often accompanied by rain or snow. A squall line is a group of squalls moving together often preceding a front of cold air moving into a warmer area.
Stage 1 sleep is experienced as the body is falling to sleep. It is a transition stage between wake and sleep. It usually lasts between 1 and 5 minutes and occupies approximately 2-5 % of a normal night of sleep. This stage is dramatically increased in some cases of insomnia and in disorders that produce frequent awakenings.
Stage 2 sleep
Stage 2 sleep follows Stage 1 sleep and is the "baseline" of sleep; it is from stage 2 that the other three sleep stages emerge. This stage is part of the 90 minute cycle and occupies approximately 45-60% of sleep.
Stage 3 and 4 (Delta) sleep
Stage 2 sleep evolves into "Delta" sleep or "slow wave" sleep in approximately 10-20 minutes and may last 15-30 minutes. It is called "slow wave" sleep because brain activity slows down dramatically. In most adults these two Stages are completed within the first two 90 minute sleep cycles or within the first three hours of sleep. Contrary to popular belief, it is delta sleep that is the "deepest" stage of sleep (not REM) and the most restorative. It is delta sleep that a sleep-deprived person's brain craves most. In children, delta sleep can occupy up to 40% of all sleep time; this is what makes children unwakeable or "dead asleep" during most of the night.
A stand test allows researchers to measure a person's response to standing, in order to better understand how gravity affects the heart and blood vessels before and after flight. When people stand upright, gravity stresses the heart by moving blood from the chest and head to the lower body.
The standard deviation is a measurement of variation in a data set.
Staphylococcus species is a genus of nonmotile, nonsporeforming, aerobic to facultatively anaerobic bacteria, with gram-positive, spherical cells. They are found on the skin, in skin glands, and on the nasal and other mucous membranes of warm-blooded animals, and in a variety of food products.
The Star Tracker is an electro-optical tracking device used while the Shuttle is in orbit to align it with other objects, as well as to track targets, such as the Mir. These functions support the docking of the Shuttle to the Mir.
Starch is a polysaccahride made up of glucose residues that exists in most plant tissues. It is also found in the human body in saliva and pancreatic juice. It is used as a dusting powder, an emollient and an ingredient in medicinal tablets and is an important raw material for the manufacture of alcohol, acetone, butanol, lactic acid, citric acid and glycerine.
Starch granule amylose
A starch granule amylose is a polysaccharide made up of glucose residues that exists in most plant tissues.
The oldest model of gravity perception in plants whereby plant cells perceive gravity as statoliths, starch filled organelles, "fall" during gravistimulation.
Static means 1) involving no variation with time, or 2) involving no movement
Static hand grip test
The static hand grip test is an isometric exercise where the subject squeezes a hand grip until the arm is fatigued (approximately 2 minutes). When the arm is fatigued, a cuff on the upper arm is inflated for 2 minutes.
A statolith is a crystal found in the ear, and is made up of particles of calcium carbonate and protein. Present in man, animals, and plants, they are responsible for the sense of equilibrium.
Steady-state refers to a stable condition that does not change over time or in which change in one direction is continually balanced by change in another.
Stellate cells (or stellate ganglion) are star-shaped nerve cell bodies in the base of the neck, from which sympathetic nerve fibers are distributed to the face and neck and to the blood vessels and organs of the upper body.
Stellate ganglion (or stellate cells) are star-shaped nerve cell bodies in the base of the neck, from which sympathetic nerve fibers are distributed to the face and neck and to the blood vessels and organs of the upper body.
Stereology is the study of the three-dimensional aspects of a structure.
Stereophotogrammetry refers to measurements made on the position or shape of a figure in a photograph.
A stereoscopic view is a type of optical view which creates a three-dimensional effect by using two photographs of the same scene taken at slightly different angles and viewed through two eyepieces.
Sterile means free from any bacteria or other microorganisms.
Sternal means of or pertaining to the sternum; in the region of the sternum. Commonly referred to as the breast bone, the sternum is the broad, flat bone located over the heart, to which the ribs attach.
The sternum is the medical term for breastbone. The sternum is the bone in the front of the chest that articulates with the ribs 1 through 7.
Steroid is any of a large number of hormonal substances with a similar basic chemical structure, produced mainly in the adrenal cortex and gonads.
A stimulus (plural stimuli) is a change in the external or internal environment of an organism that provokes a physiological or behavioral response in the organism.
Stomach awareness is a general feeling of mild discomfort in the stomach, usually described as "upset stomach."
Stomatal conductance is a numerical measure of the rate of passage of either water vapor or carbon dioxide through the stomata, or small pores, of the plant.
A stomatocyte is a red blood cell that has a single concavity appearance.
A strain is a race or stock; in bacteriology, the set of descendants that originates from a common ancestor and retains the characteristics of the ancestor.
A strain gauge is a device in which mechanical motion is converted into an electric variation that is used as a sensitive measure of strain.
The strain-gage technique is a method used to measure the change in circumference of a body part. Typically, the strain-gage is a thin, mercury-filled device placed (strapped) around the area to be measured. As the circumference of the body part changes, a measurement reading is observable on this highly sensitive device.
Streptococcus is a genus of nonmotile (with few exceptions), nonsporeforming, aerobic to facultatively anaerobic bacteria containing Gram-positive, spherical or ovoid cells, that occur in pairs or chains. These organisms occur regularly in the mouth and intestines of man and other animals.
Strip chart recorder
A strip chart recorder converts the electrical signal generated by any measurement, such as the beating of the heart or respiration rate, into a written record using an ink pen and a moving strip of paper.
Stroke volume is the volume of blood - normally about 70 ml - ejected from the heart into the aorta during the contraction of the ventricles (systole).
Struvite takes the form of crystals of magnesium ammonium phosphate which are present in some renal stones (kidney stones).
Sublimate is to cause a substance (solid or a gas) to change state without becoming a liquid.
Submicron refers to any object measuring smaller than one micron, a unit equal to one-millionth of a meter.
The substansia nigra is a large cell mass in the midbrain which is a functional part of the basal ganglia system involved in the regulation of voluntary movements at a subconscious level. Destruction or dysfunction of the substansia nigra is associated with Parkinson's Disease.
A subungual hematoma is a collection of blood beneath a nail that usually results from trauma.
Succinate dehydrogenase catalyzes the removal of hydrogen from succinic acid and converts it into fumaric acid. Succinate occurs in living organisms as an intermediate in metabolism, which is the process of energy production and expenditure.
Sulfate is a salt of sulfuric acid. Natural sulfates, such as sodium sulfate, calcium sulfate, and potassium sulfate, are plentiful in the body.
Sulfur-35 is a radioactive sulfur isotope used as a tracer in study of metabolism of cystein, cystine, methionine, etc.
Superconductivity is the flow of electric current without resistance in certain metals and alloys at temperatures near absolute zero.
A superconductor is based on the conduction of high levels of electrical current through a specially made material that is kept at very low temperatures. The low temperature keeps the conductor's resistance low to allow for increased current passage.
Superexcitability refers to an increased excitability in muscle cell or nerve fibers. In neurophysiology, excitability refers to the triggering of a conducted impulse in the membrane of a muscle cell or nerve fiber. During excitation, a polarized membrane becomes momentarily depolarized and an action potential is set up.
Supernatant is the clear fluid which, after the settling out of an insoluble liquid or solid by the action of normal gravity or centrifugal force, takes up the upper portion of the contents of a vessel.
Supersaturation occurs when the level of a substance in urine exceeds the level of that substance due to food intake. Many nutritional components not needed by the human body are excreted by the kidneys in the urine.
Supine denotes the body while lying on the back, face upward.
Suppuration is the formation of pus.
Supraventricular means situated or occurring above the ventricles, especially in an atrium or atrioventricular node.
Svet is the Russian word meaning light. It is also the name given to the Russian greenhouse, where plants are grown on the Mir station.
The SVO-ZV is the source of recycled, non-potable (non-drinkable) water on the Mir Space Station which is used for sanitary purposes.
SVOP is the acronym for System for Venous Occlusion Plethysmography, hardware used for experiments performed on the Spacelab Life Sciences-1 Shuttle mission.This item detects changes in the circumference of the arm or calf in response to venous occlusion, using the venous occlusion plethysmography technique.
To swab is to use a small piece of absorbent material on the end of a stick or wire to obtain mucus or other specimen, cleanse and area, or apply medicine.
Sympathetic means relating to the actions of the sympathetic nervous system, one of the two divisions of the autonomic nervous system. Its nerves are distributed to the blood vessels, sweat glands, salivary glands, heart, lungs, intestines and other abdominal organs, and the genitals. Sympathetic stimulation causes excitatory effects in some organs but inhibitory effects in others.
Symptomatology is the science of the symptoms of disease, their production and the indications they furnish.
A synapse is the tiny gap across which nerve impulses pass from one neuron (nerve cell) to the next.
Synchronous discharges are excitations of nerve or muscle fibers that occur at the same time.
Syncopal relates to syncope. Syncope (commonly referred to as fainting) is a loss of consciousness induced by a temporarily insufficient flow of blood to the brain. It occurs in otherwise healthy people and may be caused by an emotional shock, by standing for prolonged periods, by injury or by profuse bleeding. An attack comes on gradually, with lightheadedness, sweating and blurred vision. Recovery is normally prompt and without any persisting ill effects.
Syncope (commonly referred to as fainting) is a loss of consciousness induced by a temporarily insufficient flow of blood to the brain. It occurs in otherwise healthy people and may be caused by an emotional shock, by standing for prolonged periods, by injury or by profuse bleeding. An attack comes on gradually, with lightheadedness, sweating and blurred vision. Recovery is normally prompt and without any persisting ill effects.
Synergism refers to the act of working together to produce or enhance an effect.
Synthesis is the process of forming compounds out of simpler elements.
Syphilis is a sexually transmitted disease caused by the spirochete, Treponema pallidum, characterized by progression through three stages: local formation of chancres, ulcerous skin eruptions, and systemic infection leading to general paresis.
Systole is the phase of the heart beat during which the heart contracts, causing the blood within to be ejected.
Systolic blood pressure
Systolic blood pressure is the blood pressure measured when the ventricles of the heart are contracting.
Systolic time interval
The systolic time interval, also called electromechanical systole, is the Q-S interval; the period from the beginning of the QRS complex to the first vibration of the second heart sound.