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A hypodermic syringe is a type of tube that can be fitted to a hollow hypodermic needle to perform injections into or extractions from the body. The main body of the syringe is equipped with a tightly fitted plunger that is used by sliding it along the barrel of the tube, drawing in or pushing out the desired substance through the opposite end, which is open. Most hypodermic syringes are made of plastic, though they can also be made of glass.
One of the primary uses of a hypodermic syringe is to inject substances such as medications and vaccinations. The appropriate dosage of medicine or vaccine is drawn into the syringe and then administered by pushing in the plunger so it forces the fluid out the open end and through the hypodermic needle. Injections may be made directly into the body, for example into a muscle, or they may be made through an intravenous line which then carries them to the bloodstream; the method of administration depends on the medication.
Blood samples can also be taken using a hypodermic syringe. Attached to a hypodermic needle which is inserted into a vein, the plunger is then pulled back, creating suction. The blood is drawn out by this suction and goes into the cylinder of the syringe, or sometimes into an attached test tube that can be used to perform the necessary diagnostic tests on the blood.
When giving an injection into a blood vessel with a hypodermic syringe, it is very important to ensure there is no air in it. This is due to the risk of causing an air embolism; this is when an air bubble enters the circulatory system, where it can potentially lead to serious side effects. To avoid any air in the tube, those administering a shot will typically hold it upside down and expel a small amount of the medication from the needle first.
In medical settings, hypodermic syringes are generally disposable and only used once and then discarded. This is to minimize the risk of transmitting diseases between patients. Re-use of needles has been shown to be a significant factor in the spread of diseases such as HIV; those who share needles, such as users of injectable drugs like heroin, are often at high risk. Some patients, such as diabetics who inject themselves daily with insulin, may re-use needles but only on themselves.