Have you ever noticed that when you are ill and you visit your doctor, your doctor sometimes give you injection.
He uses a syringe and sucks the liquid from the medicine bottle. Then he keeps the syringe tip towards the roof and presses the knob of syringe and drops few drops of liquid.
Why he does so?
Actually when syringe is filled with the liquid, air bubbles are also filled in the syringe and if injection is injected with the air in your veins then air will be passed in the veins which is actually bad for health.
Venous air embolism:
If an air bubble enters a vein, this is called a venous air embolism.
Arterial air embolism:
If an air bubble enters in to an artery, it is called an arterial air embolism. These air bubbles can travel to your heart, brain or lungs and cause a heart attack or stroke or respiratory failure. Air embolisms are rather rare.