Fast heart rate: Tachycardia means fast heart beat. Sinus node is the structure where normally heart rhythm and beat is originated, and it naturally responds to stimuli when the heart needs to beat faster. Inappropriate sinus tachycardia is when the heart is beating fast, when it shouldn't. ...Read more.
The atom is the smallest subdivision of an element which still retains the properties of that element. In fact, a very good definition of an atom is: the smallest part of an element that can enter into a chemical combination. There are around 118 elements known to man, of which 20-30 are really, really important.he parallel definition (to the element one above) for the molecule is: the smallest part of a compound that can enter into a chemical combination. Another definition, equally good, is that a molecule is the smallest stable part of a compound. Water is a typical example of a compound.
Substances that are made up entirely of one kind of atom that cannot be broken down into any other simpler substance. The smallest unit of an element that still has the properties of that element. Atoms of the same element are exactly alike, but different from the atoms of every other element.