Look around you. Everything is made of chemicals of one sort or another. Life is chemistry organized into astonishing complexity and intricacy. To make sense of this organization we can look at life’s chemistry as a hierarchy—levels of organization. From simple elemental ions, to simple organic molecules, complexity rises with increasingly larger macromolecules.

A person is between 1–2 meters (m) tall, but there are many length scales and biological levels of detail which are important for understanding anatomy and physiology. For perspective on size difference, consider an atom

Atoms are basic units of matter. Atoms contain a positive center (nucleus) surrounded by a cloud of electrons that allow interatomic interactions.

We can’t really grasp how small atoms are, but think big instead of small. A length of 1010 m is more than the distance from the Earth to the moon.

Table 1. Units of Measurement
Atoms and ions Å = 10−10 m
Molecules nm = 10−9 m
Cells μm 10−6 m
Tissues mm= 10−3 m
Organs cm = 10−2 m

The smallest length scale that we will cover is the size of individual atoms, but the movement of subatomic particles called electrons, can change atomic charge. Ions are atoms that carry either a positive or negative charge from altered numbers of electrons, and many atoms and molecules exist in the body as ions.

Ionic chemistry is important in human medicine and health. Ions play an essential role in physiological processes, particularly as they move across cell membranes. Appropriate intracellular and extracellular concentrations of sodium, potassium and calcium ions are required for nerve impulses and heart beats, enable cell-to-cell communication and initiate cellular processes. For example, release of insulin by beta cells of the pancreas is mediated by ions. Transport of ions across membranes may occur by passive diffusion, through ion channels, or through pumps. Pumps often move ions against a concentration gradient. Ionic chemistry is important in human medicine. Anesthetic drugs such as Novocain block sodium channels. Neurotoxins from some snakes and puffer fish work by blocking ion movements that mormally occur in nerve transmission. Malfunctions in ionic channel or pump molecules can result in serious physiological ailments, including cystic fibrosis (mutation in a gene that codes for cell membrane chloride channel) and epilepsy.

Even subatomic particles, which are too small to see with the best microscopes in the world, play an extremely important role in maintaining proper physiology.