Our body contains numerous crystalline structures that are fundamental to the working of our organism. We stand up straight because our body has a skeleton made up of calcium phosphate crystals. We keep our balance thanks to calcite crystals that are found in the inner ear, and we chew with teeth made with apatite microcrystals.
Have you ever thought about the structure of our bones? Do you know how crystallography helps to make prostheses and implants that the body won’t reject? Would you like to know how toothpaste is made?
You don’t have to go far to find crystals in our daily lives. We can focus on ourselves and thus learn what and how important the crystals are for the working of our organism. This is what we have tried to reflect in this poster, in which we have textured the famous image of the Vitruvian Man with small plates that simulate the structure of our skeleton seen under the microscope.
|Histological cross-section of a bone sample. The mineral phase (calcium phosphate) is organised into small plates distributed in concentric layers (lamellae) around a central canal through which blood vessels circulate. Together the canal and all the lamellae are called the osteon.|
As we can see in this cross-section, the bone is not formed by a single crystal but by millions of tiny crystals (nanocrystals) of a mineral called hydroxylapatite. A monomineral bone would fracture easily. What makes a bone a structure robust enough to support the weight of a cow (or a dinosaur) is the framework/lattice/latticing of the organic matrix with hydroxylapatite crystals. Moreover, the bone structure is organised in a hierarchy of seven different levels, as you can see in this Figure.
But life did not stop at creating just the fantastic structure of bones but has used minerals to create other materials with different functions. One of these functions is that of tearing and grinding, for which life has created nothing less than the enamel of teeth.
Yet probably the most amazing and unknown crystal in the human body is that which controls balance. We do not fall over because in our inner ear there are calcite crystals that fulfil this function to perfection. They exist in all vertebrates, while in fish instead of calcite they are crystals of aragonite, which regulate sense of direction. These crystals of calcite or aragonite are found in the inner ear, immersed in a liquid of a certain viscosity. Therefore they can move according to the orientation of the gravitational field. Depending on their position, they touch different nerves that send information for the brain to process.
There are other crystals in our body that do not have a defined function but that are the result of a problem in the working of the organism. They are pathological crystals. For example, urine is a solution that contains an enormous amount of salts. In normal conditions the organism secretes substances that inhibit the formation of those crystals, but if this fails or the salts concentration greatly increases, crystalline concretions of salts such as calcium oxalate, calcium phosphates, uric acid or urates, form in the kidney. These are the so-called kidney stones.
The crystallization of uric acid is the result of another rheumatic disease, metabolic in type, that preferentially affects men (95% of cases). The disease is linked to the absence of uricase, a protein that breaks down uric acid.
Other crystals than can form in our body are those of lactic acid, responsible for the notorious pain of stiffness.