Crystals of your body

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Plantilla vitrubio 70x100

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.

cortehistologico 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.

microscopiohueso

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.

microscopiodiente

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.

otolitoSagittal otolith of a fish. Photo Giuseppe Falini.

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.

Surface_of_a_kidney_stone-wedellita

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.

 

Did you know that…

  • The bone is a specialised form of connective tissue made up of cells included in a mineralized mix of collagen fibres, proteins and carbohydrates called glycans.
  • Approximately 65% of the bone mass of an adult is hydroxyapatite crystals.
  • The front leg of a horse can support the load generated when this 500kg animal moves at 50 km/h. The light bones of birds can keep them in flight for migrations of 15000 km without landing. The antlers of a deer, used as weapons in territorial clashes, withstand terrible blows without fracturing.
  • Tooth enamel is the hardest and most mineralized substance in the body. It is 96% crystals and 4% water and proteins. This high mineral content gives it its resistance and hardness, as well as its colour and shine.
  • Fluoride catalyses the diffusion of calcium and phosphate on the surface of the tooth, causing the remineralisation of the crystalline structures of the tooth. This is why we drink fluoridated water. The remineralised surface contains hydroxyapatite and fluorapatite, which resists acid attack much better than the original mineral of the tooth.
  • Fish otoliths grow layers of calcium carbonate by accretion in a gelatinous matrix throughout their lives. The aggregation rate varies with the growth of the fish, often less in winter and more in summer. For this reason, the banding of otoliths contains the same information as tree rings.
  • Palaeontologists have studied otoliths from up to 172 million years ago in order to extract this information. Their careful study provides information on the life of the fish, including diet and water temperature, as well as where it was born and lived.
  • High levels of uric acid in the blood produce the nucleation and growth of needle-shaped urate crystals in the joints. This accumulation produces the disease called “gout”. This disease has been known since antiquity and was already being mentioned around the year 1500 BCE in the Ebers Papyrus.

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