What Is The Makeup Of Bone?

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Construction and limerick of bone

Long bones such as the femur comprise 2 distinct morphological types of bone:

Cortical (compact) os
Cancellous or Trabecular (spongy) bone

These are shown in the figure below.

Image of bone morhology

Diagram of singled-out morphological types of bone

Cortical bone forms a dense cylinder downwards the shaft of the bone surrounding the cardinal marrow crenel. While cortical os accounts for eighty% of the mass of bone in the human being body, it has a much lower surface expanse than cancellous bone due to its lower porosity.

Cancellous (or trabecular) bone is located at the ends of long basic, accounts for roughly 20% of the total mass of the skeleton, and has an open up, honeycomb structure. It has a much lower Young'southward modulus than cortical bone, and this graded modulus gradually matches the properties of the cortical bone to the cartilage that forms the articulating surface on the femoral head.

Composition

Bone itself consists mainly of collagen fibres and an inorganic bone mineral in the form of small crystals. In vivo bone (living os in the body) contains betwixt 10% and 20% water. Of its dry mass, approximately 60-70% is os mineral. Almost of the rest is collagen, just bone also contains a small corporeality of other substances such as proteins and inorganic salts.

Collagen is the primary fibrous protein in the trunk. Information technology has a triple helical construction, and specific points forth the collagen fibres serve as nucleation sites for the os mineral crystals. This is shown in the animation below.

The composition of the mineral component tin can exist approximated as hydroxyapatite (HA), with the chemical formula Ca_x(PO₄)_half-dozen(OH)₂. Nevertheless, whereas HA as has a Ca:P ratio of five:iii (1.67), bone mineral itself has Ca:P ratios ranging from 1.37 - i.87. This is because the limerick of bone mineral is much more complex and contains additional ions such as silicon, carbonate and zinc.

Cartilage is a collagen-based tissue containing very large protein-polysaccharide molecules that form a gel in which the collagen fibres are entangled. Articular, or hyaline, cartilage forms the bearing surfaces of the movable joints of the body. Mechanically, articular cartilage behaves equally a linear viscoelastic solid. Information technology besides has a very low coefficient of friction (< 0.01), largely attributed to the presence of synovial fluid that tin be squeezed out upon compressive loading.

The blitheness beneath allows you to explore the microstructure of cortical bone.

Stresses

Bones such as the femur are subjected to a angle moment, and the stresses (both tensile and compressive) generated by this bending moment business relationship for the structure and distribution of cancellous and cortical bone.

In the upper department of the femur, the cancellous bone is composed of ii distinct systems of trabeculae. Ane arrangement follows curved paths from the inner side of the shaft and radiates outwards to the contrary side of the bones, following the lines of maximum compressive stress. The second system forms curved paths from the outer side of the shaft and intersects the first arrangement at right angles. These trabeculae follow the lines of maximum tensile stress, and in general are lighter in construction than those of the compressive system.

The thickness of the trabeculae varies with the magnitude of the stresses at whatever betoken, and by following the paths of the main compressive and tensile stresses they comport these stresses economically. The greatest strength is therefore achieved with the minimum of material.

The distribution of the compact os in the shaft is also due to the requirement to resist the bending moment stresses. To resist these stresses, the textile should be as far from the neutral axis as possible. A hollow cylinder is the about efficient construction, again achieving the greatest strength with the minimum of fabric.

Diagram showing computed lines of constant stress from the analysis of various transverse sections