Bone is the basic structural unit of the skeleton. Connective bone tissue plays a major role in bone formation.
Bone tissue includes:
- cells – osteocytes;
- and intercellular substance.
The intercellular substance is very dense, which gives the bone tissue mechanical strength.
Osteocytes are surrounded by the smallest “tubules” with intercellular fluid, through which bone cells are nourished and breathed. Nerves and blood vessels pass through the bone canals.
The hardness of the bones is given by the presence of inorganic substances in their composition: mineral salts of phosphorus, calcium, magnesium.
Organic substances give flexibility and elasticity.
Bone strength is provided by a combination of toughness and toughness.
The bones of a growing organism are more flexible, the bones of an adult (but not an old) person are more durable.
The composition of the bone and the properties of the substances that make up it can be experimentally proven.
with prolonged calcination of the bone, organic compounds burn out. The bone becomes fragile, crumbles when touched into many small particles. The residues are composed of inorganic compounds. This means that in the absence of organic matter, the bone loses its flexibility and elasticity.
By immersion in hydrochloric acid solution for several days:
inorganic salts dissolve in hydrochloric acid and are washed out of the bone. The bone becomes flexible, it can be tied in a knot. This means that in the absence of inorganic salts, the bone loses its hardness.
Each bone is a complex organ.
According to their shape, bones are divided into:
Let’s consider the structure of tubular bones using the example of the femur.
In the external structure of a long tubular bone, the body of the bone (diaphysis) and two terminal articular heads (epiphyses) can be distinguished.
The epiphyses of the tubular bone are covered with cartilage.
Epiphyseal cartilage is located between the body and the heads, which ensures bone growth in length.
Inside the bone there is a cavity (channel) with yellow bone marrow (adipose tissue), which gave the name to such bones – tubular.
The epiphyses of the femur are represented by spongy substance.
The body of the bone (diaphysis) is formed inside by a spongy substance, outside by a thick plate of compact substance and covered with a membrane – the periosteum.
The blood vessels and nerve endings are located in the periosteum, due to which it provides bone growth in thickness, nutrition, bone fusion after fractures. The periosteum is absent on the articular heads (epiphyses).