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Observe the following diagram, which shows the structure of a long bone. We can see that this bone has:
Epiphyses - the ends of the bone, covered with cartilage;
Periosteum - the fibrous membrane that lines the bone externally;
Diaphysis - the portion of the bone between the epiphyses and surrounded by the periosteum.
Bone canal - the canal where the bone marrow is located.
Bones are organs formed by various types of tissue. The periosteum, for example, is a fibrous membrane of connective tissue. The red bone marrow is also formed by a type of connective tissue and can be found in the ribs and vertebrae; It produces blood cells. In the diaphysis of long bones such as the femur is the yellow bone marrow, which stores fat, the marrow.
But it is the bone tissue that confers the characteristic stiffness of the bones. In it are cells like osteocytes. Among the cells, there is the bone matrix, which represents the intercellular material, consisting basically of calcium and phosphorus salts, as well as proteins called collagen. Calcium salts and collagen-like proteins are responsible for the rigidity of bone tissue.
As for shape, bones can be long, short and flat. Long bones are longer than width and thickness. Examples: the femur (the thigh bone), the humerus (the arm bone) and the tibia (one of the leg bones).
The short bones they are almost equal in length, width and thickness. Examples are the patella, popularly called the kneecap (knee bone), the carpal bones (some of the hand bones) and the tarsus (some of the foot bones). The flat bones They are thin and flat. Examples: the shoulder blade, shoulder bone, ribs, and skull bones.
Together It is where two bones touch. Some are fixed (eg skull), where the bones are firmly joined together. In other joints (eg joints), the bones are movable, allowing the skeleton to make movements.
There are several types of joints:
Ball-and-socket type - On the shoulders, enabling swivel arm movements.
"Hinge" type - On knees and elbows, allowing you to bend.
Bones of a joint have to slide over each other smoothly and without friction, or they would wear out. The bones of a joint are held in place by sturdy cords consisting of fibrous connective tissue: the ligaments, which are firmly attached to the membranes that line the bones.