Osteoarthritis and Osteoarthritis

Bones are also called passive organs of movement because they can only move when activated by muscles. Nevertheless, bones still play a vital role in the human musculoskeletal system, as movement would not occur without them.

Based on the tissue composition and physical properties, bones are classified into two types, namely cartilage and hard bone (osteon) .

Cartilage

Cartilage is composed of spherical cartilage cells (chondrocytes). Cartilage has an interstitial substance (matrix) containing thin, flexible fibers. The cartilage matrix is ​​a mixture of protein and carbohydrates called chondrin. It also contains a high amount of collagen and small amounts of calcium carbonate and calcium phosphate. Therefore, cartilage is elastic, flexible, and strong.

During embryonic development, the human skeleton is composed entirely of cartilage. In adulthood, cartilage is found only in a few areas, such as the earlobes, nostrils, epiglottis, joint surfaces, and between the ribs and sternum. In children, cartilage contains many bone cells, while in adolescents, it contains more matrix. Note the difference between immature and adult cartilage in the image below.

Hard Bone (Osteon)

Bone is composed of hard (true) bone cells called osteocytes. Its matrix is ​​hard because it contains a large amount of calcium carbonate and calcium phosphate. If the matrix is ​​dense and compact, it forms compact bone, or hard bone, for example, in long bones. If the matrix is ​​hollow, it forms spongy bone, for example, in flat bones and short bones.

Bones are derived from cartilage. After cartilage forms at the end of the second month of embryonic development, a cavity forms within it containing osteoblasts, or bone-forming cells. Bones form sequentially from the inside out.

Tubular bones are tubular and mostly hollow. At the end of the tubular bone, there is an expansion that serves to connect with other bones. Inside the tubular bone, there is a large cavity containing yellow marrow and fatty substances. Tubular bones are usually found in the bones of the limbs, such as the upper arm bone, the ulna, and the finger bones. The largest and longest tubular bone in the human body is the femur.

Flat bones are flat and wide, hollow inside and contain red marrow, which is where red blood cells are formed. Most flat bones are hollow, so they often serve as protection or reinforcement. Examples of flat bones include the skull, shoulder blades, ribs, and sternum.

Short bones are round (small cylinders) and contain red marrow inside. Most of the tissue that makes up this bone is light and strong. Examples of short bones include the wrist bones, ankle bones, and vertebrae.