Anatomy of the bones

The human body has 206 bones, which together form the skeleton or framework. These bones give the body its shape and strength, serve as attachment points for tendons, and protect internal organs.

Different types of bones

Bones, also known as "osseous tissue", can be divided into four categories:

• Long and short long bones: Long bones consist of a middle section (the shaft) and two wider ends that form the head or socket of a joint. Examples include the tibia (long bone) and the bones in the fingers (short long bones).
• Flat bones: These are flat bones, such as those in the shoulder blade or skull.
• Sesamoid bones: These bones are embedded within tendons, such as the kneecap.
• Irregular bones: These bones have various joint surfaces or protrusions, such as the vertebrae or carpal and tarsal bones.

Continuous build-up and breakdown of bone tissue

Bones are primarily composed of minerals, proteins, and water. Bone tissue is constantly broken down and rebuilt by osteoblasts (bone-forming cells) and osteoclasts (cells that remove aged or damaged bone).

During youth, the body builds more bone than it breaks down. At birth, most bones consist of cartilage. Bones lengthen and harden until they reach peak bone mass, typically around age 30. At this point, bones are fully grown, at their strongest, and have the greatest bone mass.

After age 30, bone breakdown gradually exceeds bone formation. This leads to a decline in bone quality and strength, potentially resulting in osteoporosis, where bones become brittle and more prone to fractures. Healthy bones depend on several factors:

• Hereditary predisposition.
• A healthy and varied diet.
• Regular physical activity.
• Low stress levels, as stress impairs nutrient absorption.
• Sufficient sunlight for vitamin D production.

Bone from outside to inside

From the outside in, bone consists of several layers. The outermost layer is the periosteum, which contains many nerve fibers, making injuries (like bumping your shin) particularly painful. Directly beneath the periosteum lies a compact, hard bone layer.

Bones are not completely solid. Inside, they contain spongy bone tissue with various openings, known as the marrow cavity, where bone marrow is located. There are two types of bone marrow:

• Red bone marrow: Present from birth, red bone marrow produces new red blood cells (for oxygen transport), white blood cells (for immunity), and platelets (for blood clotting).
• Yellow bone marrow: As we age, much of the red bone marrow converts to yellow bone marrow, which primarily stores fatty acids. However, red bone marrow remains in areas such as the thigh bone, vertebrae, ribs, and hip bones.

Bone from top to bottom

From top to bottom, a long bone consists of different parts:

• Epiphysis: Located at the end of the bone, the epiphysis ensures that the joint cartilage receives adequate nutrition.
• Metaphysis: Bones grow from the metaphysis, which lies beneath the epiphysis.
• Diaphysis: The shaft of the bone, or diaphysis, contains the marrow cavity, which is responsible for producing new blood cells.