Bone structure

Bones have to withstand a great deal of pressure in everyday life. They carry our body weight and take on various strains whenever we stand and move around. Their structure and ability to adjust to physical strain make it possible to withstand this stress. Bones are not a rigid frame, but living tissue. Like all other tissues and organs of the body, bones are constantly renewed.

The outer layer of a bone is called compact or cortical bone. This layer is hard and particularly solid, and it makes sure that our bones can withstand daily physical strains. The outer layer has a thin coating called the periosteum.

Inside bones there is a supporting structure with interconnecting bony plates and rods called trabeculae. This structure is called trabecular or spongy bone because it looks a bit like sponge. Bone marrow is found in the “holes” of the spongy bone. Many of the bones contain red bone marrow at birth. Red bone marrow produces the blood cells. The longer we live, the more red bone marrow turns into fatty tissue. In adults, red bone marrow is only found in a few bones, for example in the ribs, the sternum (breastbone), and the pelvic bones.

Illustration: Healthy bone structure

Healthy bone structure

The crucial factor for the stability of a bone is how solid it is. This is strongly influenced by the amount of minerals it contains. The more minerals a bone has in it, the harder and denser it is. Bones that are not very dense break more easily. Calcium is the most important mineral for our bones. It makes them harder and stronger.

Besides the mineral content of a bone, the fine structure and the composition of the bone substance are also very important for bone stability.

Bone metabolism changes over your lifetime

Old bone tissue is continually being replaced by new bone throughout our lives. This process is part of the body’s metabolism. Cells called osteoblasts produce new bone tissue, while cells called osteoclasts break down old bone tissue. This process is controlled by and is called "bone turnover."

In children and young adults, more bone is formed than is broken down. This means that the bones grow, and become heavier and denser. At about the age of 30 our bones are about as strong as they will ever be. From then on, the rate of bone turnover gradually changes: more bone is dissolved than is produced. After about the age of 50, this process starts to speed up, especially in women. Up until menopause, the hormone estrogen protects the bones by slowing the breakdown of bone tissue. So after menopause, when this hormone level starts to drop, this protection is lost and bone tissue breaks down more quickly.

Weak bones are common in older age. But there are some ways to protect the bones and to make them stronger – even if you are already older.

Thews G, Mutschler E, Vaupel P. Anatomie, Physiologie, Pathophysiologie des Menschen. Stuttgart: Wissenschaftliche Verlagsgesellschaft; 1999.

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Updated on April 9, 2014
Next planned update: 2021

Authors/Publishers:

Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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