Bones: Basics

Bones are more than just a support holding body parts together. It is a living tissue that is constantly changing. Bones come in different shapes and sizes.

Bones perform a variety of functions. They support the structure of the body, protect internal organs from mechanical damage, provide movement, deposit calcium and other minerals. In addition, bones create an environment for the bone marrow, in which blood cells are formed.

There are 270 soft bones in the body of a newborn baby. As they grow, some of them grow together, by the age of majority their total number is 206.

The largest bone of the human body is the femur, the smallest is the stirrup in the inner ear, its length is only 3 mm.

Bones are made up of collagen, a protein that forms the elastic base of the bone. Calcium compounds give it strength, they fill the space between the collagen fibers. More than 99% of the human body's calcium is contained in bones.

Bones have a cellular structure, so with their sufficient strength they are very light.

Bone structure

Bones consist of two types of tissues: compact and spongy substances.

The compact substance is a strong dense outer layer, which makes up about 80% of the bone mass.

The spongy substance is the inner layer, which is a network of flexible trabeculae that give the bone elasticity.

Bone tissue consists of the following components:

· osteoblasts and osteocytes – responsible for the growth of bone tissue;

· osteoclasts – responsible for bone destruction;

· osteoid – a mixture of collagen and other proteins;

· inorganic mineral salts;

· nerves and blood vessels;

· bone marrow;

· cartilage;

· sheaths, including the endost and periosteum (periosteum).

Bone tissue cells

Bones are not a permanent and unchanging matter, they are constantly undergoing the processes of formation and destruction of bone tissue. Three types of cells are involved in these processes.

Osteoblasts. These cells are responsible for building new tissue and restoring existing ones. Osteoblasts synthesize a number of proteins that together make up the osteoid. The osteoid is subsequently mineralized and turns into bone tissue. In addition, osteoblasts synthesize biologically active substances (prostaglandins).

Osteocytes. These cells are osteoblasts in an inactive form. They remain in the "bone trap" that they themselves created, and cease to function. But at the same time they constantly keep in touch with osteoclasts and other osteoblasts.

Osteoclasts. These are large multinucleated cells whose task is to destroy the bone. They produce enzymes and acids that dissolve minerals in the bone. Minerals are absorbed by osteoclasts. This process is called bone resorption. Osteoclasts help to destroy improperly growing bone tissue, "pave" the way for nerve fibers and blood vessels.

Bone marrow

The bone marrow is located inside the spongy substance of the bone. His task is to create shaped blood elements. Every second, 2 million red blood cells are formed in it

Intercellular substance

Bone, in fact, is a living cell embedded in a mineral-organic matrix. This matrix is an intercellular substance. Its components:

· organic: the bulk of it is type 1 collagen;

· inorganic: hydroxyapatite, calcium and fluorine salts and others.

Collagen gives bone elasticity, namely resistance to stretching, hydroxyapatite – strength, namely resistance to compression.

Why do we need bones?

Bones perform a number of vital functions.

Mechanical. Bones create a support that holds the body. Muscles, ligaments and tendons are attached to them. If the muscles were not fixed to the bones, movement would be impossible. Bones protect internal organs from mechanical damage: the skull protects the brain, the ribs protect the lungs, and so on.

Hematopoietic. In the spongy tissue there is a red bone marrow, in which blood cells are synthesized. Some of the old and defective red blood cells are destroyed in the bone marrow.

Metabolic:

· depot of minerals (carbonates, phosphates and others), growth factors (insulin-like growth factor), lipids;

· maintaining the acid-base balance of the blood due to the absorption or release of alkaline salts;

· detoxification – bones can absorb heavy metals and other toxic compounds from the blood;

· endocrine – bone tissue cells synthesize biologically active substances that affect carbohydrate and fat metabolism;

· maintaining a normal level of calcium in the blood due to the processes of resorption and formation of bone tissue.

Types of bones

There are five types of bones in the human body.

Long bones – mainly consist of a compact substance, form the upper and lower limbs.

Short bones – contain a small amount of compact substance, these are the bones of the hand and foot.

Flat bones – contain a compact and spongy substance, these are the bones of the skull, the sternum.

Sesamoid bones – tendons are not attached to them, for example, the patella. They protect the articular surfaces from abrasion and wear.

Mixed bones – do not belong to any of the listed types, these are vertebrae and pelvic bones.

The bones of the skeleton are divided into two groups:

· axial – bones of the skull, spine, chest;

· peripheral – bones of the extremities, shoulder and pelvic girdles.

Bone reconstruction

A two-component restructuring process is constantly taking place in the bones: bone resorption by osteoclasts and the formation of a new bone by osteoblasts.

About 10% of bone tissue is replaced in an adult every year.

Reconstruction allows the body to repair damage, form a skeleton during growth, regulate the level of calcium in the blood.

If the load falls on a certain area of the bone for a long time, for example, during sports, it becomes thicker.

The process of bone reconstruction is regulated by several hormones: calcitonin, parathyroid hormone, estrogen in women and testosterone in men.

What is osteoporosis?

Osteoporosis is a disease of bone tissue in which there is a decrease in bone mineral density. This increases the risk of fractures even with a small mechanical impact. Osteoporosis most often develops in women in the postmenopausal period, but it is also possible in women before menopause and in men.

Osteoporosis occurs when bone resorption occurs too quickly, when bone formation slows down, or when both causes are combined. It can be caused by a lack of calcium, vitamin D deficiency, excessive alcohol consumption and smoking. The issues of the occurrence and treatment of osteoporosis are currently being actively studied around the world.

Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on Medical News Today: Bone: The basics.