Skeletal System – Bones Structure and functions, composition

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Let us discuss the bones in the human body, bones structure and functions, its composition and many more interesting facts about the skeletal system.

Skeletal System: Bones

Bones are the rigid organs which constitute the part of the endoskeleton of the vertebrates. Bones vary in shape and size and have complex internal and external structure. Though they are light in weight, they are very strong and hard.

Bones in new born baby: At birth, the infants consist of 270 bones, as the baby grows the bones fuse together and leaves a total of 206 bones in the adult.


The largest bone in the human body is femur and the smallest bone is the stapes (auditory ossicles) in the ear.

Bones in human body

Human Skeletal System – Bones in human body

Bones functions

  • Bones support and protect the different internal organs of our body.
  • Bones help in the production of red blood cells and white blood cells.
  • Bones help in the storage of minerals like calcium and phosphorous.
  • Bones of the skull protect the brain and bones of the ribs protect the heart and lungs.
  • Bones, skeletal muscles, tendons, ligaments, and joints together help in the movement of the body parts or the whole body.

Composition of Bones:

A living bone consists of different kinds of tissues and does not have a single uniform composition. One of the types of tissue of which the bones are made of is mineralized osseous tissue, which is also known as bone tissue. This osseous tissue makes the bones rigid. The other types of tissues that are found in the bones include bone marrow, endosteum, periosteum, nerves, cartilage and blood vessels.

Bones consists mainly of collagen fibres, which is the organic component of the bone and inorganic bone mineral namely carbonated hydroxyapatite (Ca10(PO4)6(OH)2).

Mainly there are two types of bone tissues in a single bone:

  1. Compact tissue (Cortical bone)
  2. Spongy tissue (Cancellous or Trabecular bone)

The bone is covered with a tough membranous tissue known as periosteum and is interlaced with many blood vessels.
Whereas in the larger and longer bones of the body and in the interior of the skull bones and vertebrae there are two additional kinds of tissues known as

  • Red marrow
  • Yellow marrow

Red Bone Marrow:

In the spongy bone areas, red marrow produces large number of the red blood cells at a rate of millions of red blood cells per minute. Red bone marrow is the erythropoietic regions that mean that it is the region that produces red blood cells. Marrow is required for the growth and replacement of the red blood cells as the red blood cells live only for 120 days and die after that.

Children’s bones contain greater proportions of the red bone marrow than adults’ bone marrow as the children require a larger amount of red blood cells.

With increasing age, yellow bone marrow fills the interior cavity of the bones that is previously occupied by the red bone marrow. Yellow bone marrow consists mainly of fat cells.

Calcium, an important constituent of bones:

The bone acts as the storage and distribution center for the important elements of the body like calcium. Calcium is present in the bone tissue as the basic chemical calcium phosphate.

Calcium is also required by the body and should be present in the bloodstream at required levels for the proper functioning of the heart and produce normal heartbeat, blood clotting and for the contraction of the muscles.

When there is a deficiency of calcium in the bloodstream, the bones release some amount of calcium into the bloodstream to maintain the levels.

When there is an excess amount of calcium in the bloodstream, the bone reabsorbs it.

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