The Structure and Functions of Bones
This page is divided into the following sections:
- The Functions of the Skeleton
generally - as opposed to the functions of particular bones.
- Types of Bones
- The Structure of Bone
with diagram and definitions.
1. Functions of the skeleton
2. Types of Bones
- There are axial and appendicular bones.
(The appendages are the arms and legs, which contain approx. 30 bones each.)
- There are typically 22 bones in the head.
- There are 33 bones
in the spine.
- 7 cervix (neck)
- 12 thorax
- 5 lumbar
- 5 sacral
- 4 coccyx.
- The pelvic girdle is fused to the sacrum at the sacro-illiac
The pelvis is the part that is added onto the spine.
- The thorax (chest) consists of 12 pairs of ribs:
- 7 pairs 'true' ribs - joined directly to the sternum ("breast-bone"),
- 3 pairs 'false' ribs - joined to the sternum ("breast-bone") by cartilage,
- 2 pairs 'floating' ribs (not connected to the sternum ("breast-bone") at all, connected to the diaphragm.
- The shoulder girdle consists of the scapula (shoulder blade) and the clavicle ("collar bone").
The following table summarises the five main categories of bones, together with another category (sutural bones).
3. The Structure of Bone
Bones grow from their ends (extremities). Under normal circumstances bones stop growing when the owner reaches his or her late teens or early twenties.
Bone marrow (see diagram below) produces stem cells, such as erythrocytes (red blood cells) and leucocytes (white blood cells).
Definitions of main types of bone tissue:
- Compact bone tissue forms the outer shell of bones. It consists of a very hard (virtually solid) mass of bony tissue arranged in concentric layers (Haversian systems).
- Cancellous (also known as 'spongy') bone tissue is located beneath the compact bone and consists of a meshwork of bony bars (trabeculae) with many interconnecting spaces containing bone marrow.
Diagram illustrating the general structure of long bones:
Above: Diagram illustrating the Structure of Long Bones
The diagram on the right labels the basic components of a typical long bone:
- articulartory (also known as 'articular') cartilage
- spongy bone
- bone marrow
- compact bone
- medullary cavity
- a blood vessel (indicating blood supply and circulation within bones)
Functions of parts of long bone:
- Articulatory (or articular) cartilage reduces friction and absorbs shock at freely moveable joints.
- Endosteum is the membrane that lines the cavity of a bones.
- Periosteum is a tough fibrous membrane that surrounds the outside of bones wherever they are not covered by articulatory cartilage.
- In adults the medullary cavity contains fatty yellow bone marrow.
This is the end of this page about the structure and functions of bones.