The Structure and Functions of Bones
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Introductory Note: Knowledge of the
structure and function of bones and aspects of skeletal
system generally are essential parts of training in
human biology, medicine and associated health sciences. This page is intended to include
the detail required for most Basic / First Level Courses
in many therapies, and some ITEC Diplomas.
This page is divided into the
following sections:
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The
Functions of The Skeleton
generally - as opposed to the functions of particular
bones.
-
Types
of Bones
with examples.
The
Structure of Bone
with diagram and definitions. |
1. Functions of The Skeleton |
 1.
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| Support |
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The skeleton
is the framework
of the body, it
supports the softer
tissues and provides
points of attachment
for most skeletal
muscles.
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2. |
Protection
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| The skeleton
provides mechanical protection
for many of the body's internal
organs, reducing risk of injury
to them.
For example, cranial bones protect
the brain, vertebrae protect
the spinal cord, and the ribcage
protects the heart and lungs. |
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3. |
| Assisting
in Movement |
| Skeletal muscles are
attached to bones, therefore
when the associated muscles
contract they cause bones
to move. |
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4. |
| Storage
of Minerals |
| Bone
tissues store several
minerals, including calcium
(Ca) and phosphorus (P).
When required, bone releases
minerals into the blood
- facilitating the balance
of minerals in the body. |
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5. |
| Production
of Blood Cells |
| The red
bone marrow inside some
larger bones (including,
for example, the ....)
blood cells are produced.
(Red Blood Cells, White
Blood Cells and Platelets
are described on the page:
Structure
& Functions of Blood.)
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6. |
| Storage
of Chemical Energy |
| With
increasing age some bone
marrow changes from 'red
bone marrow' to 'yellow
bone marrow'.
Yellow bone marrow consists
mainly of adipose cells,
and a few blood cells.
It is an important chemical
energy reserve. |
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2. Types of Bones |
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There are axial
and appendicular bones.
(The appendages are the arms
and legs, which contain approx.
30 bones each.) |
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There are typically
22 bones in the head. |
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There are 33 bones
in the spine.
These include:
7 cervix (neck);
12 thorax;
5 lumbar;
5 sacral;
4 coccyx. |
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The pelvic girdle
is fused to the sacrum at the sacro-illiac
joint.
The pelvis is the part that is added
onto the spine. |
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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.;
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The shoulder girdle
consists of the scapula (shoulder
blade) and the clavicle ("collar
bone").
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The following table summarises the five
main categories of bones, together with
another category (sutural bones).
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1. |
| Long
bones: |
| Long
bones have
greater length than
width and consist
of a shaft and a
variable number
of endings (extremities).
They are usually
somewhat curved
for strength. |
Examples include
femur, tibia,
fibula, humerus,
ulna and radius.
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2. |
Short
bones: |
| Short
bones are roughly cube-shaped
and have approximately equal
length and width. |
| Examples include
ankle
and wrist bones. |
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3. |
| Flat
bones: |
| Flat bones have a thin shape/structure
and provide considerable
mechanical protection
and extensive surfaces
for muscle attachments. |
| Examples include cranial
bones (protecting
the brain), the sternum
and ribs (protecting the
organs in the thorax),
and the scapulae (shoulder
blades). |
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4. |
| Irregular
bones: |
| Irregular
bones have complicated
shapes and so cannot be
classified into any of
the above (shape-based)
categories. Their shapes
are due to the functions
they fulfill within the
body e.g. providing major
mechanical support for
the body yet also protecting
the spinal cord (in the
case of the vertebrae). |
| Examples
include the vertebrae
and some facial
bones. |
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5. |
| Sesamoid
bones: |
| Sesamoid
bones develop in
some tendons in locations
where there is considerable
friction, tension, and
physical stress. They
may therefore form in
the palms of the hands
and the soles of the feet,
however their presence
and quantity varies considerably
from person to person. |
| Examples
common to everyone include
the patellae (kneecaps). |
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6. |
| Sutural
bones: |
| Sutural
bones are classified
by their location rather
than by their shape. They
are very small bones located
within the sutural joints
between the cranial bones.
The number of sutural
bones varies considerably
from person to person,
therefore these are un-named
bones. |
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3. The Structure of Bone |
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| Bones grow from their ends
(extremities).
Under normal circumstances bones stop growing
when the owner reaches his.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). |
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Definitions of main types of bone tissue:
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Compact
(also known as "compact") 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). |
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Cancellous
(also known as "spongy") tissue
is located beneath the compact bone and
consists of a meshwork of bony bars (trabeculae)
with many interconnecting spaces containing
bone marrow. |
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Diagram illustrating the general structure
of long bones:
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Above:
Diagram illustrating the Structure
of Long Bones |
The diagram to the left labels the basic
components of a typical long bone:
- articulartory (also known as 'articular')
cartilage;
- spongy bone;
- bone marrow;
- endosteum;
- compact bone;
- periosteum;
- medullary cavity, and
- a blood vessel (indicating blood
supply and circulation within bones).
The Functions
of Components 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.
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This is the end of this page about the
structure and functions of bones.
See also how many bones are in the human body and information about cranial
and facial bones and bones
of the feet and hands.
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