The Skeletal System: Summary
Function of the skeletal system
1. PROTECTS vital organs
such as the brain, heart
and the lungs.
2. SUPPORTS the body. It
gives us the body shape
we have.
3. ALLOWS MOVEMENT of
the body because muscles
are attached to bones.
4. MAKES blood cells
5. STORES
important
minerals such as calcium.
Investigation: Calcium in bones
Bone consists of two materials – minerals and organic substances. Calcium is the main
mineral and collagen (a fibrous protein) is the main organic material in bones. The mineral
matter can be removed by soaking a long bone in acid leaving the organic matter. The
organic matter can be removed by soaking the bone in boiling water, leaving the mineral
matter. Changes in the composition of bone changes the properties of the bone,
particularly in relation to flexibility.
Osteoporosis is a common bone disorder in old age. It is caused by a lack of calcium being
absorbed by the bone. Bone mass decreases and the compact bone becomes more porous.
The bone becomes brittle and can fracture more easily.
Recall the method:
Aim: To OBSERVE how the flexibility of bone changes as the calcium content is changed.
Method:
1. Cut the meat from the bones of a chicken wing.
2. Collect three similar bones. This can be done by using three wings, or by swapping with
other groups.
3. Observe and describe the flexibility of the bones
4. Put one bone in 1M HCl. Place in a refrigerator overnight.
5. Gently heat one bone using a Bunsen burner.
 Hold the bone over a Bunsen flame using a set of metal tongs.
 CAUTION - Be careful as the oil in the bone could catch alight.
 Store the bone in a refrigerator overnight.
6. Put the third bone in a container. Store in a refrigerator overnight.
7. Next day, compare the three bones for flexibility.
Bone joints
Bones don’t work on their own. The bones join together to form joints. There are three basic joints



fibrous (immovable)
cartilaginous (slightly movable)
synovial (freely movable)
Synovial Joints
Synovial joints are freely movable joints (synovial joints) provide stability as well as allowing
movement. A large range of twisting, turning and rotating movements are possible because
of movement at joints.
Joint
Synovial membrane
Synovial fluid
Bones
Cartilage
Ligaments
Tendons
Purpose/feature
Lines the inside of the joint
Secreted by the synovial membrane
Comes together to form the joint
Covers the bone ends
Connect the bones to the joint
Connect the muscle to the bone
Types of Synovial Joints
The main function of synovial joints is to provide both stability and mobility. Synovial joints are
classified by the shape of the bone ends and the type of movement they allow. There are a number
of different types of synovial joints.
Ball and socket joints


One rounded head bone (ball) fits into a
cup shaped bone (socket).
Movement in almost any direction – side
to side, back and forth, rotation.

Examples – hip, shoulder
Hinge joints



One bone curves out (convex) and fits a
second bone that curves in (concave).
Movement in one plane (like a door hinge)
– backward and forward.
Examples – elbow, knee, ankle, finger
joints
Pivot joints



A bony projection on one bone fits in a
ring shaped bony structure on the other
bone.
Movement is rotational (eg nodding no
with the head).
Examples – elbow (ulna & radius), first and
second cervical vertebrae)
Sliding Joint



Both bones are slightly curved. Bones
slide over each other
Movement in all directions (side to side &
back and forth) but not rotational.
Examples – Metacarpals in wrist,
Vertebrae
Double Hinge Joint



General term for Saddle Joints.
Movements in two planes that together
allow some rotation at the joint.
Examples: wrist, thumb
Role of cartilage and synovial fluid
Cartilage
At joints, the bone ends are covered with a layer of smooth cartilage. The cartilage has two
important functions:
1. Cartilage reduces friction & wear, between the two opposing joint surfaces during
movement. The surface is very smooth and the cartilage’s coefficient of friction is low.
The low coefficient protects the bone ends by providing a smooth, gliding surface when
movement occurs.
2. Cartilage absorbs and spreads the forces on the joint over a wider area. This decreases
the stresses on the contacting surfaces & on the bone shaft. The cartilage is deformable
like elastic and it recovers its shape quickly when the deforming force is removed.
Synovial Fluid
Synovial fluid is secreted into the joint cavity from the synovial membrane. Most of the fluid
comes from the blood capillaries on the membrane. Synovial fluid has two roles:
1. Nutrition: The fluid provides nutrients to the cartilage. The nutrients are delivered as
the fluid moves around inside the synovial cavity. This is necessary since the cartilage
itself has a limited blood supply. Wastes are also carried out of the joint via the synovial
fluid. [The part of the cartilage nearest the bone is impregnated with calcium. This
calcified layer is a barrier to the passage of oxygen and nutrients to the cartilage from
the bone. Therefore, the cartilage is largely dependent upon the synovial fluid for its
nourishment.]
2. Lubrication: The bone surfaces are kept well “oiled “ by the synovial fluid. Also, the fluid
acts as a cushion between the surfaces of the bones. This is because the joint surfaces
do not fit perfectly together and need to be kept apart.
Affects of cartilage and synovial fluid depletion
The effects of Arthritis show the importance of cartilage and the synovial fluid. This disease
is a disease that effects joints, and can attack any synovial joint in the body. Victims of
arthritis suffer pain, stiffness and swelling in their joints.
Osteoarthritis occurs when a joint wears out and therefore occurs on older people. In this
form of the disease the cartilage between the bones breaks down. This causes the bone
ends to rub against each other.