Lucia De Stefano IV A
• A skeleton is needed by animals to move and
to give their bodies structure and protection.
• There are three main types of skeleton: the
hydrostatic skeleton (or hydro-skeleton), the
exoskeleton, and the endoskeleton.
• The hydrostatic skeleton (or
hydroskeleton) is made up
of a liquid kept under
pressure in a closed area of
the body.
• It contributes to protect the
body.
• Moreover, it gives shape to
the body and gives a point of
insertion for the muscles, to
allow the motion. Most of
the animals which have a
hydrostatic skeleton have a
flaccid and flexible body
e. g. earthworm.
• A lot of aquatic and terrestrial
animals have a rigid external
skeleton, the exoskeleton.
• This is a distinctive
characteristic of the arthropods
phylum.
• The exoskeleton of arthropods
is made up of protein layers
and chitin, a polysaccharide.
• The exoskeleton does not grow
together with the animal, so it
has to be removed and
replaced with a bigger one to
allow the growth of the animal.
• The endoskeleton is made
up of hard or leathery
support elements situated
in the interior of the
animal body.
• Most of echinoderms have
an endoskeleton made up
of hard subcutaneous
plates. The endoskeleton
of echinoderms is
calcareous and is called
derma-skeleton.
• The endoskeleton of
vertebrates is made up of
cartilage or a combination
of cartilage and bone.
• All vertebrates have an axial skeleton which
supports the trunk of the body. It is formed by
the skull, the spinal column and, in most of the
vertebrates, by a rib cage.
• The spinal column is the anatomic characteristic that
defines vertebrates and is formed by a series of single
bones, the vertebrae, alternated with buffers of fibrous
cartilage known as intervertebral disks.
• The vertebrae have the same basic structure: a
cylindrical body of bone, which supports the body
weight, a dorsal arch, which forms a protected passage
for the spinal marrow, and several bone thorns and
protuberances, which form useful areas for the
insertion of muscles.
• The appendicular skeleton, which is attached
to the axial skeleton, is formed by the pectoral
girdle, the pelvic girdle and the bones of the
upper and lower limbs.
• Their functions are:
- to make locomotion possible;
- to protect the major organs of digestion,
excretion and reproduction.
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Support
Movement
Protection
Blood cells production
Storage
Endocrine regulation
• Bone contains several types of living tissues.
Most of the external area is covered by a layer of
connective fibrous tissue, the periosteum.
• Other living cells, the osteoblasts, are present
inside the osseous tissue where they secrete the
bone matrix. The bone matrix is formed by
flexible protein-based collagen fibres.
• Even the cells in the osseous tissue have a
metabolism.
• The cylindrical and elongated part of
long bones, e. g. the humerus, is called
diaphysis and is made up of dense
bone. Dense bone surrounds a central
cavity containing yellow bone marrow,
mainly made up of fat transported by
blood and stored in the bone.
• The two extremities of the bone, the
epiphysis, have an external layer of
dense bone and an inner layer of
spongy bone. The small cavities of the
spongy bone contain the red bone
marrow, which produces blood cells.
• The two extremities are covered by a
thin layer of cartilage.
• In movable joints, bones are
kept in the right position by
ligaments, solid fibrous
connective tissue bands.
• Between the humerus and the
scapula, and between the femur
and the pelvic bones, there is a
particular joint called ball and
socket joint (or spheroidal joint),
formed by a sphere in a hollow.
• In the elbows and in the knees
there are the hinge joints which
allow the movement on only one
level.
• The joint which allows us to
rotate our forearm is a pivot
articulation.
• To produce movements, the
animal muscles interact
with bones which act like
levers.
• Muscles are connected to
bones by tendons, formed
by fibrous connective tissue.
A muscle can only actively
contract; relaxation is a
passive process.
• The capacity of lifting up or
lowering our arms depends
on the existence of couples
of antagonist muscles
attached to the bones.
There are many classified skeletal
disorders.
• One of the most common is
osteoporosis.
• Also common is scoliosis. This
condition is most apparent
during adolescence, and is most
common with females.
• Arthritis is a disorder of the joints. It
involves inflammation of one or more
joints.
• When affected by arthritis, the joint or
joints affected may be painful to move,
may move in unusual directions or may
be immobile completely.
• The symptoms of arthritis will vary
differently between types of arthritis.
• The most common form of
arthritis, osteoarthritis, can affect both
the larger and smaller joints of the
human skeleton.
• A human is able to survive with just his axial
portion of the skeleton.
• Human inter-sex dental dimorphism centres
on the canines, but it is not nearly as
pronounced as in the other great apes.
• Long bones are generally larger in males than
in females within a given population.