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By Monica R. and Ryan J.
AP Biology
Period 7
The Skeletal System
What is the Skeletal System?
• In biology, the
skeletal system is
the biological
system that
provides support in
living organisms.
Types of Skeletal Systems
There are three different types of skeletal
systems:
• Exoskeleton- A hard encasement deposited on
the surface of an animal.
• Endoskeleton- Consists of hard supporting
elements, such as bones, buried within the soft
tissues of an animal.
• Hydrostatic Skeleton- Consists of fluid held
under pressure in a closed body compartment.
Exoskeleton
Some animals with exoskeletons:
• arthropods, such as insects, spiders and
crustaceans
• other invertebrate animals, such as shelled
mollusks
* The exoskeletons of mollusks contain
calcium carbonate. As the mollusk grows,
the shell enlarges as well.
* Jointed appendages are also present in
organisms with an exoskeleton.
Endoskeleton
The endoskeleton, also known as an internal skeletal
system, consists of rigid (or semi rigid) structures,
within the body. These structures are capable of being
moved by the muscular system which surrounds it. If
the skeletal structures are mineralized or ossified, as
they are in humans and other mammals, they are
referred to as bones. Cartilage is referred to as
another common component of skeletal systems,
supporting and supplementing the skeleton. Though
less ridged, they are more flexible in comparison to
the ossified bone, allowing for “manipulation” in shape
to enable bending. For example, the human ear, nose,
and ribs all consist of cartilage.
Hydrostatic Skeleton
Hydrostatic skeletons are similar to a waterfilled balloon. Located internally in cnidarians,
(coral, jellyfish etc.) and annelids (leeches,
earthworms etc.), among others, these animals
can move by contracting the muscles
surrounding the fluid-filled pouch, creating
pressure within the pouch that causes
movement. Animals such as earthworms use
their hydrostatic skeletons to change their body
shape, as they move forward, from long and
thin to shorter and wider.
Function of Bones
• Protection – protect internal organs
• Shape – provide a frame to support body
• Blood Production – the marrow produces blood cells in a
process called haematopoiesis
• Mineral Storage – bones act as reserves of minerals,
specifically calcium and phosphate
• Movement – Bones, skeletal muscles, tendons,
ligaments and joints function together to generate and
transfer forces so that individual body parts or the whole
body can move.
• Acid-Base Balance - Bone buffers the blood against
excessive pH changes by absorbing or releasing alkaline
salts.
• Detoxification – Bone tissues can remove heavy metals
and other foreign substances from the blood and store
them, reducing their effects of other tissues. These
substances can then later be excreted.
The Human Skeleton
• Function:
- Provides support for the upright body
- Surrounds and protects the brain, spinal
cord, lungs, and heart.
- Provides for a way of locomotion
• Built from over 200 bones
- Some bones are fused together
- Others are connected by ligaments,
allowing for free movement
Human Skeleton Cont’d…
• Vertebrate Frame (2 sections):
- axial skeleton, consisting of:
*skull
*vertebral column (backbone)
- rib cage
*an appendicular (relating to the
appendages) skeleton made up of limb
bones and the pectoral and pelvic girdles,
which anchor the appendages to the axial
skeleton. In each appendage, several types
of joints provide flexibility for body movement
and locomotion.
Joint Types
• Ball-and-socket joint:
Enable us to rotate our arms
and legs and move them in
several planes. (Ex: joint in the
shoulder girdle and hip)
• Hinge Joint
Restrict movement to a single
plane (Ex: joint between the
femur and tibia)
• Pivot Joint
Allows us to rotate (Ex: the
joint at the forearm and the
elbow)
• Gliding Joint
Joints in between vertebrae
• Condyloid Joint
Joint near throat and back of
neck
Pivot Joint
Hinge Joint
Cartilage in the Endoskeleton
• A type of connective tissue composed of collagenous
fibers and cells called chondrocytes. These substances
are embedded in the matrix.
• Functions:
– Provides a framework where bone deposition can begin
– Provides smooth surface for the movement of bones
• Locations in skeleton:
– Joints
– Ear
– Rib cage
– Nose
– Invertebral discs
– Bronchial tubes
Skeletal Muscle
• Muscle that is attached to bones by tendons
• Responsible for voluntary movements of the body
• Skeletal muscle is also called striated muscle because the
arrangement of overlapping filaments gives the cells a
striped, or striated, appearance when looking under a
microscope.
• Works with the skeletal system to allow movement and
locomotion
Advantages of the Human
Skeletal System
• The design of the skeleton accounts for
the demand for support based on the size
of the body
• The different types of joints allow for a
wide range of motion
• The human skeleton provide the body with
a support system as well as flexibility and
locomotion
Common Bones in Skeletal System
:)
The End
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