The Skeletal System

By Monica R. and Ryan J.

AP Biology

Period 7

What is the Skeletal System?

• In biology, the skeletal system is the biological system that provides support in living organisms.

Types of Skeletal SystemsThere 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.

EndoskeletonThe 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 water-filled 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 JointRestrict movement to a single plane (Ex: joint between the femur and tibia)

• Pivot JointAllows us to rotate (Ex: the joint at the forearm and the elbow)

• Gliding JointJoints in between vertebrae

• Condyloid JointJoint near throat and back of neck

Hinge Joint

Pivot 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

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The End