36 1 The Skeletal System -...

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Copyright Pearson Prentice Hall

36–1 The Skeletal System


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The Skeleton

All organisms need structural support.

Unicellular organisms have a cytoskeleton.

Multicellular animals have either an exoskeleton

(arthropods) or an endoskeleton (vertebrates).


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The Skeleton

The human skeleton is composed of bone.

Bones and other connective tissues, such as

cartilage and ligaments, form the skeletal system.


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The Skeleton

The skeleton:

• supports the body.

• protects internal organs.

• provides for movement.

• stores mineral reserves.

• provides a site for blood cell formation.


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The Skeleton

Axial Skeleton

Skull

Sternum

Ribs

Vertebral

column

The axial skeleton

(blue) supports the

central axis of the

body.


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The Skeleton

Clavicle Scapula

Humerus

Radius Pelvis Ulna Carpals Metacarpals

Phalanges Femur

Patella

Fibula

Tibia Tarsals

Metatarsals

Phalanges

Appendicular Skeleton

The bones of the arms

and legs, along with

the bones of the pelvis

and shoulder area

form the appendicular

skeleton (grey).


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Structure of Bones

Bones are a solid network of living cells

and protein fibers that are surrounded by

deposits of calcium salts.


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Structure of Bones

Bone marrow

Periosteum

Spongy bone

Compact bone

Haversian canal

Compact bone

Spongy bone

Periosteum

Osteocyte

Artery

Vein


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Structure of Bones

The bone is surrounded by a tough layer of

connective tissue called the periosteum.

Blood vessels in the periosteum carry oxygen and

nutrients to the bone.


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Structure of Bones

Beneath the periosteum is a thick layer of compact

bone.

Running through compact bone is a network of tubes

called Haversian canals that contain blood vessels

and nerves.


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Structure of Bones

Spongy bone is found inside the outer layer of

compact bone.

Spongy bone is also found in the ends of long bones

and in the middle of short, flat bones.

Spongy bone adds strength without adding mass.


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Structure of Bones

Osteocytes, or mature bone cells, are embedded in

the bone matrix.

Other bone cells—osteoclasts and osteoblasts—line

the Haversian canals and the surfaces of compact

and spongy bone.

• Osteoclasts break down bone.

• Osteoblasts produce bone.


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Structure of Bones

Bone marrow is a soft tissue inside the cavities

within bones.

There are two types of bone marrow:

• Yellow marrow is made up of fat cells.

• Red marrow produces red blood cells, some

kinds of white blood cells, and platelets.


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Development of Bones


The skeleton of an embryo is composed of

cartilage.

Cartilage is a strong connective tissue that

supports the body and is softer and more flexible

than bone.


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Cartilage is replaced by bone during the process of

bone formation called ossification.

Bone tissue forms as osteoblasts secrete mineral

deposits.

When the osteoblasts become surrounded by bone

tissue, they mature into osteocytes.


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Many long bones have growth plates at either end.

Growth of cartilage at these plates causes bones to

lengthen. Gradually, this cartilage is replaced by

bone tissue.

By early adulthood, cartilage in the growth plates is

replaced by bone, the bones become ossified, and

growth stops.


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Types of Joints

Types of Joints

A place where one bone attaches to another bone

is called a joint.

Joints permit bones to move without damaging

each other.


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Types of Joints

Depending on its type of movement, a

joint is classified in one of three ways:

immovable, slightly movable, or freely

movable.


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Types of Joints

Immovable Joints

Immovable joints, called fixed joints, allow no

movement.

The bones are interlocked and held together by

connective tissue, or they are fused together.

Places where bones in the skull meet are

examples of immovable joints.


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Types of Joints

Slightly Movable Joints

Slightly movable joints permit a small amount of

restricted movement.

Slightly movable joints are found in the joints

between adjacent vertebrae.


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Types of Joints

Freely Movable Joints

Freely movable joints permit movement in one or more directions.

Four common freely movable joints are:

• ball-and-socket joints

• hinge joints

• pivot joints

• saddle joints


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Types of Joints

Ball-and-socket joints permit movement in many

directions.

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Types of Joints

Hinge joints permit back-and-forth motion.


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Types of Joints

Pivot joints allow one bone to rotate around another.


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Types of Joints

Saddle joints permit one bone to slide in two

directions.


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Structure of Joints

Structure of Joints

In freely movable joints, cartilage covers the

surfaces where two bones come together.

Joints are also surrounded by a fibrous capsule

that holds the bones together while still allowing

them to move.


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Structure of Joints

Knee Joint

Muscle

Tendon

Femur

Patella

Bursa

Ligament Synovial fluid

Cartilage

Fat

Fibula

Tibia


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Structure of Joints

Connective tissue called ligaments hold bones

together in joints and are attached to membranes that

surround bones.

Synovial fluid forms a thin lubricating film over the

surface of the joint.

Synovial fluid enables the bones to slide past each

other more smoothly.


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Structure of Joints

In some freely movable joints small sacs of synovial

fluid called bursae form.

A bursa reduces the friction between bones of a joint

and also acts as a shock absorber.


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Skeletal System Disorders

Skeletal System Disorders

Excessive strain on a joint may produce inflammation, in which excess fluid causes swelling, pain, heat, and redness.

• Inflammation of a bursa is called bursitis.

• Inflammation of the joint itself is called arthritis.

Another skeletal system disorder is osteoporosis. Osteoporosis is caused by a loss of calcium in the bone.

36 1 The Skeletal System -...

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