Slide 1 of 40 Copyright Pearson Prentice Hall 32–1 The Skeletal System.

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Copyright Pearson Prentice Hall

32–1 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 canalCompact 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 as 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 fluidCartilage

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.

Slide 1 of 40 Copyright Pearson Prentice Hall 32–1 The Skeletal System.

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