Chapter 6: Bones and Bone Tissue

What makes up the skeletal system?

Bones, joints, and supporting tissues.

What are the main organs of the skeletal system?

Bones.

What tissues are found in bones?

Osseous tissue, dense regular and irregular connective tissue, and bone marrow.

What are the six functions of the skeletal system?

Protection, mineral storage and acid-base homeostasis, blood cell formation, fat storage, movement, and support.

What is the protective function of the skeletal system?

Bones protect internal structures.

What is stored in bones?

Minerals.

What is hematopoiesis?

Blood cell formation.

Where does blood cell formation occur?

Red bone marrow.

Where is fat stored in bones?

In yellow bone marrow of the medullary cavity.

How do bones contribute to movement?

Bones provide sites for skeletal muscle attachment.

How do bones provide support?

They support weight and provide a structural framework.

How are bones classified by shape?

Long, short, flat, irregular, and sesamoid.

What are long bones?

Bones that are longer than they are wide.

What are examples of long bones?

Most bones in the arms and legs.

What are short bones?

Bones that are roughly cube-shaped.

What are examples of short bones?

Carpals and tarsals.

What are flat bones?

Thin and broad bones.

What are examples of flat bones?

Ribs, pelvis, sternum, and flat bones in the skull.

What are irregular bones?

Bones with irregular shapes.

What are examples of irregular bones?

Vertebrae and certain skull bones.

What are sesamoid bones?

Bones located within tendons.

What is an example of a sesamoid bone?

The patella, or kneecap.

What is the periosteum?

A membrane that surrounds the outer surface of a bone.

What are perforating fibers also called?

Sharpey's fibers.

What is the function of perforating fibers?

They anchor the periosteum firmly to the bone surface.

What is the diaphysis?

The shaft of a long bone.

What is an epiphysis?

An end of a long bone; the ends are proximal and distal.

What is articular cartilage?

Hyaline cartilage.

What does the marrow cavity contain?

Red or yellow bone marrow.

What is the endosteum?

A thin membrane lining the marrow cavity.

What is compact bone?

The hard, dense outer region of bone.

What does compact bone help bones resist?

Stress, including compression and twisting.

What is spongy bone also called?

Cancellous bone.

Where is spongy bone found?

Inside cortical bone.

What is the structure of spongy bone?

A honeycomb-like framework of bony struts.

What forces can spongy bone resist?

Forces coming from many directions.

What are epiphyseal lines?

Remnants of epiphyseal plates that separate the epiphyses from the diaphysis.

What are epiphyseal plates?

Growth plates made of hyaline cartilage found in developing bones of children.

What is diploë?

Two outer layers of thin compact bone with a middle layer of spongy bone.

What are sinuses in bone?

Air-filled spaces that reduce bone weight.

What is the inorganic portion of bone's extracellular matrix?

About 65%; it consists of minerals, including hydroxyapatite salts of calcium and phosphorus.

What is the organic portion of bone's extracellular matrix?

About 35%; it includes osteoid, collagen fibers, and usual extracellular matrix.

What is osteoid?

The organic portion of bone matrix.

What are the four types of bone cells listed in the slides?

Osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

What do osteogenic cells do?

Differentiate into osteoblasts.

What do osteoblasts do?

Deposit bone.

What are osteocytes?

Mature bone cells located in lacunae.

What do osteoclasts do?

Resorb bone.

What do osteoclasts secrete?

Acid and enzymes.

What is an osteon also called?

A Haversian system.

What are lamellae?

Concentric rings of thin layers of bone.

What is the central canal?

A canal that contains blood vessels and nerves.

What are lacunae?

Spaces that house osteocytes.

What are canaliculi?

Little canals.

What are perforating canals also called?

Volkmann's canals.

How are perforating canals arranged in relation to central canals?

They run perpendicular to central canals.

How is spongy bone organized?

It is usually not weight-bearing and is not organized into osteons.

What are trabeculae?

Bony struts in spongy bone.

What is ossification also called?

Osteogenesis.

What is ossification?

The process of bone formation.

When does ossification begin?

During the embryonic period and continues throughout adulthood.

What are the two types of ossification?

Intramembranous and endochondral ossification.

What does intramembranous ossification form?

Many flat bones, including bones of the skull and clavicles.

Where does intramembranous ossification occur?

Within a mesenchymal membrane.

Which type of bone forms first during intramembranous ossification?

Spongy bone forms before the outer compact bone layers.

What does intramembranous ossification form?

A primary ossification center.

What are fontanels?

Areas of incomplete intramembranous ossification.

Which bones develop through endochondral ossification?

All bones below the head except the clavicles.

What do bones begin as during endochondral ossification?

A hyaline cartilage template or model.

What cells and materials make up the hyaline cartilage model?

Chondrocytes, collagen, and extracellular matrix.

What surrounds the hyaline cartilage model?

Connective tissue called perichondrium.

What happens to cartilage during endochondral ossification?

The cartilage breaks down and is replaced by bone.

What forms around the cartilage model during endochondral ossification?

A collar that becomes periosteum.

Where is the primary ossification center located?

In the middle of the diaphysis.

Where do secondary ossification centers form?

At the epiphyseal ends.

Where does cartilage remain after endochondral ossification?

At the epiphyseal plate and articular ends.

What is osteoporosis?

A disease in which bones become weak and brittle due to inadequate inorganic matrix.

What can osteoporosis increase the risk of?

Fractures and a decreased rate of healing.

How is osteoporosis diagnosed?

By bone density measurement.

What factors are listed as causes of osteoporosis?

Calcium and/or vitamin D deficiency, female gender, advanced age, lack of exercise, hormonal factors, genetic factors, and other diseases.

What prevention methods for osteoporosis are listed?

Balanced diet, supplements, weight-bearing exercise, and ERT.

What treatments for osteoporosis are listed?

Drugs that inhibit osteoclasts or stimulate osteoblasts.

How do long bones increase in length?

Through longitudinal growth.

Which cells divide during longitudinal bone growth?

Chondrocytes in the epiphyseal plate.

Where does bone growth take place at the epiphysis?

On the side closest to the diaphysis.

What is the zone of reserve cartilage?

The zone closest to the epiphysis; it contains cells not directly involved in bone growth but that can be recruited for cell division if needed.

What happens in the zone of proliferation?

Chondrocytes actively divide through endochondral ossification.

What happens in the zone of hypertrophy and maturation?

It contains mature chondrocytes.

What happens in the zone of calcification?

It contains dead chondrocytes, some of which have been calcified; calcified cartilage is replaced with bone.

What happens in the zone of ossification?

It consists of calcified chondrocytes and osteoblasts.

How long does longitudinal growth continue?

As long as mitosis continues in the zone of proliferation.

Around what ages does the mitotic rate in the epiphyseal plate slow?

Around ages 12–15.

Between what ages does the epiphyseal plate close?

Between ages 18–21.

What is an epiphyseal line?

A calcified remnant of the epiphyseal plate.

What is appositional growth?

Bone growth in width.

Which cells lay down new bone during appositional growth?

Osteoblasts.

What forms during appositional growth instead of immediate osteons?

New circumferential lamellae.

Can bones increase in width after epiphyseal plates close?

Yes. Bones may continue to increase in width after they stop lengthening.

What is achondroplasia?

The most common cause of dwarfism; it involves a gene defect that affects cartilage growth.

How does achondroplasia affect endochondral ossification?

An abnormal growth factor receptor on cartilage interferes with the hyaline cartilage model.