Learn: Comprehensive Bone Structure, Function, and Types in Human Anatomy

What are the major functions of bones?

They give the body form, provide support and protection, allow movement, store calcium and phosphorus, and produce major cellular components of blood.

How do bones protect the body?

They protect major tissues and organs, such as the ribs protecting internal organs.

How do bones allow movement?

They provide the framework through which skeletal muscle contractions produce movement.

Why is calcium important to the body?

Calcium is important for bone formation, blood clotting, nerve impulses, and muscle contraction.

What is hematopoiesis?

The production of blood cells.

Where does hematopoiesis occur?

In red bone marrow.

What are the five types of bones?

Long, short, flat, irregular, and sesamoid bones.

What are long bones?

Bones with long shafts and often uniquely shaped ends that form complex joints.

What is an example of a long bone?

The femur.

What are short bones?

Cube- or box-shaped bones that often function in coordinated groups.

What are examples of short bones?

Carpals and tarsals.

What are flat bones?

Relatively flat bones.

What is an example of a flat bone?

The sternum.

What are irregular bones?

Oddly shaped bones that may appear in groups.

What is an example of an irregular bone?

A vertebral bone.

What are sesamoid bones?

Bones that develop within tendons close to joints.

What is an example of a sesamoid bone?

The patella.

What is compact bone?

Dense, solid-looking bone tissue that forms much of the outer portion of bones.

Where is compact bone especially important?

In areas exposed to large amounts of force.

Why aren't bones made entirely of compact bone?

They would be excessively heavy.

What is spongy bone?

Cancellous bone containing open spaces partially filled by a three-dimensional network of fine, needle-like struts.

What are trabeculae?

The fine, needle-like struts that form the network of spongy bone.

What is the function of trabeculae?

Their arrangement greatly enhances the strength of bone.

What are the major parts of a long bone?

Diaphysis, epiphyses, articular cartilage, periosteum, medullary cavity, and endosteum.

What is the diaphysis?

The hollow shaft of a long bone.

What type of bone forms most of the walls of the diaphysis?

Compact bone.

What are the epiphyses?

The enlarged ends of a long bone.

What is one function of the epiphyses?

They form joints and provide areas for muscle attachment.

What is articular cartilage?

A thin layer of hyaline cartilage covering and protecting the articular surfaces of a joint.

What is the periosteum?

A dense, white, fibrous membrane covering the exterior of a bone except at joint surfaces.

What is the medullary cavity?

The hollow space extending through the diaphysis of a long bone.

What is found in the medullary cavity?

Bone marrow.

What is the endosteum?

A thin membrane lining the medullary cavity and the spaces of spongy bone.

Where is the periosteum located?

On the outer surface of bone.

Where is the endosteum located?

On the internal surfaces of bone, including the medullary cavity and spaces of spongy bone.

What does the periosteum contain?

Bone-forming osteoblasts, bone-destroying osteoclasts, and blood vessels.

What is yellow marrow?

Bone marrow made largely of fat or adipose tissue.

What are the major parts of a flat bone?

An external table of compact bone, a layer of spongy bone, and an internal table of compact bone.

How is spongy bone arranged in a flat bone?

It is sandwiched between an internal and external table of compact bone.

What covers the outside of a flat bone?

The periosteum.

What lines the internal spaces of a flat bone?

The endosteum.

What type of marrow fills the spaces of many flat bones?

Red bone marrow.

Do short, irregular, and sesamoid bones have features similar to flat bones?

Yes.

What are the three major components of bone tissue?

Cells, fibers, and extracellular matrix.

What is the major mature cell of bone tissue?

The osteocyte.

What is an osteocyte?

A mature bone cell that does not divide.

What is the most abundant protein in the body and an important fiber in bone?

Collagen.

What are the two major chemical components of bone's extracellular matrix?

Inorganic salts and organic components.

What percentage of bone matrix is inorganic salts?

About two-thirds.

What percentage of bone matrix is organic components?

About one-third.

What gives bone its hardness?

Inorganic mineral salts, especially hydroxyapatite crystals.

What is hydroxyapatite?

A rock-like mineral crystal that provides much of the hardness of bone.

What other minerals are found in bone matrix?

Magnesium, sodium, sulfate, and fluoride.

What are the major organic components of bone matrix?

Collagen fibers and a mixture of proteins and polysaccharides called ground substance.

What is the function of ground substance?

It provides support and adhesion for cellular and fibrous elements.

What gives bone both hardness and flexibility?

The combination of inorganic mineral salts and organic components.

What is the main mineral associated with bone hardness?

Hydroxyapatite.

What are the main minerals associated with hydroxyapatite?

Calcium and phosphorus.

How much of the body's total bone mass is compact bone?

About 80 percent.

What are osteons?

Cylinder-shaped structural units of compact bone, also called Haversian systems.

What are the four major structures of an osteon?

Lamellae, lacunae, canaliculi, and the central canal.

What are lamellae?

Concentric, cylinder-shaped layers of calcified bone matrix.

What are lacunae?

Small spaces containing fluid where bone cells live.

What are canaliculi?

Very fine canals radiating in all directions from the lacunae.

What is the central canal?

A canal running lengthwise through each osteon that contains blood vessels, lymphatic vessels, and nerves.

What is the basic structural unit of compact bone?

The osteon.

Why are canaliculi important?

They provide pathways for nutrients and communication between osteocytes.

How is spongy bone organized?

Into needle-like trabeculae.

Where is spongy bone commonly located relative to compact bone?

It is often found between layers of compact bone.

How do trabeculae strengthen bone?

They are arranged in patterns that provide strength while keeping the bone relatively lightweight.

What are the three major types of bone cells?

Osteocytes, osteoblasts, and osteoclasts.

What are osteoblasts?

Bone-forming cells that secrete important organic components of bone matrix.

Where are osteoblasts found?

In the inner layer of the periosteum.

What do osteoblasts do?

They produce material that forms and hardens new bone.

What are osteoclasts?

Cells that break down old bone by dissolving bone minerals.

Why are osteoclasts important?

They remove old bone and release minerals such as calcium when needed.

What would happen without osteoclast activity?

Old bone would continue accumulating and the skeleton would become increasingly bulky.

What is bone marrow?

A specialized type of soft connective tissue called myeloid tissue.

What is red bone marrow?

Marrow that produces blood cells.

Where is red bone marrow found?

In the medullary cavities of certain long bones and in spaces of spongy bone.

What happens to red bone marrow as we age?

It gradually decreases and is replaced by yellow marrow.

What is yellow bone marrow?

Marrow saturated with fat that can no longer produce blood cells.

What happens to bone marrow during infancy and childhood?

All bone marrow is red marrow.

What happens to red marrow as a person ages?

It gradually becomes yellow marrow.

Can yellow marrow become red marrow again?

Yes, under certain disease conditions such as anemia.

What is a bone marrow transplant?

A treatment used when a patient's bone marrow is severely damaged and unable to perform its functions.

Approximately what percentage of the body's calcium reserves are stored in bones?

About 98 percent.

Why are bones considered a calcium reservoir?

They store large amounts of calcium that can be released or deposited to help maintain blood calcium levels.

Why must blood calcium levels be regulated?

Calcium is essential for bone formation, blood clotting, nerve impulses, and skeletal and cardiac muscle contraction.

What hormones regulate blood calcium levels?

Parathyroid hormone and calcitonin.

What does parathyroid hormone do?

It increases osteoclast activity, causing bone breakdown and releasing calcium into the blood.

When is parathyroid hormone released?

When blood calcium levels are too low.

Where is parathyroid hormone produced?

By the parathyroid glands.

What does calcitonin do?

It stimulates bone deposition by osteoblasts and inhibits osteoclast activity.

When is calcitonin produced?

In response to high blood calcium levels.

Where is calcitonin secreted?

By the thyroid gland.

How does parathyroid hormone affect the calcium "bank" of bone?

It promotes withdrawal of calcium from bone into the blood.

How does calcitonin affect the calcium "bank" of bone?

It helps store calcium in bone by promoting deposition and inhibiting bone breakdown.

What type of feedback loop regulates blood calcium levels?

A negative feedback loop.

What is bone remodeling?

The ongoing process of removing existing bone and adding new bone.