CH. 6 Bones

What are the five main functions of the skeletal system?

Support, storage of minerals (calcium and phosphate) blood cell production, protection, and leverage

What is a foramen?

A tunnel through bone that provides a passageway for blood vessels or nerves Ex. nutrient foramen in long bones

What is the medullary cavity?

The hollow space within the diaphysis of a long bone, filled with bone marrow

What is inside the medullary cavity?

Red bone marrow (produces blood cells) and yellow bone marrow (stores fat).

What is the diaphysis?

The shaft of a long bone; a long, tubular structure composed mostly of compact bone

What is the metaphysis?

The narrow zone connecting the epiphysis to the diaphysis

What is the epiphysis?

The expanded area at each end of a long bone, mostly spongy bone, articular cartilage 

What is articular cartilage?

Cartilage covering portions of the epiphysis that form joints; avascular and relies on diffusion from synovial fluid for nutrients.

What are osteoprogenitor cells?

Mesenchymal (stem) cells that divide to produce cells that differentiate into osteoblasts; important in fracture repair

Where are osteoprogenitor cells found?

In the inner lining of the periosteum, the endosteum lining the medullary cavity, and in passageways containing blood vessels.

What do osteoblasts do?

They produce new bony matrix through osteogenesis (ossification); they secrete osteoid, which later becomes mineralized bone

What happens to an osteoblast when it becomes surrounded by bone matrix?

It becomes an osteocyte

What do osteocytes do?

Mature bone cells that maintain the protein and mineral content of the matrix, and help repair damaged bone.

Where are osteocytes found?

In lacunae between layers of matrix (lamellae), connected to other cells by canaliculi.

What do osteoclasts do?

Giant multinucleated cells that remove and remodel bone matrix by releasing acids and enzymes to dissolve it  a process called osteolysis.

What type of stem cell do osteoclasts come from?

The same stem cells that produce macrophages.

What is a lacuna (plural: lacunae)?

A small pocket between layers of matrix that contains a single osteocyte.

What is an osteon?

The functional unit of compact bone, made of concentric lamellae arranged around a central canal.

What are canaliculi?

Narrow passageways that connect lacunae to one another and to blood vessels, allowing the exchange of nutrients and waste.

What are lamellae?

Layers of bone matrix arranged around the central canal; they can be concentric, interstitial, or circumferential.

Is the matrix of bone dense?

Yes — it is very dense due to deposits of calcium salts.

What is the bone matrix made of?

About one-third collagen fibers (for flexibility) and two-thirds calcium phosphate crystals that form hydroxyapatite (for strength).

Do canaliculi allow for the exchange of nutrients?

Yes — they permit diffusion of nutrients, gases, and waste between blood vessels and osteocytes.

How are Rickets prevented?

By adequate vitamin D intake, which is required for calcium and phosphate absorption.

What is appositional growth?

Growth that increases the diameter of existing bones as osteoprogenitor cells in the periosteum differentiate into osteoblasts that add new bone layers.

During appositional growth, what happens inside the bone?

Osteoclasts remove bone matrix at the inner surface to enlarge the medullary cavity.

After embryogenesis, how do long bones continue to grow?

They grow in length at the epiphyseal cartilage (growth plate) located in the metaphysis.

How does endochondral ossification begin?

Bone replaces a cartilage model; chondrocytes enlarge, cartilage calcifies, and blood vessels bring in osteoblasts that form bone.

Where does endochondral ossification start?

In the shaft (diaphysis) at the primary ossification center.

What forms at the ends of long bones during endochondral ossification?

Secondary ossification centers in the epiphyses.

In intramembranous ossification, which cell type condenses to form osteoblasts?

Mesenchymal (stem) cells within embryonic or fibrous connective tissue.

What type of bones are formed by intramembranous ossification?

Dermal (membrane) bones such as the skull, mandible, and clavicle.

How do bones help regulate calcium levels in the blood?

Osteoclasts release calcium into the blood by breaking down bone matrix, while osteoblasts remove calcium from the blood to deposit it into new bone.

What are the three organs that control calcium levels?

Bones, intestines, and kidneys.

What does parathyroid hormone (PTH) do?

It increases blood calcium levels by stimulating osteoclasts, increasing intestinal absorption (via calcitriol), and reducing calcium excretion by the kidneys.

What does calcitonin do?

It decreases blood calcium levels by inhibiting osteoclasts, decreasing calcium absorption in intestines, and increasing calcium excretion by kidneys.

Where is parathyroid hormone (PTH) released from?

The parathyroid glands.

Where is calcitonin released from?

C cells of the thyroid gland.

What happens to bones when calcium is released into the blood?

They become weaker.

What happens when calcium is deposited into bone?

Bones become stronger.

What is a fracture?

A crack or break in a bone caused by extreme mechanical stress.

What must survive for a fracture to heal properly?

The blood supply and cellular parts of the periosteum and endosteum.

What are the four major steps in bone fracture repair?

1. Fracture hematoma forms, 2. Internal and external callus form, 3. Cartilage in external callus replaced by bone, 4. Bone remodeling completes repair.

What is the difference between a closed and open fracture?

Closed (simple) fractures do not break the skin; open (compound) fractures project through the skin and risk infection and bleeding.

What is a transverse fracture?

A break across the long axis of the bone.

What is a spiral fracture?

A twisting fracture that spreads along the length of the bone.

What is a displaced fracture?

Bone fragments are no longer in normal alignment.

What is a nondisplaced fracture?

Bone retains its normal alignment.

What is a compression fracture?

Occurs in vertebrae subjected to extreme stress, such as from a fall.

What is a greenstick fracture?

One side of the bone shaft breaks and the other bends; common in children.

What is a comminuted fracture?

The bone is shattered into several fragments.

What is an epiphyseal fracture?

A break along the growth plate; if not treated properly, it can stop growth at that site.

What is a Pott fracture?

A break at the ankle affecting both bones of the leg.

What is a Colles fracture?

A break in the distal radius, often from trying to catch yourself during a fall.