Chapter 6: The Skeletal System Overview (2nd half)

When do bones stop growing?

During adolescence

Which bones can continue growing slowly throughout life?

Some facial bones

What are the five zones of the epiphyseal plate?

1. Resting zone

2. Proliferation (growth) zone

3. Hypertrophic zone

4. Calcification zone

5. Ossification zone

What is the resting zone?

Relatively inactive cartilage on the epiphyseal side of the epiphyseal plate

What is the proliferation (growth) zone?

Chondrocytes divide rapidly, producing new cartilage on the diaphyseal side

What happens in the hypertrophic zone?

Chondrocytes enlarge, and their lacunae expand

What happens in the calcification zone?

Cartilage matrix calcifies and chondrocytes die and deteriorate

What happens in the ossification zone?

Osteoclasts erode calcified cartilage, and osteoblasts add new bone

How does a long bone grow in length?

• New cartilage pushes the epiphysis away from the diaphysis

• The cartilage is replaced by bone on the diaphyseal side

What do calcified cartilage spicules eventually become?

Spongy bone

What happens to the medullary cavity as spicules are eroded?

It gets larger

What happens near the end of adolescence?

Chondroblasts divide less often and the epiphyseal plate gets thinner

What happens when the epiphyseal plate closes?

It is replaced by bone, and longitudinal growth stops

Around what age does the epiphyseal plate close in females?

Around 18 years old

Around what age does the epiphyseal plate close in males?

Around 21 years old

What hormone stimulates bone growth during childhood?

Growth hormone

What do testosterone and estrogen do during puberty?

They cause growth spurts and later close the epiphyseal plate

What happens during bone remodeling?

Old bone is removed and new bone is added

What does thyroid hormone do for bone growth?

It helps control growth hormone activity and proper bone proportions

What happens if there is too much or too little of these hormones?

Abnormal skeletal growth can occur

When does bone deposition occur?

Where bone is injured or where extra strength is needed

What nutrients are needed for bone deposition?

Protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese

What enzyme is needed for bone mineralization?

Alkaline phosphatase

Why is calcium important in the body?

For nerve impulses, muscle contraction, blood clotting, gland and nerve cell secretion, and cell division

What are the two parts of bone remodeling?

Bone deposition and bone resorption

What do osteoblasts and osteoclasts do during bone remodeling?

Osteoblasts add bone and osteoclasts remove bone

What controls bone remodeling?

Hormones and mechanical or gravitational forces

What happens when blood calcium levels rise?

The thyroid releases calcitonin, which promotes calcium storage in bone

What happens when blood calcium levels fall?

The parathyroid glands release PTH, which causes osteoclasts to break down bone and release calcium into the blood

What does PTH do?

Causes osteoclasts to break down bone and release calcium into the blood

What does calcitonin do?

Promotes calcium storage in bone

What is Wolff’s law?

Bone grows or remodels in response to the forces placed on it

Where are long bones thickest?

In the middle of the shaft, where bending stress is greatest

Where are curved bones thickest?

Where they are most likely to buckle

How do trabeculae form?

Along lines of stress

Where do large bony projections form?

Where strong muscles attach

What is a nondisplaced fracture?

Bone ends stay in their normal position

What is a displaced fracture?

Bone ends are out of normal alignment

What is a complete fracture?

Bone breaks all the way through

What is an incomplete fracture?

Bone does not break all the way through

What is a linear fracture?

Break runs parallel to the long axis of the bone

What is a transverse fracture?

Break runs perpendicular to the long axis of the bone

What is a compound fracture?

Bone ends penetrate the skin (goes thru skin)

What is a simple fracture?

Bone ends do not penetrate the skin (doesn’t go thru skin)

What is a comminuted fracture?

Bone breaks into 3 or more pieces; common in older adults

What is a spiral fracture?

Ragged break caused by excessive twisting; common in sports injuries

What is a depressed fracture?

Broken bone is pushed inward; common in skull fractures

What is a compression fracture?

Bone is crushed; common in porous bones

What is an epiphyseal fracture?

Epiphysis separates from the diaphysis along the epiphyseal line

What is a greenstick fracture?

One side of the bone breaks while the other side bends; common in children

What is reduction?

Realigning broken bone ends

What is a closed reduction?

A physician moves the bone ends back into place without surgery

What is an open reduction?

Surgery uses pins or wires to hold the bone ends in place

Why is a cast or traction used after a fracture?

To keep the bone still while it heals

What affects how long a fracture takes to heal?

The severity of the break, the bone broken, and the person's age

What are the four stages of fracture repair?

1. Hematoma forms

2. Fibrocartilaginous callus forms

3. Bony callus forms

4. Bone remodeling occurs

What happens when a hematoma forms?

Blood vessels tear, blood clots at the fracture site, and the area becomes swollen, painful, and inflamed

What happens when the fibrocartilaginous callus forms?

A soft callus forms, capillaries grow in, and cells clean up damaged tissue

What do fibroblasts do during fracture repair?

They make collagen fibers that connect the broken bone ends

What do osteoblasts do during fracture repair?

They begin forming new spongy bone

What happens during bony callus formation?

New bone trabeculae form and the soft callus becomes a hard bony callus

When does the bony callus begin to form?

About 3–4 weeks after the injury

How long does it take for a firm bone union to form?

About 2–3 months after the injury

What is Paget’s disease?

A bone disease with an unknown cause, possibly viral

Where does Paget’s disease usually occur?

Spine, pelvis, femur, and skull

How is Paget’s disease treated?

With drugs such as Didronate and Fosamax

What does mesoderm form?

Mesenchymal cells that form membranes and cartilage

Why can sonograms show fetal age?

The embryonic skeleton develops on a predictable schedule

What is the condition of most long bones at birth?

Mostly ossified, except the epiphyses

By what age are nearly all bones ossified?

By age 25

What happens to bones in old age?

Bone loss becomes greater than bone formation

What can affect bone mass and osteoporosis risk?

A gene related to vitamin D docking

What do osteoblasts and fibroblasts do during fibrocartilaginous callus formation?

Migrate to the fracture site and begin bone reconstruction

What do osteoblasts farthest from capillaries produce during fracture repair?

An outward-bulging cartilaginous matrix that later calcifies

What is removed during bone remodeling after a fracture?

Excess material outside the bone shaft and inside the medullary canal

What happens to compact bone during fracture remodeling?

It rebuilds the walls of the bone shaft

What is the current status of rickets in the United States?

Essentially eliminated, with only isolated cases remaining

How can a breastfed infant develop rickets?

A vitamin D-deficient mother may cause vitamin D deficiency in the infant

What is osteoporosis?

Bone resorption occurs faster than bone deposition

Which bone is most vulnerable to osteoporosis?

Spongy bone of the spine

Who is most likely to develop osteoporosis?

Postmenopausal women

Why are bones with osteoporosis more likely to fracture?

They become fragile enough to fracture from sneezing or stepping off a curb