bio. 5 Define the terms ossification and calcification.

Ossification

Bone formation.

It is the process by which bone tissue develops.

Calcification

The deposition of calcium salts into tissue.

This makes the tissue harder.

What is the basic idea of endochondral ossification?

A hyaline cartilage model is gradually replaced by bone.

What type of bones are primarily formed through endochondral ossification?

Most bones of the body, especially long bones.

What is the first step of endochondral ossification?

A hyaline cartilage model forms, having the basic shape of the future bone

What forms around the outside of the diaphysis?

A bone collar.

What happens to the cartilage in the center of the cartilage model?

It calcifies.

What happens after the cartilage calcifies?

Blood vessels enter the area.

Where does the primary ossification center develop?

In the diaphysis.

What develops as the interior of the bone is remodeled?

The medullary cavity.

Where do secondary ossification centers develop?

In the epiphyses.

What cartilage remains after endochondral ossification?

Articular cartilage and the epiphyseal plate.

What is intramembranous ossification?

Bone forms directly from connective tissue, without a cartilage model being replaced.

What bones are especially associated with intramembranous ossification?

Many flat bones of the skull.

What is interstitial growth?

Growth that occurs from within the tissue as cells divide and the tissue expands internally.

What tissue is interstitial growth especially associated with?

Cartilage.

How does interstitial growth contribute to bone lengthening?

At the epiphyseal plate, cartilage grows from within, allowing the long bone to increase in length before that cartilage is replaced by bone.

What is appositional growth?

Growth that occurs by adding new tissue to the surface of an existing structure.

How does appositional growth affect a bone?

It increases the bone's diameter/thickness.

Which cells add new bone during appositional growth?

Osteoblasts add new bone matrix to the bone's surface.

Where does appositional bone growth occur?

At the outer surface of the bone, beneath the periosteum.

What is the epiphyseal plate?

A plate of hyaline cartilage that allows a long bone to increase in length

Where is the epiphyseal plate located?

Near the junction between the epiphysis and metaphysis.

How does the epiphyseal plate allow a long bone to grow longer?

New cartilage is produced on the epiphyseal side. The cartilage then changes and is replaced by bone on the diaphyseal side, pushing the epiphysis farther away from the shaft.

What happens to the epiphyseal plate when longitudinal bone growth stops?

It is replaced by bone and becomes the epiphyseal line.

Why is the epiphyseal plate clinically important?

An injury to the epiphyseal plate can interfere with normal longitudinal bone growth.

What is the correct order of the epiphyseal plate zones?

→ Resting → proliferating → hypertrophic → calcified → ossification.

What happens in the zone of resting cartilage?

Chondrocytes are relatively inactive.

What happens in the zone of proliferating cartilage?

Chondrocytes divide and form columns.

What happens in the zone of hypertrophic cartilage?

Chondrocytes enlarge.

What happens in the zone of calcified cartilage?

The cartilage matrix calcifies, and the chondrocytes die.

What happens in the zone of ossification?

Bone is deposited.

What is bone remodeling?

The continuous process of removing old/damaged bone and replacing it with new bone.

Which cells remove old bone during remodeling?

Osteoclasts resorb (break down) bone.

Which cells form new bone during remodeling?

Osteoblasts produce new bone matrix and build new bone.

What happens after osteoblasts build new bone?

The newly formed bone matrix mineralizes, becoming harder and stronger.

Why does bone remodeling occur continuously?

Bone is living tissue that experiences normal wear, microscopic damage, and changing mechanical demands.

What are the major purposes of bone remodeling?

Repairs microscopic damage, replaces old bone, maintains bone strength, allows bones to adapt to mechanical stress, and helps regulate calcium levels.

: How does remodeling help bones respond to mechanical stress?

Bone can be removed and rebuilt in response to mechanical demands, helping maintain appropriate strength.

How does remodeling contribute to calcium regulation?

Bone resorption releases calcium from bone into the blood, while bone formation can store calcium in bone.

What is the basic sequence of bone remodeling?

→ Osteoclasts resorb old bone → osteoblasts form new bone → new bone mineralizes.

How does exercise affect bone?

Bones respond to mechanical stress. Appropriate mechanical stress stimulates bone remodeling and helps maintain bone strength.

What types of exercise are especially beneficial for bone strength?

Weight-bearing activities such as walking, running, and resistance training.

What is the basic relationship between mechanical stress and bone?

More appropriate mechanical stress → bone adapts to the stress → remodeling helps maintain bone strength.

What nutrients are important for bone development and maintenance?

Calcium, phosphate, vitamin D, and protein

What is calcium's role in bone?

Calcium is an important mineral component of bone.

What is phosphate's role in bone?

Phosphate combines with calcium to form the mineral portion of bone.

Why is vitamin D important for bone?

It helps the digestive tract absorb calcium, making calcium available for bone.

Why is protein important for bone?

Protein is needed to produce the organic components of the bone matrix.

What is the role of growth hormone in the skeleton?

It promotes skeletal growth.

Why are thyroid hormones important for bones?

They are important for normal skeletal growth and development.

How do estrogen and testosterone affect bones?

They contribute to pubertal growth, bone maturation, epiphyseal plate closure, and maintenance of bone mass.

: What is the role of PTH and calcitonin in bone?

They help regulate calcium balance.

What is PTH, where is it produced, and what triggers its release?

PTH (parathyroid hormone) is produced by the parathyroid glands. Its release is triggered primarily by low blood calcium (Ca²⁺).

What is the overall effect of PTH on blood calcium?

PTH raises blood calcium levels.

How does PTH increase blood calcium?

It acts on bone and kidneys and promotes vitamin D activation. Activated vitamin D increases calcium absorption from the intestine.

What is the basic response when blood calcium is low?

Low Ca²⁺ → PTH released → calcium availability increases → blood Ca²⁺ rises.

What is calcitonin, where is it produced, and when is it released?

Calcitonin is produced by C cells of the thyroid gland and is associated with elevated blood calcium.

What is the overall effect of calcitonin on blood calcium?

Calcitonin lowers blood calcium levels.

How does calcitonin help lower blood calcium?

It can decrease osteoclast activity, reducing bone resorption and therefore reducing the release of calcium from bone into the blood.

What is the basic response when blood calcium is high?

→ High Ca²⁺ → calcitonin → decreased osteoclast activity → reduced bone resorption → helps lower blood Ca²⁺.