Lecture 23 - Bone Growth And Repair

Question 1

Ossification (osteogenesis)

Answer 1

Process of bone tissue formation

Question 2

Intramembranous ossification

Answer 2

When bone develops from fibrous membrane.

These bones called membrane bones
No cartilage involved
This process forms most of the skull and clavicle bones

Question 3

Intramembranous ossification steps

Answer 3

1. Development of ossification centre: Osteoblasts secrete organic extracellular matrix.
2. Calcification. Calcium and other mineral salts are deposited and extracellular matrix calcifies (hardens).
3. Formation of trabeculae: Extracellular matrix develops into trabeculae that fuse to form spongy bone.
4. Development of the periosteum: Mesenchyme at the periphery of the bone develops into the periosteum.

Question 4

Endochondrial ossification

Answer 4

when bone forms by replacing hyaline cartilage, which forms most of the skeleton.

These bones are called cartilage (endochondral) bones.

begins at primary ossification centre in centre of shaft. Blood vessels infiltrate perichondrium, converting it to periosteum, and mesenchymal cells specialize into osteoblasts.

Question 5

Endochondrial ossification steps

Answer 5

1. Development of cartilage model: Mesenchymal cells develop into chondroblasts, which form the cartilage model
2. Growth of cartilage model: Growth occurs by cell division of chondrocytes
3. Development of primary ossification center: In this region of the diaphysis, bone tissue replaces most of the cartilage
4. Development of the medullary (marrow) cavity: Bone breakdown by osteoclasts forms the medullary cavity.
5. Development of secondary ossification centers: These occur in the epiphyses of the bone.
6. Formation of articular cartilage and epiphyseal plate: Both structures consist of
   hyaline cartilage.

Question 6

Growth hormone

Answer 6

most important hormone in stimulating epiphyseal plate activity in infancy and childhood.

Question 7

Thyroid hormone

Answer 7

modulates activity of growth hormone, ensuring proper proportions.

Question 8

Testosterone and estrogens

Answer 8

promote adolescent growth spurts and also end growth by inducing epiphyseal plate closure.

Question 9

Growth in length of long bones

Answer 9

occurs at the ossification zone through the rapid division of chondrocytes, calcification and deterioration of cartilage at the bottom of the columns and subsequent replacement by bone tissue.

Question 10

What happens to epiphyseal plate near end of adolescents?

Answer 10

It thins and is replaced by bone

Question 11

When does epiphyseal closure occur?

Answer 11

When epiphysis and diaphysis fuse

Question 12

Growth in width or thickness of bones

Answer 12

occurs through appositional growth due to deposition of bone matrix by osteoblasts beneath the periosteum

Osteoclasts remove bone from the endosteal surface, so the bones do not get too heavy.

Bones thicken in response to increased stress from muscle activity or added weight. This process usually involves more building up than breaking down, which leads to thicker, stronger bone while ensuring that the bone is not too heavy.

Question 13

Bone fractures

Answer 13

Position of the bone ends after the fracture.
• Nondisplaced: ends retain normal position.
• Displaced: ends are out of normal alignment.

Completeness of the break.
• Complete: broken all the way through.
• Incomplete: not broken all the way through.

Whether the skin is penetrated.
• Open (compound): skin is penetrated.
• Closed (simple): skin is not penetrated.

Question 14

Bone break reconstruction steps

Answer 14

1. Hematoma formation

Immediately after bone breaks, torn blood vessels hemorrhage, forming a mass of clotted blood called a hematoma.

The site is swollen, painful, and inflamed.

2. Fibrocartilaginous callus formation

Capillaries grow into the hematoma. Phagocytic cells clear debris. Fibroblasts secrete collagen fibres to connect the broken ends. Fibrocartilaginous Fibroblasts, cartilage, and (soft) callus osteogenic cells begin the Spongy trabeculae reconstruction of bone.

This mass of repair tissue is called a fibrocartilaginous

3. Bony callus formation

Within one week, new trabeculae appear in the fibrocartilaginous callus.
Callus is converted to a bony (hard) callus of spongy bone.

Bony callus formation continues for about 2 months until a firm union forms.

4. Bone remodelling

Bone remodeling begins during bony callus formation and continues for several months.
Excess material on the diaphysis exterior and within medullary cavity is removed.
Compact bone is laid down to reconstruct the shaft walls.

The final structure resembles the original structure and responds to the same mechanical stressors.