Bone Growth and Adaptation

Question 1

What is endochondral ossification?

Answer 1

• bone development from hyaline cartilage template
• forms most of the bones in the body

Question 2

What is intramembranous ossification?

Answer 2

• bone development within fibrous connective tissue
• mesenchymal cells form osteoblasts and osteocytes
• forms mandible bones, flat bones of the skull
• also how endochondral bones increase thickness
• important in bone healing

Question 3

What does physis and growth do?

Answer 3

• allows for continued longitudinal growth of bone

Question 4

What are the layers of cartilage in endochonral ossification?

Answer 4

1. reserve/ resting cartilage (normal cartilage)
2. proliferating zones (cells dividing rapidly by mitosis)
3. hypertrophic zone (alkaline phosphate section)
4. calcification zone (cells dying)
5. ossification zone ( invasion of vessels from medullary spaces bringing osteoblasts)

Question 5

Describe the process of closing growth plates

Answer 5

• around puberty, new cartilage stops being made
• physis ossifies, uniting diaphysis and epiphysis
• no further longitudinal growth
• time of growth plate closure varies between physis, bone, species and breed
• the physis can sometimes still be visible as a line

Question 6

What does endochondral ossification do?

Answer 6

• allows longitudinal growth in bones

Question 7

What does intramembranous ossification do?

Answer 7

• allows circumferential growth of bone
• osteoblast in the periosteum deposit bone around periosteal vessels
• new layers of bone added on outer surface

Question 8

what in combination creates an increase in bone circumference?

Answer 8

• periosteal new bone formation (osteoblasts)
• endosteal bone reabsorption (osteoclasts)

Question 9

Bone can be classified by the arrangement of what?

Answer 9

• collagen fibres in the matrix

Question 10

What is lamellar bone?

Answer 10

• collagen fibres organised in parallel layers
• dense (stronger)
• typical of normal adult skeletal structure

Question 11

What is woven bone?

Answer 11

• irregular collagen fibres
• more cellular
• weaker
• seen in rapid growth such as growing animals, fracture healing
• usually later replaced by lamellar bone

Question 12

How are calcium and phosphate acquired?

Answer 12

• through diet

Question 13

How are calcium and phosphate filtered?

Answer 13

• filtered by the kidney and reabsorbed before lost in urine

Question 14

Where are calcium and phosphate stored?

Answer 14

• stored in bone
• 99% of calcium
• 85% of phosphate

Question 15

What is calcitriol?

Answer 15

• calcitriol is a hormone, and the active form of vitamin D

Question 16

What does calcitriol act to do?

Answer 16

• increase calcium and phosphate absorption from the small intestine
• enhance reabsorption of calcium and phosphate by kidney
• stimulates release of calcium from bones

Question 17

What does parathyroid hormone (PTH) do?

Answer 17

• increases reabsorption of of calcium from kidney
• reduce reabsorption of phosphate from kidney
• increases conversion of vitamin D to calcitriol

Question 18

When is PTH released?

Answer 18

• when blood calcium levels fall

Question 19

When is calcitonin released?

Answer 19

• when blood calcium levels rise

Question 20

What does calcitonin do?

Answer 20

• inhibits reabsorption of calcium from bone (osteoclasts)
• inhibits reabsorption of calcium and phosphate from kidney

Question 21

What does growth hormone do?

Answer 21

• stimulates bone turnover

Question 22

What does sex hormones oestrogen and testosterone do in bones?

Answer 22

• inhibits bone reabsorption
• affect physis closure

Question 23

What does Glucocorticoids do?

Answer 23

• inhibit osteoblasts (bone loss)

Question 24

What does TH (thyroid hormone) do?

Answer 24

• increased reabsorption of bone

Question 25

When do animals require more calcium?

Answer 25

• young animals growing
• pregnant and lactating animals
• laying birds

Question 26

Why remodel bones?

Answer 26

• to meet mechanical demands placed on it (wolff’s law)
• maintain the tissue
• mineral homeostasis (calcium and phosphate store)

Question 27

What type of animal has the quickest bone turnover?

Answer 27

• young animals