Week 5 - Bone Physiology

Question 1

What is included in the skeletal system?

Answer 1

Bones
Cartilage
Joints
Ligaments
Other connective tissues

Question 2

What are the functions of the skeletal system?

Answer 2

• Support against gravity
• Leverage for muscle action
• Protection of soft internal organs
• Storage of:
Calcium, phosphorous
Fat
• Blood cell production

Question 3

How are bones classified by their shape?

Answer 3

Flat bones
• Internal & external table
separated by diploë

Long bones
• Longer than they are wide

Short bones
• width≈length

Irregular bones
• Complex shapes

Sutural bones
• Between skull bones

Sesamoid bones
• Small, develop in tendons

Question 4

What are the features of a typical long bone?

Answer 4

Diaphysis (shaft) - compact (dense) bone, medullary cavity
Epiphyses (ends) - Trabecular (spongy) bone
Articular cartilage

Question 5

What is bone (osseus) tissue made from?

Answer 5

Ground substance - Two thirds of bone matrix. Minerals, predominantly crystals of hydroxyapatite Ca10(PO4)6(OH)2 with other calcium salts and ions.
Protein - One third of bone matrix. Most abundant protein type I collagen fibres.
Bone cells - Only 2% of bone mass

Question 6

How are Osteocytes created?

Answer 6

• Mesenchymal stem cells => => osteoblasts => osteocytes

Question 7

What is an osteoblast?

Answer 7

An immature bone cell that secretes matrix proteins.

Question 8

What is an osteocyte?

Answer 8

Mature bone cell that maintains the bone matrix.

Question 9

What is an osteoclast?

Answer 9

A multinucleate cell that secretes acids and enzymes to dissolve bone matrix.

Question 10

Describe the microscopic structure of compact bone?

Answer 10

Osteon - Basic functional unit, columnar, strong in long axis. Several ostensibly in compact bone.
Central Canal - tunnel for blood vessels
Lamellae - Concentric layers of matrix
Lacunae - contains osteocytes

Question 11

Describe the microscopic features of trabecular (spongey) bone

Answer 11

No Osteons
Trabecular - arches, rods, plates of bone. Branching network, strong in many directions.
Red marrow - Between trabecular. Forms red blood cells, provides nutrients to osteocytes.
Yellow bone marrow - Found in medullary cavity, stores fat.

Question 12

What is periosteum?

Answer 12

Membrane outside bone consisting of:
Outer(fibrous) layer - Collagen fibres continuous with bone, ligaments, tendons, joint capsule.
Inner (cellular) layer

also contains lymphatic vessels and nerves

Question 13

What is endosteum?

Answer 13

Membrane lining bone which has an incomplete cellular layer. Lines of medullary cavity, central canals and trabeculae.

Question 14

What are three types of bone formation and growth?

Answer 14

Intramembranous ossification - flat bone formation
Endochrondral ossification - formation from cartilage model
Appositional bone growth - growth in width.

Question 15

What are the steps of intramembranous ossification?

Answer 15

1. Mesenchymal cells differentiate into osteoblasts.
2. Ossification forms spicules of bone.
3. Trabecular bone formed.
4. Remodeled into compact bone

Question 16

What happens in endochronal ossification?

Answer 16

1. Chondrocytes within calcifying matrix enlarge then die
2. Osteoblasts cover the shaft in a thin layer of bone
3. Blood vessels and osteoblasts penetrate to form a primary ossification centre
4. Primary ossification centre enlarges.
5. Secondary ossification centres formed at epiphyses.

Question 17

What happens in appositional bone growth?

Answer 17

Bone deposited by osteoblasts which pushes the other bone outwards

Question 18

What is needed for normal bone growth?

Answer 18

Minerals - calcium, phosphate
Vitamins - Vitamin D3 and others
Hormones - Growth hormone, sex hormones, thyroid hormone, others

Question 19

What occurs in bone remodelling?

Answer 19

Continuous breakdown and reforming of bone tissue - resorption by osteoclasts, formation by osteoblasts
Adaptation to loading - osteocytes detect forces in bone
Calcium homeostasis - 99% of calcium stored in bones. Hormones control storage/release
. PTH stimulates bone resorption to release calcium.
. Calcitonin stimulates bone formation to store calcium.

Question 20

What occurs during fracture repair?

Answer 20

1. Bleeding and formation of clot (fracture hematoma).
2. Formation of external callus (cartilage) and internal callus (spongy bone).
3. External callus replaced by bone. Internal callus united broken ends
4. Initial swelling eventually remodelled.