Bone tissue formation

Question 1

What is bone?

Answer 1

Specialised connective tissue

Complex organ with multiple functiones

Vasculatised - constant exchange with systemic cell population, GF and hormones

Question 2

What are the roles of bones?

Answer 2

Protection and support

Locomotion

Calcium homeostasis and mineral storage

Stem cell niche and hosting of haematopoiesis

Storage of energy

Question 3

How many bones does an adult skeleton have?

Answer 3

206 bones

80 - axial
126 - appendicular

Question 4

Macroscopic structure of bones

Answer 4

Different bones have different specialised shapes according to their function

Living matrix - constant remodelling and adaptation

Variety of forms but similar architecture with varying degrees of specialisation according to mechanical requirements

Question 5

What are the different types of macroscopic structures bones can have?

Answer 5

Flat

Sutural

Short

Irregular

Sesamoid

Long

Question 6

What does the structure and composition of bones maximise?

Answer 6

Maximises strength, stiffness and flexibility of bones

Question 7

What are the components of long bones?

Answer 7

Cortical and trabecular

Mantains stiffness in the longitudinal direction

Question 8

What are bones covered by?

Answer 8

Periosteum

Highly vascularised connective tissue

Question 9

Describe the cortical component of long bones

Answer 9

Dense layer of compact bone around the bone marrow cavity

Found in the middle section of the bone (diaphysis)

Question 10

Describe the trabecular component of long bones

Answer 10

Mesh of intrconnected arches

Highly porous, spongy bone

Found at both ends of the bone (Epiphysis)

Question 11

What are the epiphyses?

Answer 11

The two ends of the long bone

Question 12

What ensures optimal load bearing in long bones?

Answer 12

Combination of cortical, lamellar bone and trabecullae bone

Question 13

Microscopic structure of bone

Answer 13

Dynamic tissue with living composite material

Specialised cells and ECM

Question 14

What do the organic and structural components of the ECM provide the bone?

Answer 14

Tensile strength

Around 10 kg/mm2

Question 15

What do the inorganic and biomineral components of the ECM provide the bone?

Answer 15

Compressive strength

Aroung 15 kg/mm2

Question 16

Describe the microscopic structure of compact bone

Answer 16

Osteon unit

Concentric organisation of lamellar bone

Blood vessels run though Canaliculi, Haversian canal and Volkmann’s canal

Question 17

What is an osteon unit?

Answer 17

Fundamental functional unit of compact bone

Question 18

What is the Haversian canal?

Answer 18

Contains the bone’s nerve and blood supplies

Found inside the osteon

Question 19

What are bone canaliculi?

Answer 19

Microscopic canals that run through bone lacunae (gaps) which carries a structure

Question 20

What are Volkmann’s canals?

Answer 20

Small channels that transmit bloof vessels from the periosteum into the bone

Question 21

Describe microscopic structure of Trabecular bone

Answer 21

Greater surface area that cortical

Suitable for metabolic activity - exchange of calcium

Highly vascular

Frequently contains red bone marrow

Traberculae are aligned towards the distribution of mechanical load

Question 22

What process happens in the red bone marrow?

Answer 22

Haematopoiesis

Question 23

What cells make up the bone structure?

Answer 23

Osteobalsts

Osteocytes

Osteoclasts

Question 24

What is the origin of osteoblasts?

Answer 24

Mesenchymal stem cells

Question 25

What are the biomarkers for osteoblasts?

Answer 25

Alkaline-phosphatase Osteocalcin

Question 26

What are the roles of osteoblasts?

Answer 26

Bone forming Secrete organic bone matrix Responsible for biomineralisation Respond to multiple signaling cues and regulate osteoclasts

Question 27

What is another name for bone matrix?

Answer 27

Osteoid

Question 28

Why is it important that osteoblasts regulates osteoclasts?

Answer 28

To balance bone resorption and formation

Question 29

What is the appearance of osteoblasts?

Answer 29

Epithelia-like cell sheet at site of matrix deposition Basophilic

Question 30

What is the source of osteocytes?

Answer 30

Osteoblasts Terminally differentiated osteoblasts form osteocytes

Question 31

Where are osteocytes found?

Answer 31

Reside in lacunae

Question 32

What are characteristics of osteocytes?

Answer 32

Long-lived Non-dividing Project cytoplasmic processes in canaliculi These cell-cell contacts allow communication + nutrient and waste exchange through gap junctions

Question 33

What is the role of osteocytes?

Answer 33

Resorb, synthesize AND mineralise matrix At lower rate than osteoblasts and osteoclasts Contribute to bone turnover

Question 34

The contribution of osteocytes to bone remodelling is at a lower rate than osteoblasts and osteoclasts TRUE or FALSE

Answer 34

TRUE

Question 35

What triggers osteocyte bone turnover?

Answer 35

Osteocytes sense mechanical forces They then respond and transduce signals Affect bone structure and cellular components

Question 36

What is the source of osteoclasts?

Answer 36

Myeloid origin Fused from precursor cells in bone marrow

Question 37

Why are osteoclasts multi-nucleated cells?

Answer 37

Formed by the fusion of precursor cells in the bone marrow

Question 38

Structural features of osteoclasts

Answer 38

Large Motile Macrophage-like - drive from the same precursors as macrophages Polar Eosinophilic Acid cytoplasm Highly secretory

Question 39

What are biomarkers for osteoclasts?

Answer 39

TRAP-positive Tartate-resistant alkaline phosphatease

Question 40

What is the role of osteoclasts?

Answer 40

As new bone material is added peripherally from the internal surface of the periosteum, there is a hollowing out of the internal region to form the bone marrow cavity Enter the bone through blood vessels Dissolve both the inorganic anc protein portions of the bone matrix

Question 41

How do osteoclasts resorb bone?

Answer 41

Ruffled border secretes protons and matrix degrading enzymes

Question 42

What is the advantage of the ruffled border?

Answer 42

Increases resorptive surface area

Question 43

What is the pH of the resorptive pit?

Answer 43

pH≤4.5

Question 44

What do osteoclasts form when they resorb bone?

Answer 44

Howship lacunae - pits of eroded bone

Question 45

What triggers resorption of the bone by osteoclasts?

Answer 45

Osteoclasts respnond to multiple hormonal, growth factor and cell-cell contact mediated signals

Question 46

Which cell is the associated cellular components of the bone tissue?

Answer 46

Mesenchymal stem cells/ bone marrow stromal cells Haematopoietic stem cells

Question 47

What is the bone marrow?

Answer 47

The medullary cavity - stem cell niche for haematopoiesis

Question 48

What is the medullary cavity replaced with as we age?

Answer 48

Adipocytes containing yellow marrow for energy storage Starts in long bones

Question 49

What two lineages arise from the medullar cavity?

Answer 49

Myeloid lineage Lymphoid lineage

Question 50

What are stromal cells of the bone marrow?

Answer 50

Additional cells Support haematopoiesis structurally and physiologically

Question 51

Characteristics of mesenchymal stem cells

Answer 51

Sub-population of stroma Trilineage potential: bone, cartilage, adipose tissue Highly proliferative and regenerative capacity for musculoskeletal tissue regeneration

Question 52

What is haematopoiesis?

Answer 52

Formation of blood cellular components Bone marrow's primary function

Question 53

What is the origin of mesenchymal stem cells?

Answer 53

No consensus has been reached Can be found in multiple tissues

Question 54

Ongoing questions about mesenchymal stem cells

Answer 54

Do they represent a bone fide stem cell population with discrete properties? What are the definitive markers of MSCs? Are they an activated form of pericytes? Are they transfdifferentitating fibroblasts?

Question 55

What is the condition caused by too many osteoclasts?

Answer 55

Osteoporosis

Question 56

What is the condition caused by too many osteoblasts?

Answer 56

Osteopetrosis