0416 - Bone and Cartilage - CS

Question 1

Structural components of bone: label this diagram

Question 2

Be aware of the following structural components of bone:1. diaphysis2. metaphysis3. epiphysis (proximal and distal)4. epiphyseal line5. periosteum6. compact cortical bone7. spongy bone8. articular cartilage9. medullary cavity10. marrow11. nutrient artery

Answer 2

Brief definitions to be added later. (Sorry!)

Question 3

Explain the basic functions of bone?

Answer 3

• Structural- Movement- Protection- Gives skeleton the necessary rigidity to function as an attachment and lever for muscles and supports the body against gravity- Acts as a calcium reservoir and is important in calcium homeostasis. Also phosphate- Is heavy and its architecture is optimally arranged to provide maximum strength for the least weight.

Question 4

What is bone composed of?

Answer 4

• Cells in abundant extracellular substance (matrix)- Extracellular matrix:- 30% organic matrix (mostly type 1 collagen fibres - about 90%)- 70% inorganic salts (calcium and phosphate): ground substance (osteoid) becomes mineralised by the deposition of calcium hydroxyapatite

Question 5

What gives bone its tensile strength?

Answer 5

Type 1 collagen fibres in the extracellular matrix

Question 6

What gives bone its hardness?

Answer 6

The ground substance (osteoid) in the extracellular matrix that becomes mineralised by the deposition of calcium hydroxyapatite

Question 7

List the types of cells in bone

Answer 7

Osteoprogenitor cellsOsteogenic cellsOsteoblastsOsteocytesOsteoclasts

Question 8

What is the role of osteoprogenitor cells?

Answer 8

Precursor cells that self replicate or differentiate into bone-forming cells

Question 9

What is the role of osteoblasts?

Answer 9

Form bone matrix - deposit osteoid and control subsequent mineralisation

Question 10

What is the role of osteocytes?

Answer 10

Maintain bone tissue - modified osteoblasts that become surrounded by newly formed bone and regulate homeostasis

Question 11

What is the role of osteoclasts?

Answer 11

Resorb bone - large multinucleated phagocytic cells that resorb bone and break down calcified matrices (originate from haemopoietic stem cells)

Question 12

Describe the appearance of woven (immature) bone, as seen on light microscopy

Answer 12

• Randomly arranged collagen fibres in the osteoid. Looks disordered.- Produced when osteoid is produced rapidly (eg. foetal bone, healing fracture and in bone diseases such as Paget’s disease)- Eventually remodeled to form lamellar bone

Question 13

Describe structure of the two types of lamellar bone, and their appearance, as seen on light microscopy

Answer 13

• Mature bone (Stronger than woven bone)- regular parallel bands of collagen fibres in the osteoid- Within mature lamellar bone, there are two subtypes: compact bone and cancellous (trabecular, spongy) boneCompact:lamellae are organised in concentric layers of mineralised bone matrix. Haversian canals (neurovascular channels) run through the middle of lamellae (along axis of bone) and provide nutrient supply to tissue.A lamella surrounding a haversian canals is together referred to as an haversian system or osteon.Osteoblasts become encased in small hollows within matrix lacunae.Osteocytes have several thin processes, which extend from the lacunae into small channels within the bone matrix canaliculi.Cancellous bone (also called trabecular bone or spongy bone): Has irregular lamellae.Bony trabeculae are separated by interconnecting spaces containing bone marrow. Lamellaedo not form Haversian systems, though still has organisation.

Question 14

In compact bone, how do osteocytes communicate with each other and exchange substances via diffusion?

Answer 14

Via canaliculiCanaliculi arising from one lacuna may anastomose with those of other lacunar and eventually, with larger, vessel-containing canals within the bone

Question 15

List and explain the two ways in which foetal bone development occurs.

Answer 15

Two ways: 1. endochondral ossification 2.intramembranous ossification.- Both involve replacement of primitive collagenous tissue by bone.Resulting woven bone then extensively remodelled by resorption and appositional growth to form the mature adult skeleton (lamellar bone).Bone development is controlled by growth hormone, thyroid hormone and the sex hormones.1. Endochondral ossification: Long bones, vertebrae, pelvis and bones of the base of the skull are formed this way. Bones preceded by the formation of a continuously growing cartilage model which is progressively replaced by bone. Cartilage model forms, then periosteal bone colar forms. Cartilage is calcified via deposition of asteoid by osteoblasts.Vascular mesenchyme enters.Zones of ossification form.Growth plate fuses as growth stops.The bones formed in this way are called cartilage bones.2. Intramembranous ossification:Bones of the vault of the skull, the maxilla and most of the mandible are formed this way.Involves the deposition of bone within primitive mesenchymal tissue.The bones formed in this way are called membrane bones.

Question 16

What are the functions of bone remodelling?

Answer 16

• Repair damage- Ion homeostasis- Bone reinforced for increased strength- Bone growth

Question 17

What are the basic functions of cartilage?

Answer 17

• Connective tissue with firm extracellular matrix - provides semi rigid and bone rigid structural support- Supports soft tissues (ear, nose, epiglottis, trachea)- Shock absorption in joints- Important in development, growth and healing of bones

Question 18

What are the structural components of cartilage? How do they appear?

Answer 18

-Few cells + abundant extracellular matrix (ground substance)-Cells isolated in cavities in matrix: condroblasts (precursor cells) and chondrocytes (mature cells)- Extracellular substance (gel like matrix): collagen and elastin fibres inground substance (sulphated proteoglycans and hyaluronic acid)-Fresh cartilage contains about 75% water - forms a gel with the components of the ground substance- Does NOT contain vessels or nerves (unlike other connective tissue). Chondrocytes depend on diffusion of nutrients - this limits thickness of cartilage- Usually surrounded by a layer of dense connective tissue called perichondrium

Question 19

What are the three types of cartilage in the body? Outline key characteristics of each and give an example of where it is found in the body

Answer 19

1. Hyaline cartilage (most common). Appears glassy and blue. It’s collagen fibres are type II. Its ground substance is mainly homogenous looking GAGs. Forms precursor of bone. Eg innasal septum, larynx, tracheal rings, articular surfaces, ends of ribs.2.Fibrocartilage: appears white with alternating layers of hyaline cartilage and thick layers of dense collagen fibres oriented in one direction. Its ground substance is sulphated GAGsfound in intervertebral discs, some articular cartilage, pubic symphysis.3. Elastic cartilage: Its ground substance is sulphated GAGs. Appears yellow. Found in external ear and external auditory canal, epiglottis, laryngeal cartilages, wall of eustachian tubes

Question 20

Describe how cartilage is formed

Answer 20

-Cartilage formation begins in the fifth week of life-Precursor cells become rounded and form densely packed cellular masses (‘centres of chondrification’.-The cartilage-forming cells (‘chondroblasts’), begin to secrete the components of the extracellular matrix of cartilage-As amount of matrix increases, chondroblasts become separated from each other-Chondroblasts become isolated in small cavities within the matrix - ‘lacunae’-Chondroblasts differentiate into mature cartilage cells - ‘chondrocytes’

Question 21

Describe the process of fracture healing

Answer 21

-Reactive phase: inflammatory phase, granulation tissue formation-Reparative phase: cartilage callus formation, lamellar bone deposition-Remodelling phase: remodelling to original bone contour