W4: Biochemistry Of Bone And Teeth 1 Flashcards
Function of skeleton/bones
Support, attachment, protection
Calcium homeostasis - store and metabolism
Dynamic tissue undergoing renewal and remodeeling
Function of teeth
To tear and chew food - mastication Speech Facial cosmetic appearance Defence/fighting Tooth repair and regeneration
Calcium store
- main body store is the skeleton. Ion exchange can occur at the mineral (hydroxyapatite) surfaces bathed in interstitial fluid
Calcium metabolism
- plasma concentration is mainly under control of parathyroid hormone, calcitonin and vitamin D
- cells are key players in process of bone remodelling
What happens if there is low dietary calcium?
Lower plasma Ca2+ concentration = increased PTH secretion =
- active vitamins D increasing intestinal calcium absorption
- decreased urinary calcium by conservation of dietary calcium
- bone loss from bone calcium release
All restore normal plasma calcium
LOOK AT ENDOCRINE?
What types of cells are in bone?
Osteoblasts, osteocytes, osteoclasts
Basic structure of a tooth
Enamel
Dentine
Pulp
Cementum
Role of osteoblasts
Bone-forming cells: secrete the organic extracellular matrix of new bone (osteoid) which undergoes mineralisation to form bone. Osteoblasts become trapped in bone in lacunae as osteocytes and are responsible for maintaining the bone matrix.
Role of osteoclasts
Large multinucleated cells responsible for bone resorption - degradation of the matrix to release calcium into bloodstream.
Fixes itself to the bone matrix with a lot of extensions and is able to dissolve the bone matrix and release calcium and other components.
The bone remodelling cycle
There is a balance between bone resorption and formation.
Cells of osteoprogenitor cells differentiate into specialised cell types.
Cells differentiate into osteoclasts which then fuse to become multinucleated cells and resorb bone. Usually brittle and old bone.
Cells move away and osteoblasts are differentiated into. They produce bone to compensate for the amount resorbed. Then osteoblasts become inactive and lining cells.
Regulation of bone remodelling
Local regulatory factors might promote the formation of osteoclasts which might resorb the bone and release growth factors which stimulate formation of osteoblasts
Osteoblasts can also release growth factors which stimulate the formation of osteoclasts
Complete feedback
Which cells are osteoclasts derived from?
Haematopoietic stem cells pools. Monocytic macrophage family,
What cells are osteoblasts derived from?
From mesodermal derived cell types, mesenchymal stem cell pools. Connective tissue type cells.
2 forms of bone
Woven bone and adult lamellar bone
What is woven bone
Immature bone, with random organisation of its collagen. Present during early development - fracture repair, healing tooth sockets etc. Gradually replaced and remodelled by mature bone.
What is adult lamellar bone?
Composed of successive layers of bone:
- compact bone (dense)
- cancellous or trabecular bone (open spongy-like bone, porous)
What is compact bone made of?
Circumferential and concentric bone layers (lamellae)
Concentric lamellae are arranged around a central channel with blood vessels, lymphatics and nerves = Haversian canal
Osteons (haversian systems) form the main structural bone units
Osteocytes in their lacunae interact with each other and with the central canal via canaliculi
The outermost layer of compact bone gives way to dense cortical bone
Lamellae merge with trabecular of cancellous bone
What are osteocytes responsive to?
Mechanical loading, where they then regulate osteoblasts and osteoclasts
Role in tooth movement
How does compact bone act as weight bearing pillars?
- biomechanicsl function
- able to withstand high levels of mechanical stress
Cancellous/trabecular bone composition
Network of bone trabeculae separated by interconnected spaces contains bone marrow
Thin and composed of irregular bone lamellae
Osteocytes are linked to blood sinusoids in the marrow via canaliculi
Trabeculae are aligned along lines of stress as to withstand forces applied to the bone while adding minimally to the mass
Hard mineralised tissues of the tooth
Enamel, dentin, cementum
What is enamel?
The hardest and most highly mineralised tissue in the body.
Properties of enamel
Mature enamel is acellular (no cells) - not living/non-vital
Insensitive
Cannot be regenerated
Structure of enamel
Prismatic structure: millions of calcium hydroxyapatite crystals are packed to form rods/prisms
Properties of dentine
Rigid but elastic and resilient so ideal to support brittle enamel
Tubular structure
Vital, permeable and sensitive
Formed throughout life
Pre dentine is the freshly laid down dentine prior to mineralisation
Capable of repair
What cells secrete the dentine matrix?
Lining the pulp is a layer of odontoblasts which secrete the dentine matrix - dentine forming cells
Types of dentine
Primary dentine formed during embryonic development, before the tooth is erupted and before tooth development
Secondary denting forms after tooth becomes functional and complete root development
Tertiary dentine is a repair response from odontoblasts/pulp cells to external stimuli or assaults (e.g., caries)
Dentine repair - reactionary
Reactionary process: minor injury to the tooth causes stimulation of odontoblasts to form more dentine, aiming to protect and seal off the viable dental core. Produces tertiary dentine formation.
What are the postnatal pulp stem cells?
Reservoir of cells for new odontoblasts
Peri vascular cells
Undifferentiated mesenchymal cells/fibroblasts
Specific stem cell population
Function of cementum
Prime function of cementum is to give attachment of the tooth to collagen fibres of the periodontal ligament.
Properties of cementum
Similar to bone in chemical composition and properties but is avascular and not innervated. Can be repaired and regenerated thus helping maintain the integrity of the root structure.
What is the inorganic component of bone?
Hydroxyapatite crystals: minerals
What is the organic component of bones and teeth?
Extracellular matrix: proteins. E.g., collagen, glycoproteins and proteoglycans
Composition of bone, dentine and cementum
- mesodermal/(ecto)mesenchymal origin
- composed of collagenous calcified matrix
- 60-70% inorganic, 20% organic, 10% water
Composition of enamel
- ectodermal - epithelial origin
- composed of 96% mineralised component
Physical characteristics of bone, dentine and enamel
Bone and dentine are hard with elastic properties
Enamel is very hard but brittle
Do dentine and cementum take part in calcium homeostasis?
They are calcified tissues but do not take part in the ion exchange. Enamel does.
What are osteocytes?
Living/viable cells. As long as the bone is bone is viable, the osteocytes are viable.
What does bone remodelling ensure?
That the bone remains renewed and viable. E.g.m if there is a micro fracture or bones are old, osteoclasts can remove this and osteoblasts can fill the resorption with fresh bone.
Dentine repair - reparative
Reparative dentine formation: major tooth decay causes progenitor cells to differentiate into new odontoblasts which then produce tertiary dentine formation.
