Normal structure of bone and bone cells Flashcards
What type of tissue is bone?
Specialised form of living connective tissue
How does the fibrous matrix in bone give it strength?
Allows bone to withstand high compressive loads
What is stored in bone?
Mineral ions
What is the most abundant mineral ion found in bone?
Calcium
What are the 2 types of bone?
Cortical/compact bone
Cancellous/trabecular/spongy bone
In cortical/compact bone, what is the proportion of bone compared to spaces?
High proportion of bone so there are few spaces
In cancellous/trabecular/spongy bone, what is the proportion of bone compared to spaces?
Low proportion of bone so there are lots of spaces
What type of bone causes a more severe bone fracture?
Cortical/compact
Why is a cortical/compact bone fracture more severe in post-pubescents than children?
Children can still change and regenerate cortical bone, but post-pubescents can’t
What is the trabeculae, that is found in trabecular bone?
Network of rods and plates
How can the substance bone matrix be described?
Non-living, intercellular
What component of bone makes up most of the bone mass?
Bone matrix
What collagenous protein is present in the bone matrix?
Type 1 collagen
What 3 non-collagenous proteins are present in the bone matrix?
Proteoglycan, osteocalcin, osteonectin
What is the function of type 1 collagen in the bone matrix?
Assembles into triple-stranded fibres that form 3D scaffold for bone cells and tissues to develop from
What are the 3 functions of proteoglycan in the bone matrix?
Aids regulation of collagen fibrogenesis, ion movement and forms compression-resistant networks between fibres
What are the 2 functions of osteocalcin in the bone matrix?
Binds to calcium, aids bone endocrine function (that can also affect other organs)
What is the function of osteonectin in the bone matrix?
Helps to influence bone mineralisation during formation as it binds HA and collagen so regulates calcium release (from HA)
In woven bone, what are 3 characteristics of the collagen pattern?
Random fibre orientation, immature form as cross-links haven’t formed between collagen fibrils to produce tight fibres, large and numerous osteocytes
What condition causes collagen to be laid down in an irregular way in woven bone?
Rapid new bone formation, such as in repair of a fracture
What are the 2 types of mature lamellar bone?
Cortical or spongy bone
Where is lamellar bone found in the body?
Almost whole of adult skeleton
What units is lamellar bone made up of?
Lamellae
In lamellae bone, is the collagen pattern in a distinct or random orientation?
Distinct
In a long bone, what is the cortex made of?
Compact bone ‘shell’
In a long bone, what structure does the cortex cover?
Medullary/marrow cavity
What is the medullary/marrow cavity function in a long bone?
Site of red marrow, where blood cells are produced in immature bone eg. children’s bones
In the medullary/marrow cavity of a long bone, what replaces the red marrow as the person ages?
Inactive yellow marrow
What gives yellow marrow its colour?
Adipose tissue
What is the diaphysis of a long bone?
Cylindrical shaft
What is the epiphysis of a long bone?
Expanded end of the bone
What is the metaphysis of a long bone?
‘neck’ region of bone that is between epiphysis and diaphysis
What part of the epiphysis structure extends into the metaphysis structure in a long bone?
Spongy bone walls
What structure does the metaphysis contain that is present in children (immature bone)?
Growth plate
What happens to the growth plate in the metaphysis as the bone matures?
Growth plate ossifies to become epiphyseal line
What is the periosteum of a long bone?
Thin layer of connective tissue that covers outer surface of bones except articular surfaces
What part of the long bone isn’t covered by the periosteum?
Articular surface
What cells are present in the inner layer of the periosteum of long bones?
Osteoprogenitor/osteogenic cells
What 2 structures are present in the outer fibrous layer of the periosteum of long bones?
Blood vessels, nerves
What are Sharpey’s fibres?
Periosteal collagenous fibres that protrude into bone matrix to bind periosteum to bone
How do blood vessels and nerves in the outer fibrous layer of the periosteum travel to supply bone cells?
Pass through Haversian canal then Volkmann canals
What is the endosteum of a long bone?
Cellular layer that covers inner surfaces of bone eg. lines medullary cavity of cortical bone, lines trabeculae in spongy bone
In a osteon/haversian system, what is the name of the central canal?
Haversian canal
What are the 4 bone cells?
Osteocyte, osteoblast, osteoclast, bone lining cell
What are the 3 functions of osteoblasts?
Synthesis and mineralisation of bone matrix
Secretion of osteoid
Bone formation
What is osteoid?
Unmineralised collagen-proteoglycan matrix that binds calcium, is the organic component of bone matrix
What happens to the bone matrix when osteoid binds to calcium?
Bone matrix hardens and osteoblasts are trapped in lacunae, entrapment causes osteoblasts to change into osteocytes
What is the shape of an osteoblast?
Cuboidal cell
What are the 2 processes that require osteoblasts to contain many organelles?
Necessary for high amounts of protein synthesis and secretion
What kind of layer do osteoblasts form on the bone surface?
Epithelioid layer
What is the main function of bone lining cells?
They are inactivated osteoblasts on the bone surface that can be reactivated into active osteoblasts
Why do bone lining cells and osteocytes co-operate?
Regulate calcium exchange from bone
What are the 3 functions of osteocytes?
Regulate bone formation and resorption
regulate calcium homeostasis
detect mechanical stress due to extent of physical loading/strain
How are osteocytes formed?
Osteoblasts trapped in lacunae in bone matrix during apposition (increase in bone diameter), and can’t secrete osteoid anymore so become osteocytes
How are osteocytes in the bone matrix interconnected?
They have long dendritic processes that reach other osteocytes
What is a canaliculi?
Narrow channel radiating from lacunae in bone matrix that contain osteocyte dendritic processes inside them, and connects with haversian canal in the osteon/haversian system
What is the function of the canaliculi?
Allows diffusion of nutrients and waste between osteocytes and blood vessels
What is the function of osteoclasts?
Bone resorption
What is the structure of osteoclasts?
Large, polymorphic/multinucleated cell
What are the organic and inorganic components of bone matrix?
Organic: Osteoid
Inorganic: HA
How is the ruffled border of the osteoclast formed?
Deep membrane invaginations to form finger-like processes
What is the function of the ruffled border of the osteoclast?
It is on the lower part of the osteoclast, that faces bone surface to secrete acid and proteases to break down bone
What is the function of the clear/sealing zone of the osteoclast?
Contains actin filaments to anchor osteoclast to bone
