MS system - bones Flashcards
Clostridioides difficile infection Escherichia coli bacteraemia Staphylococcus aureus bacteraemia Norovirus Healthcare associated infection in intensive care units Multi-drug resistant organism admission screening
Acromegaly
Fibro dysplasia ossificans progressiva
Functions of the bone
Which place in the body has little to know protection?
What is bone?
Collagen fibre framework in a mucopolysaccharide-
rich semisolid gel “ground substance”
gives bone its tensile strength
❖ Hardened by precipitation of calcium phosphate
(hydroxyapatite) crystals within matrix
gives bone its compressional strength
(cartilage is similar to bone but
not calcified)
❖ Structural strength near reinforced
concrete but lighter ❖ Made of osteoblasts, osteocytes
& osteoclasts ❖ Supplied by blood vessels & nerves ❖ Contains bone marrow
The long bone strucutre
Cross section of a long bone
What are the two major kinds of bone?
Cancellous and compact
Trabecular and cortical
Why is trabecullar bone so important?
It allows for the distribution of stresses eg around femoralk head have high surface area for metabolism ( eg regulation of Ca+2 )
Wihout bone heads would shatter
How many times stronger is trabecullar compared to columnar strength?
Bloos supply to and from the bone
What canals carry blood along the long axis of the bone?
What canals carry blood perpendicularly
How close are blood vessels to the majority of cells within bone?
Which cell is excluded from direct contact from blood vessels?
Cortical ( compact ) bone blood supply
Blood supply in cancellous ( trabecullar bone )
Composition of the bone matrix
Common disorders of the bone
Osteoblasts
Osteoblast – bone forming cell, cover the surface of bone ….forming an osseous matrix in which it becomes enclosed as an osteocyte
Osteoclast
Osteoclast – osteophage; a large, multinucleated cell derived from
haematopoietic cells…In response to mechanical stresses and
physiological demands they resorb bone matrix by demineralization
Osteocyte
Osteocyte – bone cell – trapped, “retired” osteoblasts. Mature bone
cells - embedded in lacunae, relatively inactive. Maintain bone
matrix through cell-to-cell communication (via projections in
canaliculi) and influence bone remodelling. Mechanosensing
Embedded within lacunae
Communicate via finger-like projections in canaliculi
Osteoprogenitor cells
Bone is highly dynamic tissue
equibrillium between osteoblast and osteoclast activity is controlled by signalling between the different cells in bone and via the actions of hormons
- calitonin decreases activity of osteoclasts meaning lower blood Ca levels
- Parathyroif hormone (PTH) increases activity of osteoclasts and releases Ca
Trabecular bone remodelling cycle
cortical bone remoddeling
osteoclasts reabsorb bone for need
osteoblasts lay down new matrix, eventually get surrounded and become osteocytes
Bone mass density is very dynamic and changes all throughout life, what are some of these changes caused by?
Bone mass and density can increase
- Excessive mechanical stimulation
Bone mass and density can decrease
- Non-weight bearing (immobilisation)
- Sex-hormone deficiency (e.g. menopause)
- Endocrine/nutritional disorders
Wolff’s law
- Bone adapts to the load under which it is placed
- Weight-bearing exercise, orthodontic braces, (Amerindian)
head binding
Age changes related changes in bone mass
what is it called when trabecullar bone is damaged and has breakages between links and webs
osteoporotic
Bone growth from fetus to adult
Cartilage model
Formed by chondroblasts
Reshaped by chondrocytes Replaced by bone (ossification)
Endochondral (long bones)
Intramembranous (flat bones) Bone growth begins in the shaft during fetal life
Fetal endochondral ossifcation - ossification begins in the diaphysis and the primary ossifcation centre is active befor ebirth
After birth endochondral ossification
Bone growth at epiphyseal plate summary
Bone is laid down in the shaft and in the head
The bony parts are separated by a plate of cartilage
As long as the plate of Epiphysis/head
cartilage is present and active the bone will increase in lengt
Resting zone - stage 1
Growth ( proliferating zone ) stage 2
hypertrophic zone stage three
Calcification zone stage 4
Calcification zone thin mineral layer of chondrocytes (2-3 layers) where the aging/dying chondrocytes are mineralised by depositing minerals between the columns. This destroys the chondrocytes.
Ossification ( osteogenic zone )
when does this growth at the epiphyseal plate end ?
puberty
fractures in woven bone - in brief
Depends on cells in the local periosteum
Takes 2-4 weeks for healing
– dependent on the severity and position of the
fracture and age of patient
Inflammation and additional blood flow lead to Callus formation
– osteoblasts quickly form woven bone, to bridge
the gap – woven bone is weak as the collagen fibres are
irregular
Lamellar bone laid down
– collagen organised in regular sheets to gives
strength and resilience
Remodelling by osteoclasts to restore original bone shape (more on this next semester…)
cartilage
Bone
Because the extracellular matrix of bone is inorganic and hard it may seem to be non living. In fact it is a dynamic tissue that undergoes growth, repair and remodelling throughout life
under the influence of a number of factors including the hormones parathormone which
increases the activity of osteoclasts and releases Ca ++ into the blood and calcitonin which
inhibits the activity of osteoclasts and reduces Ca ++ in the blood. Bone matrix (calcium
hydroxyapatite bound to osteoid (mixture of collagen and other proteins)) is synthesised by osteoblasts that become embedded within the matrix but maintain connections with other cells and their blood supply via microscopically small channels. Bone growth occurs when
deposition is greater that bone resorption.
Cells comprising bone tissue lie mainly in the periosteum on the inner and outer surfaces of a bone.
Osteoprogenitor cells - stem cells that give rise to osetoblasts in bone growth and
repair (compare with “mesenchymal stem cells” below) Osteoblasts secrete bone matrix (abundant rough ER, Golgi) eventually become
osteocytes Osteocytes mature cells that maintain bone matrix. Some become buried alive in
spaces in the bone matrix (lacunae) they are connected by cytoplasmic processes
lying in narrow channels (canaliculi) Osteoclasts are derived from blood monocytes. Large multinucleated cells resorb
bone as they drill through matrix (fracture sites, at epiphyses during growth, and
remodelling sites) Fibroblasts produce collagen and other fibres.
Are bones and cartilage stiffened forms of connective tissue?
Long bone structure in a summary
Diaphysis is the shaft of a long bone. It consists of:
● compact bone (osteons or Haversian systems), forms a very strong, light
cylinder that resists compressive (gravitational) forces. Osteocytes are buried
alive in the bone matrix (calcium hydroxyapatite (Ca5 (PO4)OH)). See the
diagram below for a 3D representation of the arrangement of Haversian
systems. ● medullary cavity contains bone marrow supported by cancellous bone. Red
bone marrow is one site of haematopoiesis (formation of red blood cells).
Epiphysis end of a bone that has an articular surface (sometimes referred to as the head). During childhood the ends of a long bone are separated from the diaphysis by plates of hyaline cartilage (the epiphyseal plates) where growth in length of the bone occurs. At the epiphyseal plates columns of cartilage cells undergo division and are eventually removed by osteoclasts. The spaces are invaded by osetoblasts and new bone is laid down. An individualwill continue to grow in height as long as the
epiphyseal plate is active. The production of sex steroids eventually cause the epiphyseal plates to close and the cartilage plate is entirely replaced by bone (synostosis). Girls produce
oestrogen earlier than boys produce sufficient testosterone and so girls cease to grow at an earlier age and are on average shorter than males. In any one individual the epiphyses close at around about the same time (by the end of puberty, largely due to hormonal triggers) – but, in most bones there are multiple secondary sites of ossification, which appear at different ages (before the end of puberty). By observing which of the ossification centres have been formed, it is possible to establish the approximate age of a child.
X-ray imagining can be used to observe these ossification centres. This is possible because bone shows on an x-ray image as black whereas cartilage shows as white.
bone through tendons cause the formation of bone markings such as tubercles and lines)
AH, JI Ed 200918
Periosteum covers all but the articular surfaces and consists of osteoblasts, osteoclasts, fibroblasts. It has a rich nerve and blood supply.
Bone is remodelled throughout life
BONE IS REMODELLED THROUGHOUT LIFE Old bone is continuously removed (by osteoclasts) and replaced (by osteoblasts). Normally the processes are delicately balanced to maintain bone mass. Bone is laid down (undergoes hypertrophy) in response to:
physical stress (training)
traction and pressure (NB muscular forces through the attachment of muscle to
Trabeculae of cancellous bone are laid down along the line of stress. Bone is lost (undergoes atrophy) in response to:
lack of weight bearing (immobilisation, astronauts)
menopause (lack of oestrogen) results in osteoporosis
dietary imbalance (lack of vitamin D)
Bone growth
