7 - Bone Flashcards
definition: osteology
the study of bone
definition: osteogenesis
the formation of bone
definition: osteomyelitis
an infection within bone
definition: osteopathy
a disease within the bone
definition: osteoporosis
weak bone
definition: osteosarcoma
a cancer originating from bone forming cells
the skeleton, how many bones in categories etc
- made of 206 named bones in 2 categories: axial and appendicular
- axial consists of thoracic cage, vertebral column and skull 80 bones
- appendicular consists of shoulder girdle and upper limbs, pelvic girdle and lower limbs 126 bones
- there are sometimes 4 extra bones - these are round, small bones found in the back of the knee in tendons, which alleviate some tension in the tendons
what are the three main functions of bones
**mechanical **
- protect important and delicate tissues and organs
- provide a framework for the overall shape of the human body
- form the basis of levers involved with movement
synthetic
haemopoiesis (holds and protects red bone marrow)
metabolic
- mineral storage, eg calcium and phosphorous
- fat storage eg yellow bone marrow
- acid - base homeostatis (absorbs or releases alkaline salts to help regulate blood pH - calcium is alkaline)
cancellous vs compact bone
cancellous
- forms a network of fine bony columns or plates
- these are called trabeculae
- this combines strength with lightness
- the spaces in between trabeculae are filled with bone marrow
- ‘spongy bone’
- has spicules (spiky bits) → first bit of developing bone
compact bone
- forms the external surfaces of the named bones
- comprises mose of the body’s skeletal mass
- aka cortical bone
- many nerves, blood vessels and lymphatics run through cortical bone
what type of bone is found in medulla region of bone
only cortical/compact bone
→ hollow part of the bone that contains bone marrow
definition: ossification
bone formation
what are the two types of ossification
endochondral ossification
- inside cartialage
- the formation of long bones from a cartilage template
- continued lengtheneing is by ossification at epiphyseal plates
→ appositional growth (growth at edges)
intra-membranous ossification
- the formation of bone from clusters of mesenchymal stem cells in the centre of bone
→ interstitial growth (growth in the middle)
endochondral ossification
most bones form by this method, except the clavicles and the skull bones
- mesnchymal cells first differentiate into chrondrocytes
- these build a hyaline cartilage model
- the centre of the hyaline cartilage model is the primary ossification centre
- blood vessels enter primary ossification centre
- these bring in nutrients, osteoblasts and osteoclasts
- the osteoblasts replace the chondrocytes at the primary ossification centre, begin to replace cartilage with bone
- osteoclasts then begin to collapse the bone in the middle, making it more porous, which is how bone marrow develops
long bones form first by this method - patella, wrist and ankle etc develop after birth
intramembranous ossification
flat bones develop by this method, including many in the skull
- mesenchymal cells differentiate directly into osteoblasts
- these create the primary ossification centre
- start building bone without any cartilage model
- blood vessels reach primary ossification centre
- the primary ossification centre already has osteoblasts, but the BVs bring in nutrients
cancellous bone conversion to cortical bone
- mesenchymal stem cells convert into osteoblasts
- these line recently formed trabeculae
- lay down osteoid that becomes mineralised
- osteoblasts become trapped → osteocyte
- mesenchymal stem cells come back in and make more osteoblasts, and make another layer of bone tissue, repeat again etc
- each layer of bone formed is called a lamella
- forms a structure that leaves mesenchymal stem cells within it
- those turn into blood vessels, nerves and lymphatic vessels
- this structure is known as an osteon (aka haversian system) with a haversian canal running through it
- volkmanns canals form between osteons in order to carry blood vessels
- just made immature cortical bone
immature cortical bone → mature bone
- immature bone has osteocytes in random arrangements and blood vessels that aren’t properly formed
- need to form resorption canals (full of osteoclasts)
- resorption canals job is to find weakenesses in that bone and rectify it, to make stronger bone
- the canals usually run parallel to the existing osteons
- the resorption canals move, and create new osteons
structure of mature bone (cortical)
- many osteons (haversian systems) with haversian canals running through them
- interstital lamellae between osteons
- haversian canals have blood vessels, lymphatics and nerves
- haversian canals are connected horizontally by the volkmanns canals
- the volkmanns canals join up to the outside to the periosteum and endosteum
- periosteum is dense connective tissue that surrounds bone where muscle etc attaches
- endosteum is loose connective tissue on inside of bone where bone marrow is
structure of mature bone - cancellous
- made up of trabeculae
- spaces between them filled with red bone marrow
- no haversian or volkmanns canals
- bone marrow surrounding is liquid
- section of trabecula has layers of interstitial lamella, with ostocytes trapped in between layers. Osteoclast on one side of trabeculae and osteoblasts aligned along trabecula of new bone
- teardrop shape due to gravity
- note: no blood vessels etc because surrounded by liquid bone marrow, so transport is easy
what are haversian and volkmann’s canals
- found in cortical bone only
- haversian canals have blood vessels, lymphatics and nerves
- volkmanns canals only have blood vessels
- haversian canals run through osteons (haversian system)
- job is allowing bone to deliver oxygen and nutrients to the bone
- volkmanns canals connect haversian canals horizontally
- volkmanns canals join to periosteum and endosteum
- used to communicate with osteocytes
endosteum vs periosteum
cortical bone
- periosteum is dense connective tissue that surrounds bone where muscle etc attaches
- endosteum is loose connective tissue on inside of bone where bone marrow is
where is the epiphysis, metaphysis and diaphysis of a long bone
- epiphysis is top and and bottom areas of bone (ie the bits that form joints) - consists mainly of cancellous bone
- diaphysis is shaft of long bone - predominantly hollow and filled with bone marrow. Consists of cortical bone around the sides
- metaphysis is in between epiphysis and diaphysis
- between metaphysis and epiphysis is epiphyseal growth plate (layer of cartilage) → allows bones to keep growing
bone strength
- bone (as a tissue) is very good at resisting force
- it has great tensile + compressive strength
- has a degree of flexibility
- main force lines are through the cortical bone
- lamellae of osteons can slip relative to each other
- this can resist fracture
how do osteons remodel themselves
- bone becomes weak when there are not enough haversian systems (osteons) in the cortical bone
- remodels by moving osteons around, using osteoblasts and osteoclasts
- need to get material from somewhere to make the new osteons? this comes from inside the bone (endosteum) from the cancellous bone
- osteoblasts then use that to make new osteons, and also put more tissue outside (periosteum)
- this is known as appositional growth (taken from inside and put on outside)
- bone is dynamic and is constantly remodelling itself
this happens in two stages (cutting + closing cone), details on future card
why is exercise important for bone remodelling
- bone is dynamic and is constantly remodelling itself
- exercise is a key determinant of bone strength
- inactivity increases bone resorption (1/3 mass lost when immobile)
- bone density is optimum at 25 y/o
- this is because bones widen when you exercise
- this is due to osteoclasts taking bone off the endosteum, which gets resorbed on the periosteum (see prev card) to get thicker cortical bone
