Bone structure, classification, metabolism and development Flashcards
What is bone?
A bone is a mineralised connective tissue that exabits four types of cells,: Osteoblasts, bone lining cells, osteocytes and osteoclasts.
Why do we need bones?
Provide shape and support for the body
Protection for certain organs such as the lungs
Environment for marrow
Storage area for minerals
Bone composition
The weight of bones can vary significantly depending on individual factors
Age, sex, body composition play a role in determining this
Bones on average make up around 15% of an individual’s total weight
A healthy adult weighing 70kg would be comprised of around 10.kg of bone mass
Certain conditions such as osteoporosis can have a significant impact on bone mass and therefore also impact bone weight
Why is understanding bone biology so important to overall health
Research
Developing treatments
Managing chronic conditions
Provides greater understanding of genetic determinants of health
Visualise conditions radiographically
Bone structure
Bones are composed of cells…with the main three categorised as….
Osteoblasts
Osteocytes
Osteoclasts
Cells have different roles of functions and work together to facilitate bone formation, strength and remodelling
Osteoblasts: function, activity and location.
Bone forming cells.
Secretes organic components such as collagen.
Bone formation during growth, repair and remodelling.
Bone surface
Osteocytes: function, activity and location.
Mature cells from osteoblasts.
Maintain bone tissue.
Regulate mineral homeostasis.
Form a communication network through canaliculi, allowing nutrient exchange and waste products
Lacunae
Osteoclasts: function, activity and location.
Large cells responsible for bone resorption, break down and removes old or damaged tissue.
Release enzymes and acids, which facilitates the remodelling.
Sites of bone resorption, often the bone surface
What is Bone classification?
- Bones are categorised depending on characteristics of the bone and their appearance
- We can gain lots of information from the type of bone and can help predict mechanism of injury etc.
- Depending on classification, some bones are more prone to injury than others
- Certain bone types may be more prone to pathology such as bone metastasis
- Bones are often separated into long and short bones
Axial skeleton
Provides support and protection for vital organs including the brain, spinal cord, heart and Lungs.
Appendicular skeleton
Facilitates movement and interaction with the external environment, integral to walking, running and using our hands
Bone classification types
Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones
Sutural bones
Long bones
Tibia
fibula
femur
phalanges
clavicle
radius
ulna
metacarpus
metatarsus
short bones
tarsus
carpus
irregular bones
temporal
vertebrae
sacrum
coccyx
mandible
maxilla
sphenoid
ethnic
sesamoid bones
patella
sutural bones
skull
Long bone explanation and example
Long and slender, the femur is a long bone and the largest and heaviest bone in the body
humerus
flat bone explanation and example
Thin, parallel surfaces, provide protection and due to surface areas serve as good attachment sites
scapula
sesamoid bone explanation and example
Usually small, round and flat. Sesamoid bones are within this, but not everyone has them
patella
Flat bones
frontal
rib
sternum
nasal
scapula
occipital
irregular bone explanation and example
Complex shape with several characteristics, can have flat, round, short, notched or rigid surfaces
vertebrae
short bone explanation and example
Usually small in appearance and for that reason are usually rigid and difficult to damage
carpal bones
sutural bone explanation and example
Exclusive to the skull and are small and flat with a unique shape and mimic the shape of a jigsaw puzzle
regions of the skull
Bone metabolism
The continuing process of synthesis and destruction gives bone it’s mature structure and maintains calcium levels in the body
Osteoclasts are responsible for destruction and resorption, they release calcium into the bloodstream
Whilst osteoclasts resorb bone at multiple sites, osteoblasts make new bone to maintain the skeletal structure.
At a young age bone formation happens at a greater rate than bone destruction, and when an adult reaches adulthood the two process align to maintain a balance between the two.
Osteoclasts have a role within the inner surface of the bones, in the marrow cavity and the space of cancellous bone, to widen these cavities
They do also act on the outer surfaces to reduce bony processes including epiphyseal swellings at the ends of long bones such as the humerus and femur.
Osteoclasts activity happens behind the epiphyseal growth zone to reduce former swellings to the width of the lengthening shaft.
Osteoclastic destruction helps to convert immature bone into mature compact bone.
Bone density
Reduced bone density is commonly associated with conditions such as osteopenia and osteoporosis.
Bones with low bone density are weakened and more susceptible to fractures and injury.
Individuals with low bone density has several key metabolic changes compared to healthy bone
bone density
Increased bone resorption- More bone tissue is broken down quicker than it can be replaced
Reduced bone formation- Osteoblasts cannot compensate adequately for increased bone resorption
Imbalance in bone remodelling- This imbalance is due to the above balance and can be because of age, deficiencies and hormonal changes
Thinner bone structure- Spacing between bone trabeculae increases, affecting structural integrity
Decreased mineralization- Mineralization compromised, involving deposition of calcium and phosphate salts
Altered hormone regulation- Hormonal levels of estrogen and testosterone reducing can accelerate bone loss
Impaired bone repair- Slower healing and increased vulnerability to additional damage
Bone development
Embryonic development
- Formation of mesenchymal cells
- Development of the cartilaginous model
Intramembranous Ossification
- Process of formation directly from mesenchymal cells
- Bones formed through intramembranous ossification
Endochondral Ossification
- Cartilage replacement by bone tissue
- Stages of endochondral ossification
- Types of bone formed through endochondral ossification
embryonic development weeks 4-8
Week 4:
* Heart begins to beat
* Arm buds appear
* Liver, pancreas, and gall bladder start to form
* Spleen appears
week 5:
* Eyes start to form
* Leg buds appear
* Hands appear as paddles
* Blood begins to circulate
* Facial features start to develop
week 6:
* Lungs start to form
* Fingers and toes form
Week 7
* Hair follicles start to form
* Elbows and toes are visible
week 8:
* Face begins to look human
* External ears start to form
Intramembranous Ossification
Intramembranous ossification is the process through which mesenchymal cells differentiate directly into bone tissue without an intermediate cartilage template. It plays a crucial role in the development of flat bones and contributes to the formation of the skeletal structure during embryonic and fetal development.
Intramembranous Ossification
process
Process and stage
1) Formation of Mesenchymal cells
2) Condensation of Mesenchymal cells
3) Ossification cells
4) Formation of osteoid
5) Calcification of osteoid
6) Trabeculae formation
7) Development of periosteum
8) Formation of compact bone
9) Red bone marrow formation
10) Completion of bone formation
Endochondral Ossification
Endochondral ossification is a critical process for the formation, growth, and development of most bones in the human skeleton. It allows for the dynamic changes in bone length and shape during different stages of development.
