Bone structure, classification, metabolism and development

Question 1

What is bone?

Answer 1

A bone is a mineralised connective tissue that exabits four types of cells,: Osteoblasts, bone lining cells, osteocytes and osteoclasts.

Question 2

Why do we need bones?

Answer 2

Provide shape and support for the body
Protection for certain organs such as the lungs
Environment for marrow
Storage area for minerals

Question 3

Bone composition

Answer 3

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

Question 4

Why is understanding bone biology so important to overall health

Answer 4

Research
Developing treatments
Managing chronic conditions
Provides greater understanding of genetic determinants of health
Visualise conditions radiographically

Question 5

Bone structure

Answer 5

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

Question 6

Osteoblasts: function, activity and location.

Answer 6

Bone forming cells.
Secretes organic components such as collagen.

Bone formation during growth, repair and remodelling.

Bone surface

Question 7

Osteocytes: function, activity and location.

Answer 7

Mature cells from osteoblasts.
Maintain bone tissue.
Regulate mineral homeostasis.

Form a communication network through canaliculi, allowing nutrient exchange and waste products

Lacunae

Question 8

Osteoclasts: function, activity and location.

Answer 8

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

Question 9

What is Bone classification?

Answer 9

• 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

Question 10

Axial skeleton

Answer 10

Provides support and protection for vital organs including the brain, spinal cord, heart and Lungs.

Question 11

Appendicular skeleton

Answer 11

Facilitates movement and interaction with the external environment, integral to walking, running and using our hands

Question 12

Bone classification types

Answer 12

Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones
Sutural bones

Question 13

Long bones

Answer 13

Tibia
fibula
femur
phalanges
clavicle
radius
ulna
metacarpus
metatarsus

Question 14

short bones

Answer 14

tarsus
carpus

Question 15

irregular bones

Answer 15

temporal
vertebrae
sacrum
coccyx
mandible
maxilla
sphenoid
ethnic

Question 16

sesamoid bones

Answer 16

patella

Question 17

sutural bones

Answer 17

skull

Question 18

Long bone explanation and example

Answer 18

Long and slender, the femur is a long bone and the largest and heaviest bone in the body

humerus

Question 19

flat bone explanation and example

Answer 19

Thin, parallel surfaces, provide protection and due to surface areas serve as good attachment sites

scapula

Question 20

sesamoid bone explanation and example

Answer 20

Usually small, round and flat. Sesamoid bones are within this, but not everyone has them

patella

Question 21

Flat bones

Answer 21

frontal
rib
sternum
nasal
scapula
occipital

Question 22

irregular bone explanation and example

Answer 22

Complex shape with several characteristics, can have flat, round, short, notched or rigid surfaces

vertebrae

Question 23

short bone explanation and example

Answer 23

Usually small in appearance and for that reason are usually rigid and difficult to damage

carpal bones

Question 24

sutural bone explanation and example

Answer 24

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

Question 25

Bone metabolism

Answer 25

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.

Question 26

Bone density

Answer 26

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

Question 27

bone density

Answer 27

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

Question 28

Bone development

Answer 28

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

Question 29

embryonic development weeks 4-8

Answer 29

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

Question 30

Intramembranous Ossification

Answer 30

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.

Question 31

Intramembranous Ossification
process

Answer 31

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

Question 32

Endochondral Ossification

Answer 32

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.