Principles of Skeletal System (Anatomy)

Question 1

Describe how bones are classified

Answer 1

Classified according to their shape:

• Long
• Short
• Flat
• Irregular
• sesamoid

Terminology

Crest / Ridge = long narrow line

Spine = long thin bony projection

Tuberosity = projection with a roughened surface, attachment site for muscles / tendons

Tubercle = projection with a roughened surface, a smaller tuberosity

Trochanter = projection with a roughened surface only found on femur, still a site for attachment

Fossa = a depression of a bone

Groove = a narrow linear depression

Foramen = opening

Notch - an incomplete opening

Condyle = rounded prominence with articular cartilage

Epicondyle = a projection lateral to the condyle

Facets = smaller projections covered with cartilage

Question 2

Describe the process of membranous and endochondral bone development

Answer 2

Bone developments begin at week 8 and finishes ~ 25 years

~ 300 bones at birth, 206 bones as an adult

Ossification

1. Endochondral (Cartilaginous ossification)
2. Intramembranous (Mesenchymal - within a fibrous membrane ossification, seen in mainly skull and clavicle)

Endocondral Ossification

Primary ossification centre

mesenchymal cells differentiate to osteoblasts

osteoblasts form bone collar on either side of hyaline cartilage = Hyaline cartilaginous template

Template replaced by bone as bone is depositing, deterioration of cartilage matrix

Blood vessel of periosteal bud penetrate into the depleting matrix, formation of spongy bone. Meanwhile condrycyte elongating bone and osteoblasts and osteogeneic cells helping new bone formation and depletion of maxtrix

Cartilage is replaced by bone as medullary cavity is forming; secondary ossification developing at cartilage

secondary ossification site forming spongy bones and blood vessels

Epiphyseal plate cartilage (metaphysis) between end portion (secondary site / epiphysis) and main site (diaphysis)

growth plate exists between diaphysis and epiphysis

Growth plate

Children have growth plates known as physis

where epiphyseal cartilage convert to bone, resulting in bone elongation

apophysis is where tendons attach to the bone

Intramembranous ossification

Direct mineralisation of connective tissue (mesenchyme) no artilage

Grows radially from a primary ossification centre

Question 3

Describe how bones are maintained and remodelled

Answer 3

Three main cell types:

• Osteoblasts
• Osteoclasts
• Osteocytes

Micro-structure of cortical bone

Osteons are circular areas where we find osteoblasts, osteoclasts and osteocytes

Each Osteon also has concentric layering of cells

Osteoblasts

Bone cells that are responsible for bone growth at a cellular level

• Deposit collagen and bone matrix called osteoids

Osteoblasts when trapped in bones forming/depositing, mature and become osteocytes

Each osteocyte communicates through small channels called canaliculi which control osteoblast and osteoclast activity

Osteoclasts

Secretes organic acids to dissolve mineral component of bone; enzymes to destroy organic osteoid matrix

Reabsorb bone tissue for remodelling and to free calcium to blood stream

Bone remodelling vs modelling

Remodelling = cycle of resorption and formation/deposition that optimises bone structure = maintenance

Remodelling - bone formation without prior resorption - result in an increase in bone bass, bone growth and maintenance of bone strength

Question 4

Describe the basics of bone fracture and bone deficiencies

Answer 4

Imbalance in bone remodelling

Can be caused by:

• Lack of excercise
• Hormonal changes e.g. menopause or acromegaly
• Lack of proper dietary intake: Vit A (remodelling), Vit C (connective tissue), Vit D (calcium absorption )

Bone fracture

Weakened bone has a lower breaking point

Bone fracture healing

Bone heals quickly due to its plentiful blood supply

the blood clot, encourages the growth of cartilage bridge (soft then hard callus)

followed by osteoblasts laying down new rough or woven bone

this is then remodelled into organised lamellar bone

Bone fractures in children

Fractures around the physes will usually heal quickly and many have a large tendency to remodel malunion since the bone is growing.

Question 5

Describe the classification of joints (arthrology); identify the types of joint movement

Answer 5

Joints can be cavitated or solid joints

most joints in the body are cavitated, synovial joints with synovial fluids

Solid joints are further classified to fibrous and cartilaginous

Fibrous = strong fibre connective tissues holding bones in place, very very little movements

Cartilaginous = have cartilages

Fibrous joints

Bones are bound by fibrous connective tissue, exhibit little to no mobility

Synostosis = fusion of two or more bones, e.g. sutures

syndesmosis = sheet of fibrous tissue between bones, e.g. osseous membrane

gomphosis = cone=shaped peg fits into a socket, Found in the mouth where the roots of the teeth articulate with the dental alveoli at the dentoalveolar joints.

Cartilaginous Joints

No synovial cavity

More movement than fibrous joint but still, little to no movement

bones are connected by fibrocartilage or hyaline cartilage

Symphysis = connected by fibrocartilage, e.g. intervetebral discs and pubic symphtsis

Synchrondosis = Connected by hyaline cartilage e.g. epiphyseal growth plate and costochondral joints

Synovial Joints

Synovial cavity between articulating bones

freely moveable

fibrous capsule formed by connective tissue

Pivot:

• One axis/bone projected outwards and movement is around one direction, uniaxial permitting rotation

Ball & Socket:

• multiaxial permitting movement on several axes

Condyloid:

• biaxial, permit flexion and extension, abduction and adduction and circumduction

Plane:

• usually uniaxial permitting gliding or sliding movements

Hinge:

• uniaxial permitting flexion and extension only

Saddle:

• Both surfaces are concave and interlock
• biaxial, permit movement in two different planes