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Type I fibres
need to have a small cross-sectional area so that there is a minimal distance for oxygen to diffuse from the capillaries to the mitochondria
Type II fibres
have fast actin-myosin ATPase - can use ATP very quickly and generate a lot of power.
Because it’s impossible to store much ATP, Type II fibres have to replace it very quickly and to do that they rely on anaerobic metabolism.
Thus, type II fibres don’t need many mitochondria
anaerobic metabolism is associated with…
the rapid onset of fatigue due to changes that affect the homeostasis of the muscle cells.
the human body has
206 bones
structural role of bones
- Enable movement
- support/form structure
- Protection for internal organs
bone’s role in homeostasis
Storehouse for essential minerals
* 85% of phosphorus
* 99% of calcium
site of metabolism
endocrine functions
cortical bone
Compact/dense (80% of total bone mass)
External layer
10% porous
Provide strength to structure
Cancellous bone
trabecular/spongy (20% of total bone mass)
Highly porous (50-90%)
Network of thin porous trabeculae (hydraulic properties) in directions of stress - shock absorption
large bone SA for mineral exchange
“inside”
Collagen and Hydroxyapatite Form Bone Matrix
Collagen cross links
* provides elasticity
Hydroxyapatite crystals
* Source of Pi and Ca2+
* Provides rigidity
Brittle bones
too much hydroxyapatite
Bendy bones
too much collagen
flat bones form via…
Intramembranous Ossification
long bones form via…
Endochondral Ossification
Long bone structure
Marrow cavity
Major blood supply
Epiphysis (trabecular/spongy bone)
Metaphysis (trabecular and cortical)
Diaphysis (cortical)
Endosteum
Periosteum
Longitudinal growth involves:
- Chondrocyte proliferation and hypertrophy
- Calcification of hypertrophic cartilage and apoptosis
- Degradation of transverse septa, vascular invasion
- New bone formation on calcified remnants by osteoblasts – primary spongiosa
post-natal growth
- limbs continue to develop until cessation of growth at 13-18 years of age through growth plates
- Joints are cartilaginous at birth - Epiphyses ossify in post-natal development
Osteoporosis
- characterised by compromised bone structure and strength, predisposing to an increased risk of fracture
- disrupted/thin/weak rods - some disconnected
- more osteoclasts than osteoblast (imbalanced bone remodelling)
Oestrogen
- Acts on both osteoclast and osteoblasts to:
Decrease bone resorption and increase bone formation - A marked decrease in oestrogen during menopause is associated with rapid bone loss via: Increase in bone resorption and decrease bone formation
Testosterone
- Increase bone formation
- A source of oestrogen
- Reduces with age > bone loss and fracture
Primary Risk factors for Osteoporosis
Age – older higher
Gender - female higher risk (post menopause)
Fracture previously
Height/BMI – short and frail = higher risk
Genetics
Lifestyle Risk factors for Osteoporosis
Exercise that increase bone mass - weight bearing exercise
Bone responds to load/unload
Mass increases in response to load
Osteoclast
break down bone
Osteoblast
build new bone
