lectures 2 Flashcards
Make up of bones
Mineral phase Organic phase water Hydroxyapatite( calcium phsophate) Collagen and other proteins
Calcium- where is it sotred
99% in bones
1% in serum
Why is calcium level important
For bodily functions eg blood clotting, nerve cell activity and other cellular activities
How is calcium levels maintained
Controlling rate of calcium resorption from bone into the blood and calcium deposition into the bones
Regulated by 3 main hormones - pth, vitamin d and
How can calcium be bounded
Protein bound
Diffusible- free
PTH - parathyroid hormone effect on bone calcium
FALL in blood calcium- detected by PTH receptors, PTH synthesis increased and released into teh blood
PTH binds to pTH receptors on osteoblasts, which produce RANKL, this stimulates osteoclast cells to proliferate which increases the resorption of bone which causes release of calcium from bone into the blood
What is PTH
amino acid peptide secreted by chief cells within teh 4 parathyroid glands, located on back of thyroid gland in the neck
PTH effect on kidneys and vitamin D
When theres low calcium
- decreased loss of calcium in the urine
Vitamin D is released - enhanced absorption of calcium from intestine
Vitamin D effect on calcium levels when low
Stimulates calcium and phosphate absorption in the intestine into the blood
Vitamin D role
Necessary for bone mineralisation
lack = osteomalacia
Why might you not have enough vitamin D
Not enough UV
Dietary requirements
Supplements
What is Calcitonin
secreted from parafollicular cells of the parathyroid gland in response to rising serum Ca2+ conc
How does calcitonin regulate calcium levels
When increased blood calcium levels
Inhibits osteoclast activity, inhibits ca2+ absorption by the intestines and inhibits renal tubular ca2+ reabsorption, reducing plasma ca2+ and phosphate concs
Increased ca2+ blood levels - HYPERCALCAEMIA
Thyroid gland releases calcitonin
Osteoclast acitivity is inhibited
Ca2+ reabsorption in the kidneys decreased
Ca2+ level in blood decreased
decreased Ca2+ blood levels - hypocalemia
Parathyroid glands release PTH
Osteoclasts release Ca2+ from bone
Calcium is reabsorbed from urine by teh kidneys
Calcium absorption int eh small intestine increases via vitamin D synthesis
Ca2+ level in blood increases
What is bone density
Measure of the amount of mineral ( hydroxyapatite) present in the bone
Used to diagnose osteoporosis
What can affect bone density
Availability of substrates
- Calcium intake, calcium absorption, functionality of PTH
Physiological factors
- weight bearing exercise, smoking, BMI, healthy diet
Biochemical factors
- steroid hormones, oestrogen, thyroid hormones
Bone density variation with age
Reduces whit age
In women- reduces after menopause- decreasing ostrogen levels
Do people need calcium supplements?
Vegans
Lactose intolerance
Fracture risk
Previous fracture Age Smoking status Medication ( steroids) Bone density Alcohol intake
Bone remodelling
phases names
Activation Resorption Reversal Formation Quinesence
Activation - bone remodelling
Preosteoclasts are attracted to the remodelling sites
Preosteoclasts fuse to form multinucelated osteoclasts
Resorption- bone remodelling
Osteoclasts dig out a cavity, called a resorption pit, in spongey bone or burrow a tunnel in compact bone
Calcium can be released into the blood for use in various bodily functions
Osteoclasts disappear
Reversal - bone remodelling
Mesenchymal stem cells appear along burrow where they PROLIFERATE(increase in no.s) and differentiate into pre osteoblasts
Formation- bone remodelling
Mature into osteoblasts at surface of borrow and release osteoid at the site, forming a new soft nonmineralised matrix
New matrix is mineralised with calcium and phosphorus
Quiescence- bone remodelling
Site with resting lining cells remains dormant until the next cell
Wolffs law
Everyday remodeling in response to stress
Bones will adapt based on teh stress or demands placed on them
Osteopenia
Midway point to osteoporosis - bone density is lowering but not as severe
On a scan, bones look darker - less mass
When loose bone mass and your bones get weaker
Disuse osteopenia
Loss of bone due to lack of normal stress
Bone breakage
Force to one side
Compresses on side where force is applied
On the other side - tension is caused= BREAK
TYPES OF BONE HEALING and when are they used
Primary - absolute stability and compression ( plates and screws) , no callous formed- good for joints
Secondary- relative stability, normal biological process of healing
CALLOUS formation
3 phases of healing
Reactive phase
reparative phase
remodelling
Reactive phase of healing
Haematoma formed
Blood clot
Blood supply to the bone cells that lie on either side of fracture is disrupted and they begin to die. Dead cells induce macrophages and osteoclasts to start removing the dead bone debris and cells from fracture site. Localized swelling
Reparative phase of healing
Hard and soft callous
SOFT CALLOUS – fibroblasts make fibrous tissue, new blood vessels add stability as they contain connective tissue, fibroblasts mature and differentiate into chondroblasts,
HARD CALLOUS- osteogenic progenitor cells form into osteoblasts and secrete bone matrix- woven bone
Remodelling phase of healing
- Woven bone lattice is rearranged itno the normal cortical and spongey bone arrangement. Woven bone is removed gradually by osteoclasts and replaced by osteoblasts
Factors influencing healing - 2 types and examples
FRACTURE VARIABLES
blood supply, complexity, immobilisation
PATIENT VARIABLES
nictoine, diabetes, diet, HIV ( affects osteoblasts, difficult to heal bone
What is non union
When bone doesnt heal
Atropic non union
Intermediate fragments are missing and scar tissue that lacks osteogenic potenital is left in their place
No callus forms
Hypertropic non union
Callus is formed, but the bone fractures have not joined
Can be due to inadequate fixation of the fracture and treated with rigid immobilisation or in a joint
Functions of skeletal muscle
Movement Control posture remove and store glucose Generate heat Metabolically active
Isometric contractions
Tension increases, muscle length remains the same. Important in maintaining posture
Contraction
Movement or generation of force
Isotonic contraction
Tension remains the same, muscles shorten, used in movement.
Concentric vs eccentric
Concentric = shortening muscle Eccentric = lengthening muscle
EMG
EEG
ECG
ecg = heart emg = skeletal muscle eeg= brain active
Egs of skeletal muscle relaxants
Botulinum toxin
Curare
Succinylcholine
Botulinum toxin
Prevents release of ACh containing vesicles
Causes paralysis of muscle and inhibition of secretion from exocrine glands normally stimulated by parasympathetic NS
Curare
Blocks nAChRs to cause paralysis ( used during surgery to prevent muscle spasm )
Succinylcholine
Short acting block of nAChR
Function of SR
Stores calcium
In musscles
Rapidly releases calcium ( triggered by action potential)
Rapidly restore calcium (using ATP driven calcium pumps
T tubules
Convey quickly the action potential deep inside the fiber
T tubules are continuous with surface membrane
