Week 35- Upper Limb and Bone Flashcards
What is circulating calcium critical to?
Neural function Muscular function Blood clotting Cell replication Secondary messenger signalling
Does the body respond faster to a low or high blood calcium level?
Faster response to decreases in blood calcium concentration
What is the bodies homeostatic response to low calcium levels in the blood?
- Low calcium levels
- Parathyroid gland stimulated
- Chief cells in parathyroid gland release PTH
- PTH promotes
- release of Ca2+ from bone ECM
- Slows loss of Ca2+ in urine
- Promotes kidneys to release calcitriol (active form of Vitamin D –> increases GIT Ca2+ absorption - Blood calcium raised to normal levels
What is the bodies homeostatic response to high calcium levels?
- High calcium levels
- Thyroid gland stimulated
- C-cells in the thyroid gland produce Calcitonin (CT)
- CT inhibits osteoclasts (reduced bone demineralisation)
- Decreases blood calcium
Where is Fibroblast Growth Factor-23 (FGF23) secreted?
From bone in response to increased plasma Hydrogen phosphate (HPO)
What does FGF23 do?
Reduces phosphate concentrations in the blood:
- Increases renal excretion –> by decreasing resorption
- Decreases gut absorption –> decreases calcitriol production (as phosphate follows calcium)
What are the two main bone textures?
- Compact –> dense outer layer –> smooth and solid –> 75% of bone is like this
- Spongy (cancellous or trabecular) –> honeycomb-like –> deeper than compact bone –> much larger SA –> more metabolically active
What kind of strength does collagen contribute to bone?
Tensile
What strength does calcium contribute to bone?
Compressive strength
What are the 5 major cell types in bone?
- Osteogenic cells –> mitotically active –> differentiate into osteoblasts or bone lining cells
- Osteoblasts –> mitotically active –> Bone forming cells –> secrete unmineralised bone matrix (osteoid) –> initiates bone resorbtion
- Osteocytes –> mature cells –> monitor and maintain bone matrix –> comunicate with blasts and clasts to regulate remodelling
- Bone lining cells –>on bone surfaces –> thought to maintain matrix
- Osteoclasts –> derived from haematopoietic stem cells –> bone resorbing cells
What secretes osteoid?
Osteoblasts
What is in osteoid?
- Ground substance (proteoglycans and glycoproteins)
2. Collagen fibres
What allows for the resilience of bones?
Sacrificial bonds between collagen molecules
- They stretch and break easily on impact –> dissipates energy and prevents fracture
- If there is no additional trauma these bonds reform
How much of bone mass is Hydroxyapatites?
65%
What is the composition of Hydroxyapatites?
Mainly tiny calcium phosphate crystals in and around collagen fibres
Responsible for hardness and resistance to compression
What is the effect of Wnt signalling on bones?
Cause mesenchymal stem cells to differentiate into osteoblasts
What does IGF-1 do to osteoblasts?
Increases activity
What determines IGF-1 secretion?
IGF-1 secretion by the liver is stimulated by GH (growth hormone)
What is the effect of increased vs decreased GH on bones?
Increased –> giantism –> increased bone length
Decreased –> dwarfism –> smaller bones
Where do long bones grow from in childhood?
Epiphyseal plates - endochondral (cartilage is replaced)
What does the level of bone accretion and bone resorption determine?
Bone mass
What happens in over secretion or abuse of GH?
After long bones fuse –> causes appositional growth (widening)
–> known as acromegaly
What factors is bone accretion dependant on?
- Sufficient Ca2+
- Vitamin D
- Sufficient weight bearing activity (most effective if varied and short intense bursts)
What is the bodies main driver of bone resorption?
PTH
What factors explain calcium loss with aging?
- Less osteoblast activity with increased age:
- Due to decreased IGF-1 and vitamin D production - Decline in sex steroid production in aging:
- Oestrogen in particular –> important to supress osteoclastic activity - Peak bone density normally attained in early adulthood:
- Bone density is determined by remodelling processes influenced by:
- Diet, Age, Hormonal regulation
How does oestrogen supress osteoclast activity?
Supresses RANKL –> a ligand that increases osteoclast activity
What non-pharmacological strategies is there to prevent calcium loss?
- Diet –>
- calcium intake
- protein (for collagen synthesis)
- increased body weight (increases Ca2+ storage potential) - Vitamin D –> increases calcium absorption from diet
- Exercise –> weight bearing –> minor damage –> stimulates bone remodelling
What is the three major functions of bone?
Structural –> support and insertion sites for muscles and ligaments
Protective –>skull and thoracic cage provide protection
Metabolic –> reservoir of essential minerals (calcium, phosphorus and magnesium)
What is the two divisions of the skeleton?
Axial –> the rest –> roles in structure, protection and metabolic function
Appendicular –> limbs –> primarily structural role
What does bones hard matrix consist of?
- Matrix proteins –> Type 1 collagen (framework), growth factors (bone morphogenetic proteins and transforming growth factor beta (TGF-beta), proteglycans
- Minerals –> calcium phosphate most common in complex called hydroxyapatite (provides structural resilience)
What two cell types are present in bone?
- Osteoblasts –> consisting of osteoblasts (bone forming cells), osteocytes (interconnecting network through bone matrix), lining cells (cover metabolically inactive bone surfaces)
- Osteoclasts –> bone reabsorbing cells
- Mono or multi nucleated cells
- Monocyte-macrophage lineage
- Short lived cells
- Recruited to bone surface of sites of remodelling
How frequently is the adult skeleton completely renewed?
7 years
What are the functions of bone remodelling?
- Release of minerals to maintain levels in circulation
- Allow changes in bone structure in response to growth or load bearing
- Bone homeostasis –> bone formation = bone resorption
What are the two types of bone?
- Cortical –> predominately structural or load bearing function
- Dense bone –> diaphysis (shaft or central part of long bone) of long bones. - Trabecular –> structural and metabolic functions (more prone to disease)
What type of bone disorder is osteoporosis?
Metabolic bone disorder:
- Characterised by significant loss of bone mineral density and loss of microstructure
- Bone brittle and fragile –> prone to fractures
- Imbalance between bone formation and resorption
- Abnormality in the bone remodelling process
- Mineralisation as well as collagen issue
What is the cycle of bone remodelling?
- Osteoblasts and osteoclasts transform resting bone into active remodelling sites – bone remodelling units (BMU)
- Osteoclasts in the BMU –resorb bone tissue and undergo apoptosis
- Osteoblasts migrate to the resorption zone to form new bone matrix which later becomes mineralised
What factors can stimulate osteoclasts?
- PTH
- Glucocorticoids
- High dose Vitamin D
- Interleukins
- Prostaglandins
- Tumour necrosis factor
What factors are osteoclasts inhibited by?
- Calcitonin
- Oestrogens
- Androgens
What are some types of PRIMARY osteoporosis?
- Idiopathic (unknown cause) –> in children and young adults
- Type 1 –> Post menopausal –> due to oestrogen deficiency
- Type 2 –> Associated with “normal” aging process
What are some types of SECONDARY osteoporosis?
Results from other clinical disorders eg:
- Hyperthyroidism
- Hyperparathyroidism
- GIT or renal issues
- Long term glucocorticoids
- ETC
What does the inside of an osteoporotic bone look like?
Healthy bone has small pores –> osteoporotic has large pores
What are the clinical manifestations and complications of osteoporosis?
- Initially asymptomatic
- Progressive loss of height (vertebrae compression) –> kyphosis or scoliosis
- Skeletal deformity
- Bone pain (due to compression fractures)
- Fractures
What is kyphosis?
Anterior curvature of the thoracic spine (forwards movement)
What is scoliosis?
Coronal movement of the thoracic spine
What is Osteomalacia?
Abnormal or deficient mineralisation of the organic matrix
Leads to softening of bones due to a deficiency of the Vitamin D metabolism
What is some causes of osteomalacia?
- Dietary Vitamin D deficiency
- Intestinal malabsorption
- Failure to metabolise Vitamin D (renal disease or congenital enzyme deficiencies)
- Anticonvulsant treatment –> phenytoin
What is Rickets?
Osteomalacia in children –> affects the growing skeleton
Associated with poor mineralisation of the cartilage within the epiphyseal growth plate
(mineral issue)
What are some clinical manifestations of Osteomalacia?
- Bone pain
- Altered mobility
- Muscle weakness
- Pathological fractures
- Dorsal kyphosis
- Rickets (children) –> bone growth retardation and deformation in lower extremities
What is Paget’s disease?
Disorderly bone remodelling –> forms disorganised osseous (bone) tissue which is weaker than normal bone
- Doesn’t affect whole skeleton –> tends to be localised to specific areas
What is the affect on osteoclasts in Paget’s disease?
- Affected osteoclasts are dysfunctional and morphologically abnormal (increased size, shape and possess multiple nuclei)
- Affected osteoclasts show excessive and accelerated bone resorption
What is the cause of Paget’s disease?
Aetiology linked to genetic factors –> autosomal dominant inheritance pattern
What are some symptoms of Paget’s disease?
Bone pain Bone deformation Fractures Kyphosis, spinal cord compression, paralysis (pagetic lesions on spine) Hearing a visual disturbances (impinged cranial nerves) Vertigo (damage CNVIII) Nerve root compression Headaches (pressure on cranial vault) Hydrocephalus Dental problems
What is the primary defect in osteoporosis?
Bone loss
What is the primary defect in osteomalacia/rickets?
Reduced vitamin D
What is the primary defect in Paget’s disease?
Remodelling
What are the 7 classifications of fractures?
- Complete or incomplete
- Closed (simple fractures) –> clean break with intact soft tissue
- Comminuted –> splintered with intact soft tissue
- Compound fracture –> fracture site communicates with skin surface
- Complicated fracture –> involves adjacent structures –> blood vessels, nerves etc
- Stress fracture –> small linear fractures
- Pathological fractures –> fracture of bones weakened by disease
What is the difference between a simple and compound fracture?
Simple –> fractures bone without skin break
Compound –> fractures bone and bone pierces the skin
What are the four stages of bone healing?
- Haematoma formation
- Fibrocartilaginous callous formation
- Ossification
- Remodelling