2.02 Flashcards
Define Osteoporosis
Risk factors
Imbalance of bone remodelling causing a decrease in bone mass and bone density, and a deterioration of bone microarchitecture. Affects areas of high trabecular bone the most, (spine, wrist, head of femur).
Risk factors - Age, female, menopause, genetics, low physical activity, smoking, alcohol, low Vit. D levels, low dietary Ca, drugs (e.g. corticosteroids), diseases (e.g. hyperthyroidism)
Describe the concept and mechanism of osteoporosis
Osteoporosis occurs when the coupling of bone resorption and bone formation is disrupted.
Role of hormones in the development and maintenance of bone mass
Vitamin D
• Ensures that enough blood Ca and PO4 is available
• Low Vit. D leads to increased PTH > low blood phosphate and calcium > impaired bone mineralization (rickets)
PTH
• Increases bone resorption
• Reduces bone density
• Increased by both low Vit. D or low Calcium
Sex Hormones:
• Maintains coupling between osteoblasts and osteoclasts, keeps bone cells alive, reduce bone turnover, mechanically strengthen bone
Interaction between mechanical loading, calcium-regulating hormones and sex steroid hormones
in maintenance of bone mass
Mechanical Loading is needed to promote formation of bone. Causes bone to remodel in areas that experience stresses
Sex hormones maintain bone - test - causes remodelling, strengthening. Estrogen - balances bone turnover
Calcium-reg hormones - PTH, Vit D
Bone loss due to glucocorticoid excess or sex steroid deficiency, smoking and alcohol
High concentration of GC (glutocorticoids) are CATABOLIC and associated with reduced bone mass/increased fracture risk. Via decreasing Ca absorption in gut, Ca loss in kidney, loss of osteoblasts.
Smoking can decrease blood supply to bone. Alcohol increases PTH
Mechanisms of drugs treating osteoporosis
Bone resorption inhibitors o Bisphosphonates → Kill osteoclasts on bone surface; inhibit bone remodelling (e.g. Risedronate, Alendronate, and Zoledronic Acid) o RANKL-inhibitor • Bone formation stimulators o Calcium o Vitamin D
Anatomical organization of the vertebral column
Primary curvature in fetus and new born. Reflect in-utero shape of vertebral column, remain in thoracic and sacral regions
Secondary curvature develops in cervical and lumbar spines to bring trunk above lower limbs for efficient bipedal locomotion
Issues with curvature
Kyphosis = Excess primary curvature Lordosis = Excess secondary curvature Scoliosis = Abnormal lateral Curvature of Spine
Basic components of a typical vertebrae
Vertebral column protects spinal cord, support for head and neck, movement – multi segmental, articulated, plus attached muscles
Articular process – region of bone. Articular facet – region covered with cartilage
Vertebral foramen – opening in single bone. Vertebral canal – passageway where all articulated together. Intervertebral foramen – foramen between articulated vertebrae
Features of C1, C2, C7, thoracic and lumbar vertebrae
C1 Atlas, ring of bone, no vertebral body, no spinous process, large lateral masses
C2 Axis, Dens, large superior articular facets
C7 Vertebra prominins, long spinous process
Thoracic vertebrae, demifacets on lateral sides of body for rib attachments, long downward projecting spinous process
Lumbar vertebrae - large body
Function of intervertebral discs
25% of intervertebral column, it is a secondary cartilaginous joint and functions to tie vertebral bodies together, tansfer weight, allow movement, shock absorber
Parts of intervertebral disks
Annulus Fibrosus → Fibrous outer ring; comprised of collagen
Vertebral Endplate → Cartilage plates adjacent to vertebral bodies
Nucleus Pulposus → Semifluid shock absorber in center
Location and general function of ligaments
Ligamentum flavum → Between lamina, behind vertebral canal - to maintain upright posture Interspinous ligament → Between spinous processes - to limit flexion (bending forwards) through restricting separation of the spinous processes of the vertebral column.
Supraspinous ligament → Between tips of spinous processes - helps maintain the upright position of the head
Posterior longitudinal lig. → Run along posterior sides of vertebral bodies and disks - Limits flexion of the vertebral column and reinforces the intervertebral disc
Anterior longitudinal lig. → Run along anterior sides of vertebral bodies and disks
Extrinsic back muscles
Move the upper limbs and ribs, supplied by anterior rami, except trapezius CNXI, lie most superficial on the back
Intrinsic back muscles
Located posterior to vertebral column, move the back and head, supplied by posterior rami
Intrinsic cont. Splenius, erector spinae, transversospinalis
Splenius group (Superficial) - extension, rotate to same side Erector spinae group (Middle) - straighten the back and provide for side-to-side rotation Transversospinalis group (Deepest) - rotate vertebral column to opposite side
Neural structures and meninges in the vertebral column
- Nerve roots join to form spinal nerve. Posterior roots (sensory fibers) and anterior roots (motor fibers).
Segments of spinal column - 7 Cervical, 12 Thoracic, 5 Lumbar, 5 pelvic sacral (fused), <5 coccygeal (fused) - Spinal nerves exit from intervertebral foramen
- Meninges: Pia mater – adherent to spinal cord and nerve roots, Arachnoid mater, Dura mater
Define dermatome and myotome
Dermatome – Area of skin innervated by sensory fibers from a single spinal nerve
Myotome – Area of muscle innervated by motor fibers from a single spinal nerve
Spinal plexus
Spinal Plexus: C1 – C5 = Cervical Plexus C5 – T1 = Brachial Plexus L1 – L4 = Lumbar Plexus L4 – S4 = Sacral plexus
Anterior and posterior rami
Posterior rami – supply skin of back, zygaopophyseal joints and intrinsic back muscles
Anterior rami – supply skin, joints and muscles of neck, limbs and trunk, larger than posterior rami, contribute to plexuses or continue as intercostal or subcostal nerves (T12)
Impacts of rise and fall of calcium
A drop in calcium – partial depolarization, channels open to sodium, tetanus and even seizures
Too much calcium – partially closes the channels, reduced ability to depolarize, cannot elicit action potentials, neurological dysfunction, cardiac arrythmia, dehydration, long term: kidney calcification and stones
Impacts of changes in phosphate levels
High phosphate long term – soft tissue mineral deposition, short term – inadequate bone mineralization – osteoid produced (not fully mineralized – causes Rickets/osteomalacia)
PTH - Source, function and regulation
Parathyroid gland has lots of calcium sensing receptors, which detect increases/decreases in body’s calcium levels, increases Ca release from bone
Released by low calcium via calcium sensing receptor (main modulator)
Decreased by calcitriol and by high calcium in circulation
Sources and metabolism of vitamin D, its regulation and actions
Main source of vitamin D is UVA radiation. Vitamin D is a fatty hormone, UVA radiation opens carbon rings and helps create vitamin D
Regulated by PTH
Action - facilitate intestinal absorption of calcium as well as helping form hydroxyapatite
