MSK Flashcards
Bone function
o Raises body against gravity o Determines body shape o Transmits body weight o Protects vital organs o Forms jointed lever system -> movement o Storage of bone marrow and minerals
Types of bone:
o Long bones: Tubular hollow shaft Expanded ends for articulation Femur and humerus – most bones o Short bones: Cuboidal shape Carpal bones (wrist) o Flat bones: Curved plates of bone Associated with protection Bones of the skull o Irregular bones: Various shapes Vertebrae -> spinal cord protection o Sesamoid bones: Round, oval bones embedded in tendon Patella – knee joint
Axial vs appendicular:
o Axial – skull, vertebrae, ribcage, coccyx
o Appendicular – bones of the arms and legs, scapula, pelvis
• Macro bone structure:
o Cortical – dense and compact, only space for cells/blood vessels o Trabecular (spongy) – network of bony struts filled with bone marrow
• Micro bone structure:
o Woven – quickly made, disorganised bone
o Lamellar – slowly made, organised layers of bone
• Intermembranous ossification:
o Produces flat bones – skull, teeth, clavicle
- Mesenchyme cells -> osteoprogenitor cells -> osteoblasts form primary ossification centre
- Osteoblasts secrete collagen and proteins -> forms osteoid (bony matrix)
- Osteoid is calcified -> engulfs osteoblasts to form osteocytes
- Osteoid is randomly laid down around blood vessels -> trabeculated (osteoblasts are on periphery)
- Peripheral osteoid becomes compact bone -> spongy bone contains bone marrow
• Endochondral ossification:
o Produces most bones in body – long bone most common example
o Embryonically begins as a hyaline cartilage model
- Collar formation:
- Cavity formation:
- Vascular invasion:
- Elongations:
- Epiphyseal ossification:
- Collar formation:
Osteoprogenitor cells -> osteoblasts
Osteoblasts secrete osteoid
Bony collar formed around shaft (diaphysis
- Cavity formation:
Cartilage in bone centre begins to ossify – primary ossification centre
Inner cartilage can’t get nutrients -> degrades and forms cavity
- Vascular invasion:
Vessels in periosteum invade cavity through nutrient foramen
Vessels bring blood, nutrients and osteoblasts/osteoclasts
Osteoclasts break down cartilage, osteoblasts secrete spongy bone
- Elongations:
Increased cell numbers + osteoid -> elongation of diaphysis
Vessels bud into cartilage at ends of bone – secondary ossification centre
- Epiphyseal ossification:
Ends of bone form spongy bone
Articular cartilage on end of bone – growth/epiphyseal plate on other side
• Collagen:
structure + synthesis
o Structure – 3 collagen molecules -> tropocollagen -> collagen fibril
o Hydroxypoline holds together 3 collagen molecules – assisted by vitamin C
o Synthesis – collagen molecules inside cell -> tropocollagen outside cell
(^) Types of collagen
I - skin II - cartilage III - liver, bone, spleen (reticulum) IV - basement membrane V - placenta
• Calcium function and distribution:
o Skeletal calcium – 1200g o Extracellular calcium – 1g o Functions: Normal blood clotting Muscle and nerve function o Blood distribution: Over half protein bound/complexed – not useable Under half ionised – useable Alkalosis causes more protein bound calcium – ALBUMIN
• Calcium kinetics:
3 of them
o Gut – absorption in, faecal Ca out
o Kidney – reabsorption in, excretion out
o Bones – resorption in, formation out
Ca absorption in the gut %%%%%
o Gut:
Actively absorbed in duodenum and jejunum
Passively absorbed in ileum and colon
Ca absorption in the kidney %%%%%
Majority passively reabsorbed in PCT and ascending loop
Minority actively reabsorbed in DCT – under hormonal control
• Calcium and phosphate regulation:
o Parathyroid hormone:
Secreted by chief cells in 4 parathyroid glands
Chief cells detect low serum calcium with Ca surface receptors
Calcitriol regulates PTH – binds to vit D nucleus receptor
Kidney actions:
• Increased calcium reabsorption in DCT
• Decreases phosphate reabsorption in PCT
• Increases 1,25 (OH)2 vit D metabolism
Bone actions:
• Increases osteoclast activity, decreases osteoblast activity
• More Ca from bone degradation
o Calcitriol:
Skin – 7-dehydrocholesterol -> vitamin D (via UV)
Liver – vitamin D -> 25-hydroxyvitamin D (not metabolically active)
Kidney – 25-hydroxyvitamin D -> 1,25-dihydroxyvitamin D (active)
High serum PTH/low serum calcium = more 1,25-OH vit D produced
Stimulates increased Ca and phosphate absorption in gut
-Phosphate
FGF23 major regulator of phosphate metabolism
Produced by osteocytes in response to increased phosphate levels, PTH and 1,25-OH vit D
Decreases proximal tube reabsorption of phosphate and gut reabsorption of phosphate
