Musculoskeletal & Rheumatology Flashcards
What 3 categories make up the Musculoskeletal System
Bone
Muscle
Connective Tissue
How many bones in adults and children respectively?
206 (+ sesamoids)
270 children
What is the Axial skeleton comprised of?
Cranium
Vertebral Column
Rib Cage
What is the Appendicular skeleton comprised of?
Pectoral girdle
Upper and Lower Limbs
Pelvic Girdle
What are the functions of the skeleton?
Supports body so you can stand up and not fall
Protection of your vital organs
Movement - works with muscles so you can get around
Mineral storage - Stores calcium and phosphate
Produces blood cells
How do bones develop in utero?
- Intramembranous Ossification* - First occurs after conception → flat bones
- Endochondral Ossification* - Begins 2 months into utero → long bones
Explain how intramembranous ossification leads to the development of mesenchymal to bone
- Mesenchymal stem cells aggregate and form osteoblasts by differentiation
- Ossification center forms
- Osteoblasts begin to secrete osteoid
- Peripheral mesenchymal cells continue to differentiate
- Osteoblasts secrete osteoid inwards towards the ossification center, trapping themselves, causing differentiation into osteocytes, hardening the bone -> calcification
- Osteoid continues to be deposited, assembles in a random manner around embryonic blood vessels
- Development of trabeculae with red bone marrow populating them
- Mesenchyme begins to differentiate into periosteum
- Lamellar bone replaces woven bone at outer edge creating layers#Internal spongy bone remains
- Vascular tissue within trabecular spaces forms red marrow
- Osteoblasts remain on the bone surface to remodel when needed
Explain how endochondral ossification leads to the development of mesenchymal to cartilage to bone before birth
- Mesenchymal stem cells differentiate into hyaline cartilage, which forms a ring of tissue around it (perichondrium)
- This cartilage then forms a calcified matrix, which then forms a primary ossification center (diaphysis) supplied by a nutrient artery
- Newly formed osteoblasts gather at the diaphysis wall to form a bone collar
- Chondrocytes within the central cavity enlarge, causing the matrix to calcify, making it impermeable to nutrients, causing cell death
- Central clearing forms where cells have died (supported by bone collar)
- Healthy chondrocytes elsewhere cause elongation
- Periosteal bud, which consists of arteries, veins, lymphatics, and nerves, and delivers osteogenic cells,
invades the cavity, causing the formation of spongy bone. - Osteoclasts degrade cartilage matrix while osteoblasts deposit new spongy bone, bone continues to elongate
- Diaphysis continues to enlarge and osteoclasts break down newly formed spongy bone
- Medullary cavity begins to form and cartilaginous growth now only within epiphysis causing a bony epiphyseal surface to form
- Diaphysis and epiphysis join at the epiphyseal plate, which is where bone growth happens after birth.
- Primary ossification center forms the center of long bones. Secondary ossification (epiphysis) centers form the ends of long bones (one on each end)
What are the different types of bone cells found and what do they do?
Osteogenic cell -> Bone stem cell
Osteoblasts -> Bone ‘forming’; secretes ‘osteoid’ and catalyzes the mineralization of osteoid
Osteoclasts -> Bone ‘breaking’, dissolve and resorb bone by phagocytosis and are derived from bone marrow
Osteocytes -> ‘Mature’ bone cell, formed when osteoblast becomes imbedded in its secretions and they sense mechanical strain to direct osteoclast and osteoblast activity
Where are Osteogenic cells and Osteocytes found respectively?
Osteogenic cells - Deep layers of periosteum
Osteocytes - Entrapped in matrix
Where are Osteoclasts and Osteoblasts found respectively?
Osteoblasts - Growing portions of bone, including periosteum and endosteum
Osteoclasts - Bone surfaces and at sites of old, injured, or unneeded bone
What are the organic and inorganic compositions of the bone matrix?
Organic - 40%
Type 1 Collagen 90%
Ground Substance 10% - Proteoglycans,
glycoproteins, cytokine, and growth factors
Inorganic - 60%
Calcium hydroxyapatite
Osteocalcium phosphate
Describe the structure of immature bone
Laid down in a ‘woven’ manner - relatively weak
Mineralized and replaced by mature bone
How would you describe the structure of mature bone?
Mineralized woven bone. Can be cortical (compact/lamellar) or cancellous (spongy).
Cortical bone is compact and suitable for weight-bearing. Cancellous bone is spongy and not suitable for weight-bearing.
Describe the structures of the individual mature bone types (Cortical and Cancellous)
Cortical
‘Compact’ - dense -> shell that surrounds osteon
Suitable for weight-bearing
Cancellous:
Spongy, trabecular, and has a lot of airspaces in it.
It’s light but not very strong. Not suitable for weight-
bearing
Describe what an osteon is comprised of?
Concentric ‘lamellae’ around a central ‘Haversian Canal’
The ‘Haversian Canal’ contains blood vessels, nerves, and lymphatics
What are Lacunae?
Small spaces containing osteocytes
Tiny Canaliculi radiate from lacunae filled with extracellular fluid
What are Volkmann’s Canals?
Transverse perforating canals in the bone connecting 2 Haversian systems together
What are the structures of a long bone (from to tip to center)
Epiphysis (at the joint)
Physis (growing plate)
Metaphysis (Right below physis)
Diaphysis (long bone itself)
What kind of bones undergo interstitial growth?
Long bones
What is the physis and what happens here during interstitial growth?
The physis is the zone of elongation in long bones
Physeal plates contain hyaline cartilage.
On the Epiphyseal side, the hyaline cartilage is active and divides to form a hyaline cartilage matrix.
On the Diaphyseal side, the cartilage calcifies and dies and is then replaced by bone.
What is the difference between interstitial growth and appositional growth?
Interstitial growth -> increase in length
Appositional growth -> increase in diameter or thickness
In the femur, where does growth occur?
Proximal physis around the hip and the distal physis around the knee
What is appositional growth?
Deposition of bone beneath the periosteum to increase thickness
