MSK Flashcards
Difference between woven and lamellar bone
Woven (primary) Bone:
Made quickly,
Disorganised
No clear structure
Lamellar (secondary) Bone:
Made slowly,
Organised,
Layered structure
How does collagen contribute to bone function
Provides elasticity
How do minerals contribute to bone structure
Provides stiffness
What cells form bone
Osteoblasts
What is bone modelling
Gross shape is altered, bone added or taken away
What is bone remodelling
all of the bone is altered, new bone replaces old bone
Example of a sesamoid bone
Patella
Features of long bones
Tubular shape
Hollow shaft
Expanded, articulate ends
Feature of a short bone
Cuboidal in shape
Examples of short bones
Carpals
Tarsals
3 Features of flat bones
Plates of bone
Often curved
Protective
4 Examples of flat bones
sternum
scapula
skull
ribs
Features of sesamoid bone
Round
Contain nodules for tendon attachment
What are the 2 types of macro bone structure
Cortical - compact
Trabecular - cancellous - spongy
What is cortical bone
Dense, solid, only
spaces are for cells
and blood vessels
What is trabecular bone
Network of bony struts (trabeculae), spongy appearance many holes filled with bone marrow. Cells reside in trabeculae and blood vessels in holes
Histological appearance of osteocytes
stellate, entombed in bone
What are osteoprogenitor cells
They form a stem cell population in bone
Osteoblasts/ osteocytes are derived OP cells
What is osteoid
Unmineralised bone
What are osteoclasts
Osteoblasts that have been trapped within mineralised bone
How do osteocytes connect to surroudning cells
Via canaliculi
How do osteocytes connect to surroudning cells
Via canaliculi
Function/ characteristic of osteoblasts
Form Bone - in form of osteoid
Produce Type I collagen and mineralize the extracellular matrix by depositing hydroxyapatite crystal within collagen Fibrils
High Alkaline Phosphatase activity
Make non-collagenous proteins
Secrete factors that regulate osteoclasts ie RANKL
Functions/ characteristics of osteoclasts
Resorb Bone
Dissolve the mineralised matrix (acid)
Breakdown the collagen in bone (enzymatic)
High expression of TRAP and Cathepsin K
What is bone modelling
Gross shape is altered, bone is added or taken away
Desribe the process of bone remodelling
Activation - Monocytes on bone surface differentiate to become osteoclasts
Reabsorbtion- Osteoclasts secrete acid to dissolve the bone mineral
Reversal - Osteoblasts are stimulated/recruited
Formation - Osteoblasts secrete osteoid to form bone matrix
Quiescence - Without stimulation there is no action
Difference between primary and secondary osteons
Primary fill in holes left during very rapid formation and dont cut through lamellae
Secondary cut through layers of lamellae and drive remodelling
What does OPG stand for
Osteoprotegerin
How does RANK Ligand increase bone reabsorbtion
Binds to RANK receptors on monocytes
Monocytes differentiate to osteoclasts which actively reabsorb bone
Osteoblasts secrete more RANK L in the presence of oestrogen (as well as other hormones, GFs, and cytokines)
Describe the process of intramembranous ossification
- Condensation of mesenchymal cells into flat sheet
- Osteoblast precursors (osteoprogenitor cells) form on surface
- Differentiation into mature active osteoblasts
- Osteoid formation
- Mineralisation and incorporation of osteocytes
- Further osteoid formation
Describe the process of endochrondral ossification
- Chondrocytes produce a cartilaginous precursor
- Primary ossification centre is formed as osteoblasts lay bone onto the cartilage
- Osteoclasts break down the cartilage
- POC is vascularised as blood vessels invade
- Periosteum collar is formed outside the bone as perichondrium is broken down
- Parts of the spongy bone making up the POC are broken down to form the medullary cavity
- Process repeats at ends of long bones to form secondary ossification centre
- Some layers of cartilage remain between the SOC and POC, known as the epiphyseal (growth) plate
Desribe how Vitamin D is synthesised
- 7-dehydroxycholesterol is synthesised directly from ingested cholesterol (found in fatty foods)
- This is converted to Vitamin D3 (cholecalciferol), facilitated by UVB radiation from the sun
- Vitamin D3 is converted to 25-hydroxyvitamin D3 (aka CALCIDIOL) in the liver by 25-hydroxylase
- Calcidiol is converted to 1,25-dihydroxyvitamin D (aka CALCITRIOL) in the presence of PTH which stimulates 1-a-hydroxylase - occurs in the kidneys
- The presence of calcitriol can then go on and promote gut calcium ion absorption
Difference between a synchondroses and symphyses
Both cartilagenous joints
Synchondreses - bones are directly connected by hyaline cartilage, e.g. costal cartilages
Symphyses - connecting cartilage is a plate of fibrocartilage, e.g. pubic symphysis and intervertebral disc
What are gomphoses
A peg in socket fibrous joint found only in tooth articulation
Whatare syndesmosomes
Bones are connected by a cord or sheet of fibrous membrane
e.g between tibia and filbula
Where can condyloid joints be found
Metacarpal/ phalangeal
Composition of cartilage
water
proteiglycans
collagen
What are fascicles enclosed in
endotenon
what is the tendon enclosed in
Epitenon/paratenon - Outer tendon sheath
Difference between paratenon and epitenon
Epitenon sits inside paratenon
Epitenon acts as an elastic sleeve and reduces friction
Paratenon - CT with a protective function
Describe the cell characteristics of skeletal muscle
Striations
Long and cylindrical
Multiple nuclei at the edge
Cell characteristics of cardiac muscle
Striated
Single central nucleus
Branching - intercalated discs
Describe the inverse myotatic protective reflex
golgi tendon organs are stimulated -> nerve impulse trvaels to the spinal cord via afferent 1b neurones -> synapses onto interneurones -> alpha motor neuone innervates muscle -> muscle relaxes -> prevention of muscle/ tendon damage
Give 3 places smooth muscle can be find
arterial wall
wall of intestine
lung airways
What are the functional units of myofibrils
sarcomeres - between 2 Z lines
What is the H zone
region of the sarcomere containing only myosin
Contraction times of type 1 vs 2 fibres
type 1 - slow twitch
2 - fast twitch
How are type 1 and 2 fibres distinguished histologically
Can be distinguished using immunohistochemistry
Type 1 are red/brown
type 2 are paler
What surrounds muscle spindles
fibrocollagenous capsule
Describe the CT in skeletal muscle
Endomysium - fibrocollagenous ct between individual muscle fibres
Peri - binds together groups of muscle fibres to form fascicles
Epi - binds fascicles together
What are sharpeys fibres
Connects epimysium of skeletal muscle to collagen of bone
- wide area
What are the 2 types of type 2 fibres
Describe their differences
2a undergo aerobic respiration whereas 2b undergoes anaerobic 2a has a high number of: - blood vessels - myoglobin (red) -high mitochondrial density 2b has low number of the above
Why do skeletalmuscles have striations
myofibrils in register (lined up)
What connects neighbouring sarcomeres
z line
Cell characteristics of smooth muscle
Single central nucleus
No striation or branching
Spindle shaped
What are haversian canals
Central part of osteons that contain blood vessels
has surrounding concentric rings of lamellar bone with osteocytes
What do fibroblasts synthesise
Collagen and elastin
Which layer of the trilaminar disc does skeletal muscle develop from
Paraxial mesoderm
Does skeletal muscle contain stem cells
YES
contain a population called satellite cells
What collagen is found in sharpeys fibres
Type 1
What may some tendons lie in to protect them from frictional injury
Fibrocollagenous tendon sheath
What type of collagen are osteoids rich in
Type 1
What bones form via intramembranous ossification
Flat bones of skull, mandible and clavicles
What is the name of the interconnections between Haversian canals
Volkmanns canals
What are osteoclasts derived from
Monocytes
What is uric acid formed as a result of
Breakdown of purine
