MSK Flashcards

Question

What stimulates PTH (parathyroid hormone) secretion? What does PTH do?

Answer 1

- Decreased serum calcium results in increased PTH secretion - PTH increases bone remodelling rates and calcium RESORPTION - Presence of PTH leads to the conversion of 25-hydroxyvitamin D (calcidiol) to the active 1,25-dihydroxyvitamin D (calcitriol = active vitamin D) - Combined effect leads to an increase in serum Ca2+ levels

Answer 2

- Vitamin D cannot be directly consumed, and we don't actually absorb it from the sun - Active vitamin D increases calcium absorption and is fundamental in maintaining bone mineral density

Answer 3

- 7-dehydroxycholesterol is synthesised directly from ingested cholesterol - This is converted to Vitamin D3, facilitated by UVB radiation from the sun - Vitamin D3 is converted to 25-hydroxyvitamin D (CALCIDIOL) in the liver, via the cytochrome p450 system - Calcidiol is converted to 1-25-dihydroxyvitamin D (CALCITRIOL) in the presence of PTH - The presence of calcitriol can then go on and promote gut calcium ion absorption

Answer 4

- Calcitonin is produced by C cells (parafollicular cells) in the thyroid gland - Action not really known, however is secreted in response to serum calcium ion increase, so it is potentially involved in the negative feedback mechanism to reduce bone reabsorption

Answer 5

- Dietary calcium sources included dairy, vegetables, and oily fish - Extracellular calcium accumulated via bone resorption, reabsorption in the kidney or absorption in the small intestine - Extracellular calcium used in bone deposition, kidney filtration and secretion in the small intestine

Answer 6

- FGF-23 - Produced by osteocytes in response to: - Rise in serum PO4- - Presence of PTH - Presence of calcitriol

Answer 7

- Binds to Klotho-FGF receptors, resulting in decreased expression of Na+ cotransporters in renal tubules - It also decreases calcitriol formation - Resulting in increased PO4- excretion + decreased reabsorption - FGF-23 secretion by PHEX when serum phosphate levels fall

Answer 8

- Dietary phosphate is sourced from meat, diary, nuts, and seeds - Extracellular phosphate is accumulated via bone resorption, gut absorption, or renal reabsorption - Extracellular phosphate is either used in bone formation, or is excreted (urine/faeces)

Answer 9

- Osteoblast and osteoclast activity is balanced in health - a loss of balance is pathological - They usually communicate via cytokines, with some OPG (osteoprotegerin) and RANK signalling

Answer 10

- REDUNDANT = many different types can perform one job - PLEIOTROPIC = can initiate effect on many different tissues

Answer 11

- RANK ligand stimulates increased osteoclast activity, increasing bone reabsorption: - Secreted by osteoblasts - Binds to RANK receptors on monocytes - Monocytes differentiate to osteoclasts which actively reabsorb bone - Osteoblasts secrete more RANK ligands in the presence of oestrogen (as well as other hormones, GFs, and cytokines)

Answer 12

- Osteoprotogerin (OPG) inhibits osteoclast activity, allowing increased bone formation: - Produced by osteoblasts and stromatolites cells - Binds to RANK ligands, preventing osteoclast activation - Decreases reabsorption rates

Answer 13

- Wolff's law: in a healthy individual, bone will remodel itself to become more resistant to loading - If bone loading increases, bone will remodel itself to become more resistant to loading - These changes result in responsive variation of bone density in appropriate areas

Answer 14

- Actin: - Thin filament comprising two g-strands, forming an f-actin helix - Globular protein + has troponin and tropomyosin incorporated - Interacts with myosin - Myosin: - Thick filament comprising 2 heavy chains and 4 light chains - Hydrolyses ATP - Interacts with actin

Answer 15

- Tropomyosin: - Thin filament made up of 2 helical peptide chains - Occupies each of the longitudinal grooves between 2 actin strands - Regulates muscle contraction - Troponin = 3 types, all thin filaments: - Troponin C = binds to calcium ion - Troponin I = inhibits myosin and actin action - Troponin T = binds to tropomyosin

Answer 16

Elastic filaments that maintain the alignment of the sarcomere

Answer 17

By the endomysium

Answer 18

1. An impulse reaches the neuromuscular junction 2. Presynaptic membrane depolarises, opening voltage-gated Ca2+ channels, enabling Ca2+ influx 3. Vesicles migrate and fuse with the presynaptic membrane, releasing ACh into the synaptic cleft via exocytosis 4. ACh binds to receptors on the sarcomere, depolarising the sarcomere (through LGSICs and Na+ influx) 5. This results in T-tubule depolarisation, and subsequent depolarisation of the sarcoplasmic reticulum 6. Sarcoplasmic reticulum releases Ca2+ - this initiates sarcomere contraction

Answer 19

1. Ca2+ ions from the sarcoplasmic reticulum bind to troponin C, resulting in a conformational change of troponin 2. Troponin moves, exposing actin filament binding sites 3. Myosin head binds to actin, forming cross links - power stroke is formed, shortening the sarcomere 4. ATP binds to myosin head and is hydrolysed, this releases energy, breaking the cross links, resulting in the detachment of actin and myosin 5. Myosin head reattached to the next actin binding site and the cycle is repeated, continuing sarcomere shortening and muscle contraction

Answer 20

- Ligaments = bone to bone, low Type I collagen levels, high elastin content, random organisation, blood supply for prom insertion points - Tendons = bone to muscle, high Type I collagen levels, low elastin content, highly organised, many are avascular, but some receive blood from surrounding sheath

Answer 21

- Fibrous = formed vis intramembranous ossification, tendon or ligament attached to bone via Sharpey's fibres - Fibrocartilagenous = formed by endochondral ossification, tendon or ligament attached to the bone through a gradual change from collagenous ligament, to fibrocartilage, to mineralised bone

Answer 22

- Phase 1 = "toe" region of graph, increase in load results in crumpled collagen fibres - Phase 2 = linear region, fibres straighten and stiffness rapidly increases with loading - Phase 3 = maximum deformation and ultimate tensile strength, at this point, progressive fibre failure occurs - Phase 4 = yield point, beyond this point there is complete failure of connective tissue to support loads

Answer 23

- The head of the femur and the acetabulum of the pelvis - Covered in articular cartilage

Answer 24

- Ligaments of the hip joint act to increase stability - Two groups: - Intracapascular (only one is ligament of head of femur) - Extracapascular (ileofemoral, pubofemoral, ischiofemoral)

Answer 25

- Femoral nerve - Sciatic nerve - Obturator nerve

Answer 26

Upper lateral quadrant of the gluteus is the most common site for intramuscular injections as it avoids all major nerves and blood vessels

Answer 27

- Immobile, slightly mobile, freely mobile - Mostly fibrous, mostly cartilaginous, mostly synovial

Answer 28

- Held together by fibrous tissue - Held together by cartilage - Held together by a synovial fluid filled capsule. All have articulations cartilage, a joint capsule, a joint cavity, synovial fluid, and reinforcing ligaments

Answer 29

- Fibrous joints = synarthrosis (immovable): - Sutures = only occur within bones of skull - Syndesmoses = bones connected by a cord (ligament) or sheet (interosseous membrane) of fibrous tissue - Gomphoses = a peg-in-socket fibrous joint only found in tooth articulation

Answer 30

- Synchondroses = bones are directly connected by hyaline cartilage - Symphses = connecting cartilage is a pad or plate of fibrocartilage

Answer 31

- Synovial joint = articulating bones are separated by a fluid-filled cavity. Six types: - Ball & socket - Condyloid - Hinge joint - Pivot - Saddle - Gliding

Answer 32

a) - ball within a socket - wide range of movement in all planes - shoulder and hip joint b) - oval sitting within an oval cavity - movement in two planes - metacarpophalyngeal c) - elongated oval in a curved socket - large range of movement in a single plane - elbow

Answer 33

a) - bone pivots around an axis - allows a large amount of rotation - C1/C2 b) - two saddle shaped surfaces articulating - movement in two planes - thumb c) - two flat surfaces articulating - limited movement in 2 planes - carpal joints

Answer 34

- Ligaments: - patella ligament - collateral ligaments (medial + lateral) - cruciate ligaments (anterior and posterior) - Bursae = sac filled with synovial fluid that acts to reduce wear and tear - Menisci: - C-shaped fibrocartilage - Acts as shock absorbers - Deepen the articular surface thus increasing the stability of the joint

Answer 35

- Largest sesamoid bone = patella, allows quadriceps to be able to extend the knee better - ACL prevents anterior dislocation of the tibia into the femur and the PCL prevents posterior dislocation

Answer 36

- Has an important role in stabilising the patella + stopping it from dislocating. At its most inferior border, most of its muscle fibres run horizontally so when they contract, they pull down on the patella to stop it dislocating laterally. This is important because the femur is at an angle such that if this didn't occur, the patella would otherwise dislocate laterally when the leg is flexed - Lateral condyle of the femur is large, which helps to prevent the lateral dislocation of the knee during flexion, similar to vastus medialis

Answer 37

- Type of joint - ball and socket - Bony surfaces - shallow glenoid fossa and large numeral head - Laxity of the joint capsule

Answer 38

- Rotator cuff muscles = surround shoulder joint, attaching to the tubercles of the humerus and fuse with joint capsule, resting tone of these muscles pulls the numeral head into the glenoid fossa - Glenoid labrum = fibrocartilagenous ridge surrounding + deepening the glenoid fossa - Ligaments = reinforce joint capsule, form the coraco-acromial arch

Answer 39

Glenoid fossa

Answer 40

- Attachment site for the triceps tendon - Known as the 'funny bone', runs alongside the ulnar nerve

Answer 41

- High uric acid levels in the blood cause urate/uric acid crystals to deposit in the joints - The crystals cause inflammation, which then causes the swelling, pain + redness

Answer 42

- Poorly soluble in plasma, the lower the pH the less soluble it becomes - Uric acid comes from purines

Answer 43

- Diet - Breakdown of nucleotides from tissues - Synthesis in the body

Answer 44

- Excreted in the urine - Breakdown in the gut

Answer 45

- Meat - Offal - heart, liver + kidney - Seafood - muscles - Fish - herring and sardines - Oatmeal, soya + yeast extracts - Fructose - found in soft drinks

Answer 46

- Metabolic syndrome: - obesity - raised triglycerides - raised blood pressure - Coronary heart disease - Diabetes

Answer 47

- Rickets is a skeletal disorder that's caused by a lack of vitamin D, calcium, or phosphate - People with rickets may have weak and soft bones, and, in severe cases, skeletal deformities

Answer 48

Disease characterised by low bone mass and microarchitectural deterioration of bone tissue in the absence of mineralisation defect, with a consequent increase in bone fragility and susceptibility to bone fracture

Answer 49

- Fracture = breach in continuity of the bone - Fractures occur when: - non-physiological loads are applied to normal bone - physiological loads are applied to abnormal bone

Answer 50

- Which bone and which section? E.g. proximal 1/3 of the tibial shaft - What is the nature of the fracture (aka what type)? E.g. transverse, comminuted etc. - What angle is the displacement in the most distal section of the break? - Is it intra-articular (involving the joint) or extra-articular (outside the joint)? - Is the fracture open (breaks the skin) or closed (doesn't break the skin)

Answer 51

- Transverse - Linear - Oblique, non-displaced - Oblique, displaced - Spiral - Greenstick - Comminuted - Avulsion

Answer 52

1. Haematoma formation 2. Fibrocartilage (soft) callus formation 3. Bony callus formation 4. Bone remodelling

Answer 53

1. Haematoma formation: - Traumatic rupture of blood vessels at the fracture site - Bleeding --\> haematoma formation - Reduced blood supply to bone cells, starving them of nutrients 2. Fibrocartilage (soft) callus formation: - New capillaries grow at the fracture site, supplying nutrients for repair - Dead tissues undergo phagocytosis - Connective tissues (collagen and fibrocartilage) form a repair tissue (soft callus)

Answer 54

3. Bony Callus formation: - Osteoblasts and osteoclasts migrate to the fracture site and divide - They replace soft fibrocartilage with spongy bone to form a hard callus - Forms a bulge at fracture site 4. Bone remodelling - Bony callus is remodelled in response to mechanical stress (see Wolff's law) - Strong, permanent patch at the fracture site is formed - New bond is stronger and more compact

Answer 55

B. Rickets – condition that affects bone development in children. Most common cause is Vit D deficiency Osteomalacia - is a condition of deficient bone mineralization, with sufficient or even excessive matrix. It results from vitamin D deficiency or phosphate depletion, either of which can result from a variety of antecedent conditions.. Osteoporosis - is a condition of reduced bone matrix. It results from a variety of influences, such as post-menopausal oestrogen deficiency or steroids, or it may be idiopathic. Osteopenia - is a general term meaning reduced bone mass. Osteopenia encompasses osteoporosis, osteomalacia, or a combination of both. Osteogenesis imperfecta – a genetic condition which results in bones that break easily – also known as ‘brittle bone disease’.

Answer 56

A. Compartment syndrome • This is an acute potentially limb threatening complication of fractures especially lower limb. • The muscles are enclosed in fascial compartments with little room for expansion therefore if swelling of the muscle occurs then the pressure in the compartment rises which can compromise the blood flow to the muscle.

Answer 57

A. Osteoid – this is the matrix produced by the osteoblasts. Osteocyte – this is the bone cell formed when an osteoblast becomes encased in calcium hydroxyapatite. Macrophage – a type of white cell present in the bone marrow and responsible for attacking bacteria and tumour cells. Osteoblast – this cell secretes the osteoid matrix. Osteoclasts – these cells are responsible for bone resorption.