PASS: My Wife Can't Move!

Bone Physiology

100

This hormone is the main regulator that raises serum calcium when calcium levels fall.

parathyroid hormone (PTH)

200

This pathway is the main regulator of bone resorption, where osteoblast-derived ligand activates osteoclasts.

RANK–RANKL–OPG pathway

300

Explain the three main ways PTH increases serum calcium.

• increased bone resorption
• increased renal calcium reabsorption
• increased activation of vitamin D (1,25D), increasing intestinal calcium absorption

400

A patient has poor calcium intake but normal serum calcium. Explain why this does not exclude poor bone health.

serum calcium is tightly maintained by homeostatic mechanisms, especially PTH, so the body may preserve blood calcium by increasing bone resorption and losing bone mineral content

500

Compare the main function of the RANK–RANKL–OPG pathway with the Wnt–sclerostin pathway.

• RANK–RANKL–OPG regulates bone resorption via osteoclast recruitment and activation

• Wnt–sclerostin regulates bone formation via osteoblast activity

• sclerostin inhibits Wnt signalling, reducing bone formation

Anatomy

100

This fibrocartilaginous structure deepens the acetabulum and improves hip stability.

acetabular labrum

200

This artery is the major blood supply to the femoral head in adults.

medial circumflex femoral artery

300

Name the three ligaments that stabilise the hip joint

• iliofemoral

• pubofemoral

• ischiofemoral ligaments

400

Describe the differences between the Android and Gynecoid pelvis

• The heart-shaped, narrow pelvis is an android pelvis
  • narrow pelvic inlet
  • reduced transverse diameter
  • converging side walls
  • narrow subpubic angle
  • more common in males

• The rounded, wide pelvis is a gynecoid pelvis
  • wide, oval/round pelvic inlet
  • larger transverse diameter
  • straight side walls
  • wide subpubic angle
  • more common in females

500

What are the functional groups of muscles acting on the hip and their nerve supply. 

• flexors (anterior) → femoral nerve

• extensors (posterior) → inferior gluteal nerve + sciatic

• abductors (lateral) → superior gluteal nerve

• adductors (medial) → obturator nerve

Muscle Physiology

100

This neurotransmitter is released at the neuromuscular junction to initiate skeletal muscle activation.

acetylcholine (ACh)

200

What 2 properties of axons increase conduction velocity 

• Increased diameter of the axon 

• Myelination of the axon

300

Describe the mechanism of smooth muscle contraction and explain how it differs from skeletal muscle contraction.

 

• Ca²⁺ enters from extracellular space and/or SR

• Ca²⁺ binds calmodulin

• Ca²⁺–calmodulin activates MLCK

• MLCK phosphorylates myosin light chains

• Myosin binds actin → cross-bridge cycling → contraction

400

Describe how an electrical signal in a motor neuron is converted into mechanical force in skeletal muscle.

1. Neural transmission

• AP → Ca²⁺ influx → ACh release
• ACh → receptor → Na⁺ influx → muscle AP

2. Excitation–contraction coupling

• AP → T-tubules → SR Ca²⁺ release
• Ca²⁺ binds troponin → tropomyosin shifts

3. Mechanical contraction

• Cross-bridge cycling
• Power stroke → force generation
• ATP drives cycle

500

Describe the cross-bridge cycle and explain the role of ATP at each stage.

• Myosin head binds actin (cross-bridge forms)
• Power stroke → ADP + Pi released → force generated
• ATP binds myosin → detachment from actin
• ATP hydrolysed → myosin head re-cocked
• Cycle repeats while Ca²⁺ and ATP present

Anatomy (muscle edition)

100

What muscles Flex the hip

• Iliopsoas   

• Sartorius   

• TFL   

• Rectus femoris (long head)   

• Pectineus   

• Adductor longus 

• Adductor brevis 

• Adductor magnus (anterior part)   

• gracilis  

200

What muscles Extend the hip

• Gluteus maximus   

• Hamstrings: Semitendinosis, semimembranosus, long head biceps femoris 

• Adductor magnus (posterior part)  

300

What muscles internally rotate the hip

• Gluteus medius (ant parts)   

• Gluteus minimus (ant parts)   

• TFL

400

What muscles externally rotate the hip

•Obturator externus 

• Obturator internus   

• Piriformis 

• Gemelli   

• Quadratus femoris   

• Gluteus Maximus  

500

Name the muscles that abduct AND adduct the hip

- Abduct the hip:   

• Gluteus medius 

• Gluteus minimus   

• TFL 

- Adduct the hip: 

• Pectineus 

• Adductors (longus, brevis, magnus) 

• Obturator externus   

• Gracilis

Mystery

100

Describe the synthesis and activation of vitamin D from skin to active form.

• UVB converts 7-dehydrocholesterol → cholecalciferol (vitamin D₃) in skin
• Liver converts → 25-hydroxyvitamin D (25(OH)D)
• Kidney converts → 1,25-dihydroxyvitamin D (active form) via 1α-hydroxylase

200

A patient has low vitamin D levels. Explain how this contributes to bone weakness.

• ↓ intestinal calcium absorption
• → ↓ serum calcium
• → ↑ PTH (secondary hyperparathyroidism)
• → ↑ bone resorption
• → bone weakening 

300

A patient is treated with denosumab. Describe its mechanism of action

• Denosumab is a monoclonal antibody against RANKL
• Prevents RANKL from activating osteoclasts
• ↓ osteoclast formation and activity

Difference:

• Denosumab → blocks osteoclast formation
• Bisphosphonates → kill/inhibit existing osteoclasts

400

A 68-year-old postmenopausal woman is started on a bisphosphonate. Explain the mechanism of action of this drug and how it reduces fracture risk.

• Bisphosphonates bind to bone mineral

• Taken up by osteoclasts during bone resorption

• Inhibit osteoclast function and induce apoptosis

• ↓ bone resorption → ↑ bone density

• → reduced fracture risk

500

What are the stages of Secondary bone healing?

1. Haematoma (Inflammatory phase)

• Blood vessels rupture → haematoma forms
• Inflammatory cells migrate in
• Cytokines released → initiate healing

2. Soft callus formation

• Fibroblasts and chondroblasts produce fibrocartilaginous callus
• Provides early stability
• Still weak (not mineralised)

3. Hard callus (bony callus)

• Soft callus replaced by woven bone via endochondral ossification
• Fracture becomes more stable

4. Remodelling

• Woven bone replaced by lamellar bone
• Bone reshaped along lines of stress
• Restores normal structure and strength