Musculoskeletal Pathophysiology - BONES

Question 1

What are the two divisions of bones?

Answer 1

1. Axial Skeleton
2. Appendicular Skeleton

(206 bones total)

Question 2

What are the 2 main functions of bones and the skeleton?

Answer 2

1. Mechanical functions

• support
• provide movement
• protection

2. Physiological functions

• produce blood cells
• store minerals

Question 3

What are the two types of bones?

Answer 3

1. Compact bone

• dense connective tissue
• white, smooth, solid
• makes up 80% of bone mass

2. Spongy bone

• internal
• appears porous
• internial cavity of this bone contains BM
• makes up 20% of bone mass

Question 4

What are the four classifications of bone shape?

(Bones are classified according to shape and function)

Answer 4

1. Long
2. Short
3. Flat
4. Irregular

Question 5

Long Bones

Answer 5

Length > width

Serve as rigid levers and used bu muscles to generate movement

e.g. humerous, femur, small bones in fingers & toes

Question 6

Long bone structure

Answer 6

Question 7

Short Bones

Answer 7

length ~ width

limited motion, glide across each other to alow bending in multiple directions (e.g. wrists and ankles)

e.g. carpals & tarsals

Question 8

Flat bones

Answer 8

flat, thin surfaces, may be slightly curved

extensive surfaces for muscle attatchment

protect underlying tissue

e.g. cranial bones, ribs, sternum, scapula

Question 9

Flat bone structure

Answer 9

Periosteum - outer membrane/layer of bone (outer part of Compact bone)

Diplöe - aka Spongy bone

Question 10

Irregular bones

Answer 10

elaborat e shapr - do not fit anywhere else or under any other categories

e.g. vertebrae, some bones in the skull

Question 11

Bone turnover

Answer 11

5-7% recycled weekly

0.5g in/out adult skeleton

Bones are continuously remodelled

• mineral deposition and resrption
• 2 major cell types involved
  
  • osteoblasts → osteocytes
  • osteoclasts

Question 12

What are the two major cell types involved in bone remodelling?

Answer 12

1. (osteogenic cell) → osteoblasts → osteocytes

• osteoblast:
  
  • rough ER
  • nucleus
  • mitochondrion

2. (stem cell) → fusion → osteoclast

• process: fusion
• ruffled border
• nuclei & lysosomes

Question 13

Osteoclasts

Answer 13

Facilitate mineral resorption

• by dissolving crystals and releasing minerals into blood
• pump H⁺ out of cell
• Cl^- follow by electrical attraction
• ECF HCl, pH 4.0

^{ECF = Extra Cellular Fluid}

…

• found on surface of osseous tissue (howship’s lacunae)
• arrise by fusion of unnucleated stem cells or from fused monocytes
• osseous matrix facing osteoclast is demineralised → assumption: osteoclasts involved in resorption
• osteoclasts are NOT apparent when bone resorption activity ceases (e.g. following healing of a fracture)

Question 14

Osteoblasts

Answer 14

• associated with bone formation (thus located wherer new bone is forming)
• cuboidal/pyramidal stratified
• contain enzyme: alkaline phosphatase used to calicfy the osseous tissue

Question 15

Osteocytes

Answer 15

An osteoblast which has been enclosed within bony matrix space called the “lacuna”

Question 16

Calcification

Answer 16

When osteoclasts do not dissolve crystals → hydroxyapatite crystal deposition → calcification

• tissues have inhibitors to prevent hydroxyapatite crystal deposition (calcification)
  
  • lungs
  • eyes
  • brains
  • tendons
  • muscles
  • arteries

Question 17

Osserous tissue (bone tissue)

Answer 17

Rigid form of connective tissue which forms the skeleton

Three primary componenets

1. Cells

• Osteoblasts
• Osteocytes
• Osteoclasts

2. Osseous matrix (2 componenets)

• Organic component (osteocollagenous fibres)
• Inorganic componene (calcium phosphate crystals)

3. Bone architecture
   * shape/size/structure

Question 18

Physiology of osseous tissue

Answer 18

Bones are metabolically active

• influences the rest of the body by exchanging minerals with tissue fluid
  
  • 99% Ca stored in bones
  • 1% stored in blood & tissue

Question 19

What is the normal blood (plasma) Calcium level?

Answer 19

9.2 - 10.4 mg/dL

Question 20

Calcium homeostatis

Answer 20

Depends on balance b/w:

• diatary intake (~1000mg/day)
• urinary & fecal loss (650 & 350mg/day)
• exchange b/w osseous bone tissue

Regulated by 3 hormones:

• Calcitriol
• Calcitonin
• Parathyroid hormone

Question 21

Calcitriol is also known as:

Answer 21

Activated Vitamin D

Behaves like a hormone

Produced by sequential action of skin, liver, kidneys:

7-dehydrocholestrol → UV + skin → VD₃ /cholecalciferol → liver → calcidiol → kidney → calcitriol

Question 22

Vitamin D deficiency

Answer 22

Abnormal softness of bones

Rickets in children

• Bowed legs & pelvis deformalities
• Common skull and ribcage
• Epiphyseal plates cannot be calcified → continue to widen & end of long bones visibly enlarged and abnormally long

Osteomalacia in adults

• Bones are inadequately mineralised
• Little deposition of calcium crystals
• Symptom: pain when weight put on affected bones

Question 23

Calcitonin

Answer 23

Secreted by clear cells (C cells) in Thyroid gland when calcium levels rise

Question 24

Calcitonin: Correction of hypercalcemia

Answer 24

Remember Calcitonin is secreted by C-cells in the thyroid in response to increases in calcium level aka hypercalcemia…

↑Ca²⁺ ⇒ Calcitronin secretion ⇒ ↓osteoclast activity ⇒ ↓bone resorption ⇒ ↓Ca²⁺

↑Ca²⁺ ⇒ Calcitronin secretion ⇒ ↑osteoblast activity⇒ ↑bone deposition ⇒ ↓Ca²⁺

Question 25

Roles of Calcitonin

Answer 25

Important role in children where osteoclasts liberate 5g of Ca from bone ⇒ blood, daily Weak effect in most adults where osteoclasts liberate only 0.8g of calcium into blood, daily * Calcitonin not shown to cause any *adult* diesases * may prevent bone loss in women during pregnancy and lactation

Question 26

Parathyroid Hormone (PTH)

Answer 26

Released by parathyroid glands at posterior of thyroid gland when _blood calcium is **low**_ * A 1% drop in blood calcium doubles the secretion of PTH!

Question 27

Hyp**_o_**parathyroidism

Answer 27

Causes rapid _decline_ in blood Ca levels leads to _fatal tetany_ in 3-4 days

Question 28

Hyp**_e_**rparathyroidism

Answer 28

* Leads to _excess_ PTH secretion * Usually casued by PT _tumour_ * Causes _soft bones, deformed and fragile_ * _Raises blood Ca_ and _Phospate_ * Promotes _formation of kidney stones_ composed of Calcium phosphate

Question 29

Hyp**_o_**calcemia

Answer 29

Blood Ca _deficiency_ * ↑excitability of nervous system * muscle tremors/spasms/cramps (**tetany**) * begins when Ca falls ~ 6mg/dL * at 4mg/dL larynx muscles contracy (**laryngospasm**) → suffocation Vitamin D deficeiency Diarrhea Thyroid tumours Uneractive parathyroid glands Pregnanacy and lactation **#1 cause:** accidental removal of parathyroid glands during thruoid surgery → tetany within 4 days if no HRT given

Question 30

Hyp**_e_**rcalcemia

Answer 30

Blood Ca _excess_ * At 12mg/dL and higher → depression of nervous system, emotional disturbances, _muscle weakness_, sluggish reflexed, _cariac arrest_ Causes rapid _decline_ in blood Ca levels leads to _fatal tetany_ in 3-4 days

Question 31

Osteoporosis

Answer 31

* Most common bone disease * "Porous bones" * Severe loss of bone density * Fractures can occur * Hip * Wrist * Vertebral column * Kyphosis (*widows hump*)

Question 32

Risk factors for Osteoporosis

Answer 32

_Postmenopausal_ anglo/white women at greatest risk * start out with rel. less bone density * start losing it earlier (~35) * lose bone density more rapidly

Question 33

Estrogen and Osteoporosis

Answer 33

Estrogen: * Maintains bone density (by:) * inhibits osteoclast activity Meopause-ovaries _stop secreting_ estrogen → ↑ osteoclast activity and outpaces osteoblast activity * Treatment: Estrogen Replacement Therapy (ERT)

Question 34

Other risk factors for osteoporosis

Answer 34

* 20% of men have ↓ estrogen levels * smoking * alcohol * diabetes mellitus * poor diet * little weight-bearing exercise * low body fat

Question 35

How can osteoporosis be **diagnosed** and how is it **prevented**?

Answer 35

**Diagnosis:** * DEXA (Bone density scan / bone densiometry) * *Dual Energy X-ray Absorptiometry* **Prevention:** * Calcium * Fluoridated water * ↓ Carbonated beverages * Weight bearing exercise

Question 36

**Paget's Disease**

Answer 36

A chronic condition which casues abnormal _enlargment_ and _weakening_ of the bones * affects spine, pelvis, femur, skull * increses in deformity and pain * rare before 40 * common in Aus, NZ, GB, US * Drug therapies can prevent bone breakdown

Question 37

**Osteomelitis**

Answer 37

*A bone marrow infection caused by _bacteria_ or other germs* * Often children * Inflammation/infection of bone & BM * Usually in long bones of arms and legs * (or bone around knee, hip, or ankle) **Sypmtoms:** * Swelling and pain _on movement_ **Treatment:** * Antibiotic therapy * Chronic conditions → surgery

Question 38

**Sciatica**

Answer 38

*Sciatica is pain in the buttock and leg, extending beyond the knee, caused by pressure on nerves in the lower back. Can be triggered by slipped vertebral discs, pinched nerves or some arthritese*. * Age related: ~50% of people \>60 * Compression of _tibial_ & _common peroneal nerves_, together → _sciatic nerve (ischiatic nerve)_ * Associated with muscle spasms in paravertebral and hamstring muscles Most common **Causes:** * Intervertebral disk protrusion (_herniation_) * Bone irregularity in vertebra * Spinal tumour **Treatment:** * Relieving muscle spasms with * bed rest * local warmth * massage * oil analgesics * NSAIDs * oral muscular relaxants * Surgery * Laminectomy: removal of part of vertebral arch to allow for more room for disk protusion * Spinal fusion of 2 vertebrae by removing the herniated disk

Question 39

What are two types of bone fractures *and* their causes?

Answer 39

**1.Stress fracture** * Break by abnormal bone trauma * falls * athletics * military combat **2. Pathological fracture** * Break in bone weakened by other disease * Stress that would not break healthy bones * (Secondary ?) * bone cancer * osteoporosis

Question 40

Types of bone fractures

Answer 40

Also _Nondisplaced:_ fully broken but in original position

Question 41

Healing of fractures

Answer 41

**1. Hematoma formation** The hematoma is converted to granulation tissue by invasino of cells and blood capilaries **2. Soft callus formation** Deporsition of collagen and fibrocartilage converts granulation tissue to soft callus **3. Hard callus formation** Osteoblasts deposit a temporary bony collar around the fracture to unite the broken pieces while ossification occurs **4. Bone remodelling** Small bone fragments are removed by osteoclasts, while osteoblasts deposit spongy bone and then convert it to compact bone