Metabolic Bone Disease Flashcards

1
Q

What is the role of osteoclasts?

A

Bone resorption

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2
Q

What is the role of osteoblasts?

A

Bone formation

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3
Q

What happens when osteoblasts become encased in bone?

A

they become osteocytes

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4
Q

what type of cell is an osteoclast?

A

a macrophage

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5
Q

what does the whole cycle of bone biology aim to do?

A

bone remodelling

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6
Q

what is RANK?

A

RANK is the receptor for RANK-Ligand (RANKL) and part of the RANK/RANKL/OPG signaling pathway that regulates osteoclast differentiation and activation. It is associated with bone remodeling and repair, immune cell function, lymph node development, thermal regulation, and mammary gland development.

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7
Q

describe the factors that stimulate osteoblast expression of RANK Ligand?

A

Free Rank ligand joins on to a receptor on pre osetoclast on rank and the osteoclast then stimulated to multiply and divide and resorb bone and then this triggers the bone re-modelling cycle
OPG- and the RANKL balance, gives us how much free RANKL there is as OPG is a blocker of RANKL

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8
Q

Name 2 Vitamin D related disorders?

A

rickets and osteomalacia

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9
Q

Where can you get Vit D from?

A

diet and sunshine

dietary sources are poor; oily fish and egg yolk

cod liver oil capsules are a source of vitamin d supplement

you have to get the majority of it from the sun (radiation; UVB rays)

melanocytes compete for the UVB light; the darker the skin the more vitamin D you need for 7DHC to be activated

people in prison, muslims lack vitamin D

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10
Q

what is 7DHC?

A

7-Dehydrocholesterol is a zoosterol that functions in the serum as a cholesterol precursor, and is converted to vitamin D3 in the skin, therefore functioning as provitamin-D3

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11
Q

describe 7DHCs course:

A

7DHC protein bound circulates; goes to the liver; and is hydroxylated which produces the storage form of vitamin D (stored in liver, fat, muscle)

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12
Q

Describe vit D course:

A

SKIN : 7DHC

Liver: 25(OH) Vit D

Kidney: 1,25 (0H)2 Vit D

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13
Q

how do you test someones vitamin d?

A

By measuring their 25 (OH) Vit D

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14
Q

what form of vit d is physiologically active?

A

the form in the kidney

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15
Q

what does sun tan lotion do?

A

blocks vitamin D

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16
Q

what do you do if the livers and kidneys are not working?

A

if liver and kidneys don’t work then you have to give the physiologically active form of vitamin D

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17
Q

Give an example of a bone active hormone?

A

PTH (parathyroid hormone)

PTH comes from parathyroid gland

too much PTH gives osteoporosis and so does too little

PTH and Vit D work together to move calcium in and out of the blood/ cells

if calcium is up, Phosphate is down

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18
Q

What does Severe nutritional vitamin d OR Calcium deficiency cause?

A

it causes insufficient minerlisation and thus rickets in a growing child and osteomalacia in the adult when the epiphyseal lines are closed

19
Q

what does vitamin d do normally?

A

vitamin D stimulates the absorption of calcium and phosphate from the gut and calcium and phosphate then become available for bone mineralisation

20
Q

what happens to muscle function in low vitamin d states?

A

muscle function is also impaired in low vitamin d states

(if epiphyseal plates have fused; osteomalacia

if they haven’t fused, rickets

if you have low vitamin D levels, you wont absorb as much calcium to mineralise bones and if you dont have access to calcium, you still wont mineralise bones

there are vitamin d receptors in muscles)

21
Q

Give some signs of rickets in children:

A

stunted growth

large forehead

odd curve to spine or back (kyphosis)

large abdomen

wide joints at elbow and wrist

wide bones

odd shaped legs (bendy legs)

wide ankles

(nobbly bits at the ends of ribs: rickety rosary)

22
Q

Describe osetomalacia:

A

no bendy legs or impaired growth

patient tends to present with bone pain and muscle weakness

minor fractures; looser zones; only respond if you treat with calcium vitamin d

osteomalacia; struggle to get up the stairs

23
Q

What is Paget’s disease of bone?

A

localised disorder of bone turnover

increased bone resorption followed by increased bone formation

leads to disorganised bone: bigger, less compact, more vascular and more susceptible to deformity and fracture

(most common metabolic bone disease in western world after osteoporosis

all the bars and plates in trabecular bone are going in different directions; disorganised bone

because bone turnover is increased; increased vascularity and thus more likelihood of a fracture)

24
Q

does pagets disease have a genetic component?

A

Yes, a strong genetic component

15-30% are familial

Loci of SQSTMI

25
Q

what is the restricted geographic distribution of pagets disease?

A

those of anglo-saxon origin

26
Q

What is the environmental trigger of pagets disease?

A

possibility of chronic viral infection within osteoclast

27
Q

What are some symptoms of Paget’s disease of bone?

A

Presents in a patient >40

  • bone pain (deep seated, there all the time)
  • occassionally presents with bone deformity
  • excessive heat ovr the Pagetic bone
  • neurological complications such as nerve deafness (deafness due to bone narrowing, foramina narrowing)
28
Q

what is investigation used for the diagnosis of paget’s disease?

A

X-RAY

29
Q

what is the differential diagnosis of paget’s disease?

A

malignancy (sklerotic metastatic cancer)

USUALLY asymmetric

30
Q

what is the commonest presentation of paget’s disease?

A

!!! isolated elevation of serum alkaline phosphatase !!!

31
Q

what are some other presentations of paget’s disease?

A

bone pain and local heat

bone deformity or fracture

hearing loss

rare development of osteosarcoma in affected bone

(the reason its an isolated elevation of alkaline phosphatase is because if it was raised due to a liver problem then the Gamma GT for example would be raised

32
Q

what is the treatment of choice in pagets disease?

A

INTRAVENOUS BISPHOSPHONATE THERAPY- ONE OFF IV ZOLEDRONIC ACID

(short sharp course- 1 off treatment for 30 mins- may be the only treatment needed for 5 years)

33
Q

what should you do for asymptomatic pagets disease?

A

no evidence to treat asymptomatic paget’s unless in skull or in area requrining surgical intervention

do not treat based on a raised alkaline phosphatase alone

34
Q

what is OSTEOGENESIS IMPERFECTA?

A

genetic disorder of connective tissue characterised by fragile bones from mild trauma and even acts of daily life

broad clinical range from those which are prenatally fatal to those only presenting in 40s with early ‘osteoporosis’

(collagen abnormality and the bones are very fragile

condition can have wide presentation)

35
Q

a defect in what is the cause of osteogenesis imperfecta?

A

defects in type 1 collagen

there are 8 different types: first 4 most common

36
Q

Describe type 1 OA:

A

midler form- when child starts to walk and can present in adults

37
Q

describe type II OA:

A

lethal by age 1

38
Q

describe Type III OA:

A

progressive deforming with severe bone dysplasia and poor growth

39
Q

describe type 4 OA:

A

similar to type 1 but more severe

40
Q

what are some other signs of osteogenesis imperfecta?

A

growth deficiency

defective tooth formation (dentigenesis imperfecta)

hearing loss

blue sclera

scoliosis

barrel chest

ligamentous laxity

easy bruising

(some people will have none of these, some all of them

the base cases will have growth deficiency)

41
Q

what is blue sclera in?

A

osteogenesis imperfecta- the whites of the eyes are literally blue

42
Q

what is the management of OI?

A

surgical: to treat fractures
medical: to prevent fracture, intravenous bisphosphonates
social: adaptions educationally and socially (can’t do contact sport, may need special chair in classrooms)
genetic: genetic counselling for parents and next generation

43
Q

Give the definition of osteoporosis:

A

a metabolic bone disease characterised by low bone mass and micro architectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk

A result on DXA bone scanning