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medicine unit 10 uos > Bone health > Flashcards

Bone health Flashcards

1
Q

What are the functions of calcium in the body?

A

Muscle contraction
Blood clotting
Nerve conduction
Bone mineralisation
Hormonal communication

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2
Q

Where does the total body calcium lie?

A

Bone - 99%
Body fluids - 1%
-> Ionised/free - 50%
-> Bound to anions - 10%
-> Protein bound - 40%

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3
Q

Which calcium store can be measured, and what is the normal level?

A

Ionised/free calcium in body fluids
4.64 - 5.28 mg/dL

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4
Q

What hormones and organs regulate calcium ion levels?

A

Hormones:
- Parathyroid hormone
- Calcitrol or vit D3
- Calcitonin
Organs:
- Intestines
- Kidneys
- Bone

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5
Q

What releases parathyroid hormone (PTH), and what stimulates its release?

A

From chief cells in the four parathyroid glands
Released in response to a decrease in Ca2+
Most important regulator ECF Ca2+

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6
Q

By which mechanisms does PTH raise calcium levels by?

A
  • Resorption of calcium from bone
  • Increasing renal reabsorption of calcium
  • Absorption of calcium from GIT (indirect)
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7
Q

What is the bone reabsorption mechanism?

A
  • PTH upregulates RANKL on osteoblasts on surface of bone
  • Osteoclasts adhere to bone like a suction cup under influence of RANKL and integrins and forms sealing zone with a ruffled border
  • OC secrete protons to decrease pH idssolving minerals
  • Release of proteolytic enzymes and non-proteolytic enzymes degrade the bone matrix - make pits
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8
Q

How does vitamin D become active?

A

Vitamins D2 and D3 are both inactive until undergoing two hydroxylations
- First occurs in liver to form calcidol
- Second occurs in kidneys to form calcitriol - active form of vit D

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9
Q

What is the role of vitamin D?

A

Active vit D:
increases absorption of both calcium and phosphate in the intestine
works with PTH to reduce Ca2+ loss in urine and stimulate the release of calcium and phosphorus from the bone

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10
Q

Where is calcitonin released from?

A

Secreted by C cells in the thyroid gland in response to hypercalcemia

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11
Q

What is the action of calcitonin?

A

PTH antagonist
On bones: inhibits activity of osteoclast (responsible for bone formation)
On kidney: increase urinary excretion of phosphate and calcium

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12
Q

Summarise the hormonal regulation of high blood calcium levels

A

High blood calcium level > activates thyroid gland > calcitonin released > stimulates calcium deposition in bones, reduces calcium uptake in kidneys, reduces calcium uptake in intestines > normal calcium in blood

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13
Q

Summarise the hormonal regulation of low blood calcium levels

A

Calcium levels too low > parathyroid gland stimulated > releases parathyroid hormone > stimulates calcium release from bones, increases calcium uptake in kidneys > increased Ca2+ and increases calcium uptake in intestines > increased calcium

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14
Q

What hormones are involved in regulation of bone health? (by class)

A

Calcium regulating hormones:
- PTH
- Calcitonin
- Active vit D (Calcitriol)
Sex hormones:
- Testosterone
- Oestrogen
Other hormones:
- Growth hormone
- Thyroid hormone
- Cortisol

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15
Q

What function does growth hormone have on bone regulation?

A

Stimulates bone formation
Stimulates longitudinal growth

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16
Q

What function does thyroid hormone have on bone regulation?

A

Too much stimulates bone resorption
Activates osteoclastic activity

17
Q

What function does glucocorticoid have on bone regulation?

A

Inhibits bone formation
Decreases calcium absorption form the intestines

18
Q

What function does oestrogen/testosterone have on bone regulation?

A

Maintain bone density by inhibiting activity of osteoclasts
Stimulation of osteoblasts
Calcium absorption
Inhibit bone resorption

19
Q

How can bone health maintained?

A

Calcium intake: particularly important during childhood, adolescence, pregnancy, and lactation
Vitamin D
Regular excercise: muscle strengthening, weight bearing
Avoid smoking and drinking to excess
Maintain a healthy body weight
Hormonal health

20
Q

Primary hyperparathyroidism
- Level of parathyroid hormone
- Level of serum calcium
- Level of phoshate
- Causes

A

PTH= high
Serum calcium= increased
Phosphate= decreased
Causes: parathyroid tumour, ectopic parathyroid tissueP

21
Q

Primary hyperparathyroidism symptoms and treatments

A

Symptoms:
- renal stones
- bone pain
- abdominal pain
- constipation
- Depression
Treatments:
parathyroidectomy

22
Q

Secondary hyperparathyroidism
- Levels of parathyroid hormone
- Level of serum calcium
- Level of phosphate
- Causes

A

PTH: High
Ca2+: decreased/normal
Phosphate: Increased/normal
Causes:
- Vit D deficiency
- End stage kidney disease

23
Q

Secondary hyperparathyroidism symptoms and treatments

A

Symptoms:
- Osteoporosis
- Renal stone
- Bone and joint pain
Treatments:
- Vit D supplement
- Treat underlying cause

24
Q

What is the presentation of Vitamin D deficiency in children?

A
  • Demineralisation of bone - soft pliable bones
  • Characteristic bow-leg deformity
  • Overgrowth at costochondral junction - rachitic rosary
  • Pigeon chest deformity
  • Frontal bossing
  • Osteomalacia
25
Q

What is the presentation of vitamin D deficiency in adults?

A

Softening of bones - frequent fractures

26
Q

What can be tested and detected to diagnose vitamin D deficiency?

A

Hypocalcemia
Hypophosphatemia
Increased alkaline phosphatase

27
Q

What is renal osteodystrophy/CKD mineral bone disorder? What is a key characteristic of this?

A

Incorporates all biochemical abnormalities and skeletal manifestations in patients with CKD or end-stage renal disease
GFR below 60 mL/min

28
Q

What are the symptoms of renal osteodystrophy/CKD mineral bone disorder? (5)

A
  • Bone pain and fractures
  • Joint pain
  • Bone deformation
  • Slow bone growth
  • Low bone mineral content
29
Q

Why does renal osteodystrophy/CKD mineral bone disorder occur?

A

Failure to synthesise active vit D
Kidneys produce limited calcitriol which is normally used to convert vitamin D from inactive to active
Failure to excrete phosphate - hyperphosphatemia > bind to serum calcium resulting in decreased ionised free Ca2+ > increased PTH

30
Q

What is FGF23 produced by and what is it’s function?

A

Produced by osteoblasts and osteocytes
- Increases urinary phosphate excretion
- Involved in vit D metabolism and regulation

31
Q

What happens to FGF23 levels in CKD?

A

Rise 1000 fold to maintain a neutral phosphate distribution
Promotes the suppression of 1-25,dihydroxyvitamin D production > reduction of intestinal calcium absorption increase of PTH level and ultimately develop secondary hyperthyroidism

32
Q

What is osteoporosis and what are the causes?

A

Literal meaning = ‘Porous bone’
Bones are fragile and more likely to break
Reduced mineral density and bone mass
Causes:
- Hormonal/postmenopausal
- Chronic steroid use
- Malabsorption disease
- Drug related
- Low BMI

33
Q

What are the symptoms of osteoporosis?

A

Painless unless fractures occur
Coughing can produce enough force to fracture bones
Significant height loss and curvature of the spine - if compression fractures in spine

34
Q

How may the severity of osteoporosis be measured?

A

Bone mineral density scan (BMD scan)
Measures bone density and bone loss
Bone densities given as a T score
Normal: -1.0
Low bone density: -1.0 to -2.5
Osteoporosis: -2.5 and lower

35
Q

When may a BMD be carried out?

A
  • For those with significant risk factors
  • When it is uncertain if bones are fragile
  • To decide whether drug treatment is necessary

medicine unit 10 uos (26 decks)

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