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Musculoskeletal System > Calcium, Phosphate & Vitamin D. In Bone Health > Flashcards

Calcium, Phosphate & Vitamin D. In Bone Health Flashcards

1
Q

What is the mechanical function of bone?

A

Allowing effective muscle contraction and movement

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2
Q

How do bones affect transduction ?

A

Transduce sound waves from ear drum to the inner ear

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3
Q

What do bones produce within the marrow?

A

Within their marrow: bones produce red and white blood cells as well as growth factors; and store fatty acids as yellow marrow

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4
Q

What do bones store?

A

Storage of certain minerals: including calcium & phosphorous and, to a lesser extent, zinc, copper and sodium

Temporarily absorb and store toxic heavy metals: to reduce their effects on the body

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5
Q

What are the functions of bones?

A
  • mechanical
  • protection
  • Transduce sound waves
  • bone marrow produces blood cells, growth factors and stores fats
  • stores minerals & toxic heavy metals
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6
Q

What is bone?

A

A composite material consisting of a fibrous prptein(collagen) stiffened by an extremely dense filling and surrounding of calcium phosphate crystals. There are other constituents.

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7
Q

Summarize chemical composition of bone

A

Bone is made up of the inorganic mineral hydroxyapatite- calcium apatite or, in its crystal-structure form

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8
Q

What is bone mass?

A

Bone tissue (osseous tissue and soft tissue) is remodeled constantly throughout life

Bone mass: actual amount of osseous tissue in any unit volume of bone

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9
Q

What are the intrinsic determinants of bone mass?

A

Genetics.

  • gender
  • family history
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10
Q

What are the extrinsic determinants of bone mass?

A
  • diet
  • body mass/hiatus
  • hormonal milieu
    • (PTH, Vit D & estrogen)
  • illnesses
  • exercise
  • lifestyle choices
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11
Q

What 3 forms does calcium exist in plasma?

A
  • combined with plasma proteins- nondiffusible
  • combined with anionic substances in plasma- diffuse leg but non ionized
  • ionized form-diffusiblev(most important firm)
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12
Q

What is the concentrations of calcium in plaasma?

A

In ECF(plasma) ionized- 1.2 mmol/L

Protein bound calcium- 1.0 mmol/L

Calcium complexed to anions- 0.2mmol/L

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13
Q

Summarize the amount of calcium in bone reservoirs

A

-about 98%-99% of total calcium stored in bones

Bones act as the most important reservoir:

  • release calcium when extracellular calcium drops and
  • store excess calcium
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14
Q

Contrast the function of osteoclasts and osteoblasts

A

Osteoblasts- free ionized calcium to calcium in bone matrix/ reservoir (mineralization)

Osteoclasts- calcium bone matrix/reservoir to free calcium (resorption)

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15
Q

What are the functions of the calcium?

A
  • calcium is an essential mineral
  • there is more calcium in the body than any other mineral
  • Calcium in bone provides mechanical stability and serves as a reservoir sometimes needed to maintain extracellular fluid calcium concentration
  • Required for bone formation and remodeling: to build strong bones and teeth
  • Important cofactor for several enzymes and signal fir signaling pathways I.e.(diacylglycerol, IP3)
    • Including blood clotting- ensures that blood clots normally
    • muscle contraction; regulates muscle contractions, including heart beat

-Neurotransmitter for some neuron signals and plays a prominent role in maintain8ng the resting membrane potential

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16
Q

What are the sources of calcium?

A
  • milk, cheese and other dairy foods
  • green leafy vegetables-but not spinach
  • soy beans, tofu, soya drinks with added calcium
  • fish with edible bones- such as sardines
  • nuts
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17
Q

What is the recommended daily allowance for calcium?

A

Recommended daily allowance: 25-30nmmol(1000-1200 mg) for most adults

Calcium and milk do have beneficial influences on bone mineral density

-Long-term low Ca2+ intake impair peak bone mass (PBM) development

Humans cannot adapt to very low intakes of dietary calcium. This can cause rickets without vitamin D deficiency

18
Q

What chemicals are calcium absorption and excretion dependent on?

A
  • Intestinal absorption
    • Votamin D dependent
  • Bone deposition and resorption
    • Vitamin D & PTH dependent
  • Excretion in kidneys
    • PRH dependent
19
Q

Explain absorption and excretion of phosphorous

A
  • 85% of the 600 g of body phosphorous is present in bone mineral
  • Unlike calcium, phosphorous exists intracellularly at concentrations close to those present in ECF (e.g., 1-2 mmol/L)
  • In cells and in the ECF, phosphorous exists in several forms, predominantly as H2PO4^- or NaHPO4^- , with perhaps 10% as HPO4^2-. This mixture of anions will be refferred to here as “phosphate”.
  • phosphate is widely available in folds and is absorbed efficiently by the small intestine .
  • Phosphate absorptive efficiency May be enhanced by 1,25(OH)2D(Vit D)

Excretion of phosphate is through urine- controlled according to plasma concentration levels which can be overridden by PTH

20
Q

What is the effect of PTH on calcium and phosphate levels?

A

-increases calcium ions (thus preventing hypocalcemia)
Incolved in phosphate homeostasis

PTH is stimulated by low calcium

21
Q

What is the effect of PTH on bone?

A

-PTH promotes net bone resorption , increasing plasma calcium concentration

Causes:
Osteoblasts increase cytokines (M-CSF, IL-6)

  • Proliferation of osteoclasts
  • increased bone resorption (demineralization)
  • increased plasma calcium and increased plasma PO4

Increases calcium and phosphate release from bone(increased demineralization)

22
Q

What are the effects of PTH on kidneys?

A

If both calcium and phosphate levels increase due to PTH:
-Calcium would complex with phosphate to form calcium phosphate

  • Recall that it is the free ionized form of calcium that is active
  • Due to the CaPO4 complex formation, PTH would not be effective in increasing extracellular calcium levels
  • Therefore, PTH would facilitate increased phosphate excretion from the kidneys, thereby reducing complex formation and facilitating increase in availability of free ionized calcium
23
Q

How does PTH increases plasma calcium?

A
  • bone resorption (activates osteoclasts, decreased collagen synthesis by osteoblasts
  • calcium Reabsorption in the kidneys
  • vitamin D synthesis in kidneys leads to increased calcium absorption in GIT
24
Q

What is vitamin D?

A

A fat soluble vitamin with hormone like function
Ergocalclferol-vitamin D2. Of plant origin
Cholecalciferol-vitamin D3 of animal origin

Sunlight plays a major role in the conversion of 7- dehydrocholesterol (precursor for cholecalciferol synthesis in skin) to cholecalciferol

Over the counter supplements

25
Q

Summarize the metabolism and action of vitamin D

A

25-hydroxycholecalciferol in kidney—> 1,25-dihydroxycholecalciferol (calcitriol- 1,25-diOH-D3)

1,25-diOH-D3 binds to intracellular receptor proteins

1,25-diOH-D3 receptor complex interacts with DNA in the nucleus of target

Can either selectively stimulates gene expression or repress gene expression (similar to steroid hormones)

26
Q

What are the actions of vitamin D in on the intestine?

A
  • stimulates intestinal absorption of calcium and phosphate by increased synthesis of a specific calcium binding protein calbindin
  • May also stimulate an ATP-dependent calcium pump, which transports calcium into the blood stream
27
Q

What are the actions of vitamin D in the bone?

A
  • stimulates the mobilization of calcium and phosphate from the bone by potentiation parathormone
  • In smaller quantities, promotes bone calcification
28
Q

What are the actions of vitamin D on the kidneys?

A

Inhibits calcium excretion by stimulating calcium Reabsorption; weak effect

29
Q

What is calcitonin?

A

Calcitonin is a peptide hormone

Secreted by cells in the thyroid gland in humerus

  • INHIBITS osteoclast activity (decreased bone resorption)
  • reduces plasma calcium , opposing the effects of PTH
30
Q

Summarize vitamin D and PTH on calcium and Pi levels

A
  • vitamin D increases serum Ca2+ and PO4
  • vitamin D and PTH act synergistically on ca,Fiume in the kidneys
  • PTH decreases PO4 Reabsorption in kidneys, lowering serum PO4
31
Q

What causes vitamin D deficiency in nutritional deficiency?

A

Decreased intake/fat malabsorption

-cystic fibrosis, celiac disease, Whipple’s disease, Crohn’s disease

32
Q

How can inadequate skin synthesis lead to vitamin D deficiency?

A
  • inadequate exposure to sunlight

- sunscreens, protective clothing

33
Q

What common diseases lead to vitamin D deficiency?

A

Liver disease (reduced 25-hydroxylase activity)

Kidney disease( reduced. 1-hydroxylase activity)

34
Q

What is the result of vitamin D deficiency in children?

A

Rickets

  • demineralization of bone-soft pliable bones
  • characteristic bow-leg deformity
  • overgrowth at costochondral junction-rachitic rosary
  • pigeon chest deformity
  • frontal bossing
35
Q

What is the result of vitamin D deficiency in adults?

A

Osteomalacia

Weakening of bones- frequent fractures

36
Q

What are the lab findings of vitamin D deficiency?

A
  • hypocalcemia
  • hypophosphatemia
  • increased serum alkaline phosphatase (ALP) from bone
37
Q

What are the symptoms of vitamin D resistant rickets?

A
  • similar symptoms as classical rickets + alopecia (hair loss)
  • plasma levels of 1,25(OH)2D are elevated
38
Q

What causes vitamin D resistant rickets ?

A

Caused by mutations in the gene encoding the vitamin D receptor in the intestine —> decreased calcium absorption from diet

39
Q

What are the treatments of vitamin D resistant rickets?

A

Difficult. Regular, usually nocturnal calcium infusions, which dramatically improve growth but do not restore hair growth

40
Q

Explain vitamin D toxicity/hypervitaminosis D

A
  • like all fat-soluble vitamins, vitamin D can be stored in the body and is only slowly metabolised
  • high dishes (100,000 IU for weeks or months) can cause loss of appetite, nausea, thirst, and stupor. (Non-specific symptoms)
  • enhanced calcium absorption & bone resorption results in hypervalcemia, which can lead to deposition of calcium in many organs, particularly the arteries and kidneys (soft tissue calcification)

Musculoskeletal System (41 decks)

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