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Locomotor > Physiology of bone and calcium homeostasis > Flashcards

Physiology of bone and calcium homeostasis Flashcards

1
Q

Describe how soft tissue and bone growth are measured?

A

Soft tissue: measured by weight

Bone: measured by height

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2
Q

What is required for tissue and bone growth?

A

GH and IGFs

Thyroid hormone

Insulin

Sex steroids

Bone growth: calcium and protein

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3
Q

Describe the ECM of bone?

A

Calcium phosphate crystals (hydroxyapatite) precipitate and attach to collagen fibre lattice

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4
Q

Describe the structure of bone?

A

Outer cortical bone: privdes strength

Inner trabecular bone: open, cell-filled spaces between calcified struts of lattice

Central bone marrow

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5
Q

When does bone growth occur, in terms of the state of the matrix?

A

When the matrix is deposited faster than it is resorbed

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6
Q

What are osteobalsts?

A

Bone-forming cells

Modified fibroblasts

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7
Q

What do osteoblasts produce?

A

Produces enzymes and osteoid (collagen and protein mix) to which hydroxyapatite binds

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8
Q

What does the epiphyseal plate signify in terms of bone growth?

A

Site of linear growth of long bone

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9
Q

What are chondrocytes?

Where are they found?

A

Collagen-producing cells of cartilage

Found near epiphysis

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10
Q

Describe the columns created by chondrocytes?

A

Continuously dividing columns of chondrocytes that increase in length

Collagen layer thickens and old chondrocytes disintegrate, leaving behind spaces which are filled with cartilage

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11
Q

Describe the actions of osteoblasts?

A

Lay down bone on top of cartilage base, where old chondrocytes degenerated

Revert to less active osteocytes when work is complete

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12
Q

Briefly describe the effect of osteoblast and osteoclast action on blood Ca levels?

A

Osteoblasts deposit calcium in bone > decrease blood Ca levels

Osteoclasts resorb bone and release Ca > increase blood Ca levels

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13
Q

Describe the action of osteoclasts?

A

Secrete acid and protease enzymes to dissolve bone matrix

Cause Ca to enter blood

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14
Q

Describe the morphology of osteoclasts?

A

Large

Mutlinucleate

Derived from haematopoietic stem cells

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15
Q

Which organs/structures are involved in control of blood calcium?

A

Bone

Kidneys

Intestine

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16
Q

Which hormones are involved in the maintenance of blood calcium levels?

A

Parathyroid hormone

Vitamin D3/Calcitriol

Calcitonin

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17
Q

What are the three major pools of calcium in the body?

A

Bone matrix

Extracellular (ionised Ca)

Intracellular (free Ca)

18
Q

Which of the three pools of calcium can move to other locations?

A

ECF

19
Q

Briefly describe how calcium is transferred between ECF and ICF?

A

ECF > ICF: electrochemical gradient

ICF > ECF: active transport

20
Q

Briefly describe what stimulates Ca to move between ECF and bone matrix?

A

Calcitonin: ECF > bone

PTH: bone > ECF

Calictriol: bone > ECF

21
Q

Describe what stimulates Ca to move between ECF and the intestines?

A

PTH and calcitriol stimulate absorption

(1/3 absorbed)

22
Q

Describe how calcium moves between ECF and the kidneys?

A

ECF > kidneys: passive filtration

Kidneys > ECF: stimulated by PTH, inhibited by calcitonin

23
Q

Where in the kidneys does calcium reabsorption occur?

A

Distal nephron

24
Q

How is excess calcium removed from the body?

A

Most in urine

Some in faeces

25
Q

Where is PTH released from?

When is it released?

A

Parathyroid glands

Released in response to decreased blood calcium

26
Q

Describe the actions of PTH on bone, kidneys and intestine?

A

BONE: stimulates osteoclasts via RANKL > bone resorption

KIDNEYS: increase calcium reabsorption, decrease phosphate reabsorption

INTESTINE: activates Vitamin D > increases calcium and phosphate reabsorption

27
Q

Describe the onset of action for PTH?

A

2-3 hours for bone

1-2 days for intestinal absorption

Minutes for kidney transport

28
Q

Where is calcitonin released from?

When is it released?

A

Released from C cells of thyroid gland

Released when plasma Ca is extremely high

29
Q

Describe the target tissues of calcitonin?

A

Bone and kidney (NOT intestines)

30
Q

Describe the effect of calcitonin release?

A

BONE: decrease bone resorption

KIDNEY: increase calcium excretion

31
Q

Describe the role of the thyroid and parathyroid glands in control of plasma calcium?

A
32
Q

Describe how Vitamin D is activated?

A
33
Q

Describe the effect of PTH on Vitamin D activation?

A

PTH activates kidney enzymes to activate Vitamin D

34
Q

Describe how plamsa calcium and phosphate levels affect Vitamin D activation?

A

Low plasma calcium> PTH release > Vitamin D activation

Low plasma phosphate > Vitamin D activation

35
Q

Describe the effect of Vitamin D on plasma calcium and phosphate?

A

Promotes intestinal absorption of calcium and phosphate > increase plasma calcium and phosphate

36
Q

Describe the body’s response to a decrease in plasma calcium?

A
37
Q

Which conditions may cause PTH hypersecretion?

Which may cause PTH hyposecretion?

A

Hypersecretion: tumour

Hyposecretion: autoimmune attack of glands (rare)

38
Q

Describe the effects of PTH hypersecretion and hyposecretion?

A

Hypersecretion: hypercalcemia, hypophosphatemia

Hyposecretion: hypocalcemia, hypophosphatemia, neuromuscular excitability

39
Q

Describe the effect of Vitamin D deficiency?

A

Impaired intestinal calcium absorption > low blood caclium > PTH release > bone resorption > continues > bone demineralisation

Rickets in children

Osteomalcia in adults

40
Q

What is osteoporosis?

A

Long term imbalance in resorption and formation of bone

Resorption > formation

Reduced bone architecture

41
Q

Describe the risk factors for osteoporosis?

A

Age > 50 years

Post-menopause (oestrogen withdrawal)

Low dietary calcium

Lack of exercise

Smoking

Locomotor (28 decks)

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