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Z MD1 locomotor and exercise block > bone - hormonal control > Flashcards

bone - hormonal control Flashcards

0
Q

Which dietary requirements are needed for bone growth

A

Calcium and proteins

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1
Q

which hormones play a role in growth

A
  • insulin - provides glucose energy for growth
  • GF and IGF required for protein and cell division
  • thyroid hormones - permissive role (play direct role in nervous system developmet
  • sex steroids - determines final bone length
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2
Q

Explain bone composition

A

Calcium phosphate crystals precipitate and attach to a collagen fibre lattice

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3
Q

Two types of bone

A

Compact/cortical

Trabecular/spongy

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4
Q

What is the important extra role that central bone marrow plays

A

It is haematopoietic

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5
Q

Osteoblasts are modified what

A

Fibroblasts

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6
Q

Function of osteoblasts

A

Bone forming cells - produce enzymes and osteoid to which hydroxyapatite binds to

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7
Q

What extra proteins help osteoblasts in deposition

A

Osteocalcin

Osteonectin

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8
Q

In what part of the long bone does linear growth occur

A

The epiphyseal plate

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9
Q

Where are chondrocytes located

A

Near the epiphyses in children

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10
Q

Function of chondrocytes

A

Produce collagen - the collagen layer thickens and old chondrocytes disintegrate leaving spaces for osteoblasts to deposit bone

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11
Q

What are osteocytes?

A

The less active form of osteoblasts

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12
Q

Explain the structure of osteoclasts

A

Large, mobile, multinucleate cells derived from haematopoietic stem cells

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13
Q

Action of osteoclasts

A

Secretes acid and protease enzymes to dissolve calcified matrix and collagen support
–> cause calcium to enter the blood

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14
Q

Which organs are involved in the hormonal control of the exchange of calcium

A

Bone
Kidneys
Intestine

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15
Q

Which hormones are involved in calcium metabolism

A

Parathyroid hormone
Vitamin d3
Calcitonin

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16
Q

Functions of calcium

A
  • important intercellular signal
  • structural functions (physical strength to bone matrix and helps hold cells together at tight junctions)
  • cofactor for blood coagulation
  • required for normal excitability of neurons and muscles
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17
Q

Where are the three pools of calcium storage

A

Bone matrix - major -99%
Extracellular fluid - as ionized calcium - 0.1%
Intracellular fluid - as free calcium - 0.9%

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18
Q

Roles of intracellular calcium

A

Signal in second messenger pathways

Role in muscle contraction

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19
Q

Roles of extracellular calcium

A
  • cement for tight junctions
  • role in myocardial and smooth muscle relaxation
  • neurotransmitter
  • excitability of neurons
  • cofactor in coagulation cascade
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20
Q

What is the concentration of calcium in the ECF

A

2.5mM

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21
Q

What is the intracellular concentration of calcium

A

0.001mM

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22
Q

Which pool of calcium is free to move to other locations

A

The calcium in the ECF

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23
Q

How much of our dietary calcium is absorbed

A

1/3

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24
Q

Most of our calcium is lost how

A

In the urine and some in the faeces

There are active transporters in the kidney that reabsorb the majority

25
Q

What are the kidney transporters that actively reabsorb calcium

A

ECaC
Na-Ca antiport
Ca-ATPase

26
Q

When is parathyroid hormone released

A

In response to a decrease in calcium concentration - detected by a Ca sensing receptor in the parathyroid gland

27
Q

General function of parathyroid hormone

A
  • Increases plasma calcium

- decreases plasma phsophate

28
Q

What is the action of parathyroid hormone on the kidneys

A

Increases calcium reabsorption and decreases phosphate reabsorption

29
Q

How does parathyroid hormone do its function on bones

A

Drives the actions of OPG and RANKL on osteoblasts to act on osteoclasts to:
- increases calcium and phosphate release from the bone into plasma
- favours bone resorption by osteoclasts
(increases activity of both osteoclasts and osteoblasts)

30
Q

What is the action of parathyroid hormone on the intestines

A

Indirectly increases calcium and phosphate reabsorption by vitamin D activation

31
Q

Transport of parathyroid hormone in the blood

A

Dissolved in plasma

32
Q

Explain the biosynthesis of parathyroid hormone

A

Continuous production with little stored

33
Q

Absence of parathyroid hormone causes…

A

Hypocalcemic tetany

34
Q

Onset of action of parathyroid hormone

A
  • 2-3 hours for bone
  • 1-2 days for intestinal absorption
  • within minutes for kidneys
35
Q

What releases calcitonin

A

C cells of the thyroid gland

36
Q

When is calcitonin released

A

In response to high plasma concentrations of calcium (only in extreme hypercalcemia)

37
Q

How is calcitonin transported in the blood

A

Dissolved in plasma

38
Q

General function of calcitonin

A

Decreases the activity of osteoclasts –> Decreased calcium and phosphate by reducing calcium release from bone, decreasing calcium reabsorption and increasing renal calcium excretion

39
Q

Target tissues for calcitonin

A

Bone and kidney

40
Q

What is the interaction of parathyroid hormone and vitamin d

A

PTH plays a role in turning on the kidney enzymes to get the second hydroxylation of vitamin D to make it active

41
Q

Where do the hydroxylations of vitamin D occur

A

1st - liver

2nd - kidney

42
Q

What is the action of vitamin D

A

Promotes intestinal absorption of calcium and phosphate

43
Q

How is vitamin d transported in the blood

A

Bound to plasma proteins (steroid hormone)

44
Q

What other hormone other than parathyroid hormone plays a role in vitamin D

A

Prolactin - stimulates synthesis

45
Q

What is the action of vitamin d at a molecular level

A

Stimulates the production of calbindin (a Ca binding protein) and CaSR in the parathyroid gland

46
Q

What is the other name for vitamin d

A

Calcitriol

47
Q

Where is phosphate predominantly found in the body

A

Bone
ECF
intracellular

48
Q

Action of vitamin d on phosphate

A
  • Enhances intestinal phosphate absorption in the intestine

- weakly promotes phosphate reabsorption in the kidney

49
Q

What is the action of parathyroid hormone on phosphate

A
  • promotes phosphate excretion and reduced phosphate reabsorption in the kidney
  • promotes bone phosphate release from the bone
50
Q

What causes PTH hyposecretion

A

Autoimmune attack of the glands (rare)

51
Q

What happens as a result of a deficiency in vitamin d?

A

PTH maintains calcium levels at the expense of bone causing bone demineralisation –> rickets or osteomalacia

52
Q

What causes osteoporosis

A

Long term imbalance of calcium metabolism of bone resorption>bone formation in people of 50 years, predominately in postmenopausal women

53
Q

What are the high risk factors for osteoporosis

A 
Inactivity
Malnutrition
Alcoholism 
Smoking
Postmenopausal 
Old age
Endocrine disorders such as Cushing's
54
Q

how do glucocorticoids affectbone

A

increases osteoclast activity

decreases osteoblast activity

55
Q

how does oestrogen affect bone

A
  • decreases osteoclast proliferation, differentiation and activation - promoting osteoclast apoptosis
  • increases the life span of osteoblasts and osteocytes
56
Q

what is the definition of osteoporosis

A

a reduction in bone mass more than 2.5 standa5 standard rd deviations below the normal for healthy 30 year old women

57
Q

what is the definition of osteopaenia

A

a reduction in bone mass 1-2.5 standard deviations below the normal for healthy 30 year old women

58
Q

which part of the bone mass is lost in osteoporosis

A

both cells and matrix

59
Q

how does osteoporosis cause increased risk of fracture

A

loss of trabeculae and thinning reduce the cross-sectional area so that loads on bone are relatively greater

Z MD1 locomotor and exercise block (13 decks)

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