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Physiology > Exam 6: Bone Development and Calcium Homeostasis > Flashcards

Exam 6: Bone Development and Calcium Homeostasis Flashcards

1
Q

Describe the ectoderm

A

It is on the surface and will form the skin and neural tisuses

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2
Q

Describe the mesoderm

A

The middle layer and it will form the bones, muscles, and connective tissues

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3
Q

What is programmed to initiate limb formation?

A

Lateral body wall of mesoderm

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4
Q

What does the mesoderm of each side of the developing lateral body wall form?

A

A cylindrical thickening (Wolff’s crest)

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5
Q

What develops over Wolff’s crest? Where?

A

Focal ectodermal thickenings

At the sites where individual limbs will develop

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6
Q

Describe how long bone develops

A

Condensation of mesenchyme forms cartilage model of bone
Formation of perichondrium and invasion of nutrient artery
Degeneration of chondrocytes forms medulary cavity
Transformation of perichondrium to periosteum
Periosteum form concentric layers of cortical bone in the diaphysis
Vessels at joint capsule insertion invade epiphyseal areas
Epiphyseal and metaphyseal form

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7
Q

Understand the anatomy of a long bone and the terms given to each specific region of the bone in growing and mature animals.

A

Understand the anatomy of a long bone and the terms given to each specific region of the bone in growing and mature animals.

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8
Q

What is cancellous bone?

A

Epiphyseal and metaphyseal bone that appears spongy and trabecular

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9
Q

What absorbs concussion in bone?

A

Tiny trabecular plates

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10
Q

What is compact bone?

A

Cortical bone of the diaphysis, which is dense and strong

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11
Q

What forms osteons?

A

Concentric bone lamellae that were formed during development of the diaphysis are remodeled along lines of stress by cutting and filling cones to form osteons

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12
Q

What do osteons do?

A

Strengthen bone cortex

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13
Q

What is the metaphyseal physis responsible for?

A

Growth in length of a long bone by proliferation of chondrocytes followed by enchondral ossification to form cancellous bone of metaphysis

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14
Q

What is epiphyseal physis responsible for?

A

3D growth of epiphysis by proliferation of chondrocytes followed by encohndral ossification to form epiphyseal cancellous and subchondral bones

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15
Q

What is the final shape of the ends of a bone at maturity determined by

A

Interstitial growth of cartilage in growing epiphyseal physes

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16
Q

Describe enchondral ossification

A

Chondrocytes proliferate in inner and outer mitotic layers beneath articular surface
Chondrocytes from inner mitotic layer become collagen and proteoglycan matrix
Mature chondrocytes hypertrophy, hypretrophic chondrocytes form matrix vessicles and die
Hydroxyappetite crystal form at matrix vesicle sites calcifiying cartilage
Capillary loops with osteogenic mesenchyme invade tunnels formed by dying hypertrophic chondrocytes only after cartilage calcifies
Osteoblasts layer bone on spicules of calcified cartilage to form bony trabeculae
Osteoclasts remodel calcified spicules and bone trabeculae to produce cancellous bone

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17
Q

Look at the anatomy of a growth plate

A

Look at the anatomy of a growth plate

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18
Q

What is calcium essential for?

A

Bone development and maintenance
Muscle contraction
Nerve conduction
Blood

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19
Q

What can decreased Ca cause in bone development and maintenance?

A

Limb deformity during growth
Osteomalacia with potential limb fractures
Bran disease

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20
Q

What can decreased Ca cause in nerve conduction?

A

Nerve cell hyperexcitability with tetany in most species

Paralysis in cows

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21
Q

What does decreased Ca cause in blood clotting?

A

Inadequate clot formation

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22
Q

What happens with inadequate Ca during growth?

A

Faulty enchondral ossification

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23
Q

What does faulty enchondral ossification cause?

A

Poor calcification of cartilage in physis
Delayed bone formation
Wide unstable cartilage zone in physis
Limb deviation

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24
Q

What does inadequate Ca in diet of mature horses (bran disease) cause?

A

Osteoclasts reabsorb bone to maintain serum Ca levels

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25
Q

What does Osteoclasts reabsorbing bone to maintain serum Ca levels cause?

A

Osteoblasts produce much osteoid to replace lost bone
Osteoid fails to mineralize
Bone fibrous and thickened

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26
Q

What does Ca losses due to pregnancy and lactation cause?

A 
Eclampsia
Parturient paresis (milk fever)
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27
Q

What does eclampsia cause?

A

Nerve hyperexcitability
Tonic muscle contraction leading to seizures
Stiffness, limb pain, increase temperature, ataxia

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28
Q

Describe nerve hyperexcitability

A

Lack of Ca to stabilize voltage gated Na channels-spontaneous depolarization

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29
Q

Describe parturient paresis (milk fever)

A

Ach release at motor end plate depends on adequate Ca
Need for adequate Ca at motor end plate more pronounced in cows that other species
Causes paralysis and death if not treated

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30
Q

What is the normal Ca level maintained at in most species?

A

8.5 to 11 mg/dl

31
Q

What is the level of Ca with tetany?

A

Below 6 mg/dl

32
Q

What is the Ca level that can cause death?

A

Below 4 mg/dl

33
Q

What is the nerve axon the basis for?

A

Action potential and nerve transmission

34
Q

What is action potential and nerve transmission established by?

A

NaK pump

Selective permeability

35
Q

Is K high on the inside or outside?

A

Inside

36
Q

Describe the propagation of the action potential

A

Depolarization in one area triggers a wave of depolarization that spreads in each direction
Membrane voltage change opens adjacent voltage-gated Na channels

37
Q

What does increased Ca do to nerves?

A

Makes it less excitable

38
Q

What does a nerve require when there is increased Ca?

A

Greater change in voltage to trigger action potential

39
Q

What does decreased Ca do to nerves?

A

Makes nerve more excitable
Tremors, muscle spasms, tetany
Nerve may spontaneously depolarize if Ca is low enough

40
Q

What does depolarization trigger at the motor end plate?

A

Release of Ach from synaptic vesicles

41
Q

What does Ach trigger once release from the motor end plate?

A

Muscle contraction

42
Q

What happens with hypercalcemia?

A

Depresses nervous system and muscle activity
Decreased appetite
Constipation

43
Q

Describe the 3 forms of Ca found in plasma

A

50% ionized form (active): diffusible through membranes, 4.6 mg/dl
41% protein-bound: nondiffusible, 3.9 mg/dl
9% complexed to negative ions and nonionized, 0.9 mg/dl

44
Q

What is the total amount of Ca in plasma?

A

9.4 mg/dl

45
Q

What is the Ca bank?

A

Bone

46
Q

How can Ca level in ECF be altered?

A

By Ca pumps in cell membranes of the bone lining cells

47
Q

What are the mechanisms of controlling Ca?

A

Increase or decrease GI absorption
Increase or decrease renal losses
Move Ca into or out of bone

48
Q

What are the control systems of Ca from most powerful to least?

A 
Parathyroid hormone (chief cells of parathyroid gland)
Vitamin D (diet or skin)
Calcitonin (C cells of the thyroid)
49
Q

What is the last thing for vitamin D3 to go through to be come activated?

A

Kidney

50
Q

Look at overview of vitamin D chart

A

Look at overview of vitamin D chart

51
Q

What must be done to D3 in order to have an effect on Ca levels?

A

It must be activated

52
Q

What does active vitamin D act to do?

A

Increase intestinal absorption of Ca

53
Q

What is necessary for PTH to work on bone?

A

Active vitamin D

54
Q

Describe parathyroid hormone

A

Most powerful mechanism for controlling extracellular Ca and phosphate
Acts to increase Ca

55
Q

What happens as PTH increases Ca?

A

Increases intestinal absorption
Increases reabsorption of Ca and P from bone
Decreases renal losses of Ca, increases excretion of P

56
Q

What happens if you remove 2 parathyroid glands?

A

No problem

57
Q

What happens if you remove 3 parathyroid glands?

A

Transient hypocalcemia

58
Q

What happens if you remove 4 parathyroid glands?

A

Bad news

59
Q

What stimulates calcitonin secretion?

A

Increased plasma Ca

60
Q

What does calcitonin act to do?

A

Decrease Ca (opposite of PTH)

61
Q

What does calcitonin do to osteoclasts?

A

Decreases absorptive action of osteoclasts

Decreases formation of new osteoclasts

62
Q

Describe hypoparathyroidism

A

Inadequate PTH secretion
Decreased osteocyte and osteoclast bone resorption
Ca level in ECF drops
Bone stays strong

63
Q

Describe what happens if the parathyroids are suddenly removed in hypoparathyroidism

A

Blood Ca falls from normal of 9.4 mg/dl to 6-7 mg/dl in 2-3 days
Tetany occurs
Laryngeal muscles particularly susceptible to low Ca

64
Q

Describe the primary form of hyperparathyroidism

A

Excess PTH secretion
Usually due to tumor
Extreme osteoclastic reabsorption of bone
Extremely weak bone with consequent fractures
Usually causes high Ca levels and low P levels in ECF

65
Q

What is the secondary form of hyperparathyroidism most commonly cause by?

A

Poor nutrition and decreased Ca intake

Also seen when kidney damage causes inadequate activation of vitamin D

66
Q

What does the nutritional or renal form of hyperthyroidism (secondary form) cause?

A

Low serum Ca secondarily stimulates PTH in attempt to maintain blood Ca levels

67
Q

What does increased PTH lead to in the secondary form of hyperparathyroidism?

A

Ca reabsorption from bone to maintain ECF levels

68
Q

What does Ca reabsorption from bone to maintain ECF levels cause?

A

Weakened bone, tiny or larger fractures, bone pain, lameness

Increased deposition of osteoid that fails to calcify thus bones thicken and become fibrotic

69
Q

What is rickets?

A

Inadequate vitamin D

70
Q

What does rickets cause?

A

Mildly low Ca in ECF but pronounced decrease in phosphate

71
Q

What is a sign of rickets?

A

Weak bones due to increased PTH

72
Q

What can late stages of rickets cause?

A

Tetany as bone stores depleted and ECF Ca drops

73
Q

What can excessively rapid administration of Ca containing solutions cause?

A

Slow heart and death

74
Q

What is the most common problem of excessively rapid administration of Ca depleting solutions?

A

Rapid IV tetracycline antibiotic administration

Physiology (70 decks)

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