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ANSC 311 - Metabolic Physiology > Midterm 3 - Lecture 15 > Flashcards

Midterm 3 - Lecture 15 Flashcards

1
Q

What are 5 roles of bones?

A
  1. framework and levers allowing conversion of muscle contraction to movement
  2. protection of internal organs such as brain, lungs and heart
  3. mineral storage (calcium, phosphate, magnesium and sodium)
  4. fat storage in marrow (bird marrow cavities contain air sacs)
  5. production of blood cells
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2
Q

What are 3 types of bones?

A
  1. long bones
  2. flat bones
  3. irregular bones
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3
Q

Long bones

A
  • elongated cylindrical form
  • shaft (diaphysis) and ends (epiphyses)
  • supporting columns and levers for muscles
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4
Q

Flat bones

A
  • protect internal organs
  • ribs, sternum, pelvic bones and cranium
  • attachment for muscles
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5
Q

Irregular bones

A
  • irregular shape, such as vertebrae
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6
Q

What are bones first formed as?

A
  • cartilage; replaced by bone tissue through endochondral ossification
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7
Q

When is the replacement of cartilage by bone tissue (endochondral ossification) complete?

A
  • after puberty
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8
Q

Do bones remain metabolically active after development is complete?

A
  • Yes!
  • Calcium and phosphate are mobilized during pregnancy, lactation and other
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9
Q

What is bone mobilization under control of?

A
  • endocrine control
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10
Q

What is the composition and the function of each composition of bone?

A

40% organic components by weight
- mostly collagen
- withstands tensile forces (bending)

60% inorganic compounds
- mostly calcium phosphate crystals
- withstands compressive forces

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11
Q

When does endochondral ossification start?

A
  • last third of pregnancy from center and the ends
  • 3 points of ossification: 2 secondary centers, 1 primary center
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12
Q

Where does growth in bone length occur? What is growth stimulated by?

A
  • at epiphyseal or growth plates
  • growth of cells in epiphyseal plate are stimulated by IGF-1
  • sex hormones speed up bone growth and mineralization
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13
Q

What happens to bones once an animal is fully mature?

A
  • epiphyseal cartilages become completely ossified
  • bone length becomes fixed; growth plates calcify
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14
Q

What 4 cells are involved in bone formation?

A
  1. osteoblasts
  2. osteocytes
  3. osteoclasts
  4. osteoprogenitors
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15
Q

Osteoblasts

A
  • synthesize collagen and other organic components to make osteoid
  • release calcium salts to form bone (hydroxyapatite)
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16
Q

Osteocytes

A
  • osteoblasts become trapped and become osteocytes
  • they maintain bone as living tissue
  • long thin cytoplasmic extensions that connect nearby osteocytes by gap jxns
  • revert back to osteoblasts as bone matrix dissolved
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17
Q

Osteoprogenitors

A
  • progenitor cells of the bone important in repair and fracture
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18
Q

What are osteoclasts essential for?

A
  • remodeling and removal of mineralized bone
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19
Q

How many nuclei do osteoclasts contain?

A
  • giant cells containing 5-10 nuclei
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20
Q

Where do osteoclasts form?

A
  • on inner and outer bone surfaces by fusion of the monocyte-macrophage cell line
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21
Q

What do osteoclasts do?

A
  • release organic acids to digest bone matrix
  • take up minerals by endocytosis and transport them to blood
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22
Q

When and how is bone resorption induced?

A

when plasma calcium levels drop parathyroid hormone (PTH) induces bone resorption

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23
Q

What is bone remodeling?

A

regulated degradation and renewal that occurs over longer timescale
- in adults this is a local process where osteoclasts resorb bone, then osteoblasts deposit new bone
- can alter shape and size in accordance with mechanical strain; greater force on bones = greater amount of deposition

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24
Q

What is bone resorption also referred to as?

A

bone mineralization

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25
Q

Is bone turnover faster in young animals?

A
  • yes!
  • complete turnover in 1 year as compared to 20% turned over in adults/yr
  • important reason why hypocalcemic conditions such as milk fever is less frequent in young cows
26
Q

Osteon

A
  • basic functional unit of compact bone; an osteon refers to osteocytes arranged in concentric layers around a central canal
  • canals run in parallel to bone surface and contain blood vessels
27
Q

What do bones of older animals contain a mixture of?

A
  • new and old osteons, and partially resorbed osteons
28
Q

Where is the majority of body calcium found?

A
  • in bone as hydroxyapatite
29
Q

What is the composition of plasma calcium?

A
  • 45% free ionized (active)
  • 45% bound to proteins
  • 10% complexed with anions
30
Q

What does calcium in extracellular fluid impact?

A
  • signal transduction
31
Q

What is the concentration of calcium and phosphate regulated by?

A
  • intestinal absorption
  • renal excretion/reabsorption
  • bone uptake/bone resorption
  • all processes hormonally regulated by vit D, PTH, and calcitonin
32
Q

What is parathyroid hormone produced by?

A

parathyroid glands
- 1 embedded in the thyroid
- 2nd localized in cranial part of thymus

33
Q

What happens to PTH if there is low plasma calcium?

A

increase

34
Q

What happens to PTH if there is high plasma calcium?

A

decreases

35
Q

What role does magnesium play with calcium?

A
  • magnesium plays parallel role to calcium, but with significant Mg depletion there is decrease in PTH leading to hypocalcemia
  • magnesium depletion results in tetany
36
Q

What does PTH promote?

A
  • bone resorption, intestinal absorption and reabsorption in the kidney
  • increases synthesis of active form of vitamin D
37
Q

What does the removal of the parathyroid gland result in?

A

tetany

38
Q

What is calcitonin produced by?

A

C-cells in the thyroid gland

39
Q

When is calcitonin released?

A

In response to elevated calcium levels in the plasma
- also stimulated by CCK, gastrin and secretin

40
Q

What is the fxn of calcitonin?

A
  • reduces calcium concentration in extracellular fluid by inhibiting bone resorption and increasing urinary excretion
  • elevated levels reduce population of osteoclasts on bone surface
41
Q

Is calcitonin essential in terrestrial animals? marine mammals?

A

Not essential in terrestrial animals, but probably essential for marine mammals due to high calcium concentrations in sea water

42
Q

Where does vitamin D come from?

A

consumed in the diet or produced in skin with UV exposure

43
Q

What type of molecule is Vitamin D?

A

steroid molecule with open ring structures

44
Q

What is the most active form of vitamin D?

A
  • Calcitriol (Vit D3)
  • Forms of vit D vary in activity
45
Q

What happens to vitamin D when calcium levels are adequate?

A
  • Vit D is converted to an inactive form and excreted
46
Q

What happens to vitamin D when calcium levels are low?

A
  • Vit D is converted to calcitriol (the most active form) resulting in increased calcium uptake in the intestine
47
Q

What is calcitriol considered to be?

A

Calcitriol is considered to be a hormone as it is produced in one location (kidney) and acts at a different location

48
Q

How does calcitriol ‘act’?

A

by binding intracellular receptors in cells that transport Ca2+

49
Q

Why does supplementation with calcitriol need to be done carefully?

A

can lead to hypercalcemia

50
Q

Rickets

A
  • caused by vitamin D deficiency
  • young animals continue to produce organic bone matrix (osteoid), but mineralization of matrix doesn’t occur
  • results in reduced bone strength and deformation
51
Q

What can excess vitamin D induce?

A
  • toxicity
  • calcium phosphate can precipitate in soft tissue
  • high levels in some plants consumed by grazing livestock
52
Q

How are hindgut fermenters different in terms of the relationship btw Ca2+ and vit D?

A
  • all calcium absorption is independent of Vit D
  • Ca2+ pumps in SI are turned on all the time
  • since there is no gate controlling Ca2+, removal by the kidney is particularly important
  • hypercalcemia is a hallmark of renal failure
53
Q

What does low blood Ca2+ induce?

A
  • PTH which acts on osteoclasts to mobilize more calcium from bone
  • PTH also acts on kidney to reduce urinary excretion of calcium and increase production of calcitriol which increases absorption from the intestine
54
Q

Why is a cow sometimes unable to mobilize and absorb enough calcium?

A
  • due to the cow having a non-responsive state to PTH
  • PTH is not able to go out and act on bone, intestine and kidneys to normalize calcium levels
55
Q

What is it called if a cow has the inability to normalize calcium levels?

A

hypocalcemia = milk fever

56
Q

How is milk fever (hypocalcemia) treated?

A
  • easy to treat if you catch her early by injecting calcium into the milk vein
57
Q

How can hypocalcemia (milk fever) be prevented?

A
  • feed anionic salts (S or Cl) to induce mild metabolic acidosis
  • PTH receptors recognize PTH better at low blood pH
  • side effect: feed intake depression
58
Q

DCAD

A

Dietary Cation Anion Difference
- different diets vary in proportions of cations and anions, which we are concerned about
- cations: K and Na
- anions: Cl and S
- DCAD = (K+Na) - (Cl+S)

59
Q

What does a lower DCAD indicate?

A
  • low blood pH and urine pH (mild metabolic acidosis)
  • greater capability to maintain Ca homeostatis due to being more responsive to PTH
60
Q

How low should the DCAD be?

A
  • if negative, we may need a supplement (anionic salts)
  • if slightly positive we may be able to use low-DCAD forages

ANSC 311 - Metabolic Physiology (17 decks)

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