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Drew 921 > 4_4CaPO4 > Flashcards

4_4CaPO4 Flashcards

1
Q

What percentage of the body’s calcium is intracellular?

A

1%

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2
Q

What percentage of body’s calcium is extracellular?

A

.01%

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3
Q

How does calcium exist in the blood?

A

1) 9% complexed to anions, 2) 50% ionized, 3) 41% protein bound

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4
Q

What are the functions of Calcium?

A

1) neuromuscular excitability, 2) blood coagulation, 3) hormonal secretion, 4) enzymatic regulation, 5) structural integrity of bone

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5
Q

What is the blood concentration of calcium?

A

9.4 mg/dL = 1.2 mM = 2.4 mEq/L

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6
Q

At what concentration of Calcium is a patient hypocalcemic?

A

6 mg/dL

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7
Q

What concentration does hypercalcemia occur at?

A

12 mg/dL

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8
Q

symptoms of hypercalcemia

A

12 mg/dL = neuromuscular depression; 15 mg/dL = PTH poisoning and CaPO4 precipitates

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9
Q

symptoms of hypocalcemia

A

6 mg/dL = tetany, spontaneous neural depolarization; 4 mg/dL = death

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10
Q

What percentage reduction in blood [calcium] leads to hypocalcemia?

A

35

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11
Q

How is calcium excreted?

A

90% in feces; 10% in urine; regulated by PTH

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12
Q

Describe the absorption of Calcium.

A

35% bioavailable in the presence of (required) Vitamin D

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13
Q

What is the concentration of HPO4?

A

1.05 mM

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14
Q

What is the concentration of H2PO4?

A

0.26 mM

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15
Q

How big of a change in total phosphate can the body tolerate?

A

2-3 fold

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16
Q

What are the components of bone?

A

1) organic matrix; 2) bone salts

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17
Q

function of the organic matrix of bone

A

tensile strength

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18
Q

function of the bone salts

A

compression strength

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19
Q

Describe the composition of bone’s organic matrix?

A

90% collagen, 10% ground substance = proteoglycans = chondroitin SO4 + hyaluronate

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20
Q

Describe the composition of bone salts.

A

hydroxyapatite + Mg/K/Na/CO3 adsorbed to surface

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21
Q

What is the formula of hydroxyapatite?

A

Ca10.(PO4)6.(OH)2

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22
Q

Describe the ECF of bone.

A

supersaturated with Ca and PO4

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23
Q

Why doesn’t the ECF of bone precipitate?

A

pyrophosphate inhibitor

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24
Q

Describe the formation of bone

A

1) osteoblasts secrete collagen monomers and proteoglycans; 2) collagen polymerizes to form osteoid; 3) osteoblasts are entrapped to become osteocytes; 4) Ca++ precipitates to form hydroxyapatite

25
Q

What is osteoid

A

collagen polymers + proteoglycans

26
Q

Why is bone remodeled?

A

1) adaptation to loads; 2) replacement of brittle bone

27
Q

What is an osteon

A

an area of new bone

28
Q

How is an osteon formed?

A

1) osteoclasts eat out tunnel, 2) osteoblasts fill tunnel until vascular impingement

29
Q

How is osteoclast’s Ca++ absorption stimulated?

A

PTH and Vit. D stimulate preosteoclasts via osteoBLAST release of OPGL. Differentiation to osteoclasts.

30
Q

How do osteoclasts resorb bone?

A

release proteases and acid from ruffled membrane

31
Q

What is the function of osteoblasts?

A

bone deposition

32
Q

How are osteoblasts stimulated?

A

stress, fractures; increase osteoblasts from osteoprogenitor cells

33
Q

What is the timeframe for osteoclast tunnel-carving?

A

3 weeks

34
Q

What is the timeframe for osteoblast invasion and deposition?

A

2-3 months

35
Q

What are the dimensions of the osteoclast-formed tunnel?

A

0.2-1 mM x 3 mM

36
Q

Describe Vitamin D synthesis.

A

1) skin: cholesterol - cholecalciferol; 2) liver: cholecalciferol – 25-OH-D3; 3) kidney: 25-OH-D3 – 1,25-OH-D3

37
Q

What is the formula of Vitamin D?

A

1,25-dihydroxycholecalciferol

38
Q

How does vitamin D stimulate intestinal reabsorption of Ca and PO4?

A

increases CaBP, Ca-stimulated ATPase, alkaline phosphatase

39
Q

Describe the feedback inhibition in vitamin d synthesis.

A

1) 25-OH-D3 inhibits liver conversion; 2) PTH activates kidney conversion, but Ca++ inhibits PTH

40
Q

What are the functions of Vitamin D?

A

1) increase Ca/PO4 absorption, 2) regulate bone deposition (low) and reabsorption (high)

41
Q

What are the functions of PTH?

A

1) increase Ca/PO4 absorption from bone; 2) increase Ca/PO4 absorption from intestine 3) increase PO4 excretion; 4) decrease Ca excretion; 5) stimulate Vit. D synthesis for Ca absorption in intestine

42
Q

How many parathyroid glands are there?

A

4

43
Q

How is PTH secreted?

A

as pre-prohormone from chief cells

44
Q

When is PTH secretion stimulated?

A

by low Ca++ (rickets, pregnancy and lactation)

45
Q

When is PTH inhibited?

A

high Ca++ (diet, lots of Vit. D, excess bone absorption)

46
Q

Describe PTH’s secretion in acute vs. chronic hypercalcemia.

A

chronic PTH secretion is more sensitive to low Ca due to PTH hypertrophy

47
Q

How does PTH exert its effects on bone?

A

1) Osteocytic osteolysis rapid phase; 2) osteoclast activating slow phase

48
Q

What is osteocytic osteolysis?

A

1) PTH acts on osteo cytes to absorb surface Ca and fluid, 2) osteocytes pump to osteoblasts at bone surface; 3) osteoblasts pump out Ca++ to ECF

49
Q

Describe the osteoclast activating slow phase of PTH on bone

A

PTH activates existing and generates new osteoCLASTS

50
Q

Where is calcitonin secreted?

A

parafollicular cells of the thyroid gland

51
Q

What stimulates calcitonin release?

A

increased [calcium]

52
Q

What is the function of calcitonin?

A

minor Ca++ homeostasis; promotes bone deposition: 1) decreases osteoclast absorption; 2) prevents formation of new osteoclasts

53
Q

What are symptoms of hypoparathyroidism?

A

tetany

54
Q

What are symptoms of hyperparathyroidism?

A

erosion of bone (can be completely eroded)

55
Q

What is the mechanism behind the hypoPTHism Ssx?

A

1) decreased osteoclast number and activity; 2) decreased bone and intestinal Ca++ absorption

56
Q

What is the usual cause of hyperparathyroidism?

A

tumor

57
Q

What is the mechanism behind hyperPTHism Ssx?

A

1) increased osteoclast # and activity; 2) increased bone/intestinal Ca++ absorption

58
Q

What are causes of osteoporosis?

A

1) lack of physical stress; 2) low estrogen; 3) old age; 4) malnutrition; 5) hyperPTHism

59
Q

What is the pathophys behind osteoporosis?

A

decreased bone matrix due to low osteoblast activity

Drew 921 (33 decks)

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