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Patho 2 > 1 - PTH and Calcitonin > Flashcards

1 - PTH and Calcitonin Flashcards

1
Q

What percentage of total body Ca is stored in the cells?

In the ECF?

A

0.1%

1%

rest is in the bones

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2
Q

What percentage of total body Phos is stored in the cells?

In the ECF?

A

14-15%

1%

Rest in the bones

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3
Q

What is so special about ionized calcium?

A

It can diffuse through the cell membrane

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4
Q

What percentage of plasma calcium is ionized?

A

50%

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5
Q

What are the immediate effects of decreasing phosphate in the ECF?

A

Major increases or decreases in plasma Phos have no immediate effects

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6
Q

______calcemia causes tetany

When it occurs in the hand, this is called:

A

hypocalcemia

carpopedal spasm

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7
Q

What percentage of daily calcium intake is excreted in the feces?

A

90% (900mg)

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8
Q

Why is Vitamin D important in Ca reabsorption?

A

divalent cations (like Ca) have a really hard time being absorbed from the intestines

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9
Q

Calcium is excreted in the _______

Phos is excreted in the _______

A

feces

urine

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10
Q

What is the most important factor controlling Ca reabsorption in the distal portions of the nephron?

A

PTH

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11
Q

Which bone type accounts for 80% of bone mass and forms the hard outer layer

A

cortical

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12
Q

Which bone type accounts for 20% of bone mass and is found in the interior of skeletal bones

A

trabecular

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13
Q

bone is composed of a tough organic matrix that is greatly strengthened by deposits of ________

A

calcium salts

cortical bone is about 30% matrix and 70% calcium salts!

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14
Q

The organic matrix of the bone is comprised of ___ and ____

A

collagen

ground substance (gelatinous)

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15
Q

The crystalline salts deposited in bone are made up of:

A

calcium and phosphate

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16
Q

The collagen fibers in bone have _____ strength

The calcium salts have _____ strength

A

tensile

compressional

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17
Q

Why doesn’t hydroxyapatite precipitate in the ECF if Ca and Phos are both present?

A

Pyrophosphate

inhibitor present in almost all tissues to prevent precipitation

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18
Q

What’s the difference between an osteoblast and an osteocyte?

A

When new bone is formed, osteoblasts lay down collagen and ground substance

The tissue formed becomes osteoid, and some of the osteoblasts get trapped

these osteoblasts become quiescent and are called osteocytes

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19
Q

Calcium should never precipitate in nonosseous tissues. What are some examples where it does?

A

Arteriosclerosis

Valves

Degeneratign tissues and old blood clots

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20
Q

The bones can buffer an increase or decrease in calcium within 30 minutes. How?

A

They maintain exchangeable calcium that maintains a constant equilibrium with the ECF

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21
Q

PTH causes increased bone resorption, but it doesn’t communicate with osteoclasts. How is this acheived?

A

Osteoblasts are responsible for secreting both the osteoclast growth factor (RANKL) and the osteoclast inhibitor (OPG)

Osteoblasts usually keep these in equilibrium

VItamin D and PTH stimulate production of mature osteoclasts by binding to osteoblasts and inhibiting OPG formation and stimulating RANKL formation

22
Q

Why do bones thicken when exposed to heavy loads?

A

bone adjusts its strength in proportion to the degree of bone stress

bone is deposited in proportion to the compressional load that the bone must carry

23
Q

Why is mechanical fixation so helpful in bone healing?

A

it means the patient can start beraing weight on the limb right away, which increases calcium deposition and prevents decalcification of the effected bone

24
Q

Vitamin D itself doesn’t effect calcium absorption or bone resorption. What does?

A

Its final active product, 1,25 - dihydroxycholecalciferol

formulated in the liver and kidneys into this active form

25
Q

In the absence of _______, Vit D loses pretty much all of its effectiveness

A

kidneys

26
Q

What hormone is required in order to convert Vit D to 1,25 D

A

PTH

27
Q

Why do calcium levels affect Vit D synthesis?

A

PTH secretion is supressed by elevated [Ca]

less PTH means less Vit D

28
Q

Vitamin D acts to promote:

A

Intestinal Calcium reabsorption (increases the amount of calbindin in epithelial gut cells)

phosphate absorption (increased calcium absorption acts as a transport mediator for the phos)

29
Q

The _____ cells in the Parathyroid secrete PTH

A

chief, not oxyphil

30
Q

PTH causes resorption of both calcium and phos from the bones. Why does an increase in PTH cause an increase in serum Ca but a decrease in serum phos?

A

PTH increases renal phos excretion at a much higher rate than the bone resorption

31
Q

How does osteolysis occur?

A

Osteoblasts and osteocysts form a matrix on the surface of the bone called the osteocytic membrane which separates the bone from the ECF

pumps in the membrane keep the calcium concentration lower on the bone side

when the pump becomes excessively activated (by PTH) calcium concentration in the bone falls and salts are released from the bone

32
Q

PTH has two effects on osteoclasts:

A
  1. immediate activation of existing osteoclasts
  2. formation of new osteoclasts
33
Q

What are some conditions that cuase hypertrophy of the parathyroid?

A

Conditions that lower calcium, even if it’s in minute amounts

Rickets

Pregnancy

Lactation

34
Q

If the calcium receptors in the parathyroid sense excess calcium, what do they do?

A

CRP is a G protein-coupled receptor

activation stimulates release of calcium which DECREASES PTH secretion

PTH isn’t turned on by a lack of Ca, it’s turned off by a presence of Ca

Activation is a failure of inhibition

35
Q

Calcitonin _______ the calcium concentration

A

decreases

It is the opposite of PTH

36
Q

List the three effects of PTH

A
  1. stimulates bone resorption, release Ca into ECF
  2. Decreases excretion of Ca, increases excretion of Phos
  3. converts Vit D into its active form
37
Q

Calcitonin decreases plasma [Ca] by:

A
  1. Halts osteolysis, which increases bone [Ca] which moves the balance back toward calcium deposition
  2. decreases the formation of osteoclasts
  3. Very, very minimal effect of renal excretion
38
Q

Why does calcitonin have a weaker immediate effect than PTH?

A

No effect on renal excretion, through which PTH has overriding effect

Does have a much bigger effect in children because the rate of bone resorption and formation is already so much higher

39
Q

What is renal rickets?

A

Osteomalacia from renal disease

40
Q

Primary hyperparathyroidism is associated with ______ calcium levels

Secondary hyperparathyroidism is associated with ______ calcium levels

A

increased

decreased (PTH is elevated as an attempt to increase ca levels)

41
Q

Children with rickets have a deficit of Vitamin D which leads to decreased plasma [Ca], but it also leads to decreased Phos levels. Why?

A

Vitamin D promotes phosphate absorption and calcium absorption, so the amount of both decreases

But PTH is secreted to increase the level of Ca, and this further lowers the level of Phos

There is not a regulatory check for low levels of Phos

42
Q

What is usually the culprit in osteoporosis: osteoblasts or osteoclasts?

A

Osteoblasts

43
Q

Why does a lack of Vit C cause osteoporosis?

A

Osteoblasts depend on Vit C to form osteoid

44
Q

What is tooth occlusion?

A

The upper and lower teeth fit together so that even small particles of food can be caught

45
Q

What are the differences between dentin and bone?

A

Dentin doesn’t have osteoclasts or osteoblasts, no space for blood vessels or nerves

dentin is deposited and nourished by a layer of cells called odontoblasts instead

46
Q

What is cementum?

A

Bony substance that lines the tooh socket

holds the tooth in place

increases in thickness and strength with excessive strain, and age

47
Q

What kind of cells line the pulp?

A

Odontoblasts

48
Q

What is the clinical term for baby teeth?

A

Deciduous teeth

49
Q

What is the final number of teeth in the adult?

A

28 + 4 wisdom teeth

50
Q

Which part of the tooth has deposition and absorption rates comparable to the jaw bone it sits in?

A

cementum

51
Q

Why does flourine help prevent caries?

A

flourine ions replace many of the hydoxyl ions in the hydroxyapatite crystals, making the enamel much less soluble

flourine promotes deposition of calcium when small pits do form in the teeth

52
Q

How effective is flourine?

A

makes teeth about three times as resistant to caries

Patho 2 (24 decks)

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