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SP1 Physiology/Microanatomy 2 > Lecture 22 3/8/24 > Flashcards

Lecture 22 3/8/24 Flashcards

1
Q

Where is the majority of calcium in the body located?

A

within the bone as hydroxyapatite

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2
Q

Where is the majority of calcium located when it is NOT in the bone?

A

sequestered in the plasma membrane and ER of cells

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3
Q

What are the characteristics of phosphorus in the body?

A

-85% located in bone
-15% in soft tissue
-majority of free fraction is in serum, not bound to proteins

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4
Q

How does bone play a role in calcium regulation?

A

-Ca source during low calcemia
-Ca storage during high calcemia
-collagen fibrils have “hole zones” to nest CaPO4 crystals

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5
Q

When does precipitation of calcium phosphate occur?

A

When Ca x PO4- exceeds the solubility

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6
Q

What are the characteristics of bones as dynamic structures?

A

-bone mass grows until maturity
-old bone is permanently reabsorbed and replaced by new bone

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7
Q

How does calcium turnover differ between children and adults?

A

-100% of Ca is turned over in children each year
-20% of Ca is turned over in adults each year

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8
Q

When do cells express RANKL in order to communicate with RANK on osteoclasts?

A

after stimulation via PTH

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9
Q

What is Osteoprotegerin (OPG)?

A

molecule secreted by osteoblasts that protects the skeleton from excessive bone resorption

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10
Q

How does OPG work?

A

binds to RANKL and prevents it from interacting with RANK when PTH levels are low

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11
Q

What are the steps of bone resorption by osteoclasts?

A

-podosomes and associated proteins create a sealed chamber
-acid secretion by protein pump dissolves mineral complex
-acid proteases break down collagen
-erosion of bone produces cavities
-Ca, PO4, and HyP released into ECF and blood

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12
Q

What are the steps of bone formation by osteoblasts?

A

-lay down collagen and ALK phosphatase on osteoclast cavities
-ALKP hydrolyzes PO4 to increase local amounts and cause CaPO4 precipitation
-bone mineralization
-osteoblasts bury in collagen, become osteocytes

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13
Q

What are the four main processes involved in bone remodeling?

A

-activation
-resorption
-reversal
-formation

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14
Q

Which hormones are involved in increasing blood calcium?

A

-PTH
-calcitriol

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15
Q

Which hormone is involved in decreasing blood calcium?

A

calcitonin

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16
Q

What are the characteristics of PTH?

A

-from parathyroid gland
-leads to bone breakdown

17
Q

What are the characteristics of calcitriol?

A

-from kidney tubule
-leads to bone breakdown

18
Q

What are the characteristics of calcitonin?

A

-from C cell of thyroid gland
-stops bone breakdown
-Ca back into bone

19
Q

Why can PTH not be given orally?

A

it is a polypeptide that will be deactivated by gastric acidity and intestinal bacteria

20
Q

What are the objectives of PTH?

A

-break the bone matrix
-dissolve salts
-move Ca into blood

21
Q

What does PTH stimulate osteoclasts to release?

A

-collagenase
-hydroxylase
-PO4-ase
-H+ pump
-carbonic anhydrase
-citrate
-lactate
-hyaluronate

22
Q

What is the function of collagenase, hydroxylase, and PO4-ase?

A

break down of collagen, Ca, and PO4

23
Q

What is the function of H+ pump, carbonic anhydrase, citrate, and lactate?

A

create acidic environment

24
Q

What is the function of hyaluronate?

A

modulate osteoblast adhesion

25
Q

Why must osteoclasts be activated by osteoblasts?

A

osteoclasts do not have PTH receptors, but osteoblasts do

26
Q

Why is there an increased risk of osteoporosis during menopause?

A

-estrogen increases synthesis of OPG
-estrogen levels decrease during menopause

27
Q

How does hypercalcemia impact the kidneys?

A

-decreased reabsorption of P in proximal tubules (phosphaturia)
-reabsorption of Ca in distal tubules
-conversion of calcidiol to calcitriol to increase intestinal reabsorption of Ca and P

28
Q

How is vitamin D3 produced?

A

the action of ultraviolet light on a sterol precursor within the skin

29
Q

What does calcitriol stimulate?

A

-osteoclasts
-Ca absorption by kidney
-Ca and P uptake in the intestine

30
Q

What is the function of vitamin D?

A

causes retention of mineral ions to ensure mineralization of bone matrix

31
Q

What is the function of PTH?

A

maintain proper ratio of calcium to phosphorus in ECF

32
Q

What is calcium-binding protein/calbindin?

A

vitamin D-dependent protein that directly impacts the absorptive capacity of the intestine for calcium

33
Q

What are the characteristics of calcitonin?

A

-only Ca lowering hormone
-receptors present in bone and kidney
-directly inhibits osteoclasts
-decreases differentiation of stem cells in osteoclasts
-increases kidney excretion of Ca and P
-secreted in response to blood Ca above set-point

34
Q

How does Ca above or below the set point impact feedback regulation?

A

below set-point: secretion of PTH
above set-point: secretion of calcitonin

35
Q

What are the cellular functions of phosphate?

A

-handling/storage of energy
-second signaling (phosphorylation)
-building important structures

36
Q

What are the characteristics of PTHrP?

A

-not strictly a calcium-regulating hormone
-widely produced
-numerous functions in fetus and adult

37
Q

What is the main function of PTHrP in the fetus?

A

calcium-regulating hormone

38
Q

What are the functions of PTHrP in adults?

A

-mainly a paracrine cellular regulator
-may play a role in the transport of calcium into milk

39
Q

Why is it important that PTHrP is 70% similar to PTH?

A

-PTHrP often associated with humoral hypercalcemia of malignancy
-PTHrP can stimulate PTH receptors on bone and kidney cells
-results in PTHrP functioning similarly to PTH in patients with HHM, causing hypercalcemia

SP1 Physiology/Microanatomy 2 (50 decks)

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