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Renal Physiology > Calcium & Phosphate Metabolism - Kovesdy > Flashcards

Calcium & Phosphate Metabolism - Kovesdy Flashcards

1
Q

Does dialysis represent a significant risk in the increase of calcification?

A

yes, coronary arter calcium was 2.5-5 times higher in dialysis pts

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2
Q

what is the importance of increased coronary arter calcium scores?

A

they are associated with high cv risk

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3
Q

T of F: Young dialysis pts were able to avoid increased coronary artery calcification

A

False

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4
Q

How do calcified/elderly stiff arteries affect pulse wave conduction of the heart?

A

in a young compliant artery, the normal pulse wave velocity is 8m/sec, returning during disatole

in calcified, old arteries, increased velocity of 12m/s, returning during systole, leading to abnormal heart beat

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5
Q

what does the abnormal heart beat due to calcification lead to?

A

increases vascular afterload with a propensity to develop lvh
decresaes coronary perfusion pressure
increases myocardial oxygen demand and subendocardial ischemia
increases endothelial dysfunction and atherogenesis

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6
Q

Where is the majority of phosphorus in the body? the minority?

A

85% in bone

ECF has less than 1%

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7
Q

What are the functions of phosphorus in the body?

A

key component of bony skeleton
important for metabolic processes (formatino of atp)
component of nucleic acids
important blood and urinary pH buffer

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8
Q

What is the normal concen in plasma of phosphorus?

A

3-4.5 mg/dl

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9
Q

How is phosphorus primarly present in the plasma?

A

hpo4 and h2p04

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10
Q

What is the ratio of hpo4 to h2po3 at a pH of 7.4?

A

4:1

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11
Q

Where is the majority of phosphorus excreted?

A

900 mg in urine/day

500 mg in fecal matter/day

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12
Q

Does a lower phosphate diet in dialysis pts help with their positive phosphorus balance in the body?

A

No, so they must use phosphate binders

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13
Q

What does the majority of the reabsorption of phosphate occur in the nephron?

A

pct (because mass quantity

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14
Q

what transporter does phosphate use?

A

uses Na-Phosphate transporter

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15
Q

What is TmP?

A

tubular maximum reabsorption of phosphate

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16
Q

As you increase GFR, what happens to TmP?

A

It increases as well.

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17
Q

What is the overall goal of Parathyroid Hormone?

A

To increase the serum calcium

18
Q

How does PTH work through the kidney?

A

It stimulates the activation of vit d. which increases phosphate excretion and increases calcium reabsorption

19
Q

How does PTH prevent phosphate reabsorption

A

it inactivates the na-p04 transporter in the pct

20
Q

what happens to calcium when you have excess amounts of phosphate in the blood

A

the phosphate traps the calcium, preventing the active ion form from being highly available

21
Q

What effect does the increases vit d due to increased PTH have on the small intestine

A

It increases vit d excretion which then leads to calcium and phosphate reabsorption, leading to increased calcium levels but also phosphate

22
Q

What effect on the bone does increased PTH have?

A

it causes the efflux of Ca and Phosphate, enhancing bone turnoever

23
Q

What occurs in response to PTH when you have kidney damage?

A

You lose the vitamind d production, which prevents phosphate excretion from occurring and calcium reabsorption from occurring. Also, the stomach decreases phophate reabsorption and calcium reabsorption. All thisleads to a decreased calcium concentration. Significance in the lost ability to regulate.

24
Q

Is hyperphosphatemia common or uncommon in mild to moderate kidney disease?

A

no

25
Q

What is the cutoff for hyperphosphatemia?

A

> 6 mg/dL, a strong predictor of death

26
Q

Is hypophosphatemia or hyper considered life threatening?

A

hyperphosphatemia

27
Q

How does kidney disease affect calcium and phosphate levels?

A

When you have kidney disease, you have a decrease in functioning nephrons. As such, each nephron takes on an additional load and you also secrete more PTH (attempting to lower phosphate levels and raise calcium levels). However, at a certain point, PTH being elevated isn’t enough to compensate for the renal failure, leading to hyperphosphatemia due to decreased phosphate excretion in the urine.

28
Q

Where is majority of calcium excreted? The next largest amount?

A

Most in fecal loss 700

Urine 300

29
Q

what happens to calcium levels in ckd?

A

you have less vit d. so the kidney reabsorbs less calcium and small intestine lowers calcium reabsorption, leading to hypocalcemia

30
Q

as ckd progresses, phosphate levels increase or decrease?

calcium levels?

A

calcium levels decrease

phosphate levels increase

31
Q

in ckd, can you see hypercalcemia?

A

yes, however it’s not as common or extreme as seeing hypocalcemia

32
Q

What percentage of calcium is bound to albumin, and thus inactive?

A

40%

33
Q

In CKD, you have less of what plasma protein, which could give you a decreased calcium level as well.

A

less albumin, leading to underestimating the amount of ionized calcium. you may have ionized calcium and see a decreased total calcium duet o loss of albumin-bound calcium

34
Q

what calcium is typically measured?

A

both the albumin-bound and the ionized. this is how numbers can be misleading in ckd. may have a decreased level of albumin leading to artificially low Ca levels

35
Q

What are the two main roles of calcium in the body?

A

rapidly fluctuating intracellular messenger

integral part of skeletal structure

36
Q

Does hypocalcemia increase or decrease neuromuscular excitability?

A

increase

37
Q

what are risks associated with hypercalcemia?

A

cv risk and soft tissue calcification

38
Q

in normal kidneys, how is a vitamin d deficiency compensated for?

A

decreased vitamin d decreases calcium levels, which increases PTH (loewr phosphate levels). Increased PTH triggers kidney 1alpha-hydroxylase, which is stronger than tissue 1alpha-hydroxylase. This makes up for vitamin D deficiency

39
Q

How does increased PTH in ckd lead to bone disease?

A

when you have low vit d, you get low calcium which activated and increases PTH levels. When increased PTH can’t activate kidney 1alpha-hydrxylase (bc ckd), you have decreased active vit. d and then increased po4, which feeds back to increase PTH further. Also, decreased active vit D increases PTH. PTH though is also enhancing bone turnover for calcium, which is where you get the bone disease.

40
Q

What is FGF23?

A

A circulating heparin-indpt mcul and inactivity 1alpha-hydroxylase activity

41
Q

What hpapens in fgf23 excess?

A

hereditary/acquired hypophosphatemic rickets

low serum phosphate
aberrant vitamin d metabolism
rickets osteomalacia

42
Q

what happens in fgf23 deficiency?

A

hereditary tumoral calcinosis

hyperphosphatemia
elevated1,25(0H)2d production
soft tissue calcifications
hyperosteosis

Renal Physiology (26 decks)

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