Calcium & Phosphate Metabolism - Kovesdy

Question 1

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

Answer 1

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

Question 2

what is the importance of increased coronary arter calcium scores?

Answer 2

they are associated with high cv risk

Question 3

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

Answer 3

False

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

85% in bone

ECF has less than 1%

Question 7

What are the functions of phosphorus in the body?

Answer 7

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

Question 8

What is the normal concen in plasma of phosphorus?

Answer 8

3-4.5 mg/dl

Question 9

How is phosphorus primarly present in the plasma?

Answer 9

hpo4 and h2p04

Question 10

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

Answer 10

4:1

Question 11

Where is the majority of phosphorus excreted?

Answer 11

900 mg in urine/day

500 mg in fecal matter/day

Question 12

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

Answer 12

No, so they must use phosphate binders

Question 13

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

Answer 13

pct (because mass quantity

Question 14

what transporter does phosphate use?

Answer 14

uses Na-Phosphate transporter

Question 15

What is TmP?

Answer 15

tubular maximum reabsorption of phosphate

Question 16

As you increase GFR, what happens to TmP?

Answer 16

It increases as well.

Question 17

What is the overall goal of Parathyroid Hormone?

Answer 17

To increase the serum calcium

Question 18

How does PTH work through the kidney?

Answer 18

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

Question 19

How does PTH prevent phosphate reabsorption

Answer 19

it inactivates the na-p04 transporter in the pct

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

What effect on the bone does increased PTH have?

Answer 22

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

Question 23

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

Answer 23

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.

Question 24

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

Answer 24

no

Question 25

What is the cutoff for hyperphosphatemia?

Answer 25

>6 mg/dL, a strong predictor of death

Question 26

Is hypophosphatemia or hyper considered life threatening?

Answer 26

hyperphosphatemia

Question 27

How does kidney disease affect calcium and phosphate levels?

Answer 27

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.

Question 28

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

Answer 28

Most in fecal loss 700 | Urine 300

Question 29

what happens to calcium levels in ckd?

Answer 29

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

Question 30

as ckd progresses, phosphate levels increase or decrease? | calcium levels?

Answer 30

calcium levels decrease | phosphate levels increase

Question 31

in ckd, can you see hypercalcemia?

Answer 31

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

Question 32

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

Answer 32

40%

Question 33

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

Answer 33

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

Question 34

what calcium is typically measured?

Answer 34

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

Question 35

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

Answer 35

rapidly fluctuating intracellular messenger | integral part of skeletal structure

Question 36

Does hypocalcemia increase or decrease neuromuscular excitability?

Answer 36

increase

Question 37

what are risks associated with hypercalcemia?

Answer 37

cv risk and soft tissue calcification

Question 38

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

Answer 38

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

Question 39

How does increased PTH in ckd lead to bone disease?

Answer 39

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.

Question 40

What is FGF23?

Answer 40

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

Question 41

What hpapens in fgf23 excess?

Answer 41

hereditary/acquired hypophosphatemic rickets low serum phosphate aberrant vitamin d metabolism rickets osteomalacia

Question 42

what happens in fgf23 deficiency?

Answer 42

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