Calcium and Phosphate

Question 1

The most important form of calcium in the plasma as it is responsible to the most functions of the body.

Answer 1

Diffusible Ionic calcium

Question 2

Absorption of calcium is aided by:

Answer 2

Vitamin D

Question 3

True or False:

Above 1 mmol/L, the excretion rate of phosphate is proportional to the increase in the blood.

Answer 3

true:
Above the critical level (usually at 1 mmol/L), the excretion rate of phosphate is proportional to the increase in the blood.

Renal phosphate excretion is controlled by an overflow mechanism.

Question 4

Ions influenced by phosphate for ionic balance

Answer 4

K+ and Mg+

Question 5

Zoosterol found on skin that is irradiated to form Vit D3

Answer 5

7-dehydrocholesterol

Question 6

Produced in the liver from the conversion of cholecalciferol

Answer 6

25-hydroxycholecalciferol

Question 7

Produced in the PCT of kidney from the conversion of 25-hydrocholecalciferol

Answer 7

1,25-dihyroxycholecalciferol (calcitriol)

Question 8

The conversion of 25-dihydroxycholeciferol to calcitriol in the kidneys requires which hormone?

Answer 8

parathyroid hormone

Question 9

Which of the following conditions could account for a patient having elevated PTH while at the same time being mildly hypocalcemic?
A. A PTH secreting tumor
B. Secondary hyperparathyroidism
C. A vitamin D (calcitriol) receptor defect
D. A PTHrp (PTH related peptide) secreting tumor

Answer 9

A. A PTH secreting tumor

Question 10

25-hydroxycholecalciferol to calcitriol, it will be converted into ________ which has no vitamin D effect in cases of high Calcium concentration since PTH is suppressed

Answer 10

24,25-dihydroxycholecalciferol

Question 11

Vitamin D receptors form complexes with the intracellular receptor _________
→ This complex will then bind to DNA and activate transcription

Answer 11

retinoid C-receptor

Question 12

Calcitriol increases the formation of _____ to facilitated Ca++ absorption in the intestine

Answer 12

Calbindin

- in brush border and transports calcium from the cytoplasm and will travel to the basolateral membrane.

Question 13

Apart from Ca+, calbindin also facilitate the uptake of which ions in the intestines?

Answer 13

PO4 and Mg+

Question 14

Following the sudden development of primary hyperparathyroidism, which of the following is expected?
A. Increased calbindin concentration in columnar absorptive cells
B. Decreased levels of IL-6 and M-CSF
C. Decreased levels of plasma calcium
D. Increased phosphate reabsorption in the proximal tubule

Answer 14

A. Increased calbindin concentration in columnar absorptive cells

PTH increased Vit D3 which increases Calbindin that facilitates Ca++ absorption

Question 15

Effect of PTH in the kidney

Answer 15

A rapid effect of PTH to decrease the excretion of calcium by the kidneys.
A strong effect of PTH to increase renal phosphate excretion

Question 16

Believed to be modified or depleted chief cells of the parathyroid gland that no longer secrete hormone

Answer 16

Oxyphil cells

Question 17

True or False:
In the final PTH, there is fragment of 34 amino acid attached to the N terminus of the hormone. This fragment is said to also have FULL PTH activity

Answer 17

True

Which is why, despite the PTH being rapidly removed by the kidneys, the fragments which remain for a longer period of time in system can continue the hormonal activity of the PTH.

Question 18

True or False:

A large share of the hormonal activity of PTH is caused by the C fragments

Answer 18

True
• Only 10% of the secretion is the active PTH
• 80% is the C-fragment

Question 19

Substance that inhibits hydroxyapatite crystallization which will hinder excessive calcification of bone

Answer 19

Pyrophosphate

Question 20

Keeps the level of pyrophosphate in check so that calcification of bone can occur if needed

Answer 20

tissue-nonspecific alkaline phosphatase (TNAP)

Question 21

Produced by the osteoblast to regulate bone calcification by generating pyrophosphate OUTSIDE of the cell

Answer 21

Nucleotide pyrophosphatase phosphodiesterase 1 (NPP1)

Question 22

This transports pyrophosphatase from the interior to the surface of the cell to contribute to the extracellular pool

Answer 22

Ankylosis protein (ANK)

Question 23

2 polypeptides produced by osteoblasts necessary for osteoclast development:

Answer 23

“Macrophage-colony-stimulating factor (M-CSF) and “Receptor activator of nuclear factor-kB ligand (RANKL)

Question 24

Cytokine that Inhibits bone resorption by binding with RANKL

Answer 24

Osteoprotegerin

Question 25

True or False:

Reducing calcium uptake in the kidneys and the intestines is only a MINOR effect of calcitonin

Answer 25

True:
→ Decrease of calcium concentration due to calcitonin release will occur in two ways.
1. Decrease in absorptive activity of the osteoclast and increase in deposition of calcium in the bone will occur.
2. Decrease in the formation of new osteoclasts.
▪ However, this effect is only transient, as the decrease in number of osteoclasts will eventually decrease osteoblastic activity, producing no net effect.