Calcium and Phosphate Flashcards
The most important form of calcium in the plasma as it is responsible to the most functions of the body.
Diffusible Ionic calcium
Absorption of calcium is aided by:
Vitamin D
True or False:
Above 1 mmol/L, the excretion rate of phosphate is proportional to the increase in the blood.
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.
Ions influenced by phosphate for ionic balance
K+ and Mg+
Zoosterol found on skin that is irradiated to form Vit D3
7-dehydrocholesterol
Produced in the liver from the conversion of cholecalciferol
25-hydroxycholecalciferol
Produced in the PCT of kidney from the conversion of 25-hydrocholecalciferol
1,25-dihyroxycholecalciferol (calcitriol)
The conversion of 25-dihydroxycholeciferol to calcitriol in the kidneys requires which hormone?
parathyroid hormone
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
A. A PTH secreting tumor
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
24,25-dihydroxycholecalciferol
Vitamin D receptors form complexes with the intracellular receptor _________
→ This complex will then bind to DNA and activate transcription
retinoid C-receptor
Calcitriol increases the formation of _____ to facilitated Ca++ absorption in the intestine
Calbindin
- in brush border and transports calcium from the cytoplasm and will travel to the basolateral membrane.
Apart from Ca+, calbindin also facilitate the uptake of which ions in the intestines?
PO4 and Mg+
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
A. Increased calbindin concentration in columnar absorptive cells
PTH increased Vit D3 which increases Calbindin that facilitates Ca++ absorption
Effect of PTH in the kidney
A rapid effect of PTH to decrease the excretion of calcium by the kidneys.
A strong effect of PTH to increase renal phosphate excretion
Believed to be modified or depleted chief cells of the parathyroid gland that no longer secrete hormone
Oxyphil cells
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
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.
True or False:
A large share of the hormonal activity of PTH is caused by the C fragments
True
• Only 10% of the secretion is the active PTH
• 80% is the C-fragment
Substance that inhibits hydroxyapatite crystallization which will hinder excessive calcification of bone
Pyrophosphate
Keeps the level of pyrophosphate in check so that calcification of bone can occur if needed
tissue-nonspecific alkaline phosphatase (TNAP)
Produced by the osteoblast to regulate bone calcification by generating pyrophosphate OUTSIDE of the cell
Nucleotide pyrophosphatase phosphodiesterase 1 (NPP1)
This transports pyrophosphatase from the interior to the surface of the cell to contribute to the extracellular pool
Ankylosis protein (ANK)
2 polypeptides produced by osteoblasts necessary for osteoclast development:
“Macrophage-colony-stimulating factor (M-CSF) and “Receptor activator of nuclear factor-kB ligand (RANKL)
Cytokine that Inhibits bone resorption by binding with RANKL
Osteoprotegerin
True or False:
Reducing calcium uptake in the kidneys and the intestines is only a MINOR effect of calcitonin
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.