Lect 24 - Calcium Homeostasis Flashcards
Jan 31, 2019
What is the difference between the edema seen in CHF and that in hypothyroidism?
Hypothyroidism –> non-pitting edema
CHF –> pitting edema
In regards to edema, what is a characteristic of hyperthyroidism?
Pretibial myxedema
What percentage of calcium is found in bodily fluids?
1%
What percent of plasma calcium is in free or ionized form?
50%
Plasma calcium that is not free calcium is bound to what molecules?
1) phosphate
2) citrate
3) albumin
When you have a calcium deficiency, what percentage can the GI tract absorb from your diet?
90%
What is the normal percentage of calcium that you get from diet?
30%
If calcium is deficient from your diet, where do you get it?
Bones
What does an alkalotic pH do to serum calcium? Acidotic pH?
Alkalotic pH decreases serum calcium.
Acidotic pH increases serum calcium.
What percentage of phosphate in your body is in your bones?
86%
Where is the rest of the phosphate in your body other than your bones?
ECF
In what form is the majority of the phosphate in your ECF?
Organic form
In what circumstances is calcitonin important?
For calcium regulation in utero
What are the two main hormones that control calcium homeostasis?
PTH and calcitriol
What happens in cases of excess calcium and/or phosphate in serum?
They might precipitate out and form salts
What is the most important regulator of ECF calcium?
PTH
What stimulates PTH production?
Low serum calcium
What second messengers are used in parathyroid cells?
IP3/DAG/Ca and PLC
At what two sites does PTH work?
1) osteoblasts in bone
2) kidneys
What are the cytokines released by PTH-stimulated osteoblasts?
1) M-CSF (macrophages)
2) RANK (Receptor activator of nuclear factor κ B)
3) IL-6
What effects does PTH have on the kidney?
increased reabsorption of calcium
decreased reabsorption of phosphate
How does PTH affect absorption of calcium from the GI tract?
Indirectly through Vit D
What catalyst is used to turn 7-dehydrocholesterol into cholecalciferol? Where does this take place?
1) UV light
2) skin
Where does cholecalciferol turn into 25-hydroxyvitamin D? Which enzyme catalyzes this reaction?
1) liver
2) 25-hydroxylase
Where does 25-hydroxyvitamin D turn into 1,25-hydroxyvitamin D? Which enzyme catalyzes this reaction?
1) kidney
2) 1-hydroxylase
Which hormone regulates the hormone 1-hydroxylase in the kidney?
PTH
Which two transporters are upregulated on the basolateral membrane of duodenal cells by vitamin D?
1) calcium-sodium exchanger
2) calcium-hydrogen exchanger
What are two causes of primary hyperparathyroidism?
1) ectopic parathyroid tissue
2) parathyroid tumor
What are the clinical consequences of hyperparathyroidism?
1) elevated serum calcium
2) phosphaturia
3) polyuria
4) calciuria/kidney stones
5) shortened QT interval
6) risk for peptic ulcer disease
7) cystic lesions on bone
What are four causes of secondary hyperparathyroidism?
1) diet deficient in Vitamin D
2) fat malabsorption leading to vitamin D deficiency
3) kidney disease (unable to synthesize vitamin D)
4) increased need for calcium
What are the symptoms and signs of primary hypoparathyroidism?
1) tetany
2) prolonged QT interval
3) low serum calcium
What is Chvostek sign?
Percussing the cheek in front of the ear to produce facial spasms
What is Trousseau sign?
Occluding blood flow to the lower arm to induce carpopedal spasm
