Lecture 23: Calcium Balance Flashcards
What are the effects of hypercalcemia?
Depression of nervous system, reflexes sluggish, constipation and lack of appetite
List the distribution of calcium in the ECF, cells, and bones.
ECF contains 0.1% of Ca2+ in body; Cells contain 1% of body’s calcium. The rest is stored in bones
List the distribution of phosphate storage in the ECF, cells, and bones.
Less than 1% phosphate in ECF; 14% in cells. 85% phosphate stored in bones
Compare the effect of large changes in phosphate levels in the ECF vs. large changes of calcium levels in the ECF.
Large changes in phosphate levels do not cause major immediate effects on the body; Even slight changes in extracellular calcium cause extreme changes
What are the effects of hypocalcemia?
Excitement of nervous system, tetany, possibly death
Hypocalcemia is lethal when Calcium concentration is at what level in the body?
A. 4 mg/dl
B. 6 mg/dl
C. 9.5 mg/dl
D. 12 mg/dl
A. 4 mg/dl
Usual rate of calcium intake is ~1000 mg/day. How much of this calcium is excreted?
A. 1000 mg
B. 100 mg
C. 990 mg
D. 900 mg
D. 900 mg
What hormone greatly increases the rate of phosphate excretion?
PTH
Why do hydroxyapatite crystals fail to precipitate in normal tissues (except bone)?
Inhibitors such as pyrophosphate are present in tissues and plasma to prevent precipitation
What is the purpose of exchangeable calcium in the body?
Provides a buffering mechanism to keep calcium levels in equilibrium and maintain calcium concentration in a narrow range
What are the 3 hormones that control calcium balance?
Vitamin D, PTH, Calcitonin
What is the active form of vitamin D?
1, 25-dihydroxycholecalciferol
Where are most vitamin D receptors found?
Present in most cells of the body; located mainly in nuclei of target cells
Which of the following promotes intestinal absorption of calcium over a period of two days?
A. 1,25-dihydroxycholecalciferol
B. calcitonin
C. calbindin
D. vitamin D
C. calbindin
What are the effects of administering extreme quantities of vitamin D?
Absorption of bone
What are the effects of administering smaller quantities of vitamin D?
Bone calcification by increasing absorption of calcium and phosphate from intestines
What are the results of excessive activity of the parathyroid glands?
Hypercalcemia in ECF due to rapid absorption of calcium salts from bones
What are the results of hypofunction of the parathyroid glands?
Hypocalcemia, tetany
What is the effect of PTH on the kidneys?
A. increase reabsorption of sodium
B. increase reabsorption of phosphate
C. increase reabsorption of calcium
D. increase reabsorption of sodium, phosphate, and calcium
C. increase in absorption of calcium
How does PTH affect osteoclasts?
Binds to osteoprotegerin ligand that activates receptors on preosteoclast cells and transforms them into mature osteoclasts
What conditions increase calcium ion concentration above normal?
Excess quantities of calcium or vitamin D in the diet, bone absorption caused by disease
How is calcitonin secreted and what is its function?
Secreted by C (parafollicular cells) of the thyroid gland; decreases plasma calcium concentration
What are the results of hypoparathyroidism?
Osteoclasts become almost totally inactive, calcium vevels decrease; tetany and death may occur
What is the cause of primary hyperparathyroidism?
Abnormality (like a tumor) of the parathyroid glands causes excess PTH secretions - more common in women
