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Questions and Answers
What is the percentage of non-diffusible calcium in serum?
What is the percentage of non-diffusible calcium in serum?
- 40%
- 45%
- 55%
- 4.5 mg% (correct)
What is the biologically active form of calcium?
What is the biologically active form of calcium?
- Diffusible calcium
- Ionized calcium (correct)
- Non-ionized calcium
- Protein-bound calcium
What is the primary site of action of calcitonin?
What is the primary site of action of calcitonin?
- Bone (correct)
- Kidneys
- Thyroid gland
- Parathyroid gland
How does calcitonin decrease serum calcium levels?
How does calcitonin decrease serum calcium levels?
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What is the effect of calcitonin on the kidneys?
What is the effect of calcitonin on the kidneys?
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What is the effect of calcitonin on osteoclasts?
What is the effect of calcitonin on osteoclasts?
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Study Notes
Normal Serum Calcium Level
- Normal serum calcium level ranges from 9-11 mg%
- Represented by two forms: endocrine and non-endocrine
Endocrine Forms of Calcium
- 4.5mg% non-diffusible (protein bound)
- 5.5% diffusible, which is further divided into:
- 0.5mg% non-ionized
- 5mg% ionized (biologically active)
Calcium Homeostasis
- Controlled by three main regulators:
- Calcitonin
- Parathormone hormone (PTH)
- Vitamin D
Calcitonin
- A polypeptide hormone
- Secreted by the parafollicular C (clear) cells of the thyroid gland
- A calcium-lowering hormone
Mechanism of Action of Calcitonin
- Binds with surface membrane receptors
- Activates adenyl cyclase enzyme
- Formation of cAMP from ATP
- Activates a cascade of enzyme system mediating the action of the hormone
Functions of Calcitonin
- Main action: decreases serum calcium level when it's increased above normal value
- Decreases serum calcium level by:
- Inhibiting bone resorption by osteoclasts
- Stimulating osteoblasts to deposit calcium and phosphate in bone
- Decreasing the formation of new osteoclasts (chronic effect)
- Increasing the excretion of Ca++ and PO4 in the kidneys (weak mechanism)
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Description
This quiz covers the normal serum calcium levels, its forms, and the hormones that regulate calcium homeostasis, including calcitonin, parathormone, and vitamin D.
