Parathyroid Hormone, Vitamin D and Calcium Metabolism- Multiple Choice Question

1) Which of the following organ has the highest proportion of calcium in the body?
a) Liver
b) Muscle
c) Bone
d) None of the above 

2) The plasma contributes to less than 0.5% of the total calcium in the body. 
Which of the following statement is not true regarding plasma calcium?
a) Approximately 50% of the plasma calcium is present in the ionized form
b) Approximately 40% of the plasma calcium is present in proteins
c) Approximately 10% of the plasma calcium is complexed with anions
d) None of the above 

3) Free, ionized calcium is biologically acid and tightly regulated by hormones. 
Which of the following hormone are secreted in response to increased serum calcium?
a) Parathyroid hormone
b) Vitamin D
c) Calcitonin
d) All of the above

4) Parathyroid hormone secretion is tightly controlled by the ionized calcium ions. The calcium binds to calcium-sensing cell surface receptors in the parathyroid gland.  
Which of the following second messenger is activated by calcium-sensing cell surface receptors?
a) cGMP
b) cAMP
c) Phosphoinositol triphosphate
d) Diacylglycerol

5) Which of the following is the indirect action of parathyroid hormone?
a) Increased bone reabsorption
b) Increased renal calcium reabsorption
c) Increased intestinal calcium reabsorption
d) All of the above

6) The parathyroid hormone binds to its cell surface receptor and activates the following cell surface receptor?
a) cGMP
b) cAMP
c) Phosphoinositol triphosphate
d) Diacylglycerol 

7) The parathyroid hormone promotes the synthesis of active Vitamin D3. 
Which of the following enzyme is activated by the parathyroid hormone?
a) 25-alpha hydroxylase
b) 1-alpha hydroxylase
c) 24-alpha hydroxylase
d) All of the above

8) Which of the following laboratory measurement are used to detect bone demineralization and remodeling?
a) Osteocalcin
b) Alkaline Phosphatase
c) Hydroxyproline
d) All of the above 

9) The synthesis of active vitamin D3 from the precursors involves sequential steps that occur in the skin, liver, and kidney.  
Arrange the correct reaction order for the synthesis of active vitamin D3:
a)  1 hydroxyvitamin D
b)  Inactive Vitamin D
c) 7 dehydrocholesterol
d) 1, 25 dihydroxy vitamin D

10) Primary hyperparathyroidism is a disorder caused by the parathyroid adenoma. The following biochemical results are  the characteristic feature of hyperparathyroidism, EXCEPT
a) Increased PTH hormone
B) Increased Vitamin D3
c) Increased urinary cAMP & calcium excretion
d) Decreased serum calcium and phosphate

11) Humoral hypercalcemia is caused by the hypersecretion of PTH-related peptides. The humoral hypercalcemia is characterized by the following, EXCEPT
a) hypercalcemia
b) Hypophosphatemia
c) Increased urinary phosphate excretion
d) Increased serum PTH levels

12) The Pseudohypoparathyroidism type Ia is the result of defective Gs protein in the kidney and bones. The pseudohypoparathyroidism is characterized by: 
a) Hypercalcemia, hyperphosphatemia, and elevated PTH level
b) Hypercalcemia, hyperphosphatemia, and decreased PTH level
c) Hypocalcemia, hyperphosphatemia, and  elevated PTH level
d) Hypocalcemia, hypophosphatemia, and  elevated PTH level

13) Vitamin D stimulates the absorption of calcium and phosphate in the intestinal cells. 
Vitamin D acts via:
a) Binding to G protein receptor and activating adenylyl cyclase
b) Binding to Tyrosine  kinase receptor and activate phosphotyrosines
c) Binding to the cytosolic receptor, localization and increased gene expression 
d) All of the above 

14) Which of the following condition are associated with vitamin D deficiency?
a) Lipid malabsorption
b) Hypoparathyroidism
c) Renal Osteodystrophy
d) All of the above

15) The familial hypocalciuric hypercalcemia is caused by the mutation in the calcium-sensing receptor. The mutation results in...................................
a) Decreased secretion of PTH
b) Increased set point for calcium homeostasis
c) Decreased renal reabsorption of calcium
a) All of the above

1-c) Bone
2-d) None of the above 
3-c) Calcitonin
4-b) cAMP
5-c) Increased intestinal calcium reabsorption
6-b) cAMP
7-b) 1-alpha hydroxylase
8-d) All of the above
9- Correct reaction sequence: c) -->b)-->a)-->d)
10-d) Decreased serum calcium and phosphate
11-d) Increased serum PTH levels
12-c) Hypocalcemia, hyperphosphatemia and  elevated PTH level
13)-c) Binding to the cytosolic receptor, localization and increased gene expression 
14)- d) All of the above
15-b) Increased set point for calcium homeostasis


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