This document contains notes from Dr. Kunal on calcium homeostasis. It includes questions, answers, and explanations about various aspects of calcium regulation in the body, such as the conversion of vitamin D metabolites, the actions of parathyroid hormone and calcitonin, and factors that affect calcium excretion and bone mineralization. The notes provide an overview of calcium homeostasis through worked examples and discussions of clinical cases involving disorders of calcium regulation.

1. Dr Kunal; MBBS, MD
Associate Prof. Physiology
drkunal10@gmail.com
Calcium Homeostasis
Modified Flipped Class
8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

2. Question
1. Exposure to ultraviolet light directly
facilitates which of the following?
a. Conversion of cholesterol to cholecalciferol
b. Conversion of cholecalciferol to 25-
hydroxycholecalciferol
c. Conversion of 25-hydroxycholicalciferol to
1,25-Dihydroxycholicalciferol
d. Formation of calcitriol in the liver and kidney
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

3. Answer
1. Exposure to ultraviolet light directly
facilitates which of the following?
a. Conversion of cholesterol to cholecalciferol
b. Conversion of cholecalciferol to 25-
hydroxycholecalciferol
c. Conversion of 25-hydroxycholicalciferol to
1,25-Dihydroxycholicalciferol
d. Formation of calcitriol in the liver and kidney
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

4. Question
1. Which of the following is the direct action
of PTH?
a. Controls the formation of 25-
hydroxycholicalciferol
b. Controls the rate of calcium transport in the
mucosa of the small intestine
c. Controls the rate of formation of calcium-
binding protein
d. Inhibits the reabsorption of phosphate from
renal tubules
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

5. Answer
1. Which of the following is the direct action
of PTH?
a. Controls the formation of 25-
hydroxycholicalciferol
b. Controls the rate of calcium transport in the
mucosa of the small intestine
c. Controls the rate of formation of calcium-
binding protein
d. Inhibits the reabsorption of phosphate from
renal tubules
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

6. Explanation
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis
PTH
PTH causes internalization and degradation
of Na-Pi-IIa and thus a reduction in renal
Pi reabsorption

7. Question
1. Which of the following increases the rate of
excretion of calcium ions by the kidney?
1. A decrease in calcitonin concentration in the
plasma
2. An increase in phosphate ion concentration
in the plasma
3. A decrease in the plasma level of PTH
4. Metabolic alkalosis
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

8. Answer
1. Which of the following increases the rate of
excretion of calcium ions by the kidney?
a. A decrease in calcitonin concentration in the
plasma
b. An increase in phosphate ion concentration
in the plasma
c. A decrease in the plasma level of PTH
d. Metabolic alkalosis
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9. Explanation
 The concentration of PTH strongly regulates the
absorption of calcium ion from the renal tubules.
 A reduction in hormone concentration reduces
calcium reabsorption and increases the rate of
calcium excretion in the urine.
 The other choices either have little effect on or
decrease calcium excretion.
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

10. Question
1. After menopause, how hormone
replacement therapy (HRT) with estrogen-
like compounds is effective in preventing
the progression of osteoporosis.
a. by stimulating the activity of osteoblasts
b. by increasing the absorption of Ca from GIT
c. by stimulating Ca reabsorption by renal
tubules
d. by stimulating parathyroid hormone (PTH)
secretion
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

11. Answer
1. After menopause, how hormone
replacement therapy (HRT) with estrogen-
like compounds is effective in preventing
the progression of osteoporosis.
a. by stimulating the activity of osteoblasts
b. by increasing the absorption of Ca from GIT
c. by stimulating Ca reabsorption by renal
tubules
d. by stimulating parathyroid hormone (PTH)
secretion
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12. Explanation
 Estrogen have an osteoblast- stimulating effect.
 After menopause, When the amount of estrogen
in the blood falls to very low levels the balance
between the bone-building (osteoblastic) activity
and the bone-degrading (osteoclastic) activity is
tipped toward bone degradation.
 When estrogen is supplimented as HRT, the bone-
building activity of the osteoblasts is increased to
balance the osteoclastic activity.
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

13. Question
1. A young woman comes to the emergency department
with a vertebral compression fracture. Radiographs
of the spine indicate generalized demineralization.
She is vegetarian, does not smoke or drink alcohol.
She has been in renal failure for the past 5 years and
undergoes hemodialysis three times each week.
Which of the following plasma level is NOT expected
in her blood report?
a. calcium concentration of lower than normal.
b. Cholecalciferol is several times greater than normal
c. 1,25-dihydroxycholecalciferol concentration is at the
lower limit of detectability
d. Parathormone level is very very low
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

14. Question
1. A young woman comes to the emergency department
with a vertebral compression fracture. Radiographs
of the spine indicate generalized demineralization.
She is vegetarian, does not smoke or drink alcohol.
She has been in renal failure for the past 5 years and
undergoes hemodialysis three times each week.
Which of the following plasma level is NOT expected
in her blood report?
a. calcium concentration of lower than normal
b. Cholecalciferol is several times greater than normal
c. 1,25-dihydroxycholecalciferol concentration is at the
lower limit of detectability
d. Parathormone level is very very low
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

15. Question
1. A 34-year-old patient with chronic asthma is
started glucocorticoid therapy. The treatment
may result in bone loss because
glucocorticoids do which of the following?
a. Increase calcium absorption from the GI tract
b. Increase osteoblast growth
c. Inhibit osteoclast formation and activity
d. Suppress vitamin D activation
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

16. Question
1. A 34-year-old patient with chronic asthma is
started glucocorticoid therapy. The treatment
may result in bone loss because
glucocorticoids do which of the following?
a. decrease calcium absorption from GI tract
b. Increase osteoblastic
c. Inhibit osteoclast formation and activity
d. Suppress vitamin D activation
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

17. Explanation
 Glucocorticoids lower plasma Ca2+ levels by inhibiting
osteoclast formation and activity.
 Over long periods of time, glucocorticoids cause
osteoporosis by decreasing bone formation and
increasing bone resorption.
 They decrease bone formation by inhibiting protein
synthesis in osteoblasts and also by decreasing the
absorption of Ca2+ and PO4
3- from the intestine and
increase the renal excretion of these ions.
 Vitamin D formation is facilitated when plasma Ca2+
levels are low.
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

18. Question
1. A 35-year-old woman having an anxiety attack
collapses. The emergency medical technician
who arrives on the scene notes that she is
hyperventilating and has facial and carpopedal
spasms. What may be the cause for her
carpopedal spasms?
1. Paralysis of nerves
2. Hyperventilation leading to alkalosis
3. Anxiety causing excess excitation of nerves and
muscles
4. She may had been suffering with hypocalcemia
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

19. Answer
1. A 35-year-old woman having an anxiety attack
collapses. The emergency medical technician
who arrives on the scene notes that she is
hyperventilating and has facial and carpopedal
spasms. What may be the cause for her
carpopedal spasms?
a. Paralysis of nerves
b. Hyperventilation leading to alkalosis
c. Anxiety causing excessive contraction of
muscles
d. Her vitamin-D level is very low
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis

20. Explanation
 Membrane excitability is related to the ease with
which depolarization opens Na+ channels. The
opening of the Na+ channel in response to
depolarization is, in part, related to the
extracellular Ca2+ concentration; the lower the
extracellular Ca2+ concentration, the easier it is
for Na+ channels to open when the membrane
depolarizes. Hyperventilation (lowering arterial
CO2 tension) decreases extracellular Ca2+
concentration by increasing arterial pH. When pH
rises, H+ is released from plasma proteins in
exchange for Ca2+, and ionized Ca2+ decreases
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8/11/2023 Dr Kunal's Physiology Notes: Ca Homeostasis