1) Calcitonin decreases plasma calcium concentration while parathyroid hormone (PTH) increases it. Vitamin D is produced in the skin and metabolized in the liver and kidneys to increase calcium absorption from the gut. 2) PTH secretion is regulated by calcium levels in the blood. It increases bone resorption and calcium reabsorption in the kidneys while decreasing phosphate reabsorption. 3) Ionized calcium levels in the blood regulate PTH secretion. High levels decrease secretion while low levels increase it.

1. Physiology MCQ

2. The following are true about calcium
regulating hormones:
a.calcitonin increases the plasma calcium concentration .
F. calcitonin is a calcium lowering hormone.
b. vitamin D is produced in the skin.
T.
c. vitamin D is metabolized to its active form in the
liver and kidney.
T.
d. vitamin D increases calcium absorption from the gut.
T.
e. parathyroid hormone increases the serum
concentration of phosphate.
F. PTH decreases serum concentration of phosphate

3. Parathormone:
a. Secretion is regulated by a pituitary feedback
control system.
F . Regulated directly by the calcium level in the blood.
b. Acts directly on bone to increase bone resorption.
T
c. Decreases the urinary output of calcium.
T. PTH also increases renal tubular reabsorption of
calcium at the same time that it diminishes
phosphate reabsorption.

4. d. Decreases phosphate excretion.
F. It increases phosphate excretion by
reducing renal phosphate reabsorption.
e. Promotes absorption of calcium from
the intestines.
T. by increasing the formation in the
kidneys of 1,25
dihydroxycholecalciferol from vit. D.

5. The concentration of ionized calcium in plasma is
a. The main regulator of parathormone
secretion.
True. Parathormone secretion is stimulated by
a fall in the ionized Ca2 level.
b. Less than the free ionized calcium
concentration in intracellular fluid.
False. It is more than 105 times higher.

6. c. About 50 per cent of the total plasma calcium
concentration.
True .Most of the rest is bound to protein, mainly
albumin.
d. Reduced when plasma pH rises.
True. In alkalosis more calcium is protein-bound.
e. Reduced when the plasma protein level
rises.
False.The ionized calcium level is regulated
independently.

8. Vitamin D
A. Increases the intestinal absorption of
calcium.
True .This occurs mainly in the upper small
intestine.
B. Is essential for normal calcification of
bones in childhood.
True. In its absence bones are weak and
deformed (rickets).

9. C. Requires hepatic modification for activation.
True. Initial (25-) hydroxylation occurs here.
D. Cannot be synthesized in the body
False .It can be produced in mammals by the
action of ultraviolet light on7-
dehydrocholesterol in skin.
E. Deficiency may result in hyperparathyroidism.
True .The low blood calcium level stimulates
parathormone secretion

10. Calcitonin is secreted by:
a. Thyroid follicular cells.
b. Thyroid parafollicular cells.
c. Parathyroid cells.
d. None of the above.

11. Parathormone
a. Decreases the renal clearance of
phosphate.
False. It increases it by depressing
phosphate reabsorption.
b. Mobilizes bone calcium independently of
its actions on the kidney.
True. It does so in the absence of the
kidneys
.

12. c. Depresses the activity of the anterior
pituitary gland.
False: It does not affect the anterior pituitary.
d. In the blood rises when the calcium level
falls.
True: Blood calcium level determines its rate
of secretion.
e. Stimulates the final activation of vitamin D
(cholecalciferol) in the kidney.
True: From 25-hydroxy to 1,25-
dihydroxycholecalciferol.

13. Sudden complete loss of parathyroid
function
a. Leads to skeletal muscle spasms.
True .This is a central feature of
tetany.
b. May be fatal if treatment is not
given to raise the blood level of
ionized calcium.
True: Due to severe convulsions

14. c. Causes haemorrhagic disease due to lack
of calcium for haemostasis.
False: Calcium levels do not fall below the
levels needed for haemostasis
d. May be treated in the short-term by
slow intravenous injection of calcium ions.
True: This is the acute treatment of choice,
e.g. calcium gluconate.
e. May be treated in the long-term by regular
doses of vitamin D.
True :This acts by increasing intestinal
calcium absorption

15. The risk of tetany is increased by
a. Sudden rises in plasma bicarbonate.
True In alkalosis, the calcium-binding
power of the plasma proteins increases.
b. Sudden rises in plasma magnesium.
False Like calcium, magnesium ions tend
to prevent tetany.

16. c. Removal of the anterior pituitary gland.
False The pituitary is not involved in
calcium homeostasis
d. The onset of respiratory failure.
False The acidosis in respiratory failure
reduces calcium binding by protein
e. The onset of renal failure.
False The acidosis in renal failure also
reduces calcium binding by protein.

17. Parathormone secretion is
usually increased
a. In patients with chronic renal failure.
True. Phosphate retention results in a fall in the
ionized calcium level in blood; this stimulates the
parathyroid to produce more parathormone
(secondary hyperparathyroidism)s
b. In people taking excessive amounts of vitamin D
False The increased level of ionized calcium in
blood depresses parathyroid activity.

18. c. In patients with anterior pituitary tumours
secreting
False Pituitary hormones are not involved in the
regulation of parathyroid activity.excessive
amounts of its hormones.
d. When blood phosphate levels fall.
False This raises ionized calcium levels and
depresses parathyroid activity.
e. When plasma protein levels fall.
False This decreases the total blood calcium but
not the ionized calcium level that regulates
parathormone secretion.

19. For each action or function
related to calcium and
phosphate metabolism A–E,
select the most appropriate
option from the following list.
1. Increased blood calcium.
2. Decreased blood calcium
3. Increased urinary phosphate
4. Decreased urinary phosphate
excretion.
5. Increased alimentary
absorption of calcium.
6. Decreased alimentary
absorption of calcium
7. Hydroxylation of
cholecalciferol.
A. An action of parathormone
which increases the likelihood of
renal calculi by its effect on renal
tubular function.
B. A hepatic function which is
necessary for normal absorption
of calcium from the gut.
C. An outcome of the action of
parathormone on osteoclasts.
D. A renal function which is
necessary for the absorption of
calcium from the gut.
E. A consequence of vitamin D
deficiency in childhood which
can lead to softening and
deformity of bones (rickets) due
to inadequate mineral content.