22. Four principal actions of vitamin
D
4. Acts directly on
the parathyroid
glands to decrease
preproPTH
mRNA
1. Increase
Bone resorption
2. Increase GI Ca2+ absorption
through Ca2+ channel and
pump upregulation
3. Ca 2+ reabsorption via
increased TRPV5 expression
in the proximal tubules
28. PTHinhibits phosphate reabsorption by
degradation of Na+-Pi Co-transporters
in the renal epithelium’s apical membrane
When ECF phosphate
levels are low
Na+-Pi Co-
transporters retain
phosphate
29. Increasedplasma phosphate
1. Lowers plasma levels of free Ca 2+ to
stimulates PTH secretion
2. Inhibit the formation of 1,25-
dihydroxycholecalciferol
35. When plasma Ca2+ raised
1. Ca2+ is sensed by a GPCRlinked to PLC.
PLC liberates DAG and IP3
2. DAGactivates PKC
3. PKC inhibits PTH release
4. IP3 starts Ca2+ release from the ER
5. A rise in intracellular free Ca2+
also inhibits PTH secretion
36.
37. PKC and Ca2+ effects
together cause plasma Ca2+ to fall
through PTH
Reduced reabsorption
from the renal tubule
and decreased bone
resorption
52. ACTIONS of Calcitonin
1. lowers Ca2+ and PO4
-3 levels
2. Inhibit bone resorption
3. inhibits the activity of osteoclasts
4. Increases Ca2+ excretion in the urine
54. Glucocorticoids
Lower plasma Ca2+ levels
by inhibiting osteoclast
formation and activity
but long term they
cause osteoporosis by
decreasing bone
formation and
increasing bone
resorption
55. Decrease bone formation by
inhibiting protein synthesis in osteoblasts
Glucocorticoids
Decrease the absorption of Ca2+ and PO4
3–
from the intestine
Increase the renal excretion
of Ca2+ and PO4
3–
56. Growth hormone
Increases Ca2+ excretion in the urine, but it
Increases intestinal absorption of Ca2+ (Greater)
Net positive calcium balance
Insulin-like growth factor I (IGF-I) generated by
the action of growth hormone stimulates
protein synthesis in bone
60. 1. With regards to calcium metabolism
a. It is the ionised calcium concentration which
influences the physiological effects
b. The normal value of ionised calcium is 2.12
2.65mmol/l
c. Calcitonin plays a major role in calcium
homeostasis in humans
d. Absorption of Ca2+ from the GI tract is regulated
by parathyroid hormone
e. 98-99% of filtered calcium is reabsorbed in the
kidney
62. 2. Total plasma calcium:
a) increases with phosphate
b) increases with a rise in albumin,
c) changes its degree of ionisation with pH
changes
d) is decreased in osteoporosis
e) is affected by vitamin D
63. 3. A patient with parathyroid deficiency 10 days after inadvertent
damage to the parathyroid glands during thyroid surgery would
probably have
A. low plasma phosphate and Ca2+ levels and tetany.
B. low plasma phosphate and Ca2+ levels and tetanus.
C. a low plasma Ca2+ level, increased muscular excitability, and spasm of
the muscles of the upper extremity (Trousseau sign).
D. high plasma phosphate and Ca2+ levels and bone demineralization.
E. increased muscular excitability, a high plasma Ca2+ level, and bone
demineralization.
64. 6. Which of the following is not involved in
regulating plasma Ca 2+ levels?
A. Kidneys
B. Skin
C. Liver
D. Lungs
E. Intestine
65. 5. In an experiment, a rat is infused with a small volume of a
calcium chloride solution, or sodium chloride as a control.
Compared to the control condition, which of the following
would result from the calcium load?
A. Bone demineralization
B. Increased formation of 1,25-dihydroxycholecalciferol
C. Decreased secretion of calcitonin
D. Decreased blood coagulability
E. Increased formation of 24,25-dihydroxycholecalciferol
66. 7. 1,25-Dihydroxycholecalciferol affects
intestinal Ca2+ absorption through a
mechanism that
A. includes alterations in the activity of genes
B. activates adenylyl cyclase
C. decreases cell turnover
D. changes gastric acid secretion
E. involves degradation of apical calcium
channels
67. 8. Which of the following would you expect to
find in a patient whose diet has been low in
calcium for 2 months?
A. Increased formation of 24,25
dihydroxycholecalciferol
B. Decreased amounts of calcium-binding
protein in intestinal epithelial cells
C. Increased parathyroid hormone secretion
D. A high plasma calcitonin concentration
E. Increased plasma phosphate