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CASE FILES: BIOCHEMISTRY
B IO C H E M IS T R Y PE A R L S
Intracellular calcium ion is largely sequestered within mitochondria
and the lumen of the endoplasmic reticulum.
PTH acts on three major targets—small intestine, kidney, and
bone—to restore calcium ion concentrations in the extracellular
fluid to the normal range if they fall too low.
Hyperparathyroidism causes elevated levels of calcium and
phosphate.
PTH acts by binding its 7-helix plasma membrane receptor to acti-
vate the adenylate cyclase/protein kinase A signaling system.
PTH stimulates demineralization of bone and release of calcium and
phosphate into the blood by stimulating osteoclast formation
and activity, increases small bowel absorption of calcium ion,
and acts directly on the kidney to suppress calcium ion excretion
in the urine.
REFERENCES
Chaney SG. Principles of nutrition II: micronutrients. In: Devlin TM, ed. Textbook
of Biochemistry with Clinical Correlations, 5 th ed. New York: Wiley-Liss, 2002.
Litwack G, Schmidt TJ. Biochemistry of hormones I: polypeptide hormones. In:
Devlin TM, ed. Textbook of Biochemistry with Clinical Correlations, 5th ed.
New York: Wiley-Liss, 2002.
Pathophysiology of the endocrine system. An online textbook from Colorado State
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