Calcium homeostasis, i.e., maintaining a blood calcium level of about 10 mg/dL, is critical for normal body functions. Hypocalcemia can result in problems with blood coagulation, muscle contraction, nerve functioning, and bone strength. Hypercalcemia can result in lethargy, sluggish reflexes, constipation and loss of appetite, confusion, and coma. Calcium homeostasis is controlled by PTH, vitamin D, and calcitonin and the interactions of the skeletal, endocrine, digestive, and urinary systems.
hypercalcemia
condition characterized by abnormally high levels of calcium
hypocalcemia
condition characterized by abnormally low levels of calcium
1. When calcium levels are too high or too low, which body system is primarily affected?
A) skeletal system
B) endocrine system
C) digestive system
D) nervous system
D
2. All of the following play a role in calcium homeostasis except
A) thyroxine
B) calcitonin
C) parathyroid hormone
D) vitamin D
A
3. Which of the following is most likely to be released when blood calcium levels are elevated?
A) thyroxine
B) calcitonin
C) parathyroid hormone
D) vitamin D
B
1. An individual with very low levels of vitamin D presents themselves to you complaining of seemingly fragile bones. Explain how these might be connected.
Vitamin D is required for calcium absorption by the gut. Low vitamin D could lead to insufficient levels of calcium in the blood so the calcium is being released from the bones. The reduction of calcium from the bones can make them weak and subject to fracture.
2. Describe the effects caused when the parathyroid gland fails to respond to calcium bound to its receptors.
Under “normal” conditions, receptors in the parathyroid glands bind blood calcium. When the receptors are full, the parathyroid gland stops secreting PTH. In the condition described, the parathyroid glands are not responding to the signal that there is sufficient calcium in the blood and they keep releasing PTH, which causes the bone to release more calcium into the blood. Ultimately, the bones become fragile and hypercalcemia can result.