Weight: 5%
Minimum Pass Grade: 50%
Each question is worth 10 marks.
1. Maintenance of calcium ion homeostasis is critical to neurological, cardiac and skeletal muscle
function. Consider the roles of two hormones involved in the regulation of the concentration of
calcium ions in the blood. Parathyroid hormone increases the concentration of calcium ions in the
blood, while calcitonin decreases the concentration. Based on this information predict the body’s
response to restore calcium balance if a person swallowed 100 antacid tablets made of a calcium
compound in 10 minutes. Include in your answer the definition of homeostasis, the type of feedback
loop involved and all of the components of a feedback loop.
Answer:
Homeostasis is the condition of equilibrium in the body’s internal environment due to the constant
interaction of the body’s regulatory processes. In this case, the level of calcium ion in blood normally stays
between a narrow range to maintain homeostasis. Multiple negative feedback systems will be involved in
the situation described above, including hormones such as calcitonin, parathyroid hormone, and caltitriol
etc.in order to maintain the balance of calcium ion level in blood. In summary, their functions are:
Calcitonin – to decrease blood calcium ion level
Parathyroid hormone- to increase blood calcium ion level
Calcitriol- to decrease calcium absorption from dietary sources
After swallowing 100 anatacid tablets the person’s blood calcium level would rise considerably in 10
minutes. One negative feedback loop is: high level of calcium ion in blood will
stimulateparafollicular cells (receptors) in the thyroid gland (control centre) to secret calcitonin (the
output). Calcitonin inhibits activity of osteoclasts (effector), speeds blood calcium ion uptake by
bone (effector), and accelerates calcium ion deposition into bones. The result is that calcitonin
promotes bone formation and decrease blood calcium ion level.
At the same time, another negative feedback loop is involved: high level of calcium ion in blood will
be detected by parathyroid gland cells (receptor), and consequently lower parathyroid hormone (the
output) produced by parathyroid gland. Osteoclasts (effector) activities decrease, and kidney