Final answer:
The question involves the outcome of various conditions on blood calcium levels, which are regulated via a negative, not positive, feedback loop consisting of hormones that maintain calcium homeostasis.
Step-by-step explanation:
The student's question involves categorizing the outcome of various conditions on blood calcium levels. In biology, specifically in human physiology, blood calcium levels are regulated by hormones like parathyroid hormone (PTH) and calcitonin. These hormones interact in a feedback mechanism to maintain homeostasis. The statement in part d suggests a misunderstanding of the physiological process as blood calcium regulation is typically maintained by a negative feedback loop, not a positive one.
In a negative feedback loop, when blood calcium levels rise, the secretion of calcitonin increases, which helps to decrease the blood calcium levels by inhibiting osteoclast activity, reducing calcium absorption in the intestines, and increasing calcium excretion in the kidneys. Conversely, when blood calcium levels fall, PTH is secreted, increasing osteoclast activity, promoting calcium reabsorption in the kidneys, and increasing calcium absorption in the intestines to elevate blood calcium levels back to normal.