The blood calcium level is lowered by the deficiency of

Options

A. Parathormone
B. thyroxine
C. calcitonin
D. Both (a) and (c)

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which hormone deficiency leads to a decrease in blood calcium levels.

2. **Identifying Key Terms**: The term "hypercalcemic effect" refers to the ability of a hormone to increase blood calcium levels. Conversely, a deficiency in such a hormone would lead to lower blood calcium levels.

3. **Identifying Relevant Hormones**: The hormone responsible for increasing blood calcium levels is parathormone (also known as parathyroid hormone or PTH), which is secreted by the parathyroid glands.

4. **Mechanism of Parathormone**: Parathormone acts on three main organs:
- **Bones**: It stimulates the resorption of bone, releasing calcium into the bloodstream.
- **Gut**: It enhances the absorption of calcium from the gut.
- **Kidneys**: It reduces the excretion of calcium in urine, retaining more calcium in the body.

5. **Understanding the Antagonistic Hormone**: Calcitonin, secreted by the thyroid gland, has the opposite effect of parathormone. It decreases blood calcium levels by promoting bone deposition and increasing calcium excretion from the kidneys.

6. **Conclusion**: Therefore, if there is a deficiency of parathormone, the blood calcium levels would decrease due to the lack of its hypercalcemic effects.

7. **Final Answer**: The blood calcium level is lowered by the deficiency of parathormone.

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