Negative BMR is observed with:
**Core Concept**
Basal Metabolic Rate (BMR) is the amount of energy expended by the body at rest, and it is influenced by various physiological factors. Thyroid hormones play a crucial role in regulating energy metabolism, and alterations in thyroid function can significantly impact BMR.
**Why the Correct Answer is Right**
A negative BMR indicates a decrease in resting energy expenditure. This is typically observed in cases of hypothyroidism, where the thyroid gland produces insufficient thyroid hormones (T3 and T4). As a result, the body's metabolic rate slows down, leading to a decrease in BMR. The thyroid hormones regulate the activity of various enzymes involved in energy metabolism, including the citric acid cycle and fatty acid oxidation. In hypothyroidism, the reduced levels of thyroid hormones result in decreased activity of these enzymes, contributing to the decrease in BMR.
**Why Each Wrong Option is Incorrect**
**Option A:** Pituitary disturbances, such as hypopituitarism, can affect thyroid hormone production by reducing the secretion of Thyroid-Stimulating Hormone (TSH). However, a pituitary disturbance itself does not directly cause a negative BMR; it can only indirectly affect BMR through its impact on thyroid hormone production.
**Option C:** Parathyroid glands regulate calcium and phosphate metabolism, and their disturbances can lead to disorders such as hyperparathyroidism. While parathyroid disorders can have various systemic effects, they do not directly influence BMR.
**Option D:** All of the above is incorrect because, while pituitary and parathyroid disturbances can have indirect effects on thyroid hormone production and metabolism, they are not the primary causes of a negative BMR.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that a negative BMR can be a sign of hypothyroidism, and it's not just a simple arithmetic calculation. A thorough clinical evaluation, including thyroid function tests, is necessary to diagnose and manage thyroid disorders.
**✓ Correct Answer: B. Thyroid disturbance**